Impulse SCM7B37 User Manual

Scm7b37, Isolated thermocouple input modules, Scm7b

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Isolated Process Control Signal Conditioning Products

SCM7B

For information call 800-444-7644

78

SCM7B37

Isolated Thermocouple Input Modules

Description

SCM7B37 modules accept a single channel of input from Type J, K, T, E, R,

S, or B thermocouples. The signal is filtered, isolated, amplified, and converted

to a high level analog voltage for output to the process control system

(Figure 1).
Cold junction compensation (CJC) is performed using an NTC thermistor (see

“Additional SCM7B Part Numbers” section for P/N and AN701 for further

information) externally mounted under the field-side terminal block on the

backpanel (Figure 1). Open thermocouple detection is upscale using a 30nA

current source in the input circuitry.
These modules incorporate a five-pole filtering approach to maximize both time

and frequency response by taking advantage of both Thomson (Bessel) and

Butterworth characteristics. One pole of the filter is on the field side of the isolation

barrier; four are on the process control system side.
After the initial field-side filtering, the input signal is chopped by a proprietary

chopper circuit and transferred across the transformer isolation barrier,

suppressing transmission of common mode spikes and surges. The signal is

then reconstructed and filtered for process control system output.
Modules accept a wide 14 - 35VDC power supply range (+24VDC nominal).

Their compact packages (2.13"x1.705"x0.605" max) save space and are ideal

for high channel density applications. They are designed for easy DIN rail

mounting using any of the “-DIN” backpanels.

Figure 1: SCM7B37 Block Diagram

Features

• Interfaces to Type J, K, T, E, R, S, and B

Thermocouples

• Provides High Level Voltage Outputs
• 1500Vrms Transformer Isolation
• Accuracy, ±0.03% of Span Typical,

±0.1% Max

• ANSI/IEEE C37.90.1 Transient Protection
• Input Protected to 120Vrms Continuous
• Noise, 500µV Peak (5MHz), 250µV RMS

(100kHz)

• CMRR, 160dB
• NMR, up to 85dB
• Easy DIN Rail Mounting
• CSA Certified, FM Approved
• CE and ATEX Compliant

Refer to AN701 for V

out

to

temperature conversion information

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