XTR103 Burr-Brown Corporation, XTR103 Datasheet - Page 8

• Manufacturer Part Number: XTR103
• Description: 4-20mA Current Transmitter with RTD EXCITATION AND LINEARIZATION
• Manufacturer: Burr-Brown Corporation

FIGURE 4. Three-Wire Connection for Remotely Located RTDs.
FIGURE 3. Low-Scale Output Current Adjustment.
with R
with narrow temperature measurement spans) the output
current adjustment may not provide sufficient range. In these
cases, offset can be nulled by adjusting the value of R
TWO-WIRE AND
THREE-WIRE RTD CONNECTIONS
In Figure 1, the RTD can be located remotely simply by
extending the two connections to the RTD. With this two-
wire connection to the RTD, line resistance will introduce
error. This error can be partially corrected by adjusting the
values of R
G
. If the input stage is set for high gain (as required
Z
, R
®
Resistance in this line causes
a small common-mode voltage
which is rejected by XTR103.
G
XTR103
1
1
, and R
1
XTR103
XTR103
10k
Equal
a small common-mode voltage
which is rejected by XTR103.
5k
RTD
2
2
2
LIN
line resistances here creates
.
16
16
3
5k
(R
±500µA typical
output current
adjustment range.
LINE
±50µA typical
output current
adjustment range.
(a)
(b)
)
2N2222
1.5k
R
CM
*Q
predictable output
current if any one
RTD connection
is broken:
Q
2
2
*
optional. Provides
R
Z
0.01µF
Z
.
8
R
G
Figure 4, shows a three-wire RTD connection for improved
accuracy with remotely located RTDs. R
through a third wire to the RTD. Assuming line resistance is
equal in RTD lines 1 and 2, this produces a small common-
mode voltage which is rejected by the XTR103.
OPEN-CIRCUIT DETECTION
The optional transistor Q
behavior with open-circuit RTD connections. It assures that
if any one of the three RTD connections is broken, the
XTR103’s output current will go to either its high current
limit ( 34mA) or low current limit ( 3.6mA). This is easily
detected as an out-of-range condition.
REVERSE-VOLTAGE PROTECTION
Figure 5 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 are subject to voltage surges which can damage
semiconductor components. To avoid damage, the maxi-
mum applied voltage rating for the XTR103 is 40V. A zener
diode may be used for D
applied to the XTR103 to a safe level. The loop power
supply voltage must be lower than the voltage rating of the
zener diode.
Open RTD
4
5
6
3
Terminal
V
V
R
R
1
2
3
–
+
G
G
13
IN
IN
8
I
R
XTR103
R
12
LIN
1
I
R
) has no voltage loss, but high current will flow
3.6mA
3.6mA
34mA
I
O
9
V+
10
7
15
11
Q
1
2
2
in Figure 4 provides predictable
(Figure 6) to clamp the voltage
1
offers series protection, but
0.01µF
Z
’s current is routed
2
to withstand the
L
. A diode
2