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70
Anhang
Elektrische Störungen beim Messen im Labor
Bei Messungen in (auch hochohmig) gegen Erde abgeschlossenen Meßlösungen kann ein Meßfehler infolge einer Bildung von Erdschleifen (galvanisch und/oder kapazitive Kopplung) entstehen.
Erdungsfreies Messen mit netzunabhängigen
Meßgeräten ohne angeschlossene
Peripheriegeräte (Schreiber etc.) gewährleistet in der Regel einen störungsfreien Betrieb. Bei
Verwendung von netzversorgten Geräten muß jeweils für eine entsprechende galvanische
Trennung gesorgt werden - das ist besonders bei angeschlossenen Rechneranlagen zu beachten.
Wir empfehlen die Verwendung einer optischgekoppelten Schnittstelle (Art.-Nr. 0554.0006) in
Verbindung mit einem PC-Adapter (Art.-Nr.
0554.0071).
Die einfachste Prüfmethode für den Anwender besteht darin, einen Sensor in ein möglichst gut isoliertes Medium zu tauchen und abwechselnd das Medium zu erden und erdfrei zu halten.
Verändert sich die Anzeige, fließt ein unzulässig hoher Störstrom. Hilfreich ist in diesem Fall der
Betrieb des Gerätes mit Batterie oder Akku.
Bei Parallelmessungen (pH - Leitfähigkeit) mit dem
Meßgerät testo 252 sind folgende Punkte zu beachten:
• Der Meßwert gilt nur, wenn beide Sonden in die Meßlösung eintauchen.
• Bei niedriger Leitfähigkeit (< 100 µS/cm) sollten Glas/Platin-Zellen angewendet werden. Eine Streufeldelektrode verursacht in diesem Bereich einen
Meßfehler.
Anhang
Elektrische Störungen beim Messen im Labor
• Eine pH-Elektrode gibt prinzipbedingt kleine Mengen des Referenzelektrolytes
(z. B. KCl, 3M) an die Meßlösung ab.
Dadurch kann bei parallelen Messungen des LF/pH-Wertes bei sehr niedrigen leitenden Meßlösungen die Messung der elektrolyttischen Leitfähigkeit verfälscht werden. Abhilfe hiergegen wären: große
Meßvolumen, kleine Meßdauer, nicht in diesem Parallelmodus kalibrieren.
71
72
Notizen
Bedienungsanleitung
Instruction manual testo 252 de en
Measuring instrument for
- pH / redox
- conductivity
- temperature
Hold
Auto
Man
Date Time
Max Min
DIN/NBS
Cycle Step
Cal Bat
V /
Over m m p
¡ mS/cm
%mg/lx
% /
NaCl
K
2
1
No
HOLD
MAX
MIN
SELECT
ENTER
0
I
RECORDER
0554.0070
START
STOP
O
I
Printer
Memory in out
PC-Adapter
0554.0071
74
Table of contents
Warning .......................................................................4
General description .........................................................5
Instrument description .....................................................6
User Instructions
Power supply
Battery/rech. battery connection ...........................7
Battery life .......................................................8
Charging the rech. battery...............................8
Operation with mains unit .................................... 9
Connection of probes ..................................................9
Configuration menu ...................................................10
Parallel measurements...............................................13
pH measurement
Preparing a pH electrode ...........................................15
Calibrating a pH electrode .........................................16
automatic calibration with specified buffer solutions .............................16 manual calibration with any chosen buffer solutions .........................22
Measuring..................................................................26
Automatic stability recognition of the measuring signal ..............................................28
Response times and temperature compensation .......29
pH error messages ...................................................30
Other possible malfunctions................................32
Redox measurement......................................................
33
Conductivity measurement
Preparing a conductivity measurement
Storing cell constants..........................................34
Setting a temperature coefficient.........................36
Measuring..................................................................37
Theory .....................................................................38
Conductivity error messages .....................................40
Temperature measurement ...........................................41
Display variations ...........................................................42
Table of contents
Description of probes pH electrodes ............................................................46
Storing the electrodes.........................................48
Calling up the calibration data .............................49
Printing the calibration data.................................50
Conductivity sensors .................................................51
Care and maintenance........................................52
Measuring the cell constant with the conductivity standard or calibration solution........53
Conductivity calibration with standard solution ....53
Temperature probes ..................................................56
Buffer solutions ..............................................................57
Technical data, instrument ...........................................58
Analogue outputs .......................................................... 61
Options for storing...printing...processing the measuring results ..............................................62
Ordering data ..................................................................64
Appendix.............................................................................
Temperature coefficients of several selected solutions ......................................68
Calculation of conductance at 25 ° C .......................69
Electrical interference during measurements in laboratories ............................................................70
Measuring instrument conforms with EN 50 082-1 and
EN 55 011 Group 1 ClassA
75
4
Warning
Read before using instrument!!!
When measuring food the electrodes should always be first cleaned with clear water so that buffer solutions, storage and refill solutions do not enter the food cycle. If the electrode is damaged during a measurement on food you should remove the food in question along with the broken electrode.
The housing of the electrode is made partially of glass: RISK OF BREAKAGE!
The membrane of the electrode should always be kept damp.
Use the protective cap when not measuring.
The probes are not suitable for measurements in solutions with a large organic content (e. g. ether, ester, ketone etc.) or aromatic or halogenated hydrocarbons.
Inappropriate storage, special environments (e.g. environments containing sulphide or protein, highly-alcaline environments), high temperatures or large changes in pH or temperature can influence the life of pH electrodes.
Never leave buffer solutions open during storage! Never calibrate in buffer bottles! Do not pour used buffer solutions back into the storage bottle.
Never use destilled water for storing the pH electrodes.
Spilled electrolyte solution should be wiped up immediately with a damp cloth. Electrolyte solution can damage metallic and electrical parts.
General note:
Testo uses redox as a synonym for ORP.
General description
The modular testo 252 measuring instrument, for storing, printing and evaluating data via a PC, is the result of many years experience in the development and production of measuring instruments to high standards. It is a complete system for the monitoring and analysis of water and aqueous substances (e.g. meat or cheese).
Specialised probes enable the measurement of pH values, conductivity, redox and temperature in the respective ranges. High temperatures and/or extreme pH values can reduce the life of the electrodes.
These products were mainly developed for engineers with advanced knowledge and experience in everyday measurement technology.
We expect those trained in measurement technology to be able to recognise the tolerances from the standard conditions and to be able to assess their effect on the measured result. These influences are for example calibration and temperature compensation. The following instructions should, therefore, be of some help.
The new pH Technical Manual containing a summary on the whole pH measurement range will be available in Summer ´95:
“pH measuring technology Manual”
(Order no. 0981.3483)
It also contains lots of practical tips and tricks.
5
Instrument description
RECORDER
0554.0070
START
STOP
O
I
Printer
Memory in out
PC-Adapter
0554.0071
Logger (option) for storing and printing measured values in the field
PC adapter (option) for transferring measured data to a PC
HOLD/MAX/MIN for holding pH/temperature values in display and for calling up the highest/lowest pH + temperature value since the beginning of the measurement
Arrow keys for changing values or for calling up selection possibilities
(Print) key for transferring measured data to the
IR printer
Hold
Auto
Man
Date Time
Max Min
DIN/NBS
Cal Bat
V /
Over m m
¡ mS/cm
%mg/lx
2
1
% / ¡
NaCl
K
Cycle Step
No
HOLD
MAX
MIN
SELECT
ENTER
0
I
2 line display
Battery compartment
On/off key
Page key for selecting the different operating modes
Enter key for confirming the entries or for confirming the choice of menu m pH mV ¡C / ¡F
Interface for connection of PC adapter and logger
IR transmitting diode
Analogue output connecting sockets
Connection socket for mains unit
6
User Instructions
Power supply
Battery operation with 9V PP3 block battery alcali manganese IEC 6 LR 61 or with NiCd rech. battery of the same size.
The setting battery or rech. battery must be checked in the configuration menu (see page 10) and corrected if necessary.
Battery/rech. battery connection
The battery compartment is on the side of the instrument. In order to insert the battery/rech. battery, slide off the battery cover from the side of the instrument.
Observe correct polarization!
Close the battery/rech. battery compartment.
The battery or rechargeable battery setting in the configuration menu controls the different capacity utilization of the battery or rechargeable battery.
bAt means: the capacity is used up to 6.2 V.
Accu means : the capacity is used up to 7.0 V.
During operation with mains unit, the rech. battery is only charged as long as the instrument is on. Should the auto off function be on, "PSU" appears in display once the instrument has switched itself off, to inform the user that the battery is still being charged.
(c. f. page 11)
7
8
User Instructions
Power supply
Battery life testo 252 together with
→ Temperature probe battery (alcali-manganese) 30 h rech. battery 7 h
→ pH electrode without temperature battery (alcali-manganese) 30 h rech. battery
→ pH electrode with temperature battery (alcali-manganese) rech. battery
→ Redox electrode battery (alcali-manganese)
7 h
30 h
7 h rech. battery
→ Conductivity sensor battery (alkali-manganese)
30 h (at 20 mS/cm)
30 h
7 h
10 h (at 200 mS/cm) rech. battery 7 h (at 20 mS/cm)
3 h (at 200 mS/cm)
These are average values. This data may differ depending on the manufacturer of the
Remove empty batteries from the measuring instrument immediately!
batterie/rech. batteries, storage conditions and production batch.
Charging the rech. battery:
The rechargeable battery can be charged outside the measuring instrument via recharger
0554.0025.
Duration of approximately 13 hours.
It is possible to recharge the rech. battery inside the measuring instrument via mains unit
0554.0088. The measuring instrument is still operational whilst the battery is being charged. The duration of this procedure is approx. 7 hours. When the recorder is fixed it is automatically charged at the same time.
testo
251 pH m
V term
User Instructions
Power supply / Connection of probes
Remove batteries from the measuring instrument and the connected option
(logger). Risk of explosion!
The measuring instrument automatically recognises which type of probe is connected. This does not apply to the connection of pH electrodes without a temperature sensor. The electrode/ probe must be connected before the instrument is switched on (please observe when changing electrodes/probes).
Switch off the measuring instrument when connecting the sensor or carrying out other configuration modifications on the measuring unit because the specific parameters can only be read if the instrument is switched on.
9
HOLD
MAX
MIN
I
0
SELECT
ENTER
10
SELECT
ENTER
SELECT
ENTER
User Instructions
Configuration menu
The configuration menu contains selection options specific to the instrument:
→ Select temperature unit: °C or °F
→ Avoid continuous measurement with the
”Auto-Off function”
→ Switch to battery or rech. batt. operation
→ Activate or deactivate the transmission standby option to the infra-red printer,
→ Activate pH calibration 1 or 2 and deactivate the pH measurement mode.
→ Reset the calibration data from the pH electrodes to standard values: yes or no
→ Select used conductivity measuring cells and deactivate the conductivity meas. mode
→ Select reference temperature trEF if the conductivity meas. mode is active
Keep the HOLD/MAX/MIN key pressed whilst switching on the instrument via the I/O key
.
Confirm the menu with Enter.
You can change the unit of temperature
(° C ↔ ° F) with the arrow keys.
Confirm that the setting is correct, by pressing
Enter.
When the auto-off function is on, the instrument is protected from unwanted endless mesurements in that it switches itself off automatically after 10 minutes (calibration time is excluded from this function). One segment corresponds to
2 1
/
2 minutes.
OFF means that you always have to switch the instrument off by hand.
SELECT
ENTER
User Instructions
Configuration menu
The "bat(tery)" or "accu" setting controls different capacity utilization of the battery or rech. battery. bAt means: the capacity is used up to 6.2 V.
Accu means : the capacity is used up to 7.0 V.
During operation with mains unit, the rech. battery is only charged as long as the instrument is on. Should the auto off function be on, "PSU" appears in display once the instrument has switched itself off, to inform the user that the battery is still being charged.
If you want to send the measuring results to the infrared printer (available as option), the transmitting function must be activated by confirming the setting "yes Ir".
Should you not need the IR printer, the use of the instrument is facilitated by confirming the setting
"no Ir".
SELECT
ENTER
Man
SELECT
ENTER
You can store electrode (calibration) data for two separate electrodes (e.g. a laboratory electrode and a field electrode). The electrode (data) activated in the configuration menu is activated during the measurement and can be altered
PRINT through calibration. When effecting a measurement you must activate the electro de(calibration) data which corresponds with the electrode used ( → pH1 e.g. laboratory electrode, → pH2 e.g. field electrode).
no pH deactivates the pH part of the measuring instrument, so that the conductivity/temperature measuring instrument is easier to use.
11
SELECT
ENTER
SELECT
ENTER
Cal
Man
° p
SELECT
ENTER
Hold Max Min
DIN/NBS
Cal Bat Over m m
V
Man
Date Time Cycle Step No
/ ¡ 1
2 mS/cm
%mg/lx
Print NaCl
% / ¡ K nW 24TP
Bat m V
12
Cal
PRINT p p
User Instructions
Configuration menu
With reference to the selected pH calibration (pH1 or pH2) the calibration data from the pH electrodes can be set to theoretically possible standard values
(S = 58 mV/pH at 25 ° C and AS = 0 mV). The query does not appear if “no pH” was selected.
This enables you to carry out a measurement e.g.
even after unsuccessful calibration or should you not have a buffer solution for calibration. Measuring errors to max. one pH unit are, however, possible.
Select the conductivity probes which you are going to use for the next measurement.
Type A ➔ 2 and 4 pin conductivity meas. cells, low resolution (c.f. p. 59)
Type B ➔ 2 and 4 pin conductivity measuring cells, high resolution (c.f. p. 59) no Cond ➔ blocks the conductivity measurement and simplifies the handling as a pH/mV/°C measuring instrument. This setting is recommended for measuring pH or redox only.
trEF = reference temperature. Standard setting:
25 °C. 20 °C and 18 °C can be selected. Using the set temperature coefficients (tC) the instrument calculates the measured conductivity according to the selected reference temperature. If the value of the reference temperature is changed the instrument is automatically adapted to the temperature coefficients. If measurements are to be carried out with the setting nW (natural water) trEF = 25°C must be set. trEF can no longer be adjusted if the temperature coefficient tC is set to nW.
c.f. P. 36 “Preparing a conductivity measurement.
A segment test and display of the battery voltage follows the confirmation of the last setting. The instrument then enters the measuring mode. The instrument is now ready for operation, in accordance with your settings.
User Instructions
Configuration menu / Parallel measurements
The settings in the configuration menu remain even after the instrument is switched off if the configuration menu is gone through right to the end i.e. until the jump back to the measurement menu.
Parallel measurement of pH and conductivity
→ All of the pH and conductivity sensors can be combined
.
→ “no pH”, or “no Cond” should not be selected
→ The temperature sensor in the conductivity electrode is always used for the automatic temperature compensation of both, pH and conductivity measurement.
In this way pH electrodes without an integrated temperature have automatic temperature compensation.
Measuring conductivity without pH
→ “no pH” in the pH configuration menu can be switched on via the arrow keys. In this way the pH parameter not in use is switched off.
Therefore the following can be avoided:
- Measurement errors such as electostatic discharge in the high impedant pH amplifier
- Error messages which block the trans- mission of measured data from the testo 252 to the logger and to the
PC adapter. c.f. P. 28, 29, 38 and
“Accessories”.
The same applies to other probe combinations and parallel measurements.
13
14
User Instructions
Parallel measurements
Measuring pH without conductivity if a pH electrode with no integrated temperature sensor connected.
Switch on “no cond” in the conductivity configuration menu via the arrow keys.
Temperature compensation options:
→ Use temperature probes from our accessories or
→ The NTC of the conductivity electrodes type 08 or type 11 can be used for automatic temperature compensation or
→ Use another conductivity probe with 30k NTC,
Pt 100 or Pt 1000 together with the 4 mm socket. The pH electrode is automatically temperature compensated or
→ The temperature must be input manually
(cf. p. 26).
Read p.29 for the basics on temperature compensation.
All of the connected probes must have been immersed in the same measuring solution.
Make sure there is pressure compensation during measurement with type 02 and 05.
pH measurement
Preparing a pH electrode
Only for type 02 and type 05:
In order to guarantee pressure compensation, the refill opening should be open for the duration of the measurement.
Hold the ring of the probe sleeve adapter
- Remove the storage cap. Keep hold of the probe sleeve adapter ring and remove the storage cap by turning.
- Rinse the electrode in water and blot dry with tissue paper. Rubbing the electrode dry can considerably prolong the response time of the electrode due to static charging.
Remove the storage cap
Remove air bubbles by shaking (type 02 and 05).
Check the level of the electrolyte
Only for type 02 and type 05:
Check the inside of the glass membrane for air bubbles. Remove any bubbles present by carefully shaking the electrode up and down.
- Check the level of the electrolyte in the electrode. Add more electrolyte should the level drop below 20 mm from the refill opening.
Make sure that the correct electrolyte solution (type 02/05) is used.
Should any electrolyte solution be spilt, wipe it up immediately with a damp cloth. Electrolyte solutions can damage metal and electrical parts.
The electrode is now ready for use.
15
16 pH measurement
Calibrating a pH electrode/Automatic calibration
Calibration should always be carried out before the first measurement. This should be repeated before every measurement when carried out in extreme solutions or when a very high level of accuracy is to be achieved.
The calibration possibilities of testo 252 are vast .
The main possibilities are as follows:
1 point calibration and
2 point calibration, whereby the temperature curve which corresponds with the pH value necessary for calibration is entered automatically or manually
(depending on whether you wish to use a Testo buffer solution (or DIN buffer) or your own buffer solution for calibration). With automatic calibration,
3 point calibration is possible.
The following DIN buffer solutions are permitted for 3 point calibrations: pH 4.008; pH 6.865; pH 9.180
Automatic calibration with specified buffer solutions
When a
Testo buffer or DIN buffer is used, the temperature dependence is automatically taken into consideration and compensated
, according to the temperature value which has been entered or measured (should you not be using a Testo or
DIN/NBS buffer, you can skip the following pages and go to the chapter on manual calibration). cf. descriptions of the pH electrodes from page 46 and from page 64.
Man
TESTO
BUFFER
I
0 pH measurement
Automatic calibration with specified buffer solutions
In the following example we assume that you have connected a pH combination electrode (without temperature sensor).
When a temperature sensor is connected
(integrated or separate) the manual entry/correction of the temperature value is no longer necessary. The use of the instrument is thus obviously facilitated.
Never calibrate in buffer bottles! Do not pour used buffer solution back into the storage bottle! Never leave buffer solutions open during storage!
Rinse electrodes in water after each calibration and carefully blot dry.
Rinse the electrode in water. Carefully blot the electrode dry and place the electrode in the buffer solution (Testo buffer!).
Switch the measuring instrument on.
You are now in the measuring mode. Select the calibration (CAL) menu with the page key .
p m V
Auto
SELECT
ENTER
Confirm the choice of menu with Enter.
17
DIN/NBS
* pH measurement
Automatic calibration with specified buffer solutions
1 point calibration
The temperature specification, previously used in the measurement mode, is displayed. You have to correct the temperature value using the arrow keys.
The input of a temperature value is necessary:
- as the buffer values are temperature dependent (see the Chapter on buffer solutions).
so that the pH electrode is temperature compensated.
°
SELECT
ENTER
Confirm your entry with Enter. The temperature input is allocated to buffer 1.
DIN/NBS
DIN/NBS
SELECT
The display sequence that follows contains the last buffer solution used, as a suggestion for this calibration. You can select all the buffer solutions stored in the memory of the instrument
(offered by the manufacturer of the instrument) via the arrow keys .
ENTER
Confirm the selected buffer with the Enter key.
* the outlined instrument displays are not valid when a separately connected or integrated temperature sensor is used.
18
Man
Cal m V
Cal m V pH measurement
Automatic calibration with specified buffer solutions
CAL flashes during calibration (duration of calibration: min. 20 s, max. 10 min).
A signal sounds the end of the calibration procedure.
Should the calibration procedure end abruptly after max. 10 minutes, the electrode is probably damaged (see pages 29 - 32 and 70 - 71 for error messages and remedies). Contact our service department if you have any problems.
Man
Continue calibration:
2/3 point calibration
°
SELECT
ENTER
1 pt calibration ok? →
Cancel
Man
→ CAL dAtA page 49
Man m V
Measuring mode p
1
Press the page key to cancel the calibration mode →
1 point calibration has been completed. This is the quickest way of adapting the instrument to the pH electrode
(accuracy after 1 point calibration: approx. ± 0.1 pH units). A slope of -58 mV/pH
(25 °C) is assumed and only the zero point is calibrated.
You can return to the measuring mode via the display of the calibration data
(please read about the importance of the calibration data on page 49).
2 point/3 point calibration
Should you require a more accurate calibration, continue calibration.
You will be asked for the temperature value after every further point of calibration. Correct if necessary with the arrow keys, confirm the entry with Enter.
19
Man
DIN/NBS
Cal m V
SELECT
ENTER pH measurement
Automatic calibration with specified buffer solutions
Select the buffer solution required from those on offer with the arrow keys and confirm with Enter
(a difference of 0.5 pH units must lie between the individual buffers → the instrument blocks this area automatically and thus only offers the relevant buffers).
The instrument is calibrating, " CAL" flashes on the screen (duration of calibration: min. 20 sec, max.10
min). A signal sounds the end of the calibration procedure
With Puffer 1 + 2 : are pH 4.008; pH 6.865 or pH 9.180 used?
yes no
Man
→ CAL dAtA page 49 m V
If pH values other than the following DIN buffers: pH 4.008; pH 6.865 and pH 9.180, were used for previous calibrations, the instrument automatically ends calibration and jumps to the calibration data.
Man
Measuring mode p
1
Continue calibration
20
Continue calibration;
3 point calibration pH measurement
Automatic calibration with specified buffer solutions
2 pt calibration ok?
→ Cancel m V
After 2 point calibration, you can return to the measuring mode with the page key via the display of calibration data (please read about the importance of the calibration data on page 49).
Man
→ CAL dAtA page 49
Hold Max Min Cal
Man
DIN/NBS
Bat Over m m
V / 1
2 mS/cm
%mg/lx
Print NaCl
% / ¡ K nW 24TP
Measuring mode
DIN/NBS
SELECT
ENTER
SELECT
ENTER
Correct the temperature value with the arrow keys, confirm the value.
Select the buffer and confirm.
As a result of 3 point calibration, your instrument has been calibrated for measurements with highly differing pH values. Rinse the electrode in water before beginning a measurement.
21
Buffer
pH measurement
Manual calibration with any chosen buffer solutions
Manual calibration with any chosen buffer solutions
Rinse the electrode in water. Carefully blot the electrode dry and place in the buffer solution.
I
0
Switch the measuring instrument on. p
Man
Hold
Man
Auto
Man
Auto p
1 m V
¡
You are now in the measuring mode. Select the
(CAL) menu with the page key.
Man
SELECT
ENTER
Swop to the manual calibration mode by pressing the arrow key.
Confirm the selection of the manual calibration mode with Enter.
1 point calibration
A temperature value of 25 ° C is displayed. You have to correct the temperature value using the arrow keys. The input of a temperature value is necessary for the temperature compensation of the pH electrode.
* the outlined instrument displays are not valid when a separately connected or integrated temperature sensor is used.
22
pH measurement
Manual calibration with any chosen buffer solutions
DIN/NBS
°
SELECT
ENTER
Confirm your entry with Enter. The temperature input is allocated to buffer 1.
A buffer of pH 7.00 will be suggested. You can correct the value by using the arrow keys. Enter the pH value corresponding to the temperature.
(The temperature variation of the solution is indicated on the buffer bottle).
Man
Cal m V
SELECT
ENTER
DIN/NBS m V
Confirm the corrected buffer value with the Enter key.
CAL flashes during calibration (duration of calibration: min. 20 sec, max. 10 min).
A signal sounds the end of the calibration procedure.
Should the calibration procedure end abruptly after max. 10 minutes, the electrode is probably damaged (see pages 29 - 32 and 70 - 71 for error messages and remedies). Contact our service department if you have any problems.
Man
23
24
Continue calibration:
2 point calibration pH measurement
Manual calibration with any chosen buffer solutions
1 pt calibration ok? →
Cancel
Man
→ CAL dAtA page 49
Hold Max Min Cal
Auto
Man
DIN/NBS m V
Bat Over m m
V / p
¡ 1
2 mS/cm
%mg/lx
NaCl
% / ¡ K nW 24TP
Press the page key to cancel the calibration mode
→ 1 point calibration has been completed. This is the quickest way of adapting the instrument to the pH electrode (accuracy after 1 point calibration: approx. ± 0.1 pH units). A slope of -58 mV/pH
(25 °C) is assumed and only the zero point is calibrated.
You can return to the measuring mode via the display of the calibration data (please read about the importance of the calibration data on page 49).
Measuring mode
SELECT
ENTER
SELECT
ENTER
2 point calibration
Should you require a more accurate calibration, continue calibration.
You will be asked for the temperature value after every further point of calibration. Correct if necessary with the arrow keys, confirm the entry with Enter.
Enter a second buffer value (via the arrow keys ).
A difference of ±0.5 pH units must lie between the individual buffers. The instrument blocks this area automatically. Confirm this buffer value with Enter.
Cal m V
Man
Cal m V
Man
Man
→ CAL dAtA page 49 m V
Hold Max Min Cal
Man
DIN/NBS
Bat Over m m
V / ¡ 1
2 mS/cm
%mg/lx
Print NaCl
% / ¡ K nW 24TP
Measuring mode pH measurement
Manual calibration with any chosen buffer solutions
The instrument is calibrating, "
CAL" flashes on the screen (duration of calibration: min. 20 sec, max.10
min). A signal sounds the end of the calibration procedure.
After 2 point calibration, return to the measuring mode with the page key via the CAL data.
25
pH measurement
Measuring
You have prepared the electrode and measuring instrument according to the chapter
"Instructions of use", and the instrument has been switched on.
In the following example we assume that you have connected a pH combination electrode (without temperature probe). Should you use another electrode, look up the meaning of the different parts of the display in the chapter "Display variations" (see pages 42 and 13).
→ Have you activated the right calibration (i. e. pH 1 or pH 2) in the configuration menu?
26
Hold Max Min Cal
Auto
Man
DIN/NBS
Bat Over m m
V / ¡ 1
2 mS/cm
%mg/lx
Print NaCl
% / ¡ K nW 24TP
Man
SELECT
ENTER p
Insert the electrode into the measuring solution.
The instrument displays the pH value and a temperature value. The pH value is based on the temperature value displayed. As you have not connected a temperature sensor, you must correct the temperature value manually .
You can change the temperature value by pressing the arrow key . (If you have activated the infrared printer in the configuration menu - "Yes Ir" is stored in the printing mode, that means you have to press the arrow key twice).
The flashing unit of temperature indicates that the alteration mode has been selected.
Confirm the choice of the alteration mode with
Enter .
Man p
1
2 pH measurement
Measuring
"Man" flashes on the screen indicating that the temperature value can now be entered manually.
Use the arrow keys to change the value.
Man p
1
SELECT
ENTER p
Man
Confirm this temperature value
The pH value is recalculated.
with Enter. m V
You can call up the corresponding mV value by pressing the page key . In this case we are dealing with the voltage of the pH electrode and not a redox value.
This value is not temperature compensated.
27
HOLD
MAX
MIN
Man
HOLD
MAX
MIN
Hold
Man pH measurement
Automatic stability recognition of the measuring signal
p
1
¡ K
The pH value does not settle straight away due to its dependance on several factors. The measuring instrument offers the possibility of observing the measured values over a period of time, showing the trends of the value and signalling the relative stability of the measured value (tolerances
< ± 500 µV/10s) with a tone.
Select this mode with the arrow key.
Hold
Man p
1
¡ K p
1
Whilst the measuring instrument analyses the measured values,
"HOLD" flashes on the screen
.
The display trend appears during this period, indicating either increasing or decreasing signal inputs.
Press the
Hold/Max/Min key to end this mode and return to the measuring mode.
If the tolerances are negligible, a tone sounds. "HOLD" is then held in display.
28
pH measurement
Response times and temperature compensation
Response times
The more the temperature of the measuring connector differs from that of the object of measurement, the longer the measured value from the pH electrode takes to stabilise. Isothermic conditions are therefore favourable for accurate measurements. The storage of pH measuring connectors in the recommended storage solution contributes towards quick response times.
Temperature compensation
Two important factors influence the behaviour of temperature in pH measuring technology: a) the change in the pH value with the temperature and b) the temperature dependancy of the pH electrode itself.
On a)
The change in the pH value of the measuring solution cannot be compensated with the temperature; it should be measured.
On b)
The determining factor is the temperaturedependent change in voltage at the pH membrane.
It is calculated according to the so-called Nernst equation and effects the slope S of the pH electrode.
When the temperature increases, the slope S increases. This correction is automatically carried out by the instrument and thus forms the basis of the temperature compensation (after calibration, the slope S
25 based/calculated on 25 °C is displayed for better comparison).
The testo 252 enables the user to measure the temperature value for temperature compensation via a connected temperature sensor (integrated in the pH electrode or separately connected*) or to enter the value manually.
* the use of surface probes is not permissible here.
29
30 p
Print-out of infrared printer:
“pH value out of range”
Short descriptions of the error messages can be obtained by printing out measured values on the infrared printer.
pH measurement
pH error messages
Error messages are displayed after a delay of 5 seconds
Error 1
Cause: The pH measuring range of the instrument was exceeded (pH < -2 or pH >
16). As aqueous solutions have, as a rule, a pH value between pH -2 and 16, this error message may indicate incorrect calibration.
Error 2
Cause: The temperature measuring range of the corresponding probe was exceeded.
Error 3
Cause: Certain ambient temperatures are valid
(see page 57) for the Testo buffers (or
DIN) used for calibration, and the actual ambient temperature was above or below this value. Observe the different values on the bottles of the buffer solutions.
Error 4
Cause: The slope S of the electrode is not within the range -62 to -50 mV/pH (at 25 ° C), i. e. your electrode is worn and must be replaced, or you used the wrong buffer during calibration and therefore the slope was wrongly calculated (in this case you can recalculate the slope through a new calibration).
Error 5
Cause: The electrode’s zero point (AS) is outside the range -60 to +60 mV (in relation to pH 7), i. e. your electrode is worn and must be replaced, or you used the wrong buffer during calibration and the slope was wrongly calculated (in this case you can recalculate the slope through a new calibration).
pH measurement
pH error messages
Error 6
Cause: The maxium set tolerance of the pH electrode (10 min) was exceeded during calibration. Should this occur several times, the electrode is worn and must be replaced.
Error 8
Cause: The slope S b in the alcaline range distinguishes itself by more than 3% from the slope S a in the acidic range
(only relevant with 3 point calibration).
You may have confirmed an incorrect buffer. Repeat calibration. Should this error repeat itself, the electrode is faulty and must be replaced.
31
32 pH measurement
Other possible malfunctions during measurement
Symptom: Unstable measured value
Cause: Easily recognisable disturbances such as broken electrode, broken cable, formation of visible coatings on the electrode, long-term flooding of the connection head, etc.
Symptom: Zero point of electrode outside the tolerance (±60 mV at pH 7)
Cause: An incorrect or unusable buffer was used during calibration.
Cause: Measuring solution which has penetrated the diaphragm can poison the reference system through chemical reactions and thus change the reference potential or make it instable.
Cause: There are (a few) pH electrodes whose zero point does not lie at
7. These electrodes can only be pH used in the measuring mode "mV".
Cause: The electrode was refilled with the wrong reference electrolyte (type
02/05).
The glass membrane can cause malfunction due to the formation of physical coatings. These coatings can alter the characteristics of the electrode. Physical coatings and changes in the membrance can take place in such a manner that they are invisible to the naked eye. Damage of this kind can take place e. g. in measuring solutions with a flouride content, which corrode the glass membrane.
Redox measurement
Man
Hold
M a n p
° p
1 m V
Calibration of the measuring instrument is not necessary with a redox measurement.
Remove the storage cap before beginning a measurement.
Dip the electrode into the measuring solution.
- The measured value can be read once the display has stabilised. The final measured value will in most cases only be achieved after 30 minutes.
Temperature compensation is not necessary.
Rinse the electrode in distilled water and dry.
- Replace the storage cap.
Error 1
Cause: Measured value > + 1800 mV or < -1999 mV
33
34
Conductivity measurement
Preparing a conductivity measurement
Storing cell constants
The cell constant of the conductivity sensor varies depending on the type and production batch. The cell constant is indicated on the identification label or the cable of the conductivity sensor and must be stored in the instrument before the first measurement (and each time a different conductivity sensor is connected). I
0
Hold Max Min Cal Bat Over m m
V / ¡ 1
2 mS/cm
Auto
Man
DIN/NBS
%mg/lx
Print NaCl
% / ¡ K nW 24TP
Date Time Cycle Step No
Bat m V
DIN/NBS
Bat m S/cm nW 24TP
Switch on the measuring instrument.
You are now in the measuring mode.
%mg/lx
NaCl
Select the calibration menu via the arrow key .
Auto
By pressing the arrow/print key you will enter the
Cond uctivity cal ibration mode
(Cal cond)
SELECT
ENTER
SELECT
ENTER
Confirm the selection of the Cond uctivity Cell constant mode with Enter.
S/cm
•••
Conductivity measurement
Preparing a conductivity measurement
The cell constant lies between 0.010 to 20.00/cm.
Alter the presetting with the arrow key. The cell constant of the conductivity measuring cell used is located on the probe lead.
SELECT
ENTER
Confirm the corrected value with Enter.
Read page 53 onwards for more information on conductivity calibration.
35
0
I
Hold Max Min
DIN/NBS
Cal Bat Over m m
V / p
1
2 mS/cm
%mg/lx
Print NaCl
% / ¡ K
Man nW 24TP
Date Time Cycle Step No
Bat m V
SELECT
ENTER
% /
•••
% / °
SELECT
ENTER
Conductivity measurement
Preparing a conductivity measurement
Setting a temperature coefficient
In order to achieve comparable measuring results, a conductivity value, measured at a certain temperature, is converted in relation to the reference temperature. The specific temperature coefficient of the measuring solution must, therefore, be stored in the instrument before the beginning of each measurement ( → Table "Temp.
coefficients of several selected solutions" in the appendix)
If the reference temperature (trEF) in the configuration menu is changed the temperature coefficient is automatically converted to the new reference temperature.
tC=nW (natural water is only possible at trEF= 25 °C)
(cf. configuration menu from page 12 on)
Once you have entered the measuring mode, press the arrow key. If the infrared printer was activated (Yes ir”) in the configuration menu press the arrow key twice.
" %/°C " flashes to indicate that you have selected the alteration mode for the temperature coefficients
Confirm the selection of this mode with Enter.
The abbreviation tC for temperature coefficient appears.
Alter the value according to your knowledge, otherwise enter the standard value (see table
"Temp. coefficients of several selected solutions").
Otherwise enter 2.2 %/° C as a "good mean value" for solutions with an unknown temperature coefficient; "nW" is the setting for measurements in natural water (appears after next highest value after 10.00 %/°C).
The setting “nW” is only possible with a set reference temperature trEF=25°C.
Confirm the entry with Enter.
The measuring instrument automatically enters the measuring mode.
36
Type 8 Type 11
Conductivity measurement
Measuring
You have connected the sensor according to the chapter "Instructions of use" and prepared the measuring instrument according to "Storing cell constants" and "Setting a temperature coefficient". The instrument is switched on.
Place the sensor in the measuring solution.
With type 11, the measuring solution must be up to the air vents. Make sure that all the air has escaped from the measuring cell (move the measuring cell gently when dipping into the solution) → otherwise the measured values fluctuate and are pressure dependent .
With type 8 , the solution must be just over the level of the 4 electrodes. The air vent must not be immersed.
After a short adaption phase, the conductivity value, based on the set reference temperature, and the temperature are displayed.
By pressing the page key, you can call up the salt content of the electrolyte which corresponds with the conductivity. This value in mg/l NaCl is calculated from the conductivity measured.
37
38
Conductivity measurement
Theory
The molecules of three large groups of substances
(salts, acids and electrolytes) separate into electrically charged ions when dissolved in water.
This process is called dissociation.
Example of dissociation:
Table salt (NaCl)
NACl → NA
+
+ Cl
-
When an alternating electromagnetic field is placed over the elelctrolyte, the electrodes can move the ions. This movement of ionic charge can be considered as an "electrical current", similar to that of electrons in a copper wire. This current is used to measure the electrolytic conductivity.
As a result of this ionic current in the electrolyte, an increase in the number of ions in the electrolyte ( → higher concentration) causes an increase in the electrolytic conductivity. This is only valid up to a certain limit in the concentration. Should this limit be exceeded, the ions will begin hindering each other. This means that dissociation is incomplete in high concentrations of matter; the conductivity increases slower than the concentration of matter.
When the electrolyte is of a simple composition, i.e.
only water and one dissociated matter (e.g. table salt NaCl), the concentration of the dissolved matter can be calculated from the conductivity value, (provided that the concentration is not too high).
Conductivity measurement
Theory
Almost all electrolytic solutions are very heavily dependent on temperature. This is due to the ionic nature.The mobility in liquids increases with a rise in temperature, i.e. the movement of the charged ions accelerates and the electrolytic conductivity measured is thus higher. At a reference temperature of T=+25 °C, the conductivity increases by approx. 2% per degree celsius. In measuring technology, this alteration is usually described as a temperature coefficient with the unit
%/°C.
39
40
Conductivity measurement
Conductivity error messages
Error messages are displayed after a 5 second display.
Error 1
Cause: The measuring range (0 µS/cm to 2000 mS/cm ) of the instrument has been exceeded. This can indicate an incorrect cell constant or temperature coefficient.
Error 2
Cause: The temperature measuring range of the corresponding probe has been exceeded.
Error 3
Cause: The max. limit temperatures for the calibration were either exceeded or were not reached.
Error 4
Cause: The stored cell constant must be within the range 0.01 and 20.00/cm. It is possible that an incorrect value was stored during calibration for the calbration solution used.
Error 6
Cause: The conductance exceeds the measuring range, although the specific conductivity of the measuring solution is still within the measuring range. Check that the stored temperature coefficient and cell constant are correct. Should no errors be found here, the product of the actual conductance, temperature and temperature coefficient is really outside the measuring range. Reduce the temperature of the measuring solution as much as possible or alter the temperature coefficient to 0.0%/°C and convert the conductance yourself.
Ø
Temperature measurement
Connect the temperature probe. When the measuring instrument is switched on, the temperature value appears immediately in the display (when using an individual, special temperature probe). Should you use combination probes, turn to the chapter
"Display variations" to determine the importance of the different segments of the display.
As a rule we distinguish between surface, immersion and penetration measurements as well as measurements of air/gas temperatures. The corresponding probe is to be used for each type of application.
General instructions for immersion, penetration or air measurements
- The minimum immersion depth corresponds with approx. 5 times the diameter of the probe.
- The response times can be accelerated by gently moving the probe. for surface measurements
The tip of the surface probe must be in a vertical position.
We recommend the use of heat paste for measurements on rough surfaces (for a better heat conductance).
Surface probes are not permissible for temperature measurements used for compensation of the pH value ( → earth loops)
41
42
Connection possibilities
Display variations
Display reading
Pt100 temperature probe
(8 pin DIN plug)
°
° C
(Pt100)
° C
(Pt100) pH combination electrode
(without integrated temp. sensor) pH
° p
1 manual entry necessary for temp.
compensation pH
Pt100 temperature probe and a pH combination electrode (without integrated temp. sensor)
° p
1
Man
Connection possibilities
° C
(Pt100
Pt1000
NTC 5 k
NTC 30 k)
Ø 4 mm
1 pH
° C
2 pH
Display variations
Display reading
pH electrode with integrated temperature sensor p
1
°
1 Testo electrode
2 other electrodes
The sensor integrated in the electrode is in this case always used for temperature compensation of the pH electrode.
Pt100 temperature probe in connection with a pH electrode with integrated temp. sensor.
°
° p
1
° C
(Pt100) pH
(°C)
The sensor integrated in the electrode is in this case always used for temperature compensation of the pH electrode.
43
Connection possibilities conductivit y
( ° C) conductivit y
( ° C) pH
Display variations
Display reading
Conductivity sensor with integrated temperature sensor.
Auto
DIN/NBS mS/cm
° nW 24TP
X
%mg/lx
NaCl
Conductivity sensor (with integrated temp.
sensor) and a pH combination electrode (without temp. sensor).
Auto
DIN/NBS mS/cm
° nW 24TP
%mg/lx
NaCl
X
Auto
The temperature sensor in the conductivity measuring cell is used for temperature compensation.
44
Display variations
Connection possibilities
conduc-tivity
(° C) pH
(° C)
Display reading
Conductivity sensors (with integrated temp.
sensor) and a pH electrode (with temp. sensor).
Auto
DIN/NBS mS/cm
° nW 24TP
%mg/lx
NaCl
X
Auto
Auto ¡ p
1
The temperature sensor in the conductivity measuring cell is used for temperature compensation.
45
46
Description of probes
pH electrodes
Watch out for the measuring ranges in the sensor. These may be destroyed if overheated.
To avoid grinding never use pH electrodes or conductivity measuring cells with surface temperature probes.
As practical equipment for pH measurements, we offer a variety of electrodes which are suitable for all types of measurements.
There is a choice of combination electrodes with or without a temperature sensor as well as redox electrodes.
pH combination electrodes
Combination electrodes represent a constructive combination of a glass electrode with a reference electrode. The advantage of this solution is the small amount of space and the small volume of measuring liquid required for a measurement.
The important features of pH combination electrodes:
- the composition of the membrane glass
(which influences the measuring characteristics of the glass electrode),
- the composition of the reference electrode
(mostly KCl),
- the diaphragm, which enables the connection from the internal reference system to the measuring solution
- the possibility of an additional temperature measurement.
The table opposite supplies the necessary information on the different electrodes.
Special electrodes are available on request for applications in lacquers and paints, highlyviscose solutions, photographic solutions, measurements on pure surfaces, part aqueous solutions with < 10% H
2
O, non aqueous substances, and for measurements at O ° C (+32
°F).
0650.0823
0650.0225
0650.1623
0650.1223
0650.0623
pH/° C pH/° C pH pH pH
Description of probes
pH electrodes
Comparison of pH electrodes
cf. pl 64 onwards
47
48
Description of probes
pH electrodes
Storing the electrodes
Electrodes should always be stored in a storage cap which contains a few ml of electrolyte solution
(re-filling solution). Different electrodes require different electrolyte solutions which are included in our range of accessories.
Electrodes with liquid reference electrolytes can also be stored, only in an emergency and for a short time, in an open container which contains a neutral to slightly acidic solution. Electrodes with gel electrolyte should always be stored in 3 molar
KCI in order to avoid the loss of electrolyte solution.
All electrodes should be stored in an upright position so as to ensure that the electrolyte solution does not pour out of the refill opening.
Electrodes that have been stored in dry conditions show unstable pH values. Should an electrode have dried out, it can be regenerated overnight in water.
Man m V m V/ p m V/ p
Description of probes
pH electrodes
Calling up the calibration data of the pH electrodes (CAL data)
The specific calibration data of each calibration are stored in this menu and can be recalled at any time. We recommend that you print out or note these values after each calibration (via logger or infrared printer).
By comparing the values you can detect faulty electrodes before beginning a measurement.
The instrument jumps to the "Calibration data" menu once calibration has been completed.
Should you have interrupted the calibration after one or two points, press the page key to enter the
"Calibration data" menu.
AS (zero point of electrode), SA * and Sb ** (slopes) are displayed. SA and Sb can only be distinguished from each other after 3 point calibration ( →
1 point calibration = displacement of the zero point, slope is given; → 2 point calibration = straight through two calibration points).
Permissible values (in relation to 25 ° C):
|AS| < 60 mV
-62 mV/pH < S < -50 mV/pH
Optimal values (in relation to 25 ° C):
AS = 0 mV
S = -59.2 mV/pH
* slope in acidic range ("A" for acid)
** slope in alcaline range ("B" for base)
49
Auto Hold
Auto
Auto
Man
¡ p
1 p
1
¡ m V
¡
Auto
Man
SELECT
ENTER
SELECT
ENTER
Description of probes
pH electrodes
You can recall this information anytime in the CAL dAtA menu. Select the calibration files (via the page key) and confirm CAL dAtA and dAtA pH (with
Enter).
Printing the calibration data
→ via logger
Position of switches on logger: print switch to I, memory switch in middle position.
Start printing manually with hand key.
→ via infrared printer
Activate the infrared printer transmitting mode in the configuration menu
Set up printer and call up print via the print key
("Print" flashes in the display) and confirm with
Enter.
50
Description of probes
Conductivity sensors
The measuring cell sets up the correlation between the ionic conductance or resistance and the conductivity value:
- the measuring cell limits the conduction of the current on account of its geometrical form (length and cross-section). The relation of the length to the cross-section is described as a cell constant .
- the polarisation on the electrode surfaces of the measuring cell can be described as follows: the ions which separate from the electrodes and the change in concentration of the solution at the electrodes cause an electromotive counterforce, which weakens the passage of flow and lets the conductivity of the solution seem smaller than it actually is. Polarisation effects reduce with an increasing measuring frequency and an increasing electrode surface.
The electrode material also plays and additional important role (also in relation to the response time).
The sensors with the 4 electrode technology, which we offer, have taken advantage of the fact that polarisation only occurs on electrodes where the current leaks into the electrolyte. This 4 electrode structure, however, requires a larger volume of samples than the usual 2 electrode sensors.
Non Testo products
It is also possible to connect the conductivity measuring cells from other firms. In the configuration menu (see page 10) you have to differentiate between conductivity measuring cells of type A and type B. 2 and 4 pin measuring cells can be connected in both modes. With type B there is an increased resolution available in the range
< 1µS/cm. Please order additional connection allocations as required.
51
52 testo
Description of probes
Conductivity sensors
Care and maintenance
In order to clean the sensor, pull back the cable duct from the sensor.
Clean the electrodes underneath the cable duct with a soft brush and rinse with clean water
Check whether the air vents and cable duct are clean.
Push the cable duct back into place.
The cell coefficient of the measuring cell should be tested at intervals, the regularity of which is to be determined by the type of application.
Type 8 Type 11
DIN/NBS
Bat m S/cm nW 24TP
%mg/lx
NaCl
Description of probes
Conductivity sensors/Conductivity calibration with a standard solution
Measuring the cell constant with the conductivity standard solution 1413 µµ S/cm
(25°C), 1.413 mS/cm → Part no. 0554.2334, or another solution with a known conductivity.
The cell constant of conductivity sensors changes slightly with age. We recommend that it be checked regularly at 1/2 yearly intervals.
Place the sensor in the conductivity standard solution.
With type 11, make sure that the solution is up to the air vents and that all the air has escaped from the sensor (move the sensor gently when inserting into the solution) dependent.
→ otherwise the measured values fluctuate and are pressure-
With type 8, the measuring solution should reach the level just above the 4 electrodes. The air vents must not be immersed.
cf. Measuring from page 34 onwards.
Conductivity calibration with a standard solution
You are now in the measuring mode.
Select the calibration menu with the page key .
Auto
Jump to " CAL Cond " with the arrow/print key and confirm the choice of menu with Enter.
SELECT
ENTER
53
54
Description of probes
Conductivity calibration with a standard solution
Jump to Cond uctivity Soln with the arrow/print key and confirm with Enter.
SELECT
ENTER
SELECT
ENTER mS/cm SELECT
ENTER
A setting appears which is valid for the conductivity standard solution we offer (at 25 °C). If this temperature setting of 25 °C is fulfilled, you can confirm with Enter and the cell constant is recalculated and automatically stored.
If the temperature deviates from 25°C refer to the
Table on page 69. Enter the conductivity value of the standard solution in accordance with its temperature.
mS/cm m S/cm
If you are using any calibration solution or the solution be based on any other temperature, you can set the value to that of your solution by using the arrow key. Enter the conductivity which the calibration solution has at the temperature just measured. Set the unit of measurement (µS, mS or
S) according to the unit indicated on your measuring solution and confirm the unit with Enter.
mS/cm
Description of probes
Conductivity calibration with a standard solution
Change the decade of the conductivity value with the arrow key and confirm the setting with Enter.
mS/cm
SELECT
ENTER
SELECT
ENTER m S/cm m S/cm
SELECT
ENTER
Auto m S/cm
Use the arrow keys to change the individual figures and Enter enables you to jump to the next figure in the value displayed.
Once the last figure has been confirmed, the cell constant is recalculated and displayed.
Store this newly-calculated cell constant in the hand instrument with the Enter key. mS/cm
° nW 24TP
You are now in the measuring mode. The measuring instrument is now operational. The conductance in relation to the reference temperature (25 ° C) and the actual (measured) temperature of the measuring solution are displayed. Correct the temperature coefficients if required. For example at 20°C the Testo conductivity standard solution has a temperature coefficient of 1.91%/°C. (cf. p. 69)
55
56
Description of probes
Temperature probes
As a rule, all Pt100 probes with 8 pin DIN plugs from the Testo range can be connected.
Pt100 sensors are suitable for temperature measurements in a large measuring range (-200 to
+600 ° C/-330 to + 1110 ° F).
The accuracy of the Pt100 measuring sensors corresponds with the tolerances indicated in DIN
IEC 751, class A.
Observe the measuring range given for the temperature probe (see ordering data)! The measuring range of the instrument might not be the same as that of the temperature probe!
Buffer solutions
An important part of maintenance is checking the accuracy of the measured value. This is done with solutions of a known pH value, so-called buffer solutions. There are a variety of different buffer solutions whose pH values cover the complete pH range. One generally distinguishes between DIN (or NBS buffers) and technical buffers.
DIN or NBS buffers distinguish themselves through a very high accuracy (max. 0.005 pH units). The disadvantage is that the low buffer effect makes the solution susceptible to dirt and dilution.
Technical buffers shows tolerances of up to ±0.02
pH units, the pH value is, however, much more stable.
The temperature-controlled pH changes of the buffer solutions stored in testo 252 are listed in the following table:
40
45
50
55
60
25
30
35
38
DIN buffer Testo buffer
° C 1.679 4.006 6.865 9.180 2.00
4.00
7.00
10.00
10 1.670
4.000
6.923
9.332
2.00
4.00
7.07
10.18
15
20
1.672
1.675
3.999
4.001
6.900
6.881
9.276
9.225
2.00
2.00
4.00
4.00
7.04
7.02
10.14
10.06
1.679
1.683
1.688
1.691
4.,006 6.865
4.012
4.021
4.027
6.853
6.844
6.840
9.180
9.139
9.102
9.081
2.00
1.98
1.99
4.00
4.01
4.02
7.00
6.99
6.98
10.00
9.95
9.91
1.694
4.031
6.838
9.068
2.00
4.03
6.97
9.85
1.700
4.043
6.834
9.038
1.707
4.057
6.833
9.011
1.99
4.05
6.96
9.78
1.715
4.071
6.834
8.985
1.723
4.087
6.836
8.962
1.99
4.08
6.96
9.75
Use the solutions offered in the ordering data, as their temperature curves are stored in the measuring instruments.
57
58
Technical data
pH values / redox values / temperature
pH values
The calibration data of 2 pH electrodes is saved.
Measuring range: pH -2 to 16
Max. deviation:
± 1 digit
± 0.01 pH
Resolution: 0.01 pH
The temperature compensation of the pH electrodes are effected over the whole measuring range of the temperature sensors or probes used.
Redox values
Measuring range: -1999 mV to + 1800 mV
Max. deviation:
± 1 digit
± 0.2 mV (-999.9 mV to +999.9 mV)
± 1 mV (remaining range)
Resolution: 0.1 mV (-999.9 to +999.9 mV)
1 mV (-1000 to 1999 mV and
+1000 to +1800 mV)
Temperature
Sensor Temperature range
°C
(Tolerances
± 1 digit)
°F
(Tolerances
± 1 digit)
-20.0 to 100.0
-4.0 to 212.0
Connection
5 K - NTC
5 K - NTC
30 K - NTC
PT 1000
PT 100
PT 100 manual (pH)
-20.0 to 100.0
-20.0 to 100.0
-20.0 to 120.0
-4.0 to 212.0
-4.0 to 212.0
-4.0 to 250.0
4 mm socket
4 mm socket
4 mm socket
-199.9 to 600.0
-325.0 to1110.0
4 mm socket
-199.9 to 600.0
-325.0 to 110.0
DIN plug
-10.0 to 150.0
+14.0 to 302.0
not applicable
Accuracy
BNC-TRIAX socket
°C
± 0.2
°F
± 0.4
± 0.2
± 0.5
± 0.5
± 2.5
± 0.4
± 1.0
± 1.0
± 0.2
> 200°C:
± 0.2 %
± 0.4
> 325°F:
± 0.2 %
—
± 5.0
—
Resolution: 0.1 °C / 0.1 °F
1 °C (from 200 °C) / 1 °F (from 999.9 °F)
Technical data
Conductivity
Conductivity:
Automatic measuring range switch: measuring ranges:
0.000 to 1.999 µS/cm (type B)
0.00 to 1.99 µS/cm (type A)
02.00 to 19.99 µS/cm
20.00 to 199.9 µS/cm
0.200 to 01.99 mS/cm
02.00 to 19.99 mS/cm
20.00 to 199.9 mS/cm
200.00 to 2000 mS/cm
The switch points of the measuring ranges in the display are not identical to the switch points in the microelectronics (depending on the cell constants and the temperature) salt content: 1 mg/l to 200 g/l NaCl (calculated)
Temperature measuring range of conductivity probes
(Refer to “Temperature” on p. 58 for accuracy):
Conductivity probe (5 K NTC)
-20 °C to 100 °C DIN socket
- 4 °F to 212 °F
Non Testo probe (manual)
-10 °C to 150 °C
+14 °F to 302 °F
Using suitable adapter cables the 4mm socket or the TRIAX socket can be used (see “pH values” for measuring ranges). The instrument must be set at combined mode (pH and conductivity) so that the connections in the pH range can be checked for temperature sensors if the temperature sensor is not available in the conductivity probe. These can also be used for temperature compensation in the conductivity measurement.
59
60
Cell constant:
Temperature compensation:
Technical data
Conductivity/storage and operating temperature/Warranty
0.01 to 20 (1/cm)
-10 to +150 °C (man/auto)
+14 °F to 302 °F,
Always observe the permitted ranges for the electrodes/°C sensors
Temperature coefficient linear: 0 to 10%/°C
0 to 5.54 % / °F (adjustable) non-linear
(trEF = 25 °C): Compensation according to the non-linear function of natural water (DIN 38404, 0 to 50 °C)
Reference temperature, adjustable: T ref
= 18 °C, 20 °C or 25 °C
A change in the reference temperature automatically corrects the temperature coefficients
The calibration data of 2 conductivity electrodes was saved (type A/B)
Max. deviation:
(± 1 digit)
Resolution:
±0.5 % of conductivity m.v.
±1.2 % of NaCl m.v.
max. 0.01 µS/cm and 0.1 mg/l automatic range switch
Storage and operating temperature of the instrument:
Storge temperature: -20 to 60 °C
Operating temp.:
Weight:
0 to 50 °C
Approx. 270 g (w/o battery)
Approx. 320 g (with battery)
Warranty
Meas. instrument: 3 years
Electrodes and conductivity measuring cells: 1 year
Temperature probe: 1 year
Logger: 1 year
- not incl. printer -
Accessories: 6 months
- +
Analogue outputs
The testo 252 measuring instrument has two parallel analogue outputs. Depending on the probes plugged-in, different signals are given out at the analogue outputs. The value in the top line of the display is always the output from the top analogue output.
In order to connect the analogue output, please use the connecting lead 0409.0084 listed in the ordering data.
Output via:
Miniature sockets for banana plugs Ø 2 mm.
Output signals
Temperature probe
1 mV/ ° C 0.5 mV/ ° F pH electrode
25 mV/ pH
1 mV/ ° C 0.5 mV/ ° F
Redox electrode
0.25 mV/mV
Conductivity sensor
0.25 mV/ mS
2 mV/ g/l(NaCl)
Load:
≤
10 k
Ω
Observe correct polarisation when connecting the analogue outputs!
61
62
Options
for storing...printing...processing
Logger
The logger provides a permanent record of the measuring results. The logger is simply connected onto the instrument which thus becomes a complete measuring system. The measured data is printed with date and time "in the field" or stored for later evaluation.
IR printer up to 2500 values
Storage capacity
Print-out up to 750 print-outs consisting of date, time, no of measured value and measured values
Printer alphanumeric thermoprinter
16 character/line
Printing speed
Permissble ambient temperature
Storage and transport temperature
Weight
Power supply approx. 1 line/sec.
0 to +40 °C (+32 to +104 °F)
-30 to +60 °C (-20 to +140 °F) approx. 250 g (8.8 oz) battery/rech. battery or mains operation (only together with rech. battery)
The data is stored at the touch of a button without irritating cable connections or time-consuming written work.
Type of printer
Printing capacity
Receiver radius
Operating temperature
Storage and transport temperature
Dimensions
Weight
Power supply infrared controlled thermal printer, adjustable contrast approx. 300 print-outs per roll max. 1 m
0 to +50 °C (+32 to +122 °F)
-40 to +60 °C (-40 to +140 °F)
186 x 91 x 61 mm (7.3" x 3.6" x 2.4")
0.43 kg/1 lb (incl. batteries)
4 miniature batteries
1.5 V or NC rech. batteries
Options
for storing...printing...processing
PC adapter
The PC adapter enables the problem-free transfer of data to your PC. The measured data is then evaluated with the Comfort Software or prepared by the standard software for evaluation in Lotus,
Harvard Graphics etc.
Standard software
Storage of measured data in ASCII format
Further processing with the aid of current spread sheet programmes
(Lotus, Star-Planer, MS-Excel,
Symphonie, Harvard Graphics, Quattro Pro)*
Prerequisites • IBM XT/AT or compatible computer
• DOS from 3.1
*The above-mentioned programmes are registered trade marks of the respective manufacturers.
Comfort Software
Graphic evaluation of measured data with the WINDOWS user surface.
Multiple windowing display and evaluation of several files of measured data in different windows
Functions
• simple zoom function
• mathematical smoothing function
• statistical calculation functions
(mean value, deviation…)
Print-out of measured data
Prerequisites in graphical or tabular form
• IBM AT or compatible computer
• DOS from 3.1
• WINDOWS from 3.0
Other • easy use with mouse option
• colour superimposition of freely-selectable limit values
63
Ordering data
Description
Measuring instruments and options
testo 252
Measuring instrument for pH, mS/cm, ° C, mV,
Part no.
0560.2520
Description
Electrodes for non-critical environments
Meas. range Part no.
Type 01 (universal electrode) economical, unbreakable plastic electrode with gel electrolyte, thus practically maintenance-free. pH 0 to14 0650.0623
Fixed cable with BNC plug
Application range: 0 to +60 °C/+32 to + 140 °F (short-term +80 °C/+175 °F)
Type 02 laboratory electrode pH 0 to 14 0650.1223
highly-accurate glass electrode with excellent chemical resistance. Long life due to liquid electrolyte incl. standard probe sleeve adapter and storage cap without fixed cable. Application range: 0 to +80 °C/+32 to +175 °F
(short-term +100 °C/+210 °F)
Type 04 universal electrode
(with integrated temperature sensor) pH 0 to 14
0 to 60 ° C (32 to 140 °F) unbreakable plastic electrode with gel electrolyte, thus pratically maintenance-free, incl. standard probe sleeve adapter and storage cap, without fixed cable
Application range: 0 to +60 °C/+32 to +140°F (short-term +80°C/+175°F)
0650.0823
Description
Electrode for critical environments
Meas. range Part no.
Type 05 special electrode
(with integrated temp. sensor) pH 0 to 14
0 to 60 ° C (32 to 140 °F) unbreakable plastic electrode with liquid electrolyte, few problems with dirt, high accuracy in critical substances and short response times due to hole diaphragm, incl. standard probe sleeve adapter and storage cap
Application range: 0 to +60 °C/+32 to +140 °F
06501623
Refer to p. 46 onwards for additional probe descriptions.
64
Ordering data
Description
Electrode for solids and semi-solids
Meas. range Part no.
Typ 03 penetration electrode highly-accurate glass electrode with solidified inner buffer, short response times, insensitive to dirt, incl.
pH 2 to 14 0650.0225
standard probe sleeve adapter and storage cap, without fixed cable without fixed cable
Application range: 0 to +40 °C/+32 to +104 °F (short-term +60 °C/+140 °F)
Description
Redox electrode
Meas. range Part no.
Type 06 redox electrode ±1999 mV rugged glass electrode, insensitive to electrode poisoning due to two chamber system, incl. standard probe sleeve adapter and storage cap without thermometer, without fixed cable
Application range: 0 to +80 °C/+32 to 175 °F
Description
Electrode accessories
0650.2523
Meas. range Part no.
S7-BNC electrode cable necessary for electrodes without fixed cable
Electrode cable S7-BNC (5 m)
Description
Conductivity sesnors
0554.2317
Meas. range Part no.
Type 08 conductivity sensor with glass shaft, highest level of accuracy up to
Type 11 conductivity sensor with plastic shaft, highest level of accuracy up to
Description
Storage solutions, electrolyte, buffer
600 mS/cm
300 mS/cm
0650.3025
0650.3026
Part no.
Testo buffer set pH 4/pH 7 (50 ml each)
Testo buffer set pH 4/pH 7/pH 10 (50 ml each),
Testo buffer pH 2 (50 ml)
Testo buffer set pH 4/pH 7 (500 ml each)
Testo buffer set pH 7/pH 10 (500 ml each)
0554.2321
0554.2320
0554.2322
0554.2337
0554.2338
65
66
Ordering data
Description
Storage solutions, electrolyte, buffer (continuation)
DIN buffer set pH 4.008/pH 6.865
(250 ml each)
DIN buffer set pH 6.865/pH 9.180
(250 ml each)
Storage solution (50 ml) for electrodes type 01, 02, 04, 06
(refill solution for type 02)
Storage solution
(50 ml) for type 03 electrodes
Storage and refill solution (50 ml) for electrodes type 05
Conductivity standard (1413 mS/cm)
0.01 mol/l KCI, for calibration of conductivity sensors
Redox standard 358 mV (50 ml), for calibration of redox electrodes
Part no.
0554.2339
0554.2340
0554.2332
0554.2318
0554.2319
0554.2334
0554.2333
Description
Pt100 temperature probes
Meas. range Part no.
Type 04 immersion probe for quick measurements in liquids and powdery
Type 25 penetration probe with sharpened measuring tip, V4A material, water-resistant, boil-proof 150 mm, Ø 3 mm, t
99
-50 to +400 ° C* 0605.0473
-60 to +750 °F substances, l = 150 mm, Ø 3 mm, t
99
210 mm, Ø 4 mm, t
99
= 7 sec.
Type 15 immersion probe -50 to +160 ° C* 0605.1570
specially for use in laboratories, probe shaft halar-coated
-60 to +320 °F l =
= 10 sec.
-200 to 600 ° C* 0605.2573
-330 to +1110 °F
= 30 sec.
l =
Type 97 air probe for quick air measurements
-50 to +600 ° C* 0605.9773
-60 to +1110 °F l = 150 mm, Ø 9 mm, t
99
= 75 sec.
Type 99 surface probe for measurements on metallic surfaces l = 150 mm, Ø 8 mm, t
99
= 40 sec.
-50 to +400 ° C* 0605.9973
-60 to +750 °F
*Accuracy of Pt100 probes according to DIN IEC 751, class A
Ordering data
Description
Calibration certificates
Part no.
Standard calibration certificate , meas points -20°,0°,60°C (-4°F, +32°F, +140°F) for immersion probes and 60°, 120°C (140°, 248°F) for surface probes
0520.0001
Special calibration certificate, meas. points freely selectable from -40 to 1000°C
(for surface probes +50 to +420°C)
0520.0101
DKD calibration certificate , meas. points freely selectable from
-40 to +1000°C
0520.0201
Standard calibration certificate, conductivity
Measuring point 1.413 mS/cm 0520.0009
Calibration certificate for pH measuring instrument with probe0520.0008
Analyser certificate for pH buffer solution (for 2 solutions) 0520.0007
Description
System accessories
Mains unit for mains operation and charging of rech. batteries
(in hand instrument and logger)
9 V rech. battery for meas. instrument
Charger for external charge of 9 V rech. battery
Analogue output connection lead (for one channel)
Logger, incl. battery, stores and prints measured values
Set of rech. batteries for logger (4 x 1.24 V)
Thermopaper for logger (5 rolls)
Standard software, incl. PC Adapter, for storing measured data in ASCII format
Comfort software, incl. PC Adapter, for graphic evaluation of measured data under WINDOWS
Galvanic separation for serial interface
Infrared printer incl. 4 miniature batteries and 1 roll of thermopaper, prints the measured value in the field
Battery charger with 4 NC rech. batteries for infrared printer
Thermopaper for infrared printer (6 rolls)
Carrying case (leather) for testo 252 measuring instrument
Carring case (leather) for testo 252 meas. instrument and logger
System case for testo 252 ,
Logger, PC adapter, probes and accessories
Spare cladding tube for type 08 mS (0650.3025)
Spare parts set for pH electrodes (standard probe sleeve adapter, storage cap and vent plugs)
Technical manual on pH measuring engineering
Part no.
0981.3484
0554.0088
0515.0025
0554.0025
0409.0084
0554.0070
0515.0088
0554.0149
0554.0071
0554.0109
0554.0006
0554.0345
0554.0110
0554.0115
0516.0090
0516.0091
0516.0250
0554.0049
67
Appendix
Temperature coefficients of several selected solutions
The values in the following table are mean temperature coefficients for 18 ° C T
26 ° C. They were converted to a reference temperature of 25 ° C in accordance with the following formula. The values indicated are from the book "Zahlenwerte und
Funktionen, Bd. 2, Teil 7" by Landold-Börnstein.
( )
δδ
T (22±4 ° C)
•
100%
κ
25 ° C
•
Compound αα Compound αα
HCl
HNO
3
H
2
SO
4
NaOH
KOH
2.55
2.55
2.48
2.48
2.61
2.55
1.71
1.76
2.27
2.34
2.34
2.41
2.61
2.94
3.13
2.88
1.27
1.32
1.37
1.41
1.41
2.13
2.34
2.34
1.42
1.41
1.40
1.37
1.33
1.29
1.25
1.25
1.65
1.65
1.66
1.70
1.75
1.82
1.91
1.88
2.12
2.47
2.93
3.42
3.98
4.46
4.66
Concentration c in Mol/l p in weight % c = 1.405
2.877
4.420
11.303
c= 1.017
2.108
3.276
4.533
5.873
p=
7.300
8.801
10.376
13.640
96.00
96.87
97.13
98.42
c =
99.98
100.14
100.21
100.51
101.12
0.641
1.319
2.779
99.08
99.44
99.58
99.66
99.74
99.75
99.78
99.79
4.381
6.122
8.002
10.015
12.150
14.400
15.323
c = 0.777
1.612
2.508
3.467
4.491
5.583
6.744
NaCl
KCl
NaNO
3
KNO
3
Na
2
SO
4
K
2
SO
4
NH
4
OH
NH
4
Cl
NH
4
NO
3
2.12
2.17
1.88
1.78
1.90
1.81
2.10
1.99
1.79
1.77
1.73
1.71
2.06
2.07
2.13
2.03
1.59
1.51
1.49
1.91
1.88
1.87
1.91
1.82
1.88
1.86
1.85
1.88
1.96
2.00
1.76
1.66
1.39
1.78
1.71
1.59
1.50
1.44
1.41
2.04
2.13
2.21
2.49
1.74
1.65
1.53
1.45
Concentration c in Mol/l p in weight % c = 0.884
c = c = c = c =
1.206
c = 0.298
0.620
0.250
c =
0.500
0.059
0.467
0.933
1.626
2.240
2.496
0.250
0.500
1.000
0.368
0.768
3.039
3.213
0.607
1.255
2.688
4.329
0.509
1.051
1.830
2.843
3.924
5.085
5.421
0.691
1.427
2.208
c = c =
2.307
4.550
8.870
0.984
1.923
2.924
3.952
5.003
0.637
1.301
2.711
4.233
5.882
7.664
68
Appendix
Calculation of conductance at 25 ° C
For an approximate conversion of a conductivity value, measured at any temperature, into the value at reference temperature (e.g. 25 ° C), the temperature coefficients should be used according to the following equation (see also
DIN 38404, section 8):
α
TR
κ
ΤΜ
− κ
TR
= • • 100%
TR
Τ
M
1
- T
R
α
TR
T
R
T
M
κ
TR
κ
ΤΜ
Temperature coefficient at +25 ° C
Reference temperature (25 ° C)
Measured temperature of the measuring solution
Electrical conductivity at reference temperature
(25 °C)
Electrical conductivity at a measured temperature
Temperature variation of the Testo conductivity standard 1413 µS/cm
Temperature Conductivity in °C of the standard solution
Temp. coeff.
of the standard sol.
referred to
25 °C
Temperature Conductivity Temp. coeff.
in °C of the of the standard solution standard sol.
referred to
25 °C
12
13
14
15
16
17
10
11
8
9
6
7
4
5
2
3
0
1
0.970
0.995
1.020
1.045
1.070
1.095
1.121
1.147
1.173
1.199
0.776
0.800
0.824
0.848
0.872
0.896
0.921
0.945
1.84
1.85
1.85
1.86
1.87
1.88
1.88
1.88
1.89
1.89
1.80
1.81
1.81
1.82
1.82
1.83
1.83
1.84
30
31
32
33
34
26
27
28
29
22
23
24
25
18
19
20
21
1.441
1.469
1.497
1.525
1.553
1.581
1.610
1.638
1.667
1.225
1.251
1.278
1.305
1.332
1.359
1.386
1.413
1.98
1.95
1.96
1.96
1.97
1.98
1.98
1.99
2.00
1.90
1.91
1.91
1.91
1.91
1.91
1.91
—
69
70
Appendix
Electrical interference during measurements in laboratories
During measurements in grounded measuring solutions, a measuring error can occur as a result of the earth loops (galvanic and/or capacitive coupling).
Not grounded measurement with mains independant measuring instruments (to which no complementary instruments are connected, e.g.
recorder) guarantees as a rule interference-free operation. When using mains operated instruments, a galvanic separation must be installed for each instrument - this is particularly valid when computer systems are connected. We recommend the use of an optically-coupled interface (article no. 0554.0006) in conjunction with a PC adapter (article no. 0554.0071).
The simplest test methods for the user involve dipping a sensor in a well-insulated solution and then alternately ground and un-ground the solution. Should the display change, there is a very high disturbing current. It is useful in this case to operate the instrument with batteries or rech.
batteries.
During parallel measurements (pH conductivity) with testo 252 measuring instruments, please note the following points:
• The measured value is only valid when both probes are immersed in the measuring solution.
• For low conductivity solutions (< 100 µS/cm) glass/platinum cells should be used.
Appendix
Electrical interference during measurements in laboratories
• A pH electrode emits small quantities of reference electrolyte (e.g. KCl, 3M) into the measuring solution. The measurement of electrolytic conductivity can as a result be incorrect during parallel conductivity/pH measurements in measuring solutions of a very low conductance. A remedy would be: large volumes of measuring solution, short duration of measurement, no calibration in this parallel mode
71
testo AG
Postfach 11 40, 79849 Lenzkirch
Testo-Straße 1, 79853 Lenzkirch
Telefon: (07653) 681-0
Fax: (07653) 681-100
E-Mail: [email protected]
Internet: http://www.testo.com
0973.2640/05.95/T/wh/21.06.2004
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