XTR104 Burr-Brown Corporation, XTR104 Datasheet - Page 8

• Manufacturer Part Number: XTR104
• Description: 4-20mA Current Transmitter with BRIDGE EXCITATION AND LINEARIZATION
• Manufacturer: Burr-Brown Corporation

FIGURE 3. Bridge Sensor, V
Use R
result, connect V
Gain is affected by the varying the excitation voltage. For
each 1% of corrected nonlinearity, the gain must be altered
by 4%. As a result, equation 2 will not provide an accurate
R
equation calculates the required value for R
for this effect.
B must again be a signed number in this calculation—
positive for positive bowing nonlinearity, and negative for a
negative-bowing nonlinearity.
A more accurate value for R
measuring the actual gain constant of the linearization in-
puts, K
reference voltage, V
change at the linearization inputs, V
surement with a known, temporary test value for R
measurements can be made during operation of the circuit
by providing stimulus to the bridge sensor, or by temporarily
unbalancing the bridge with a fixed resistor in parallel with
one of the bridge resistors. Calculate the actual K
Where: V
G
when nonlinearity correction is used. The following
Bridge Sensor
LIN
LIN
R
= 632 . Because the calculation yields a negative
V
TEST
R
LIN
R
(see equation 4). Measure the change in the
R
G
R
(1
is the measured change in reference voltage, V
®
–
LIN
= 23.32
is a temporary fixed value of R
G
is the change in voltage at V
XTR104
+
K
LIN
0. 04 • B) V
R
LIN
B
24000 • 0. 01
0. 2 • ( 1. 9)
to V
R
1
, in response to a measured voltage
for the example above.
+
–
IN
LIN
V
LIN
and V
2500
R
R
Connected for Negative Nonlinearity.
FS
V
can be determined by first
• R
1
LIN
–
LIN
TEST
1
LIN
R
632
to V
2
. Make this mea-
G
LIN
to compensate
+
(1)
(1)
IN
LIN
.
.
R
LIN
G
LIN
(in
1
3
5
6
4
2
. These
:
V
V
R
R
V
V
+
+
–
–
G
G
12
).
IN
LIN
LIN
IN
V
(6)
(7)
R
R
.
XTR104
8
8
R
LIN
7
9
FIGURE 4. Parabolic Nonlinearity.
I
O
R
V+
LIN
10
B
E
10
–1
–2
–3
I
NOTE: (1) V
Pins 3 and 4 must be reversed for B > 0 (see Figure 1).
O
9
8
7
6
5
4
3
2
1
0
3
2
1
0
13
11
= 4-20mA
0
0
0.1
0.1
BRIDGE TRANSDUCER TRANSFER FUNCTION
LIN
Positive Nonlinearity
0.2
0.2
inputs connected for negative nonlinearity (B < 0).
WITH PARABOLIC NONLINEARITY
B = +2.5%
NONLINEARITY vs STIMULUS
0.01µF
0.3
0.3
Linear Response
Normalized Stimulus
Positive Nonlinearity
Normalized Stimulus
0.4
0.4
B = +2.5%
0.5
0.5
Negative Nonlinearity
0.6
0.6
R
+
–
L
Negative Nonlinearity
4-20mA
B = –1.9%
0.7
0.7
B = –1.9%
0.8
0.8
V
0.9
0.9
+
–
PS
1
1