IMC CANSAS - Sense and Initial Unbalance

414 Properties of the Modules
imc CANSAS Users Manual - Doc. Version 1.9 - 05.12.2014© 2014 imc Meßsysteme GmbH
6.20.2.4 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 UNI8 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.
The bandwidth (without lowpass filter) is for DC-bridge measurement 200 Hz, too.
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.
Possible initial unbalance
input range [mV/V]
bridge balancing
(VB = 2.5 V) [mV/V]
bridge balancing
(VB = 5 V) [mV/V]
bridge balancing
(VB = 10 V) [mV/V]
±1000
200
500
150
±500
200
100
250
±200
30
100
50
±100
30
15
50
±50
6
15
7
±20
20
3
7
±10
20
10
15
±5
7
10
5
±2
9
3
5
±1
-
4
5
±0.5
-
-
-