LTC2984 datasheet(35/78 Pages) AD

35 / 78 page

LTC2984

2984fb

For more information www.linear.com/LTC2984

APPLICATIONS INFORMATION

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 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.

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.

Table 33. Total Excitation Current for All RTD Wire Types

(4) EXCITATION CURRENT

B17

B16

B15

B14

CURRENT

Reserved

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.

(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 LTC2984.

See Custom RTD section near the end of this data sheet

for more information.

LTC2984 Datasheet(PDF) 35 Page - Analog Devices

LTC2984 Datasheet(HTML) 35 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78

Datasheet Download

Link URL