Chapter 2
Configuration and Installation
2-26
ni.com
The value of all the nulling resistors on your terminal block is 39 k
Ω
. Notice
that these resistors are socketed for easy replacement. These sockets best fit
a 1/4 W resistor lead size.
To determine your nulling range, use the following formula (refer to
Figure 2-9 for visual help):
where
R
g
is the nominal strain-gauge resistance value.
R
d
is either a completion resistor or a second strain-gauge nominal
resistance.
R
null
is the nulling resistor value.
V
exc
is the excitation voltage (3.333 or 10 V).
For example, assuming:
V
exc
= 3.333 V
R
g
= 120
Ω
R
d
= 120
Ω
R
null
= 39 k
Ω
V
nulling
= ±2.56 mV
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
V
nullingrange
V
exc
2
----------
V
exc
R
d
R
null
R
g
+
(
)
R
null
R
g
R
d
R
null
R
g
+
(
)
+
-----------------------------------------------------------
–
±
=
ε
–4
V
r
GF
1 2
V
r
+
(
)
-------------------------------
=
V
r
strained voltage static unstrained voltage
–
V
exc
--------------------------------------------------------------------------------------------------------
=