National Instruments SCXI-1321 - Manual (Page 10)

SCXI-1321 Terminal Block Installation Guide 10 ni.com
Assuming a strain-gauge range with a gauge factor of GF = 2 and a
quarter-bridge configuration, this range corresponds to ±1,498
µε, as given
by the strain formula for a quarter-bridge strain-gauge configuration:
where
Figure 3. Quarter-Bridge Nulling Circuit
ε
4V
r
–
GF 1 2V
r
+ ( )
------------------------------- =
V
r
strained voltage static unstrained voltage –
V
exc
-------------------------------------------------------------------------------------------------------- =
CH+ CH+
CH–
EX+
EX–
+
–
+
–
R
1
R
2
4.5 k Ω
4.5 k Ω
R
SCAL
301 k Ω
R
Trim
10 k Ω
R
Null
39.1 k Ω
(Screw Adjusts Potentiometer)
R
L
R
L
R
L
R
3
(dummy)
R
4
(gauge)
EX+
CH+
CH+
CH–
EX+
EX–
R
Trim
SCXI-1121 SCXI-1321 Transducer
V
EX
Note: R
1
and R
2
are completion resistors.