LTC2995 datasheet(36/90 Pages) AD

36 / 90 page

LTM2985

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

(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 33). The current selected

is the total current flowing through the RTD independent

of the wiring configuration. The RSENSE current is 2x the

sensor excitation current for 3-wire RTDs.

Table 33. Total Excitation Current for All RTD Wire Types

(4) EXCITATION CURRENT

B17

B16

B15

B14

CURRENT

External

5µA

10µA

25µA

50µA

100µA

250µA

500µA

1mA

Table 34. RTD Curves: RT = R0 • (1 + a • T + b • T2 + (T – 100°C) • c • T3) for T < 0°C, RT = R0 • (1 + a • T + b • T2) for T > 0°C

(5) CURVE

B13

B12

CURVE

ALPHA

European Curve

0.00385

3.908300E-03

–5.775000E-07

–4.183000E-12

American

0.003911

3.969200E-03

–5.849500E-07

–4.232500E-12

Japanese

0.003916

3.973900E-03

–5.870000E-07

–4.400000E-12

ITS-90

0.003926

3.984800E-03

–5.870000E-07

–4.000000E-12

RTD1000-375

0.00375

3.810200E-03

–6.018880E-07

–6.000000E-12

*NI-120

N/A

*NI-120 uses table based data.

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 RSENSE

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 34).

(6) Custom RTD Data Pointer

In the case where an RTD not listed in Table 34 is used,

a custom RTD table may be entered into the LTM2985.

See Custom RTD section near the end of this data sheet

for more information.

LTC2995 Datasheet(PDF) 36 Page - Analog Devices

LTC2995 Datasheet(HTML) 36 Page - Analog Devices

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