Figure 2-9. Nulling Circuit - National Instruments SCXI-1121 User Manual

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Assuming a strain-gauge range with a gauge factor of GF = 2 and a
quarter-bridge configuration, this range corresponds to ±1,498 µ as given
by the strain formula for a quarter-bridge strain-gauge configuration:
where
strained voltage static unstrained voltage
V = ------------------------------------------------------------------------------------------------------- -
r
Trimmer
Potentiometer
SCXI-1321
Using the SCXI-1321 with RTDs and Thermistors
When using this terminal block with RTDs or thermistor-type transducers
and with the SCXI-1121 excitation set in the Current mode, you must
disable the nulling circuit of the channel of interest. You can do this in two
steps:
1. Place the enable/disable jumper in position D (disable) as shown in
Table 2-12.
2. Remove the nulling resistor from its sockets.
Chapter 2
–4V
r
= -------------------------------
GF 1 + 2V
–
V
exc
R
g
R
null
R

Figure 2-9. Nulling Circuit

2-27
Configuration and Installation
r
EX+
R
CH+
CH–
R
d
EX–
SCXI-1121 User Manual