XTR104 Burr-Brown Corporation, XTR104 Datasheet - Page 9

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

Then, R
accurate value of K
different value for each XTR104.
It is also possible to make a real-time adjustment of R
with a variable resistor (active circuit trimming). This is
done by measuring the change in V
to-V
correct for each 1% of nonlinearity, the excitation voltage,
V
change in reference voltage, V
V
Example: A bridge sensor has a –1.9% nonlinearity. Apply
the full-scale bride output, V
and adjust R
Note that with all the calculation and adjustment methods
described above, the full-scale bridge output is no longer
equal to V
longer 5V. All the calculations and adjustment procedures
described above assume V
output with constant 5V excitation. It is not necessary to
iterate the calculations or adjustment procedures using the
new full-scale bridge output as a starting point. However, a
new value for R
A refined value for R
trimming, or by measuring linearization gain (equation 7)
will improve linearity. Reduction of the original parabolic
nonlinearity of the sensor can approach 40:1. Actual results
will depend on higher-order nonlinearity of the sensor.
If no linearity correction is desired, make no connections to
the R
remain a constant +5V. The V
remain connected to the bridge output to keep these inputs
biased in their active region.
FIGURE 5. Potentiometer Sensor Application.
R
LIN
, must make a 4% change at full-scale input. So the
FS
can be calculated by:
LIN
change in voltage applied to the V
LIN
pins (R
FS
can be calculated using equation 5 using the
LIN
because the excitation voltage at full scale is no
for:
G
LIN
V
must be calculated using equation 6.
V
R
=
'
LIN
R
’
LIN
= 5V + 0.2 • B = 4.62V
= 0.2 • B
). This will cause the V
, arrived at either by active circuit
from equation 7. K
8k
2k
10k
2.5V
3V
to
10k
10k
FS
FS
+
to be the full-scale bridge
LIN
R
(10mV), to the V
, for a full-scale change in
5V
and V
R
2.5V
in response to a zero-
–
2.5k
LIN
R
G
LIN
1
3
5
6
4
2
LIN
inputs should
V
V
V
V
R
R
R
+
–
–
+
G
G
inputs. To
12
LIN
LIN
IN
V
IN
LIN
can be a
output to
R
XTR104
inputs
R
8
LIN
LIN
(8)
9
7
V
R
I
+
LIN
O
9
10
B
E
13
11
OTHER SENSOR TYPES
The XTR104 can be used with a wide variety of inputs. Its
high input impedance instrumentation amplifier is versatile
and can be configured for differential input voltages from
millivolts to a maximum of 1V full scale. The linear com-
mon-mode range of the inputs is from 2V to 4V, referenced
to the I
You can use the linearization feature of the XTR104 with
any sensor whose output is ratiometric with an excitation
voltage. For example, Figure 5 shows the XTR104 used with
a potentiometer position sensor.
REVERSE-VOLTAGE PROTECTION
Figure 6 shows two ways to protect against reversed output
connection lines. Trade-offs in an application will determine
which technique is better. D
causes a 0.7V loss in loop supply voltage. This may be
undesirable if V+ can approach the 9V limit. Using D
(without D
in the loop supply if the leads are reversed. This could
damage the power supply or the sense resistor, R
with a higher current rating is needed for D
highest current that could occur with reversed lines.
SURGE PROTECTION
Long lines may be subject to voltage surges which can
damage semiconductor components. To avoid damage, the
maximum applied voltage rating for the XTR104 is 40V. A
zener diode can be used for D
voltage applied to the XTR104 to a safe level. The loop
power supply voltage must be lower than the voltage rating
of the zener diode.
There are special zener diode types (Figure 7) specifically
designed to provide a very low impedance clamp and with-
stand large energy surges. These devices normally have a
diode characteristic in the forward direction which also
O
terminal, pin 7.
1
) has no voltage loss, but high current will flow
0.01µF
R
1
+
–
L
4-20 mA
offers series protection, but
XTR104
2
(Figure 7) to clamp the
V
+
–
2
PS
to withstand the
L
. A diode
2
®