Figure 2-9. nulling circuit, Figure 2-9, Nulling circuit -29 – National Instruments SCXI-1121 User Manual
Page 43
Chapter 2
Configuration and Installation
© National Instruments Corporation
2-27
Assuming a strain-gauge range with a gauge factor of GF = 2 and a
quarter-bridge configuration, this range corresponds to ±1,498 µ
ε
as given
by the strain formula for a quarter-bridge strain-gauge configuration:
where
Figure 2-9. Nulling Circuit
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.
ε
–4V
r
GF 1
2V
r
+
(
)
-------------------------------
=
V
r
strained voltage
static unstrained voltage
–
V
exc
--------------------------------------------------------------------------------------------------------
=
Trimmer
Potentiometer
EX+
R
d
R
g
R
null
CH+
EX–
SCXI-1321
R
R
CH–