Impulse SCM7B37 User Manual
Scm7b37, Isolated thermocouple input modules, Scm7b
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