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C HAPTER 7 ____________________________________________________________MAINTENANCE
CHAPTER 7
MAINTENANCE
Reference measurements
Reference measurements are needed to verify whether the transmitter readings are within specifications. This way the user can check if the transmitter needs calibration or service.
The reference measurement should be made as close to the checked sensor as possible and the readings should be read at the same time, when possible. A re-calibrated DMP248 transmitter can be used as a reference.
Self-diagnostics
The DMP248 transmitter goes through a self-diagnostics procedure when the power is switched on. If the procedure does not reveal any errors or faults, the transmitter starts operating normally. If errors or faults are found, check first if the DRYCAP
sensor is damaged. If it is intact, send the transmitter to Vaisala or a Vaisala representative for repairs. The error messages the transmitter outputs are listed in
Appendix 5.
If any errors occur during operation, the error messages are output on the local display if the transmitter displays measurements; if the menus are used, error messages are not output. The LEDs indicate errors at all times. During operation, however, the error messages are not output automatically through the serial interface. If there is any reason to doubt that there is something wrong with the transmitter, use command ERRS:
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OPERATING MANUAL _______________________________________________________________
ERRS <cr>
If there are no error messages, only a prompt is displayed:
>ERRS <cr>
>
When errors have occurred, the transmitter outputs the error code (see
Appendix 5 for all error messages):
>ERRS <cr>
E40 f ( all ) out of range
>
Temperature channel adjustment with Pt 100 simulators
Switch the power off and disconnect the wires to the Pt 100 sensor from solder lugs TP5, TP6 and TP7.
TP6 TP7
X88
F IGURE 7-1
TP5
Location of solder lugs TP5, TP6 and TP7 and connector X88
Connect a Pt 100 simulator to connector X88 and set it at the lowest temperature to be calibrated.
Pt 100
X88
F IGURE 7-2 Connecting the Pt 100 simulator to connector X88
Switch the power on.
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C HAPTER 7 ____________________________________________________________MAINTENANCE
Adjustment using serial commands
Give command CT and enter the first point value and press <cr>:
>CT <cr>
'C : xx.x Ref1 ? yy.y <cr>
Press any key when ready
Set the Pt 100 simulator at the highest temperature to be calibrated, and press any key. Enter the second point (gain) reference reading. If second reference is not needed, press <cr> to complete one point offset correction.
Adjustment using display commands
Select Cali in the main menu and then T ; select two-point calibration T
2 point cal
. Change the first point reading with the arrow keys and press ENT.
Set the Pt 100 simulator at the highest temperature to be calibrated, and adjust the second point (gain) to the reference reading.
Adjustment using LED commands
Connect an ammeter/voltmeter to the analogue outputs (connector
X2). Give command
¡¡l¡
, and adjust the first point (offset) with the arrow switches to the same reading with the reference and press
ENT switch.
Set the Pt 100 simulator at the highest temperature to be calibrated, and adjust the second point (gain) to the reference reading. If there is no second reference, press ENT to complete one point offset correction.
Disconnect the Pt 100 simulator and reconnect the Pt 100 wires to solder lugs TP5, TP6 and TP7.
The correct connections according to the wire colours are:
TP5 blue
TP6 green
TP7 yellow
TP8 black
If there is not a Pt 100 simulator available, the adjustment can be made with two resistors of 84
Ω
and 154
Ω
whose resistance is known precisely. Measure the resistor with a resistance meter. Look up the
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OPERATING MANUAL _______________________________________________________________ corresponding temperature value from a Pt 100 conversion table or calculate it using the following equation:
T
=
D0
+
R x {D1
+
R x [D2
+
R x (D3
+
R x D4)]} (7-1) where
D0
D1
D2
D3
D4
=
=
=
=
=
-243.5673014
2.278542701
0.002050681
-6.15025E-06
1.34949E-08
Measurement of output currents using test points
If a current output has been connected e.g. to a process computer, the output current cannot be measured at the output connector X2 without disconnecting the external load. The output current can, however, be measured at test points CH1+/CH1- and CH2+/CH2- without disconnecting the output wires. These test points can therefore be used in one point offset correction against an accurate reference or in checking the current output without disconnecting the analogue output from the process.
CH1 +
+ CH2
X15
X2
OPENED COVER OF THE DMP248
F IGURE 7-3 Location of the CH1 and CH2 test points
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7____________________________________________________________ MAINTENANCE mA
CH1+ CH1-
TEST POINTS
X2
CH1+
CH1-
R
L
F
IGURE
7-4 Circuit diagram of the analogue output current test points
Adjusting the contrast of the display
The contrast of the display can be adjusted using the trimmer "LCD display contrast" located next to the press switches.
Vaisala Service Centers
NORTH AMERICAN SERVICE CENTER
Vaisala Inc., 100 Commerce Way, Woburn, MA 01801-1068, USA.
Phone: +1 781 933 4500, Fax +1 781 933 8029
Email: [email protected]
EUROPEAN SERVICE CENTER
Vaisala Instruments Service, Vanha Nurmijärventie 21 FIN-01670 Vantaa,
FINLAND.
Phone: +358 9 8949 2758, Fax +358 9 8949 2295
E-mail: [email protected]
ASIAN SERVICE CENTER
Vaisala KK, 42 Kagurazaka 6-Chome, Shinjuku-Ku, Tokyo 162-0825, JAPAN.
Phone: +81 3 3266 9611, Fax +81 3 3266 9610
E-mail : [email protected]
www
.
vaisala.com
V AISALA _________________________________________________________________________ 71
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