XTR1037
®
FIGURE 2. Operation Without External Transistor.
TABLE I. RZ, RG, and RLIN Resistor Values for Pt100 RTD.
TMIN 100°C 200°C 300°C 400°C 500°C 600°C 700°C 800°C 900°C 1000°C
–200°C 18/90 18/185 18/286 18/396 18/515 18/645 18/788 18/946 18/1120 18/1317
653 838 996 1087 1131 1152 1159 1158 1154 1140
–100°C 60/84 60/173 60/270 60/374 60/487 60/610 60/746 60/895 60/1061
1105 1229 1251 1249 1231 1207 1181 1155 1128
0°C 100/81 100/167 100/260 100/361 100/469 100/588 100/718 100/860
1287 1258 1229 1201 1173 1145 1117 1089
100°C 138/78 138/162 138/252 138/349 138/453 138/567 138/691
1211 1183 1155 1127 1100 1073 1046
200°C 175/76 175/157 175/244 175/337 175/437 175/546
1137 1110 1083 1056 1030 1003
300°C 212/73 212/152 212/235 212/325 212/422
1066 1039 1013 987 962
400°C 247/71 247/146 247/227 247/313
996 971 946 921
500°C 280/68 280/141 280/219
930 905 881
600°C 313/66 313/136
865 841
700°C 345/64
803
800°C 375/61
743
MEASUREMENT TEMPERATURE SPAN ∆T (°C)
RZ/RG
RLIN
11
14
XTR103 0.01µF
E
E
INT
I
O
V+
For operation without external
transistor, connect pin 11 to
pin 14. See text for discussion
of performance.
10
7
(Values are in Ω.)
NOTE: Values shown are for a Pt100 RTD.
Double (x2) all values for Pt200.
LOOP POWER SUPPLY
The voltage applied to the XTR103, V+, is measured with
respect to the IO connection, pin 7. V+ can range from 9V to
40V. The loop supply voltage, VPS, will differ from the
voltage applied to the XTR103 according to the voltage drop
on the current sensing resistor, RL (plus any other voltage
drop in the line).
If a low loop supply voltage is used, RL must be made a
relatively low value to assure that V+ remains 9V or greater
for the maximum loop current of 20mA. It may, in fact, be
prudent to design for V+ equal or greater than 9V with loop
currents up to 34mA to allow for out-of-range input condi-
tions. The typical performance curve “Loop Resistance vs
Loop Power Supply” shows the allowable sense resistor
values for full-scale 20mA.
The low operating voltage (9V) of the XTR103 allows
operation directly from personal computer power supplies
(12V ±5%). When used with the RCV420 Current Loop
Receiver (Figure 8), load resistor voltage drop is limited to
1.5V.
LINEARIZATION
On-chip linearization circuitry creates a signal-dependent
variation in the two matching current sources. Both current
sources are varied equally according to the following equa-
tion: IR1 = IR2 = 0.8 +
(IR in mA, VIN in volts, RLIN in ohms)
(maximum IR = 1.0mA)
This varying excitation provides a 2nd-order term to the
transfer function (including the RTD) which can correct the
RTD’s nonlinearity. The correction is controlled by resistor
RLIN which is chosen according to the desired temperature
measurement range. Table I provides the RG, RZ and RLIN
resistor values for a Pt100 RTD.
If no linearity correction is desired, do not connect a resistor
to the RLIN pins (RLIN = ∞). This will cause the excitation
current sources to remain a constant 0.8mA.
ADJUSTING INITIAL ERRORS
Most applications will require adjustment of initial errors.
Offset errors can be corrected by adjustment of the zero
resistor, RZ.
Figure 3 shows another way to adjust zero errors using the
output current adjustment pins of the XTR103. This provides
a minimum of ±300µA (typically ±500µA) adjustment around
the initial low-scale output current. This is an output current
adjustment which is independent of the input stage gain set
RLIN
500 • VIN