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Programmable Multimeter HM 8112-2
As the instrument is an electrical apparatus, it may be operated only by trained personnel.
Maintenance and repairs may also be carried out only by qualified personnel.
In correspondence concerning this istrument, please quote the type number and serial number as
given on the type plate.
HM 3112-2
6% Digit Display with 14mm LED £ 1.999.999 digit
True RMS Measurement Capability
Resolution 100 nV, 1m, 10nA
Digital Offset Correction
10 Measurements per Second
Programmable Measuring Time from 0.1s - 10s
IEEE-488 Bus standard
Built-in Self Test Function
Computing Capabilities such as Offset, dB, dBm
The HAMEG HM8112-2 6% digit multimeter is
an excellent instrument for either benchtop or
automated system applications. The unitcan measure
a signal to the precision of 1999999 digits and can
resolve voltages as small as 100nV DC. True RMS
values are measured on AC signals through DC-
coupled circuitry. A separate guard connection
ensures a high common-mode rejection. This
instrument combines excellent accuracy with seven
high-performance measuring functions, keeping
operation extremely easy and straight forward.
Resistance measurement can be made as a 2- or 4-
wire measurement with a resolution down to 0.001.
Separate digital offset and zero functions allow
measurements referenced to auser-defined baseline
as well as compensation of offset values at any time
via the front panel. Temperature measurements are
possible with a PT-100 sensor in 4wire configuration.
Measurement results as well as any selected
data can be retrieved via the built-in IEEE-488
interface. It also allows for remote control and
monitoring of all of the multimeter's functions
including digital calibration. Achoice of integration
times (100ms, 1s, 10s), as weil as 5% or 6%-digit
E High Input Resistance: 1GO (0,2V and 2V range)
E Electronic Calibration via Keyboard
or IEEE-488 Bus for all Ranges
HB Automatic or Manual Range Setting
E Built-in 4-pole 10-Channe! Scanner
(Model HM8112-25)
Trigger Input for Manual or Controlled Triggering
Temperature Measurement with 0.01°C resolution
Ш 4-Wire Resistance Measurement
display can be made. In "talk only" mode,
measurement results and instrument settings
can be down-loaded to a "listen-only" device. Inthe
trigger mode individual measurements can be
initiated through a separate trigger input on the
instrument's rear panel or via the IEEE-488
Extensive power-up self-test routines verify
internal analog and microprocessor circuitry, giving
a clear indication of any error detected. The easy to
use firmware ofthe HM8112-2enables the measured
value to be displayed as %-value, corrected with an
offset or converted to dB.
The HM8112-2 is also available with a built-in 10-
channel 4-pole scanner (HM81 12-2/5) for applications
that require multiple measurement points. Channel
selection is possible via front panel or IEEE-488
interface where individual channels may vary their
measurement functions. The switching contacts of
the scanner are low-resistance (<20m®) and low in
thermo-electric voltage (<1uV).
The HM8112-2 is ergonomically designed and
featuresrapid single button function range selection,
as well as easy operation.
(Ref. temp.: 23°C+1°C) CURRENT mA, mA,
Ranges: +2mA, 2A 2mA, 2A
DIRECT VOLTAGE Ve Integration Times (sec.): 0.1; 1; 10 0.1; 1; 10
Full Scale / Resolution: 199.999/10nA 199.999/10nA
Ranges: +0.2V, +2V, +20V, +200V, +1000V% Accuracy: (1 year, 23+5%C) * DC 20Hz - 10kHz
Accuracy: >’? , Temperature Ranges 2mA and 2A 0.01+0.005 0.2+0.07
24h, 23x1°C year, 23+5C Coefficients” Temperature Coefficient: " * 0.002+0.001 0.01+0.004
Range % rdg. % fs. %rdg %fs. +[%rdg.+%fs.] Maximum Burden9: Range 2mA:<10mV; 2A:<600mV
+0.2V 0.002 0.0007 0.006 0.0007 0.0006 0.00015 Overload Limits: 250V (3A fuse protected) ?
+2V 0.002 0.0005 0.005 0.0005 0.0003 0.0001 Crest Factor: 7:1 (Peak value max. 1.5 fs)
+20V 0.002 0.0005 0.005 0.0006 0.0003 0.0001 Transient Response Time: 0.5sec. to reach final value within 0.1%
+200V 0.002 0.0005 0.005 0.0006 0.0003 0.0001
+1000V 0.002 0.0005 0.005 0.0005 0.0003 0.0001
Integration Times: 0.1sec. 1+10sec. RESISTANCE kQ
Fullscale: 199.999 1,999.999 Integration Times: 0.1sec. , 1sec., 10sec.
1000V Range 100.000 1,000.000 Full Scale/Resolution: 199.999/1mQ 1,999.999/1mQ
Resolution: 14V 100nV 1,200.000 (10M range)
input Resistance: +0.2V, +2V 1GQ Accuracy: ® * Temperature
+20V, +200V, +1000V 10MOQ 24h, 234 1% 1year, ON Coefficients 5)
lieu ; o Range %rdg. % fs. %rdg. %fs. +[%rdg.+%f.s.]
Zero Stability: Temperature drift less than 0.3pV/ C 2000 0.002 0.001 0.005 0002 0.002 0.0005
Long term stability better than SuV in 90 days
. . 2kQ 0.002 0.0005 0.005 0.0005 0.0015 0.0005
Measuring gaps: None. 125ms for range or function changes.
. " и 20kQ 0.002 0.0005 0.005 0.0005 0.0015 0.0005
Overload Protection: (between „V/Q-HI and N/QO-LOW ) 200kQ 0.002 0.0005 0.005 0.0005 0.0015 0.0005
+0.2V, +2V ranges: for 60sec. + 1000v 2MQ 0.002 0.0005 0.005 0.002 0.002 0.0005
+20V, +200V, +1000V ranges continuous +1000V* TOMO 0.01 0.003 0.05 0.006 0.01 0.0005
Between , V/Q-LOW” and GUARD 50V DC or AC rear Current through measured resistor:
Between GUARD and case 200V DC or AC ak Range 2000, 2KN 0.7mA
Interference Rejection 20k€2 ТОНА
(Measured by increasing the peak-peak interference signal level until MO | oMO LA
a display error of 1 digit results with 1sec. measuring time).
Series mode interference rejection
50Hz/60Hz power line frequency ............. : better than 60dB
Common mode interference rejection (connected to one input terminal
via low resistance path, 1kQ inserted in series with one input lead)
DC or 50/60HZ ..............eneeenrenierniare ee : 140dB
0.2V, 2V, 20V, 700V*
Open circuit terminal voltage: 14V max.
Overload limit: +300V ax (125V pa with Scanner)
4 wire resistance measurement (PT100/IEC751)
Range: —200°C to +850°C
Resolution: 0.01°C; Measurement current is IMA, nominal
Tolerance: +0.05°C (1 year, without counting probe tolerance)
Temperature coefficient: 10°C - 18°C, 28°C - 40°C <0.001°C/°C
0°C - 10°C, 40°C - 50°C <0.002°C/°C
Conversion Method:
True RMS value with DC coupling of the input.
Input Resistance: 10MQ Il <60pF
Transient Response Time: 0.5s to 0.1% rdg.
Overload Limits:
Channels/Contacts per Channel/Function:10/4/1 of 10
input V/Q2 : x1000V ak OT 700 Yıms roy Thermoelectric EMF: Less than 1pV after 90min. warm-up
with the restriction of 10 VxHz Max. Voltage: 125V__, or 10°VxHz (whichever is less)
Between GUARD and case : 200V peak Max. Switch Current: 3A
Between ,,V/Q-LOW"” and GUARD : 50V peak
Accuracy: +[% of reading (% rdg.)
+ % of full scale (% f.s.)]" (1 year, 23°+5°С) IEEE-488-BUS INTERFACE
Range DC-20Hz 20Hz-10kHz 10kHz-50kHz 50kHz-100kHz Supported IEEE-488-Bus Functions:
0.2V 0.5+0.07 0.3+0.1 SH1/AH1/T5/L3/RL1/DC1/DT1/SR1
27 D0.5+0.07 0.3+0.1 1+0.4 3+0.4 Output Data: Numerical data for measurement result, function,
20V 0.5+0.07 0.3+0.1 140.4 3+0.4 range, and integration time
oy EN e Don 3+0.4 8+0.4 Input Data: Function, range, integration time, start command,
+. (DC - 2) nominal calibration value..
Temperature Coefficient: GENERAL
10°C to 18°C and 28°C to 40°C / x2 at 0—50°C N ;
Freq. (kHz) +[% rdg. + % f.s.] PC Warm up time: typ. 90min. to specified accuracy.
0-20 0.01 0.004 Power requirements: 110/220V+15%; 45-60Hz; 17VA
20-100 0.04 0.005 Ambient temperature: —40°C to +70°C (storage)
- . . . 4. +10°C to +40°C (operation)
Integration o 909 o h oy 10 seconds Humidity: 10%-75%, no condensation
ull Scale: 199.999 (700.00 in the range) Dimensions: 285x85x365mm (WxHxD). Weight: approx. 4kg
Crest Factor: 7:1 peak value (max. 1.5xf.s.) Safety: Class |, according to ¡EC 348
” Shield connected to , V/Q-LOW"” input socket, 3 +[% of reading (% rdg.) + % of full scale (% f.s.)]
sinusoidal signal greater than 5% of full scale. 4 +1 Digit after offset correction (rdg. = reading / f.s. = full scale)
5 10°C to 18°C and 28°C to 40°C/x2 at 0°C-50°C
2) Max. 125V with a max. 10°VxHz when the scanner is incorporated. 8 Burden is the voltage across any external load shunt
Control Elements HM 8112-2
G) POWER OFFSET (Pushbutton/LED)
Power switch; mains connector at rear side. Activates the “Offset”-function.
(2) REMOTE/LOCAL (Pushbutton/LED) (9 РВС./ЕМТЕВ (Pushbuttons)
The remote-LED is lit when the instrument is operated via Pushbuttons for selection and activation of internal programs.
the IEEE-488 bus. Return to local by actuating the local-
switch is possible, provided the instrument is not in “Local (9 GUARD (4mm banana socket)
lockout state”. Shield to obtain a high common mode rejection.
3 TRG./READY (Pushbutton/LED) © V, Q, T (4mm banana sockets)
Pushbutton for manual triggering of the HM8112-2. The Input for voltage, resistance, and temperature
LED “Ready” indicates that the unit is ready for measurements.
(2 A (4mm banana sockets)
(9) FUNCTION (Pushbuttons and LEDs) Input for current measurement and source terminal for 4-
Pushbuttons for activating the desired measuring function. wire resistance and temperature measurements.
(5 UP/DOWN Range selection. @ Display (7segment LEDs).
(9 AUTO (Pushbutton) (9 CHANNEL (7segment LED)
Pushbutton for activating the autorange function. Readout for selected scanner channel.
С) ZERO Pushbutton for activating the “Zero-correction”- (9 PRG. (7segment LED)
function. Readout for selected internal program.
6 6 e
io MAINS/LINE (8 TRIGGER INPUT (BNC socket) Input for external triggering.
Mains connector, line voltage selector and fuses. (9 SCANNER INPUT 50 pole sub D connector (Option).
(7 IEEE 488 60 Meas. - Cal. (Slide switch)
IEEE-488 interface connector. Selector between measurement mode and calibration mode.
Subject to change without notice HM8112-2
General Information
The operator should not neglect to carefully read the
following instructions, to avoid any operating errors and to
be fully acquainted with the instrument when later in use.
After unpacking the instrument, check forany mechanical
damage or loose parts inside. Should there be any
transportation damage, inform the supplier immediately
and do not put the instrument into operation.
This instrument has been designed and tested in accor-
dance with IEC Publication 1010-1, Safety require-
ments for electrical equipment for measurement,
control, and laboratory use. It corresponds as well to
the CENELEC regulations EN61010-1. Allcase and chassis
parts are connected to the safety earth conductor.
Corresponding to Safety Class 1 regulations (three
conductor AC power cable). Without an isolating
transformer the instrument must be plugged into an
approved three contact electrical outlet, which meets
International Electrotechnical Commission (IEC) safety
Any interruption of the protective conductor inside or
outside the instrument or disconnection of the
protective earth terminal is likely to make the
instrument dangerous. Intentional interruption is
The instrument must be disconnected and secured against
unintentional operation if there is any suggestion that safe
operation is not possible. This may occur:
— if the instrument has visible damage,
— if the instrument has loose parts,
— if the instrument does not function,
— after long storage under unfavourable circumstances
(e.g. outdoors or in moist environments),
— after excessive transportation stress (e.g. In poor
When removing or replacing the metal case, the instrument
must be completely disconnected from the mains supply.
If any measurement or calibration procedures are
unavoidable on the opened-up instrument, these mustbe
carried out only by qualified personnel acquainted with
the danger involved.
Symbols As Marked on Equipment
/N ATTENTION - refer to manual
/N Danger - High voltage
7 Protective ground (earth) terminal
Before being shipped, each instrument must pass a 24 hour
quality control test. Provided the instrument has not
undergone any modifications HAMEG warrants that all
products of its own manufacture conform to HAMEG
specifications and are free from defects in material and
workmanship when used under normal operating conditions
and with the service conditions for which they were furnished.
The obligation for HAMEG shall expire two (2) years after
delivery andis limited to repairing, or atits option, replacing
without charge, any such product which in HAMEGs sole
opinion proves to be defective with the scope of this
Thisis HAMEGs sole warranty with respectto the products
delivery hereunder. No statement, representation,
agreement or understanding, oral or written, made by an
agent, distributor, representative or employee of, which
is not contained in this warranty will be binding upon
HAMEG, unless made in writing and executed by an
authorized HAMEG employee. HAMEG makes no other
warranty of any kind whatsoever, expressed or implied,
and all implied warranties of merchantibility and fitness
foraparticular use which exceed the aforestated obligation
are hereby disclaimed by HAMEG be liable to buyer, in
contract or in tort, for any special, indirect, incidental or
consequential damages, espresses, losses or delays
however caused.
In case of any complained, attach a tag to the instrument
with a description of the fault observed. Please supply
name and department, address and telephone number to
ensure rapid service.
The instrument should be returned in its original packaging
for maximum protection. We regret that transportation
damage due to poor packaging is not covered by this
This instrument is intended for connection to 220V or
110V, 50/60Hz mains input voltage. Before installing the
instrument, ensure that it is set to the local line voltage.
On delivery the unit is set to either 110V or 220V, as
indicated on the line voltage selector on the rear panel. If
the line voltage setting is incorrect, set the line voltage
selector in accordance with the local line voltage before
connecting the instrument to the line.
The instrument is protected by two primary fuses. These
have to be changed when the line voltage changes.
For 220V /110V use delayed action fuses. Remove the line
plug before fitting the fuses. Ensure that only fuses of the
specified type are used.
Subject to change without notice
Range selection
Range selection is automatic when the “Auto” key has been
pressed, or manual with the range keys. When the “up” or
“down” keyis pressed, the autoranging function is switched
off and the active range is switched one step up or down for
each keypress.
The autoranging function makes a preliminary decision within
the first third of the set measuring time, whether the active
range is the correct one. The brief measurement takes 200
ms and produces no service request when SRQ is selected.
If the set range is retained after the preliminary decision,
then two further checks are made after elapse of the
complete measuring time:
1. The next higher range is selected if the range limit is
reached or exceeded.
2. Ifless than 8% of the set range is reached, then the next
lower range is selected. The next measurement then
commences in the newrange 100 msecafter switchover.
Digital Display
The measurement results and error messages are shown on
the display of the HM8112-2. Certain operating modes of the
multimeterare indicated here too, e.g. the selected programm
(digit 15) or the activated scanner channel (digit 14).
The HM 8112-2 executes an automatic self-test on power-
up. Progress of the individual test routines is indicated in the
display by the message “Contr.1-3”. No voltage greater
than 300 V should be present at the input sockets during
self-test. If an error occurs during the self-test, this error is
reported by a corresponding error message and the
multimeter aborts further execution of the self-test. To
resume execution of the self-test routines press any key.
Contr. 1 initializes the DMM and checks the analog section.
Contr. 2 checks the battery backed-up RAM
Contr. 3 checks the program ROMs
Error Messages
The DMM recognizes the following error situations caused
by incorrect operation or manual control. They are reported
in the main display or via the IEEE-488-bus with the designation
“Error” and a code number. The code numbers have the
following meanings:
1 - Overflow formeasurement: Reading exceeds therange
2 - Overflow calculation: Calculated result exceeds the range
4 - Error during offset measurement: The offsetis too large
5 - Error during calibration:
5.1 Nominal value <5% or >100% of range
5.2 Calibration switchontherearof the unitis setto “MEAS”.
6 - IEEE 488 bus interface error: The DMM has received a
message string containing more than 32 characters.
8 - Error 2 during self-test : The redetermined and the old
check sum do not agree {lithium battery exhausted).
9 - Error 3 during self-test : Error in the program ROMs.
Zero-Correction / Offset
Zero point displacement (drift) is one possible source of
error. Normally this type of error is immediately evidentby a
display reading differing from Zero when the input is shorted
at VDC ranges. A zero point correction can be made with the
“Zero” key.
For this purpose place a short circuit at the “V/Q” input and
then press the “Zero” key. The instrument makes a zero
point measurement whose durationis determinedby the set
integration time. With 6% digit display, the zero point
measurement takes 20 seconds for the functions “Vo”.
"MAge “ during which time the display shows “null” andthe
remaining time in seconds until the end of the measurement.
With 5% digit display, the zero point measurement takes 2
seconds and only the text message “null” appears in the
display. The keyboard is disabled during the correction
The maximum possible zero correction is 1% of the
measuring range!
If the deviation exceeds this limit, then the message ” Error
4 ” appears in the display or on the IEEE-488-bus, and the old
correction value is preserved.
The sequence of the correction measurementdiffers slightly
from the description given above. for the functions “KOhm”,
“V_" and “mA_". For these functions the zero point is
corrected immediately by continual observation of the
measured value. If autoranging was switched on before
calling the “zero point correction”, all ranges of one function
are corrected in succession for zero point. Now the zero
point measurement takes 10 seconds for each 6% digit
display span, and 1 second for each 5% digit display span.
When the measurement duration is 10 seconds, the display
shows “null” and the remaining time. When the measuring
time is 1s, only the text message “null” appears in the
For the current measuring ranges, the zero point is
corrected with open-circuit sockets, because of anactive
current sink circuit!
No short circuit is placed internally in the multimeter for the
offset correction, so that the user can place the short circuit
at any desired location in the external circuit, to include
external error sources in the compensation. This is particulary
important for the 2-wire resistance measuring function. The
error due to the finite resistance of the measuring leads can
be eliminated by the zero-point correction.
Greater deviations than 1% canbe corrected by activating
the “Offset” -function.
In this case the precedented display value is subtracted from
the actual measurement and only the calculated value is
displayed. The function “Offset” is active as long as no other
function is selected or by actuating the “Offset"key a
second time..
Subject to change without notice
M5 8112
Operation Instructions for Ve
Connect the voltage to be measured to the two input
terminals marked “V/Q/T" and “ground” on the front panel.
A voltage which is positive at the red socket relative to the
black socket gives a positive readout in the display. Make
sure that the maximum permitted values of 50V,,. between
the “LOW” input and guard (see section “shielding”), and
200 V,; or peak-peak AC between guard and case, are not
Input resistance in DC ranges
In order to make full use of the excellent linearity of the
measuring method of the HM 8112-2, the input resistance
for voltage measurementis extremely high in some ranges.
For example, this still permits relatively accurate
measurements up to +/-2V even when the internalresistance
of the measured voltage source is 100 kQ. Inthe 20V, 200V
and 1000 V,. measuring ranges, 100 Q internal resistance
of the measured voltage source already give an error of 1
digit when using 100,000 digits resolution (input resistance
of the DMM 10 MQ). For input resistance, display span and
resolution see the following table:
Range Display span Input Resistance max. Resolution
02 V .2000000 V 1GQ 100 nV
2 V 2.000000V 1 GO 1 UV
20 V 20.00000V 10 MQ 10 pV
200 V 200.0000 V 10 MQ 100 pV
1000V 1000.000 V 10 MQ 1 mV
Overload Protection
All ranges are effectively protected against destruction by
voltages greater than the fuli-range value. The max. overload
+0.2V,+2V ranges: +1000V for 60 sec or +700V cont. *
+20V, +200V, +1000V ranges: +1000V continuous *
* only 125V when scanner is equipped
However, bear in mind that overloads in the lower ranges will
inevitably cause heat-up of the safety resistors and diodes,
so that subsequently thermoelectric voitages may cause a
zero displacement until internal temperature equilibrium has
been reestablished.
Common mode supression / Shielding
Common mode voltages are voltages which occur between
the low point of the voltage to be measured and mains
(power) ground, or between power ground of the voltage
source and ground potential of the measuring unit. Common
mode voltages attempt to generate currents in the same
direction via both input sockets. To achieve an optimum
shielding effect, connect the guard input to a DC-voltage
potential equal to that of the “LOW” input such that currents
flowing in the shield do not flow through resistances in the
voltage source circuit and voltage measuring leads, which
could disturb the voltage being measured.
A high rejection factor for direct voltage and common mode
voltage can be obtained in critical cases by appropriate
connection of the guard input. If problems due to common
mode voltage are expected in a given measuring task, then
the guard input (blue socket) should be strapped to the
“LOW” input (black socket).
The common mode rejection of a measuring unit is the
capability of indicating only the wanted difference signal
between the “HI” and “LOW” input, with ideally complete
supression of any response to a common voltage which
both input terminals may have with respect to ground.
Whereas an ideal system would give no response to a
common mode signal, so that it would show no error due to
this cause, in a practical system stray capacitances, finite
insulation resistance and resistive circuit asymmetry will
convert a portion of the common mode voitage to a series
voltage. The common mode rejection factor of the
HM 8112-2 is better than 140 dB even when the resistive
asymmetry of the measuring leads has any value up to 1kQ.
Operating Instructions for Q/kQ
Resistance measurements with the HM 8112-2 are made
according to the following principle: A load-independent
current {I} is passed through a resistance (Rx) which is to be
measured. This current also flows via a known internal
range resistor. The voltage drop across Rx is measured via
the input sockets “V,.” and the ratio of this voltage drop to
the voltage drop across the internal range resistor IS
determined. Thus any drift or ageing of the reference
voltage source has no effecton theaccuracy of the resistance
The HM 8112-2 makes resistance measurements in 2-wire
circuit or in 4-wire circuit. For measuring small resistances
too with high accuracy, careful compensation of the
measuring lead resistances and of thermoelectric EMFs Is
required, with the aid of the zero point correction facility. For
this purpose connect the two measuring leads with their
test clips to one side of the resistor to be measured, and
then make offset correction by pressing the “Zero” key.
This correction compensates for all possible sources of
error, such as measuring lead resistance, contactresistance
and thermoelectric EMFs. Shielded measuring should be
used when measuring large resistances (100 kQ or greater).
The currents through the resistance to be measured have
the following values in the respective ranges:
2 kQ-range 700 pA
20 [email protected] 70 pA
200 kS2-range 7 pA
2 MQ-, 10 MS2-ranges 0,7 HA
The polarity of the current flowing trough Rx is defined such
that the end of Rx which is connected to the upper “HI”
socket of the “М/О” при! has a negative potential with
respect to the other end of Rx.
M6 8112
Subject to change without notice
Operating Instructions for V, Measurements
The HM 8112-2 measures the "True-RMS” value of the.
input voltage, i.e. the RMS value of the applied DC and AC
A recommenced arrangement for measuring alternating
voltages consists of a two-conductor shielded cable with the
shield connected tothe “guard” -input. Forallmeasurements,
the “guard” and the "V/Q-LOW"-input should be connected
to the measuring point which lies closest to ground potential.
Somewhat poorer shielding is achieved by using a single
coaxial cable and establishing a link between the “guard”
and the “V/Q-LOW"-input. This often used arrangement is
nevertheless satisfactory for most measurements exceptin
very high ambient noise levels and/or when measuring very
small voltages.
In the 200 V and 1000 V ranges and when measuring
alternating voltages with high frequencies (above 100kHz
for 200V range, above 10kHz for 1000V range), it must be
ensured that the applied AC voltage does not exceed the
RMS value product of 10%V x Hz.
When measuring alternative voltages or currents a constant
zeropoint offset due to the “calculated conversion principle”
occurs. This offsetis eliminated by setting the display to zero
when the measured signal is smaller then 200 digit. This
doesn't affect the measurementaccuracy of the instrument
(see specifications for AC-values). The specification are valid
for sinusoidal input signal greater then 5% of full scale and
the shield connected to the "V/Ohm/T"-input socket. This
holds also for the mA. ranges.
Measuring mA__and mA,
When connecting the measuring circuit to the DMM,
bear in mind that the two black “LOW”-sockets of the
inputs “V/Q” and “A” areconnectedtogether internally.
Thus it is not possible to connect simultaneously two
measuring leads for current measurement and two
leads for voltage measurements, if there is a potential
difference between the respective measuring points.
The internal connection between the “V/Q" socket and
the “A”-"LOW” socket is protected against current
overload by a 3.15A fuse (slow blow).
Offset correction by keypress is possible for the current
measuring ranges too. But in contrast to all other functions,
the offset correction for current measuring ranges must be
made with the input sockets open circuit.
A 0.1 Q shunt is used in the 2A range. But in the 2 mA range
a current compensation circuit is used which permits load
voltages smaller than 10 mV. The current measuring ranges
are protected by power diodes and an additional quick blow
3.15A fuse.
Before replacing blown fuses, disconnect the mains plug
and all measuring cable plugs. The 3A (quick blow) fuse is
located near the input sockets of the instrument and the
3.15A (slow blow) fuse is located close to the large blue 0.1
Q shunt at the front right inside the HM8112-2.
Temp. Measurements °C,°F, Kelvin
Temperature measurements with the HM 8112-2 are
performed with the aid of a PT-100 temperatur sensor. As
accessory, HAMEG supplies an immersion test probe with
colored {red and black) connectors {HZ 87). These must be
attached so that the colors line up. It is connected in 4 pole
configuration to the inputs "V/Q/T”-HI//LOW and “Ohm-
source” -HI/LOW input sockets.
The temperature is measuredindirectly by means of a 4-wire
resistance measurement. The test current is approx. 1тА.
The resistance thus measured is compared with a table
which complies with IEC 751 andis stored in the DMM for
conversion to the corresponding temperature in *C,*F, or
A zero point correction can also be performed for temperature
measurement. Because of the conversion and linearization
which are subsequently performed, the sequence used for
adjustment differs slightly from that for the other functions.
Each of the inputs “V/Q/T”-HI/LOW and “-source”-HI/
LOW is shorted. In response, the HM 8112-2 reports
"ERROR1”. If the “Zero” key is now pressed a zero point
correction is performed. Afterwards the message “donk”
appears in the display.
In continuation, the sensor can now zero-adjusted at a
precisely known temperature or with the aid of a reference
resistance, the value of whichis precisely known. Adjustment
is performed by calibrating to this precisely known value. At
this point, it is the linearity of the sensor which determines
the accuracy of temperature measurements over the entire
temperature measurement range, taking into account the
base error of the HM 8112-2, namely £0.05 °C.
Operating Instruction
for Scanner/Multiplexer (Option)
When the DMM is equipped with the scanner option, the
maximum permitted voltage at the subminiatur type D
50-polesocket onthe rear oratthe “V/Q”-inputsockets,
is 125V peak-peak, with the restriction for the RMS
product to be lower than 10°V x Hz.
The optional Scanner is equipped with bistable relays,
whose contacts are in arbitrary state when the power
supply is switched on or off. This may short-circuit
measured signals inan uncontrolled manner and without
due precautions this might damage your measuring
circuit or the scanner. Thus it is very important to make
sure that the unit is switched on or off only when no
measuring cables are connected if the signal sources
can deliver voltages or currents which exceed the limit
values specified in the technical data for the HM 8112-2.
We expressly point out that we accept no liability for
consequential damage. Damage to the relay contacts is
also not covered by our warranty obligations.
Subject to change without notice
M7 8112
The multiplexer is of type “1 0f 10”, i.e. one freely selectable
channel at a time can be connected through. The inputs are
collected on a 50-pole subminiature type D socket connector
mounted on the rear of the unit. The 4 output lines of the
multiplexer are connected internally to the multimeter input
terminals “V/Q" and "A". The front terminals too can be
switched-in and switched-out via the IEEE 488 bus interface.
The front terminals are in switched-in state immediately
after power-up of the DMM. A shield is provided separately
for each multiplexer channelandis connected to the “guard”
terminal on the front of the unitand topin 1 of the subminiature
type D socket connector. An adapter card (HZ 81) is also
available which plugs onto the subminiature socket connector
and provides screw terminals for the multiplexerinputs. For
channel selection see "HM 8112-2 firmware”.
Switch-on and switch-off of the external trigger facility is
made with the “up” key as soon as the program 6 (TRG.) is
activated. The display shows “trig on” or “trig off”, after
alternate actuations of the “up” key. Deressing any other
key exits the program and the last displayed status is taken
over. lf stat mode has been chosen, then the actual measured
value appears in the display.
The HM 8112-2 can be triggered for a single measurement
via the BNC-Connector on the rear panel or by means of the
trigger key. Another start mode under software control is
posible too, via the IEEE-488-bus. All start modes have the
same time sequence. The start time is the positive slope of
a trigger pulse with a time delay not exceeding 25 ms.
Trigger or
*S1” Get
Measuring circle
-ntegration tine
Start End End
to to+2ms te
-End of measurement
-Change of display
-lEC-Message renewed
Via the IEEE bus, the DMM is placed in start mode by the
command “S1“. Each further transmission of “S1” then
corresponds to a trigger as described above. The HM 8112-2
can also be started by the addressed command GET (Goup
Execute Trigger). The display and the IEEE message are
refreshed at the end of the measuring time. If service
request is switched on, the SRQ line is activated. In “TALK
ONLY” mode, the DMM sends a message to a connected
device in “LISTEN ONLY” mode. Range and function
switching operations carried out shortly before triggering
may lead to delay times of up to 225 ms.
HM 8112-2 Firmware
The HM 8112-2 features programs for comfortable operation.
PRG 1 MUX Controls the optional scanner
PRG 2 %Dev Calculates deviation between measured
values in %.
PRG3 dB Calculates deviation between measured
values in dB.
PRG 4 dBm Calculates the measurement resultin dBm.
PRG 5 Time Setting of integration time and resolution
РВС 6 TRG Control for the external trigger facilities
PRG 7 IEEE Setting of device adress and termination
PRG 8 Cal Calibration routine
PRG O Clear Resets the DMM
The utility programs are selected using the PRG key (or via
the IEEE-488 bus). When the utility programs have been
activated, the letter “P” appears in the display. Each time the
"PRG" key is pressed the program selector advances one
position. Once the desired program has been reached, the
selection is confirmedby pressing the Enterkey. The number
of the selected program can be read in the display (digit 15).
If more than 4 seconds are allowed to elapse between
selection of a program and confirmation by pressing the
Enter key, the HM 8112-2 exits this mode and returns to the
previously selected operating mode.
PRG 1 - Scanner (Option)
When selecting PRG 1, full control of the optinal scanner is
possible by the front panel. After activating the program
(PRG 1 + Enter) a new channel can now be selected with the
range keys. The 10 channels are numbered consecutively
from 0 to 9. Between channels 9 and 0 “F” appears in the
display in order to indicate the state multiplexer disabled. The
front-panel jacks can also be addressed within this program.
After selecting a channel (the number of the channel appears
in digit 14 of the display) itis confirmed by pressing the Enter
key. Pressing any other key also causes the newly selected
channel to be activated, but results in termination of this
program. Channel selection is also possible via the IEEE 488
bus interface using the command “MX”.
PRG 1 permits complete sequences to be stipulated for the
scanner, with appropriate measurement function, range and
integration time in each case. The combinations thus
stipulated for the individual channels are stored in the memory
of the HM 8112-2, and remain stored until power down. In
orderto execute a measurement which has been programmed
in this way, it is necessary only to call the corresponding
channel. After carrying out the following programming
sequence, the corresponding combinations are stored for
the selected channel.
PRG1 - Enter; select channel with Up/Down keys; Enter;
function - range - measurement time; PRG1 - Enter;
PRG 2 - %Dev Calculates, as a percentage, the deviation
of the current measurement value from the previous value.
R = 100 x (X-C)/C
Where R is the calculated value which is displayed, and C is
a constant reference value (previous measured value). A
M8 8112
Subject to change without notice
measured value is assigned to the variable C by the program
if the Enterkey is depressed within 4 seconds after depressing
the PRG key.
PRG 3 - dB Calculates the current measurement value by
applying the formula:
В = 20 xlog (VC) (see PRG 2)
Where R is the calculated value which is displayed, and C is
a constant reference value. À measured value is assigned to
the variable C by the program if the Enter key is depressed
within 4 seconds after depressing the PRG key.
PRG 4 - dBm Calculates the deviation of the current
measurement value from the previous measurement value
by applying the formula:
R = 20 x log (X/C) C= 0.775 V into 600 Q
C= 1,29 mA
for voltage
for current
PRG5-Time The “up” and “down” keys are used to set
the integration time. The following meas. times are available:
0.1 sec. ......... 100 ms integration time, display 5% digit
1-5sec. ......... 1 s integration time, display 5% digit
1-6sec.......... 1s integration time, display 6% digit
10 sec.......... 10s integration time, display 6% digit
Pressing any key or “Enter” exits this program and the
integration time indicated in the display at this instant gets
PRG 7 - IEEE When activating PRG 7 the DMM is then
in status “set device address”. The display shows e.g.
“IEEE.07.8" which means that the unit is set at present to
device address 7 and end character type 8. The DMM is set
like this as delivered from the factory. The “07” in the display
is flashing, to indicate that the device address can now be
changed. Use the “up” key to change the device address.
The first actuation of this key starts a cyclic run-through of
device addresses from 01 to 30. After address 30 the
characters "—” appear in the display for operating status
“TALK ONLY”. The process is stopped by pressing the
“up” key again. To select the end characterby its designation
number, press the “down” key. The digit after the decimal
point now flashes, indicating that the end character can now
be changed. Selection of one of nine possible end characters
is made with the “up” key in the same manner as for
selecting the address.
Terminating charakter
СВ + ЕО!
CR + LF + ЕО!
Press any key except a range key to transfer this address
information into working memory and exit the program. If it
is desired to take over these new settings into protected
memory, set the calibration switch on the rear of the DMM
to position “Cal” before takeover of the address data.
Designation number
NOOSE (С) Вю — ©
PRG 8 Calibration routine
IEEE 488 - Bus - Interface
Capabilities of the IEEE 488 bus interface
SH1 Handshake source function
AH1 Handshake sink function
T5 Talker function
L3 Listener function
RL1 Remote control
DC1 Reset function
DT1 Trigger function
SR1 Service request function
The keyboard of the HM 8112-2 is disabled after the DMM
has been accessed once via the IEEE 488 bus interface. The
keyboard is enabled again when the "REN" becomes inactive
or when the controller transmits the addressed command
GTL (go to local).
The “TALK ONLY" capability in conjunction with a printer
with “Listen Only” attribute, permits set-up of a self-
complete measuring station. After each end of measurement
(e.g. after a trigger), the DMM outputs a measured value
with the selected terminating characters to the IEEE bus.
The DMM does not interrupt its continuous measuring
sequence within the talker function. It understands the
commands DCL (Device Clear), SPD (Serial Poll Disable), and
SPE (Serial Poll Enable). The command DCL sets the DMM
into status “DC-Volts measurement with 1000 V range”.
Programming the HM 8112-2 via the IEEE 488 Interface
To program the DMM, proceed as follows: Data input is
possible as a character string of 2 to 32 characters, e.g.
“VDR3AOM3Q1L1" or “VDR3" or “R3". Every command
consists of 2 characters. The sequence of several commands
within one string is arbitrary, with the exception of the
command “NV”. The ISO-7-bit code is used for command
transfer. Any spaces in the transferred string are ignored. If
the DMM receives more than 32 characters (excluding any
spaces), then it evaluates the first 32 characters and also
reports a transmission error.
Description of the device messages
VD Selects the measuring function “direct voltage”
VA Selects the measuring function “alternating voltage”.
02 Selects the “resistance” measuring function (04=4-wire).
ID Selects the “direct current” measuring function.
IA Selects the “alternating current” measuring function.
TC, TK, TF Selects the “temperature” measuring function.
RX The measuring range within each function is selected
with “RX”. “X" stands for the designation number of the
desired measuring range. Note that some measuring
ranges can be selected only in conjunction with a
corresponding measuring function, e.g. R6 only for
function “k”.
Subject to change without notice
M9 8112
R1 Range 02V,, V,. kQ .. не.
R2 Range 2 Ví.: Va К@ 2mA, 2MA,
R3 Range 20V. Ve kQ
R4 Range 200V.. Vo kQ en co
R5 Range 1000V,, V_, 2000kQ, 2000mA,, 2000mA,
R6 Range 10000 ...... 12000kQ ces
A0/A1 (A/Zero) switches off autoranging; A1 autoranging on
TX Sets the integration time and the number of digits
shown in the display for the measurement result.
6% digits are always transmitted via IEEE 488 bus.
T1 Integration time 100ms; display 5% digits
T2 Integration time 1s; display 5% digrts
T3 integration time 1 5; display 6% digits
T4 Integration time 10s; = display 6% digits
ZO Starts an offset correction.
SO (S/Zero) Starts the continuous measuring sequence.
S1 Stops the cont. measuring sequence. The delay until
execution of the commands “S00” and “S1" may amount
up to 25msec.
MOSelects a multiplexer channel. “F"= Multiplexer off
MO-M9 Selection of channels 0-9
LO (L/Zero) Short format: The DMM transmits only the first
data block (measurement data and text messages)
L1 Long format: The DMM transmits both data blocks
(measurement data and text messages in first block and
programming data in second block).
00 (Q/Zero): The multimeter transmits no SRQ.
Q1 The multimeter transmits a Service Request SRQ with:
each new measurement result, each errormessage, reset
NVXXXXXXXX After NV the DMM expects a 6-digit
unsigned decimal integer number as nominal value for
calibration via the |EEE 488 bus. Anominal value for calibration
must be transmitted alone, i.e. no further command from
the table above may be contained in the same string. The
DMM commences the calibration routine after recetving the
nominal value.
P1 Display of the offset-corrected value R = X-C
P2 % Deviation В = 100 x (X-C)/C
P3 dB R = 20 x log (X/C)
P4 dBm R = 20 x log (X/C) with
C = 0.775 V into 600 Ohm for voltages and
C = 1.29 mA for current
PxEN Enter meas. value for constant x at P 2-4; X = 1,2,3
ID? sends the instruments identification string “HM8112-2”
STA? sends device status (2nd data block)
DO/D1 0=Display off, 1 = Display active
Bx Returns the code of the switch, which was
depressed last. x =1,.....9, A..F
ЕО! EOI active when selected
EOS1/EOS2 terminates the device message; the code
0.....8 selected determines whether the string
is sentwith 10r 2 (EOS1 or EOS2) terminators.
END Terminating character(s) as selected when setting the
DMM address. For terminating character No.8, EOl is
transmitted together with the final (26th.) string charac.
Description of the transmitted data set
The device messages transmitted from the DMM consists
also of a data set which is generated and transmitted as a
block, with end specification. The data set consists of two
data blocks. The first data block contains programming
status data. Each data block consists of a character string
with a fixed number of characters, so that no end character
is required or sent between the two data blocks. The first
character string contains 12 characters and the second
character string contains 20 characters + terminating
character(s). The 1SO-7-bit code is used for transmission.
1st. character 13th character 32th character
| | |
VA2 12111111
O2 . 3 . 2
04 . 4 . 3 .
ID 6 9 4 9
{ \/ \
1st. data 2nd. data
block block
+/- Sign of mantissa for VD and ID,
Zero for VA,02 and IA
000000 7 digit mantissa
E+X 1-digit exponent with sign
VD, VA,02,ID,!A Measuring functions
The contents of the display is transmitted in the 12 characters
of the first data block. These are measurement results and
text messages. The measurement results are always
transmitted right justified, i.e. termination with the 12th
The first character is always the sign, “+” or “-", for DC
measurements. All not required leading digits before the
measurement result are filled with zero. No sign is output for
resistance, alternating voltage and current measurements
and all notrequired leading digits in front of the measurement
resultare filled with zero. Measurement results are outputin
exponential form without spaces, e.g. +01.9876E+2. The
text messages have the format “ERR. X", “NULL”, “CAL.”
These messages are always leftjustified, i.e. they commence
with the first character of the data block. All not required
characters are filled with spaces (blank).
The second data block always commences with the 13th
character. This data block outputs the programmed status of
the DMM. Output of the second data block can be enabled or
disabled with the DMM command “L1” or “LO” respectively.
M10 8112
Subject to change without notice
Service request function (SR interface function)
The IEEE 488 bus interface of the DMM is equipped with a
service request function (SR function, SRQ). The individual
status bits transmitted with a service request have the
following meanings:
Bit 1: End of measurement
Bit 3: Overflow during measurement
Bit 4: Error messages
Bit 6: Reset
Bit 7: SRQ
Bit 1, end of measurement, can appear together with the
other status bits, in order not to falsify the SRQ in the case
of fast measurement sequences. Bit 6 appears with a reset,
i.e after power-up or in the case of a strong external source
interference event. A reset always takes the multimeter to
basic status (DC, 1000V, etc.), so that the controller must
reprogram the DMM after detecting a reset.
Messages in "Talk-only"-mode
The transmitted data set has a fixed length of 23 bit.
According to the end of string sign of the DMM the actual
date and time provided by the HM8148 will be transmitted
e.g. +01.93455E+1ADCMS XX00-00-00 00-00-00
which is measurement value, channel designation, program-
number (otherwise 2 blanks), date, and time.
Querying the Keyboard-code via the IEEE-488 bus
If a key is depressed while the DMM is under remote control,
this does not result in the corresponding function being
executed: instead, the status byte which the DMM places on
the bus in response to a poll contains a code indicating the
most recently depressed key. This information can be taken
advantage of to permit use of the DMM as a controller in
remotely controlled test systems. Interpretation on
information on depressedkeys is up to the program employed
for operation of the system. For example, itis possible to use
the keys as yes/no answers to query procedures for selection
of menu numbers, or starting of test sequences.
The codes listed in the table are assigned to the keys. Each
code begins with the letter “B”. When a key is depressed,
the IEEE-488 output buffer is updated by loading it with the
corresponding key code. As soon as this message has been
placed on the bus, the buffer is initialized to “BO”. This fact
must be taken into account when performing cyclic queries.
Once the buffer has been reset to " BO”, the DMM continues
outputting this code in response to queries until another key
is depressed. It then outputs the corresponding key code
once. Once this has been read out, the DMM is again
initialized to “BO” until the next key is depressed. If the SRQ
function is enabled, each press of a key results in a SRQ
being sent. The key assignments are as follows:
1 Local; 2Trig, 3Vo: SA, 6A
7 kQ; 8 TEMP; 9 UP; 10 Auto; B Down; C Zero;
D Offset; E PRG.; F Enter
Display-Mode under IEEE-control
In display mode, the computer being used to control the
system can directly output texts in the display of the DMM,
independently of the other device functions. Display mode
is activated with “D1”. The subsequently emitted ASCII
characters are written into the display as text. All ASCH
characters for which a segment code is definedin the “ASCII
segment table” are displayed. Any other character results in
an empty space. All characters arriving after “D1” and the
output text are ignored. If “D1” (text) is used together with
other commands in the same character string, then “D1”
must be the last command in the character string. “DO” is
used to disable the display mode. The following characters
can be depicted in the display:
a E ma Em == E
! | HEARN I I | 00
== || [| = mm a.
Cons LT ры
a == ma |__|] == ==
aaa | Ea ! nia I
аа = mi a п нЕ
01 (AC LTE a |
mn || == L
! 11 1] 1 ! Г
нЕ ' a a
an |” |, Ta LE
| I i EI
|__| == Em me ==
aT UT 1 UC | a
по ВЕ | !
a um ||
AE, ,
I | | 18 | 18
|| п a == Eu
CAE A 1 А |.
For more programming examples for the IEEE 488
interface please see German manual.
Allow a period of 2 hours to elapse after switching on,
before commencing calibration, so that the DMM has
reached thermal equilibrium.
The DMM has a digital calibration facility which permits
individual range or complete recalibration. Itis not necessary
to open the unit for recalibration. Recalibration is possible
under front panel keyboard control or via the IEEE 488 bus.
The correction values from the first calibration carried out in
the HAMEG factory are stored in the program EPROM and
ina CMOS RAM with a battery as backup power supply. The
DMM normally uses the correction values which are stored
in the CMOS RAM. The battery service life is about 10 years.
Toprevent unintentional destruction of the correction values,
they are protected in memory by setting a recessed sliding
switch S2 which is above the [EEE-Bus connector atthe rear
of the unit. The settings of this switch are marked “MEAS”
and “CAL”. To recalibrate the DMM, move the switch with
the aid of a screwdriver or similar tool from “MEAS” to
The “CAL” operating mode is indicated by periodic
appearance of the legend “CAL” in the main display. In this
status the correction values stored in the CMOS RAM are
Subject to change without notice
M11 8112
unprotected and can be overwritten. If correction values
have been lost accidently by improper calibration attempts
and recalibration is not possible because no calibration
standards are available, then the correction values which
have been stored by HAMEG in the program EPROM at the
time of initial calibration of the instrument, can be copied into
the CMOS RAM. For this purpose, set the mains switch of
the multimeter once to “OFF” and then to “ON” again,
whereby the calibration switch on the rear side of the
instrument must be left in setting “CAL”. Hereby the
calibration correction factors are automatically copied from
the EPROM to the battery backed-up CMOS RAM and all
correction values for the input offset are cleared. Thus itis
necessary thereafter to make new compensation of the
input offset for all functions and ranges.
For this purpose, place a short circuit at the input sockets
“IQ” of the digital multimeter, select measuring function
"Vo" and "Auto" forautoranging and then press the “Zero”
key. The multimeter now corrects alt VDC measuring ranges
in automatic succession and places the found correction
values in the RAM which can subsequently be protected. To
correct a single measuring range, select just this range,
leaving autoranging (" Auto”) switched off.
Calibrating the Direct Voltage Measuring ranges
First select the measuring range whichis to be calibrated and
then connectan exactly known positive or negative reference
voltage to the input terminals. This reference voltage should
not be less than 5% or more than 100% (preferably 50% to
100%) of the range span. The DMM now displays a
measurement result which has been calculated using the old
calibration factor. If this actual value differs unacceptably
from the nominal value (known value of the reference
voltage), then call the calibration program. The nominal
value can now be set using the “up” and “down” keys. The
“down” advances the digit opened for correction. When the
digit tobe corrected in the display has been reached, it starts
counting cyclically 0-9 after a short delay. This counting can
be stopped and started again with the “up” key. When all
digits have been corrected to the nominal value, start the
actual calibration measurementby pressing the “Enter” key
. “CAL.” thereupon appears in the display and the remaining
time of the calibration measurement is counted down to
Zero in the display, similar to the sequence of events for a
Zero point measurement.
Thereafter the unit exits the calibration program and new
functions and ranges can be selected. The calibration program
is also aborted when any other key except “up”, “down” or
“Enter” is pressed, in which case the old calibration factor is
retained and no change has been made. To recalibrate
several measuring ranges individually, start the entire
procedure as described above for each range. After
completing allintendend recalibrations, make quite sure that
the recessed slide switch on the rear panel of the unit is
returned from “Cal” to “Meas”, so that the calibration data
are protected again.
Calibration procedure via the IEEE 488 bus is basically
analogous to the described procedure via the front panel
keyboard. The nominal value is set as integer number with
the command "NVXXOXXX" (see calibration program in the
section headed "IEEE 488 bus interface”). The calibration
program and the calibration measurement are started
automatically on transmission of the nominal value. When no
further ranges and functions are to be calibrated, terminate
the calibration procedure by returning the slide switch on the
rear panel of the unit from setting “Cal” to setting “Meas”.
Calibrating the resistance measuring ranges
The resistance measuring ranges are calibrated in 2-pole
circuit. First connect the zeropointby the procedure described
in before. Also observe the instructions given in the section
headed “ operating instructions for resistance measurements
Q/kQ", in particular regarding compensation of the measuring
leads resistance. Calibration procedure for the resistance
measuring ranges is otherwise analogous to calibration of
the direct voltage measuring ranges.
Calibrating the Alternating Voltage Measuring Ranges
The alternating voltage measuring ranges shouldbe calibrated
with a sinusoidal alternating voltage with a frequency of
1kHz. For the function V, too, the zero point must first be
compensatedin function setting V,.- The calibration procedure
is analogous to calibration of the V,. anges.
Calibration of the Current Measuring Ranges
For the current measuring ranges too, make the same
calibration preparations as specified before. The zeropoint
measurement must be made with open circuitinput sockets.
Do not leave any measuring cables connected to the input
sockets for the zero point measurement (see also operating
instructions for mA; and mA, J). 1kHz sinusoidal reference
currents are required for calibrating A, anges. The calibration
current (reference current) mustnotbe greater than 1 Ainthe
2 A range.
Attention! Do notforget to return the calibration switch
to position “Meas”!
Calibration of temperature measurement ranges
Before calibrating the HM8112-2 for temperature measure-
ments an offset compensation must be carried out. For this
the input sockets must be short-circuit, and offset
compensation must be activated. Thereafter the message
"doneE" is read in the display or via the IEEE-bus.
Zero compensation means the internal "adjustment" of the
input amplifier and doesn't mean any adjustment of the
external probe. To compensate for probe tolerances it must
be placed in a medium of known temperature, and the
temperature mustbe transferred to the DMMviathe keyboard
or the IEEE-interface.
M12 8112
Subject to change without notice
Service manual
These service instructions for the HM 8112-2 are intended
as a supplement to the user manual, to give the experienced
electronics engineer the information required for
maintenance, fault tracing and repair of the instrument.
The service tasks described here may be carried out only
by qualified technicians. When the cover of the
instrument is removed, human contact with points
carrying potentially lethal voltages is possible. Thus the
following safety precautions must be observed.
a) Before opening the case, disconnect the mains plug and
all connections at the measuring sockets.
b) Always use an isolating transformer when making
measurements and adjustments in the opened DMM.
c) When the instrumentis in the openedstate, connect only
non-dangerous voltages to the measuring inputs.
This instrument is guaranteed to be in perfect condition
when leaving the factory. HAMEG accepts no liability forany
damage caused by incorrect operation or improper handling
of this instrument.
The analog section of the Digital Multimeter HM 8112-2 is
aligned with respect to alternating voltages. Replacement of
components and especially replacement of the printed circuit
board to repair the instrument may make realignment and
recalibration necessary. The data stored in the battery
backed-up RAM may be lost during repair work, due to a
short circuit on the printed circuit board, disconnection of the
RAM from the battery or even by electrostatic discharge. As
a general rule, any repairs of the HM 8112-2 shouldbe carried
out only at a workplace which is suitably protected against
static electricity. Bear in mind that the lithium battery
may explode if it is short-circuited.
Functional principles of the HAMEG DMM HM 8112-2
The measured signal is taken via the attenuator and via the
preamplifier to the converter. The converter transforms the
analog signal into a proportional pulse group which is sent via
the “MEASUREMENT RESULT" line (CB=U9, Pin 8) to the
microprocessor circuit board. The pulses are transmitted in
basic state HIGH or LOW, depending on the polarity of the
measured signal. A sub-measurement is complete after
every 25 ms. This is reported to the SERIAL TO PARALLEL
CONVERTER (U12) via the line "END OF SUB-
MEASUREMENT” (U9,Pin 11) by means of a pulse. The
converter and preamplifier offset of the measured data is
subtracted in the microprocessor section. The data are then
multiplied by a calibration factor. The subtrahend and the
calibration factor are determined at the time of zero
measurement and calibration respectively (see user manual)
and stored in battery backed-up RAM. The results are then
filtered by software according to the setintegration time and
finally output to the seven segment display and to the IEEE
488 bus. The data from the keyboard evaluator (U 4) are sent
via (U 12) and Q 5 to the relay control circuit (U 10), for
function and range selection of the DMM.
Microprocessor printed circuit board
Unsolder the transformer connecting wires from the mains
PCB, the mains ground connection from the floor of the case
and the two connecting wires of the trigger socket.
Disconnect the plug connectors to the display and analog
circuit board. Remove the screws: 2 x IEEE 488 bolts, 4 x
transformer mounting screws, 1 x screw on printed circuit
board, 1 x screw on the 5 V regulator. The heat dissipated by
the 5V regulator {under the microprocessor circuit board)
must be cooled by an adequately dimensioned heatsink
even when the circuit board is operated shortly in the
removed state (e.g. by a 40x100x20 mm ribbed heat sink).
When remounting the microprocessor circuit board, the
case of the 5V regulator must be attached to the case of the
instrumentin electrically isolated manner (using the insulating
nipple and the mica disc). The washer, the insulating nipple
and mica insulating disc below this nipple on the 5V regulator
must be remounted in this order.
Analog circuit board
Release the three mounting screws of the circuit board and
the plugged ribbon cable connection to the microprocessor
circuitboard (observe the correct DIP-PLUG ORIENTATION).
The analog circuit board can now be folded out to the front
for repair. To take out this circuit board completely, itis also
necessary to disconnect the five leads which go to the
display board (or to the scanner board).
Scanner circuit board (option)
Release the mounting screw of the printed circuit board and
the plugged ribbon cable connection to the analog circuit
board (observe the correct DIP-PLUG ORIENTATION).
Unscrew the two bolts of the 50-pole subminiature D plug)
out of the rear panel of the instrument. The scanner circuit
board can now be pulled slightly towards the front panel and
can then be folded out upwards. To take it out completely,
also disconnect the leads which go to the analog and display
circuit board.
Functional tests / Power supply voltages
Microprocessor circuit board:
+ 5V: Power supply for the uC-board and for display board.
+15V: Power supply for the analog board and for the scanner
board. A 5V regulator on each of these circuit boards produces
another internal supply voltage from the +15V supply (U8 + U4).
The “DIGITAL” ground (5V supply ground) on the
microprocessor boardand display boardis electrically isolated
from the case of the DMM and from the “ANALOG” ground
(+/- 15V supply ground) of the analog board and scanner
board. Thus voltage measurements must be referenced to
the corresponding ground potential. The fourth line which is
totally electrically isolated is the GUARD connection.
Subject to change without notice
M13 8112
The 5V regulator (U 1) under the microprocessor board is
screwed directly but electrically isolated (mica disc) to the
case of the instrument for efficient cooling. R 1 and R 2 (each
10 Ohms on microprocessor board) are safety resistors for
the +/-15V supply. R 1 and R 2 mustbe replaced after current
overload (repair).
Analog circuit board
The +/- 15V supplies transferred by the plug connector
between the microprocessor board and the analog board,
must be presentat the reference element (U 4) on the analog
circuit board: +15 V at pin 3, -15 V at pin 2, analog ground at
pin 4, the reference voltage of about 7V at pin 1. +5V with
respectto +/-15V “ANALOG” ground mustbe present at the
cathode of CR 4 and at pin 10 of U 9. An auxiliary voltage of
1.2 V is also present at pin 6 of U 9.
Scanner circuit board
+15 V transferred by the plug connector between the analog
board and the scanner board, are presentat pin 1 of U 1 and
the generated +5 V supply should be measured at pin 16 of
U 3, in each case with respect to +/-15V “ANALOG” ground.
Microprocessor circuit board
CLOCK: The microprocessor clock signal {about 800 kHz) is
generated in U 9 on the analog circuit board and lies at U 9,
pin 7. The opto-coupler U 13, pin 6 transfers the "CLOCK"
signal to the microprocessor board.
ERG: The RESULT signal lies at U 9, pin 8 on the analog
board. The opto-coupler U 14, Pin 6 transfers the “ERS”
(RESULT) signal to the microprocessor board.
UME: The sub-measurement end signal lies at U 9, pin 11 on
the analog board. The opto-coupler U 15, pin 5 transfers the
“UME” signal to the microprocessor board. U 16, U 17 and
U 18 service the IEEE 488 ROUTINES. U 4 evaluates the
keyboard and handles the display elements.
Analog circuit board
The ranges and functions of the HM 8112-2 are set with
bistable relays which are driven by HIGH (greater than or
equal to 13 V) and LOW (smaller than or equal to 0.6 V)
signals at the outputs of U 10 (Pin 4, 5, 6, 7, 8, 9, 10, 12). U
10 obtains its data from the microprocessor via the interface
U 12 (Pin 18) and the opto-coupler Q 5 on the analog board.
When repair is necessary (Q5 defective), it may be necessary
to adjust the base resistor R38 (100k), to improve the
transfer performance of QS.
Scanner circuit board
U 1 on the scanner board is, analogously to U 10 on the
analog board, responsible for the relay drive and thus for
channel selection in the scanner: HIGH (greater than or equal
to 13 V} at pin 1 to pin 10 of U 1 connects through the
respective channels 0 (KO) to 9 (K9). The relays R1 and R2 are
driven from U 1 pin 11 and pin 12. In instruments with the
scanner option fitted, R1 and R2 connect and disconnect the
front panel sockets.
Functional test for attenuator + preamplifier
Direct voltage measurement:
Switch the DMM to the Vdc function. Connect a reference
voltage (e.g. U_ = 1 V_.) to the V/Qinput of the instrument.
Using the auxiliary DMM (6 digits), measure the voltage Uvv
at the output of the preamplifier (U3, pin 6) with respect to
+/-15V analog ground. Switch through the respective Ve
measuring ranges and in each case measure the voltage
Uw. Table 1 lists the nominal values for Uvv in the respective
measuringranges, forinput reference voltages of 0.1V,.and
1 Voc.
V,cTange UN Uw/N
0.1 1.000
2 1 1.000
20 1 0.100
200 1 0.010
1000 1 0.001 Tabie 1
Resistance measurement
Switch the HM 8112-2 tothe kQ measuring function. Connect
a reference resistor (e.g. R _, = 1 kQ) to the V/Q input of the
instrument. Using the auxiliary DMM (6% digits), measure the
voltage drop Ua across Rref (see sketch). The current source
(U 1) produces the voltage drops Ua across the reference
resistor as listed in Table 2 in the respective measuring
kQ-Range В/О U Voit
0.2 1 - 0.7
2 1 - 0.7
20 1 - 0.07
200 1 - 0.007
2000 1 - 0.0007
10000 1 - 0.0007 Table 2
Current measurement
Switch the DMM HM 8112-2 tothe mA. measuring function.
Feed a reference current (e.g. |, = 1mA) through the “A”
input of the instrument. Using the auxiliary digital multimeter
(6% digits), measure the voltage Uvv at the output of the
preamplifier (U3, pin 6) with respect to + 15V analog ground.
The readings listed in Table 3 should be obtained for the two
direct current measuring ranges (I, = 1mA).
mA-Range | /mA Uvv/Volt
2 + 1 - 1.000
2000 + 1 + 0.001 Table 3
Integrator output signal
The integrator output signal can be measured at U 9, pin 12
with an oscilloscope (with respect to +/-15Vanalog ground).
With negative direct voltage applied to the V/Ohm input of
the HM 8112-2. The oscillogram shown next page should be
M14 8112
Subject to change without notice
Umax integrator
AN A Output
ov \ CB pin 12
va va
0.2\ | ||| | CB pin 8
CB pin 11
In the instrument which is to be repaired, disconnect the
circuitboard which is suspected tobe defective and connect
a replacement circuitboardvia the “extension”. Whenit has
been verified in this manner, which circuit boardís) is/are
defective, replace it/themin the HM 81 12-2. The DMM must
be recalibrated and a new Vac alignment made after every
replacement of a circuit board.
Data may be lostin the course of repairs on the microprocessor
circuit board. Thereafter the HM 8112-2 may not start at all,
or may startincorrectly, after switch-on. In this case switch
to “CAL” (CAL-MEAS switch on the rear panel) and then
switch the instrument off and on again. Thereby bear in mind
the following:
I Offset correction values are erased permanently!
Calibration factors: The values for all ranges and functions
which have been determined in the HAMEG factory and
stored in the EPROM, as well as the initialization values for
the IEEE address (07.8), for the integration time ( 1 sec, 5%
digits) and for channel preselection (no channel selected) are
loaded into the battery backed-up RAM.
The analog circuit board must always be replaced together
with the EPROM which contains the specific calibration data
for this board. When only the microprocessor board has
been replaced and the “old” analog board remains in the
instrument, the corresponding “old” EPROM with the
calibration data for this “old” analog board must be inserted
again into the now “new” microprocessor board. The
procedure for loading the calibration data from the EPROM
into the battery backed-up RAM is described in the user
manual part.
Aids: AC calibrator (voltage and current); DMM (6% digits).
The offset of the ms value rectifier TRUE RMS CONVERTER,
U 5) mustbe compensated before carrying out the frequency
alignment of a HM 8112-2. For this purpose, switch the
instrument to the 2V AC measuring range. Plug a shorting
jumper into the V/Q input sockets. Using the auxiliary digital
multimeter (6% digits), measure the voltage Ua rms with
respect to +/-15V analog ground at the output of the true rms
converter (pin 10, U 5). Adjust the trimmer R 23 to make
Uarms zero (tolerance £50 pV). The frequency alignment of
the HM 8112-2 can then be carried out.
IMPORTANT For checking the frequency response, it is
essential to close and efficiently ground the cover of the
case. A special cover with holes for access to the trimmers
is ideal.
1. 0.2 V,: No alignment required
2. 2V,: Noalignment required
3. 20 V,: 1. INPUT: 10V/90Hz; note the display reading
2. INPUT: 10V/10kHz; adjustthe trimmer cap.
C 5 (20V,) to make the display reading the
same as for 10V/90Hz.
NOTE: The 10V/90Hz display reading changes. Thus repeat
the steps 1. and 2. alternately until both are correct.
1. INPUT: 100V/90Hz; note display reading
2. INPUT: 100V/10kHz; adjust the trimmer
cap. C 3 (200V, ) to make the display reading
the same as for 100V/90Hz.
The 100V/90Hz reading should not change.
4. 200 V.:
1. INPUT: 100V/90Hz; note display reading
2. INPUT: 100V/1kHz; adjust the trimmer cap.
C7 (1000Vac) to make the display reading as
closely as possible equal to the reading for 90
Hz (deviations up to 2000 digits are tolerated).
5. 1000 V,.
NOTE: The alignment of the 200 V range may change,
thus repeat alternately until both are correct.
Setthe MEAS-CAL switch to “MEAS”; switchthe HM 8112-
2 off, then SWITCH IT ON again. The DMM thereupon runs
through a sequence of internal check routines: CONTROL
1.2.3. Thereafter, the DMM is set to the 1000 Vdc range and
the display reads 0000.00.
2. INITIALIZATION in setting “CAL”
WARNING: All calibration data are erased.
Switch the HM 8112-2 off, set the MEAS-CAL switch to
“CAL” and then switch the instrument on again. The
instrument thereupon runs through a sequence of internal
check routines: CONTROL 1,2,3. The display flashes
alternatingly: “CAL” and (1000 Vdc) 0019.XX or 0025.XX.
These digits (=CONVERTER OFFSET) appear in all functions
and measuring ranges.
Subject to change without notice
M15 8112
FAULT-SYMPTOMS POSSIBLE CAUSES 11.V__ offset can not be corrected U5
1. No Initialization, not even 1. RAM (U 7) 2. U3
in “CAL” setting 2. Socket J5 3. Plug connector
3. U9 4. RC-combination near U 3
| 5. US
2.No clock signal 1. Opto-coupler U 13 6. U10
2. Plug connector 7. U12
3, U9 8. 05
4. Crystal Y1
13. Display reading runs up until “ERR 1” appears U 9
3. No ERG signal (Result) Opto-coupler U 14
2. Same as for Fault 2. “ERR 1" in "kQ" 1. Q1
| 2. Q2
4. No UME signal (end of 1. Opto-coupler U 15 3. Ul
submeasurement) 2. Same as for Fault 2. 4. U4 7V reference
5. Incorrect INITIALIZATION 1. U12 ЕВА Г. Uvv lies above the range
in setting “CAL” 2 UTO limit (greater than 2V); there are many possible causes
3 SH 10 for this. Uw o.k.; then check U 6, U 7, C 18, 03
“ERR 1” "kQ" with open V/Q input,
6.RESET on HV INPUT The microprocessor board
is not screwed down firmly ~~ “ERR 4” ok. in “V_", "V," 0.1V, 1V with open V/Q
(C18 with respect to case input
"ERR 8” 1. Data loss
7.1EEE 488 function 1. Plug connector 2. Lithium battery low; nominal voltage min. 3.2 V
2. Control IC U16 3. See explanations below.
3. Driver IC U 17,18
Unusually severe electrical disturbance in the operating
8. Fault in RANGE 1. U12 environment of the HM 8112-2 (electric fields, induction
SELECTION 2. U 10 currents, etc.) may affect the data held in the battery backed-
3. U9 up RAM (U 7), so that some or even all the data (calibration
4. Relays factors, offset correction values, IEEE address, integration
9. “NULL” impossible U 9 time and channel preselection) may be changed or lost. The
error display “ERR 8” then indicates this state of the
10. No current measurement 1. 3.15A fuse (quick blow) instrument. The HM 8112-2 must now be recalibrated and/
2. 3.15A fuse (slow blow) or the lost data must be reloaded.
M16 8112 Subject to change without notice
HM 8112-2
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[email protected]
Bestückungsplan Adapterplatine
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Component Locations Preamplifier
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Frequency Synthesizers
R- and LC-Meters
Spectrum Analyzers
Power Supplies
Curve Tracers
Time Standards
Industriestraße 6 f
D-63533 Mainhausen
Telefon: +49 (0) 6182 / 800-0
Telefax: +49 (0) 6182 / 800-100
E-mail: [email protected]
[email protected]
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