© 2018 imc Test & Measurement GmbH
imc C-SERIES - Manual, Version 4 R 3 - 2018-10-19
102 Device description
5.7.1.3 Quarter bridge
A quarter bridge can consist of a single strain gauge resistor,
whose nominal value can be 120 Ω or 350 Ω.
The amplifier internally completes an additional 120 Ω or 350 Ω
quarter bridge switchable by software.
The quarter bridge has 3 terminals to connect. Refer to the
description of the full bridge for comments on the Sense lead.
However, with the quarter bridge, the Sense lead is connected to
+in(A) and sense(F) jointly.
If the sensor supply is equipped with the option “±15 V”, a
quarter bridge measurement is not possible. The pin I_1/4B for
the quarter bridge completion is used for–15 V instead.
·
In the predecessor model C-50xx there is an internal 120 Ω completion resistor for bridge
measurement. A 350 Ω completion resistor for quarter bridge measurement is available as an
alternative.
·
No direct current measurement is possible with the included connector ACC/DSUB(M)-UNI2, but it is
possible only with the special shunt connector with a 50 Ω shunt resistor (differential measurement).
5.7.1.4 Sense and initial unbalance
The SENSE lead serves to compensate voltage drops due to cable resistance, which would otherwise
produce noticeable measurement errors. If there are no sense lines, then SENSE (F) must be connected in
the terminal plug according to the sketches above.
A bridge measurement is a relative measurement (ratiometric procedure) that calculates what fraction
of the supplied bridge excitation voltage is given off from the bridge (typically in the 0.1% range,
corresponding to 1 mV/V). Calibration of the system in this case pertains to this ratio, the bridge input
range, and takes into account the momentary magnitude of the supply. This means that the bridge
supply's actual magnitude is not relevant and need not necessarily lie within the measurement's
specified overall accuracy.
Any initial unbalance of the measurement bridge, for instance due to mechanical pre-stressing of the
strain gauge in its rest state, must be zero-balanced. Such an unbalance can be many times the input
range (bridge balancing). If the initial unbalance is too large to be compensated by the device, a larger
input range must be set.
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