Balancing And Adjustment; Zero Balance - HBM MC3 Bedienungsanleitung

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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
T < 50 ppm should be connected via terminal 21/2 and 21/4 or 21/2 and
K
21/1.
Calculation of the resistance required for this purpose is made via the follow-
ing equation:
0.25·R
B
R +
A
R = bridge resistance in Ohm
B
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
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.
HBM
*)
. This balance is mainly necessary in the small
MC3
A1705−3.2 en/de/fr