HBM MC3 User manual

A1705-3.2 en/de/fr
Measuring amplifier
for strain gage transducers
MC3
Operating manual
Bedienungsanleitung
Messverstärker für
DMS−Aufnehmer
Amplificateur de mesure
pour capteurs à jauges

English Page 3 −20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Deutsch Seite 21 −38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Francais Seite 39 −59. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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MC3
HBMA1705−3.2 en/de/fr
Contents Page
Safety instructions 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 Controls 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Description of Operation 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Electrical connection 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Mounting 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Construction of the MC3 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Measuring cable 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Transducer connections 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5 Measuring signal output 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6 Limit switch 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7 Supply voltage 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8 Bridge supply voltage 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 Balancing and adjustment 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1 Zero balance 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Current output 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 Measuring range 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Adjustment 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5 Limit switch 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.6 Measuring signal output 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 Circuit diagram 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Contact Allocation, Components Layout 19. . . . . . . . . . . . . . . . . . . . . . .

4MC3
HBM A1705−3.2 en/de/fr
Safety instructions
Appropriate use
The MC3 with the connected transducers may be used for measurement and
directly related control and regulation tasks, only. Any other use is not ap-
propriate.
To ensure safe operation, the MC3 may only be used according to the specifi-
cations given in this manual. When using the transducer, the legal and safety
regulations for the respective application must also be observed. The same
applies if accessories are used.
General dangers of failing to follows the safety instructions
The MC3 complies with the state of the art and is operationally reliable. If the
device is used and operated inappropriately by untrained personnel, residual
dangers might develop.
Any person charged with device installation, operation, maintenance or repair
must in any case have read and understood the operating manual and the
safety instructions, in particular.
Conditions on site
Protect the equipment from direct contact with water.
Maintenance and cleaning
The MC3 is maintenance-free. Please note the following when cleaning the
housing:
−Before cleaning, disconnect the equipment from the power supply.
−Clean the housing with a soft, slightly damp (not wet!) cloth. Never use
solvents, since these could damage the labelling.
−When cleaning, ensure that no liquid gets into the equipment or connec-
tions.
Remaining dangers
The MC3 scope of performance and supply covers part of the measuring-
technology, only. The plant designer/constructor/operator must in addition de-
sign, realise and take responsibility for the measuring-system’s safety such
that potential remaining dangers are minimized. The respective regulations
must in any case be observed. Residual dangers regarding the measuring
system must be specified explicitly.

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MC3
HBM
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If there is any risk of remaining dangers when working with the MC3, it is
pointed out in this introduction by means of the following symbols:
Symbol: DANGER
Meaning: Maximum danger level
Warns of a decidedly dangerous situation in which failure to comply with
safety requirements can lead to death or serious physical injury.
Symbol: WARNING
Meaning: Dangerous situation
Warns of a potentially dangerous situation in which failure to comply with
safety requirements can lead to death or serious physical injury.
Symbol: CAUTION
Meaning: Potentially dangerous situation
Warns of a potentially dangerous situation in which failure to comply with
safety requirements could lead to damage to property and slight or moderate
physical injury.
Symbols for operating instructions and useful information:
Symbol: NOTE
Means that important information about the product or its handling is being
given.
Symbol:
Meaning: CE mark
The CE mark enables the manufacturer to guarantee that the product com-
plies with the requirements of the relevant EC directives (see Declaration of
Conformity at http://www.hbm.com/HBMdoc).

6MC3
HBM A1705−3.2 en/de/fr
Safe operation
Do only quit error messages if the reason for the error has been eliminated
and there is no more danger.
Reconstruction and modifications
HBM’s express consent is required for modifications regarding the MC3
construction and safety. HBM does not take responsibility for damage result-
ing from unauthorized modifications.
In particular, repair and soldering works on the boards are prohibited. If com-
plete componentry is replaced use original HBM components, only.
Qualified personnel
The device may be used by qualified personnel, only; the technical data and
the special safety regulations must in any case be observed. When using the
device, the legal and safety regulations for the respective application must
also be observed. The same applies if accessories are used.
Qualified personnel means: personnel familiar with the installation, mounting,
start-up and operation of the product, and trained according to their job.
Maintenance and repair work on an open device with the power on should
only be undertaken by trained personnel who are aware of the above-men-
tioned dangers.

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MC3
HBM
A1705−3.2 en/de/fr
NOTE
This manual apply to MC3 measuring amplifier from Hardware
Version 1.00. The label on the printed circuit board is visible when
the housing cover is opened (see (7) in the following figure).
1 Controls
The controls are accessible on opening the top of the housing.
2
4
5
1
3
6
7
R44
R58
R26 P21
P22
P24
P23
S21
S22
Fig. 1.1: Control elements
Notes:
1 A screwdriver type potentiometer P 24 −setting the switching point of the
limit switch.
2 Switch S 22 −Selection of voltage or current output (option).
3 Screwdriver type potentiometer P 21 −Zero balance for amount.
4 Screwdriver type potentiometer P 22 −Zero balance for phase.
5 Screwdriver type potentiometer P 23 −Fine adjustment of meas. range.
6 Switch S 21 −Measuring range adjustment

8MC3
HBM A1705−3.2 en/de/fr
7 Hardware-Version MC3
Definition of the slide switch positions:
Position 1: Circle visible
Position 2: Circle obscured
Fig. 1.2: Dimension (in mm)

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MC3
HBM
A1705−3.2 en/de/fr
2 Description of Operation
Measuring amplifier MC3 is used with strain gages in a full bridge circuit or
with strain gage transducers to construct an uncomplicated and economical
measuring system.
Suitable indicating equipments for connection to this system include digital in-
dicators for switchboard installation (e.g. DA2510).
The MC3 supplies the bridge supply voltage of the transducer, amplifies the
transducer output signal and outputs a dc voltage signal of −5 V ... 0 ... + 5V
proportional to the measured value.
A limit switch with open collector output can be adjusted over the range of
0 ... + 5 V.
When equipped with an optional final stage, an output current of
4 mA ... 20 mA is available.
Strain gages or strain gage transducers in full bridge circuit with a bridge re-
sistance of 300 ohm ... 1400 ohm may be connected. Generator G generates
a sinusoidal bridge supply voltage of 2 V (rms) with 1 kHz carrier frequency.
The connected transducer outputs a signal proportional to the measured
value when under mechanical load and this is pre−amplified in the differential
amplifier of the MC3.
The voltage necessary for balancing the transducer zero signal is added to
the measurement signal in accordance with amplitude and phase and both
are amplified depending upon the measuring range selected. Finally, the mea-
surement signal is rectified in demodulator D with the correct phase.
The output amplifier EV with low pass filter amplifies the rectified measure-
ment signal to the output level of 5 V under the rated load of the trans-
ducer. The residual carrier voltages are suppressed to a value of < 1 %. The
measuring frequency range is 0 Hz ... 30 Hz at −1 dB (or 0 ... 65 Hz at −3
dB).

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HBM A1705−3.2 en/de/fr
Strain gage
full bridge
(300 Ω... 1400 Ω)
Fig. 2.1: Block circuit diagram: DV = Differential amplifier; TV = Carrier fre-
quency amplifier; D= Demodulator; EV/TP = Output amplifier with low
pass; G = Generator; GR = Limit value switch; K= Stabilizer; S 21 =
Measuring range selector switch; P 21, P 22 = Zero signal adjustment
The switching point of the limit switch GR can be set in the range of 0V...+ 5V.
Both the set voltage and the measurement signal are applied to a comparator.
If the set level should be exceeded by the measurement signal, a transistor is
switched. Switching processes can be carried out via the collector connec-
tions which are taken out. Maximum load 30 V; 50 mA; switching capacity
1.5 W.
If the MC3 should be equipped with an optional final stage, operation can be
carried out with ”live zero”. An impressed current of from 4 mA (zero signal,
transducer unloaded) to 20 mA (rated output signal) is then available at the
output. This is particularly advantageous because faults such as line breaks
or other electrical defects are recognised immediately. Current or voltage out-
put can be selected by a slide switch.

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MC3
HBM
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3 Electrical connection
3.1 Mounting
Since measuring amplifier MC3 can operate in any attitude, it can be installed
to suit space requirements. Two bores (4 mm diameter) in the underside of
the housing should be used for mounting.
2 holes for screwes ∅4 mm
Fig. 3.1: Drilling pattern
3.2 Construction of the MC3
The electrical circuitry of the MC3 measuring amplifier is accommodated in a
robust cast housing of protection class IP 65 (dustproof and hoseproof) to DIN
40050. The housing cover can be removed by unscrewing. The cables for
connection of the power supply, indicator, limit switch output and transducer,
with a maximum diameter of 8 mm can be introduced into the equipment via
three screwed glands Pg 7. The cable ends should be screwed to terminal
strips KI 21, KI 22 and KI 23 in the MC3 in accordance with their application.
The allocation of terminal numbers (21 /1 ... 22/9) and their use may be seen
on page 12 and as a connection diagram on the inside of the MC3 cover. To
ensure correct electrical connection it is recommended that the ends of the
wires be twisted or provided with a thimble.

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HBM A1705−3.2 en/de/fr
3.3 Measuring cable
Maximum length: 25 m.
Measured value transducers should preferably be connected to the MC3 wire
screened low capacitance measuring cables. Cable Kab 5/00−4 is recom-
mended by HBM as extension cable.
HBM measuring cables are available for all HBM transducers made up with
various connection elements. Suitable measuring cables are also available by
the metre .
3.4 Transducer connections
Resistive transducer in full bridge circuit (300 Ohm ... 1400 Ohm).
Strain gages in full bridge circuit or strain gage transducers may be connected
to measuring amplifier MC3. Connection resistance is 300 Ohm ... 1400 Ohm.
The transducer lead should be introduced through the gland opposite termi-
nals 21 /1 ... 22/5. The allocation of the cable wire colors specified for HBM
transducers to their function and to the MC3 terminal strip is indicated below.
Function Cable wire (color) Terminal No.
Transducer
supply
2 (black)
3 (blue) 21/2 21/3
Transducer
output
1 (white)
4 (red) 21/1 22/4
Screen 5 (yellow) 22/5
NOTE
When operating with a current final stage or with the limit switch,
the transducer output signal must have a positive sign. Should this
not be the case, the connections to terminals 21 /1 and 21/4
should be switched.

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MC3
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3.5 Measuring signal output
−5 V ... 0 ... + 5 V, RL 2.5 kΩ
(Option 4 mA ... 20 mA, RL< 400 Ω)
The output signal at full scale deflection is available at terminals 22/5 and 22/6
at 5 V. The permissible connection resistance is > 2.5 kΩ.
If the MC3 is provided with a current final stage, an impressed current of 4 mA
(live zero point) to 20 mA is optionally available at 22/5 and 22/6 for the output
voltage of 0 V ... + 5 V. The permissible load resistance RLis < 400 Ω.
3.6 Limit switch
At the limit switch, the amplified measurement signal is compared with a pre-
set limit value (reference voltage). The desired reference voltage can be set
with potentiometer P 24 to a value within the range of 0 V ... + 5V. If the set
limit is exceeded, a transistor is turned on and voltage is no longer applied to
the open collector output (terminal 22/7).
3.7 Supply voltage
The measuring amplifier requires only an unregulated dc voltage of between
+ 10.5 V and 26 V for its operation.
The positive pole of the supply voltage should be connected to terminal 22/9
and the negative pole to terminal 22/8. Should these be switched, the MC3 is
blocked internally.
WARNING
Do not connect the supply voltage to other terminals, because this can
cause damage to and failure of the MC3.
3.8 Bridge supply voltage
Within the measuring amplifier, a generator generates a symmetrical sine
wave voltage of 2 V 5% with a frequency of 1 kHz.
When the power supply is connected, the MC3 is immediately ready for op-
eration.

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HBM A1705−3.2 en/de/fr
4 Balancing and adjustment
4.1 Zero balance
0.1 mV/V bridge output signal (or 0.25 mV/V by changing a resistor)
When carrying out the zero balance it is advisable to perform the adjustments
using an indicator, preferably a digital indicator. To balance the transducer
zero signal, S 22 at the output should be switched to impressed voltage (circle
visible). With no mechanical load on the transducer, the output voltage moves
towards zero in the measuring range 2 mV/V (S 21, circle visible). The resid-
ual voltage can be set to zero using P 21 (R balance, fine balance). Poten-
tiometer P 22 (C balance) must remain in the central position.
If the balance range is not sufficient, it can be extended by reducing R 26. It
should be noted, however, that this measure limits the zero point setting in the
measuring range 0.2 mV/V and a zero signal drift caused by temperature oc-
curs.
If this extension to the balance range is not sufficient, a coarse value balance
is needed. An additional precision resistor with a temperature coefficient
TK< 50 ppm should be connected via terminal 21/2 and 21/4 or 21/2 and
21/1.
Calculation of the resistance required for this purpose is made via the follow-
ing equation:
R0.25·RB
A
RB= bridge resistance in Ohm
A= zero point detuning in mV/V R in kOhms
It is only necessary to achieve this resistance value approximately, because
fine balance can be carried out with P 21.
For correct adjustment of the zero point in accordance with amount and
phase, the measuring range 0.2 mV/V (S 21, circle not visible) should then be
set. After zero balancing with P 21, the residual carrier at the output is re-
duced to a minimum with P 22*). This balance is mainly necessary in the small
measuring range and when using relatively long cables (e.g. greater than
10 m for 350 Ohm transducers). If the bridge resistance is relatively high, the
phase balance will be necessary even for shorter cables.
*) If the cable capacitance is relatively high, it is advisable to carry out the phase balance at the
output (terminals 22/5 and 22/6) with an oscilloscope (ripple kept to a minimum with P 22). This
is particularly important if a low capacitance HBM cable is not used.

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MC3
HBM
A1705−3.2 en/de/fr
4.2 Current output
In operations with current output, a balance should be carried out as de-
scribed under ”voltage output”. The zero signal remains stable when switching
from current to voltage output. Each time the measuring range is switched,
the zero signal must be balanced again.
4.3 Measuring range
The MC3 measuring amplifier is provided with two switchable measuring ran-
ges as standard. The MC3 is set to measuring range 0.2 mV/V at the fac-
tory (S 21, circle not visible). This setting enables a measuring range between
0.2 mV/V and 2 mV/V to be selected by unsoldering resistor R44 (R44/1;
R44/2) and soldering in a resistor R44 to be computed (see following formula).
The resistance value for R 44 as a function of the desired measuring range
may be obtained from:
R44 2 · 27.4kOhm
A
Measuring range A in mV/V
The resistor should have a temperature coefficient TK of < 50 ppm. In addi-
tion, a maximum measuring range fine adjustment of 40 % referred to the full
scale deflection set can be carried out with screwdrivertype potentiometer
P 23.
The second measuring range is set at 2 mV/V (switch S 21, circle visible)
at the works and cannot be changed.
4.4 Adjustment
Measuring amplifier MC3 can be adjusted either with an electrical signal from
a calibration equipment or with a defined transducer output signal.
After zero balance a defined signal should be applied to the measuring signal
input of the MC3 (terminals 21/1 and 21/4) using on HBM calibration equip-
ment, or a connected transducer should be detuned mechanically by a given
amount. The corresponding output voltage should then be set with the fine
range adjustment (P 23) using the ratio 0.2 mV/V or 2 mV/V. The resistance of
the calibration equipment and the transducer to be connected should be the
same.

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HBM A1705−3.2 en/de/fr
4.5 Limit switch
Adjustment range: 0 V ... + 5 V.
The switching point of the limit switch is set within the range of 0 V ... + 5 V
using P 24. In order to define the switching point a resistor of > 500 Ohms
with reference to supply voltage terminal 22/9 should be connected to the limit
switch output (open collector) terminal 22/7. The adjustment can also be car-
ried out via the connected indicator.
The maximum voltage of + 5 V should be set by turning P 24 clockwise (to
stop). In order to determine the voltage at which the transistor switches, the
amplifier should be detuned with P 21 until the desired voltage appears at the
output.
This should be carried out within the measuring range 0.2 mV/V; if necessary,
the resistance value needs to be reduced by unsoldering R26/1 and soldering
R26 in (value is to be determined empirically).
P 24 should then be turned slowly anticlockwise until the voltage at terminal
22/7 drops to about 0.2 V residual voltage. This is the switching point*).
In order to avoid ”fluttering” around the switching point, the tripping point is lo-
wer than the set switching point by the hysteresis voltage of 25 mV.
The hysteresis voltage can be increased by unsoldering R58/1 and soldering
R58, with a smaller resistance value, in. The value is to be determined empi-
rically.
Works setting 25 mV = 10 megohms; resistance value is inversely propor-
tional to the hysteresis voltage.
4.6 Measuring signal output
Switch S 22 must be in position 1 (circle visible). Only if the MC3 is equipped
with the final stage for current output can S 22 be used to select the desired
mode of operation.
Position 1 (circle visible) = voltage output
Position 2 (circle obscured) = current output
*) Another possible way of setting the switching point is as follows: Connect a digital voltmeter to
measuring point 10 (see wiring diagram) and set the reference voltage with P 24.

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MC3
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5 Circuit diagram
Base−pcb

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HBM A1705−3.2 en/de/fr
Fig. 5.1: Final stage (option)
The final stage module is factory mounted.
If required, the final stage module is delivered in a sac.
Mounting the final stage:
1. Dismount the main board
2. Screw the distance bolts with nuts onto the main board
3. Mount the final stage module onto the bolt
4. Bend the flat ribbon cable and solder it onto the main board. Ensure
correct pin assignment on main board and final stage.
5. Put the complete unit back into the housing
6. Use switch S22 to set the signal output to current output (Position 2,
Circle obscured)
7. Perform balancing only on the main board (P21 and P23,
see chapter 4.1 Zero balance and chapter 4.4 Adjustment).

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MC3
HBM
A1705−3.2 en/de/fr
6 Contact Allocation, Components Layout
R44
R58
R26 P21
P22
P24
P23
S21
S22
Fig. 6.1: Components Layout
•Terminal strip
Terminal strips KI 21, KI 22, KI 23: The separate screw terminals numbered
from 1 to 9 are located on the two terminal strips KI 21 and KI 22. The supply
voltage, transducer and indicator or recording equipment can be connected
accordingly.
•Zero balance
P 21: Using the screwdriver type potentiometer P 21, the zero signal of a con-
nected transducer can be balanced up to a maximum of 0.25 mV/V.
P 22: Using screwdriver type potentiometer P 22, the capacitive effects of
long transducer leads can be balanced.
•Measuring range
S 21: The measuring ranges 2 mV/V and0.2 mV/V can be selected us-
ing slide switch S 21.
Position 1 (circle visible) = Measuring range 1 = 2 mV/V
Position 2 (circle obscured) = Measuring range 2 = 0.2 mV/V (set in the
works)

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HBM A1705−3.2 en/de/fr
•Fine measuring range adjustment
P 23: Using potentiometer P 23, a fine measuring range adjustment of 40 %
referred to the set value can be carried out.
•Measuring signal output (option)
S 22: The desired mode of operation, voltage or current output, can be selec-
ted using slide switch S 22*).
Position 1 (circle visible) = Voltage output
Position 2 (circle obscured) = Current output
+ 10.5 V ... + 26 V
Power supply
0 V
max. + 30 V, 50 mA
Open−Collector output
(Limit value switch)
Uo= 5 V, Ra> 2.5 kΩ
io= + 4 mA ... + 20 mA, Ro= < 400 kΩ
Measuring signal output
Zero
Kl 23
Kl 22
Kl 21
Strain gage full
bridge or strain
gage transducer
(300 Ω... 1400 Ω
Fig. 6.2: Contact Allocation of terminal strips Kl 21, 22, 23
*) This switch is also included if the MC3 is not equipped with a final stage for current output. In this case it
should always be left on position 1 (circle visible ).