LTC2983
30
2983fc
For more information www.linear.com/LTC2983
APPLICATIONS INFORMATION
Table 29. Total Excitation Current for All RTD Wire Types
(4) EXCITATION CURRENT
B17 B16 B15 B14 CURRENT
0 0 0 0 Reserved
0 0 0 1 5μA
0 0 1 0 10μA
0 0 1 1 25μA
0 1 0 0 50μA
0 1 0 1 100µA
0 1 1 0 250µA
0 1 1 1 500µA
1 0 0 0 1mA
Bits B18 and B19 are also used to enable excitation current
rotation to automatically remove parasitic thermocouple
effects. Parasitic thermocouple effects may arise from the
physical connected between the RTD and the measure-
ment instrument. This mode is available for all 4-wire
configurations using internal current source excitation.
(4) Excitation Current
The next field in the channel assignment word (B17 to
B14) controls the magnitude of the excitation current
applied to the RTD (see Table 29). The current selected
is the total current flowing through the RTD independent
of the wiring configuration. The R
SENSE
current is 2x the
sensor excitation current for 3-wire RTDs.
In order to prevent soft or hard faults, select a current
such that the maximum voltage drop across the sensor or
sense resistor is nominally 1.0V. For example, if R
SENSE
is 10kΩ and the RTD is a PT-100, select an excitation
current of 100µA for 2-wire and 4-wire RTDs and select
50µA for a 3-wire RTD. Alternatively, using a 1kΩ sense
resistor with a PT-100 RTD allows 500µA excitation for
any wiring configuration.
(5) RTD Curve
Bits B13 and B12 set the RTD curve used and the cor-
responding Callendar-Van Dusen constants (shown in
Table 30).
(6) Custom RTD Data Pointer
In the case where an RTD not listed in Table 30 is used,
a custom RTD table may be entered into the LTC2983.
See Custom RTD section near the end of this data sheet
for more information.
Table 30. RTD Curves: RT = R0 • (1 + a • T + b • T
2
+ (T – 100°C) • c • T
3
) for T < 0°C, RT = R0 • (1 + a • T + b • T
2
) for T > 0°C
(5) CURVE
B13 B12 CURVE ALPHA a b c
0 0 European Standard 0.00385 3.908300E-03 –5.775000E-07 –4.183000E-12
0 1 American 0.003911 3.969200E-03 –5.849500E-07 –4.232500E-12
1 0 Japanese 0.003916 3.973900E-03 –5.870000E-07 –4.400000E-12
1 1 ITS-90 0.003926 3.984800E-03 –5.870000E-07 –4.000000E-12
X X RTD1000-375 0.00375 3.810200E-03 –6.018880E-07 –6.000000E-12
X X *NI-120 N/A N/A N/A N/A
*NI-120 uses table based data.
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