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SCM5B37

Thermocouple Input Modules

The SCM5B modules are designed with a completely isolated computer

side circuit which can be floated to

±50V from Power Common, pin 16. This

complete isolation means that no connection is required between I/O

Common and Power Common for proper operation of the output switch. If

desired, the output switch can be turned on continuously by simply

connecting pin 22, the Read-Enable pin to I/O Common, pin 19.

The SCM5B37 can interface to nine industry standard thermocouple types:

J, K, T, E, R, S, C, N, and B. Its corresponding output signal operates over

a 0V to +5V range. Each module is cold-junction compensated to correct

for parasitic thermocouples formed by the thermocouple wire and screw

terminals on the mounting backpanel. Upscale open thermocouple detect

is provided by an internal pull-up resistor. Downscale indication can be

implemented by installing an external 47M

Ω resistor, ±20% tolerance,

between screw terminals 1 and 3 on the SCMPB01/02/03/04/05/06

backpanels.

Signal filtering is accomplished with a six-pole filter which provides 95dB

of normal-mode-rejection at 60Hz and 90dB at 50Hz. Two poles of this filter

are on the field side of the isolation barrier, and the other four are on the

computer side.

After the initial field-side filtering, the input signal is chopped by a

proprietary chopper circuit. Isolation is provided by transformer coupling,

again using a proprietary technique to suppress transmission of common

mode spikes or surges. The module is powered from +5VDC,

±5%.

A special input circuit on the SCM5B37 modules provides protection

against accidental connection of power-line voltages up to 240VAC.

For Class I, Division 2 hazardous location applications, refer to Dataforth

installation manual MA1146 (available upon request).

FEATURES

q INTERFACES TO TYPES J, K, T, E, R, S, C, N AND B

THERMOCOUPLES

q HIGH LEVEL VOLTAGE OUTPUTS

q 1500Vrms TRANSFORMER ISOLATION

q ANSI/IEEE C37.90.1-1989 TRANSIENT PROTECTION

q INPUT PROTECTED TO 240VAC CONTINUOUS

q 160dB CMR

q 95dB NMR AT 60Hz, 90dB at 50Hz

q

±0.05% ACCURACY

q

±0.02% LINEARITY

q

±1µV/°C DRIFT

q CSA CERTIFIED, FM APPROVED, CE COMPLIANT

q MIX AND MATCH SCM5B TYPES ON BACKPANEL

DESCRIPTION

Each SCM5B37 thermocouple input module provides a single channel of

thermocouple input which is filtered, isolated, amplified, and converted to

a high level analog voltage output (Figure 1). This voltage output is logic-

switch controlled, allowing these modules to share a common analog bus

without the requirement of external multiplexers.

FIGURE 1. SCM5B37 Block Diagram.

–V

LPF

LPF

+In

–In

–EXC

Backpanel

Term Block

1

2

6

5

3

Surge

Suppression

and

Protection

+V

Isolated

Field-Side

Power

Power

Oscillator

Isolated

Computer-Side

Power

V

OUT

20

19

22

I/O Common

RD EN\

+5V

Power Common

4

3

2

1

+EXC

–V

+V

4

NC

Thermocouple

Precision

Reference

CJC

Temp

Sensor

+2.5V

17

16

100M

Ω

Isochopper™

Amplifier

Pat Pending