XTR104 Burr-Brown Corporation, XTR104 Datasheet - Page 10

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

protects against reversed loop connections. As noted earlier,
reversed loop connections would produce a large loop cur-
rent, possibly damaging R
RADIO FREQUENCY INTERFERENCE
The long wire lengths of current loops invite radio frequency
interference. RF can be rectified by the sensitive input
circuitry of the XTR104 causing errors. This generally
appears as an unstable output current that varies with the
position of loop supply or input wiring.
If the bridge sensor is remotely located from the XTR104,
the interference may enter at the input terminals. For inte-
grated transmitter assemblies with short connections to the
sensor, the interference more likely comes from the current
loop connections.
FIGURE 6. Reverse Voltage Protection.
FIGURE 7. Over-Voltage Surge Protection.
Sensor
Bridge
–
®
XTR104
R
B
+
L
.
XTR104
0.01µF
V+
I
O
10
B
E
7
13
11
0.01µF
R
G
1
3
5
6
4
2
0.01µF
V
V
R
R
V
V
+
+
–
–
12
G
G
IN
LIN
LIN
IN
V
R
XTR104
8
1N4001
R
1N4148
LIN
D
10
7
9
2
I
D
O
R
1
V+
LIN
Bypass capacitors on the input often reduce or eliminate this
interference. Connect these bypass capacitors to the I
terminal (see Figure 7). Although the DC voltage at the I
terminal is not equal to 0V (at the loop supply, V
circuit point can be considered the transmitter’s “ground”.
LOW-IMPEDANCE BRIDGES
Low impedance bridges can be used with the XTR104 by
adding series resistance to limit excitation current to 2mA.
Equal resistance should be added to the upper and lower
sides of the of the bridge (Figure 8) to keep the bridge output
voltage centered at approximately 2.5V. Bridge output is
reduced, so a preamplifier, as shown, may be needed to
reduce offset and drift.
10
B
E
I
O
13
11
= 4-20mA
0.01µF
Use either D
See “Reverse Voltage Protection.”
Zener diode 36V: 1N4753A
General Semiconductor Transorb™ 1N6286A, special
low impedence clamp type. Use lower voltage zener
diodes with loop power supply voltages less than 30V
for increased protection.
Q
1
R
Maximum V
minimum voltage rating of zener diode.
L
1
or D
or
D
2
2
.
PS
must be less than
V
PS
R
+
–
L
4-20mA
V
+
–
PS
PS
) this
O
O