Isolated Process Control Signal Conditioning Products
Isolated Process Current/Voltage Input Modules
The SCM7B32 current input modules accept input signals in the 4-20mA or
0-20mA ranges from the field and provide a high-level output to the process
control system (Figure 1). Current to voltage conversion occurs internal to the
module, which is factory calibrated to ensure the highest accuracy.
SCM7B33 voltage input modules accept input signals in the +1V to +5V or 0 to
+5V ranges from the field and provide a high-level output to the process
control system. As an alternative, the SCM7B33 can be used with an external
250Ω resistor (Dataforth SCM7BXR1 or equivalent), to accept input signals in
the 4-20mA or 0-20mA ranges. Using the external sense resistor allows the
module to be removed without disrupting the current loop. All SCM7B33s are
shipped with a SCM7BXR1 resistor.
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 (conversion-SCM7B32 only), the input signal
is chopped by a proprietary chopper circuit and transferred across the trans-
former isolation barrier, suppressing transmission of common mode spikes and
surges. The signal is then reconstructed and filtered for process control system
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.
• Accepts Current or Voltage Input
• Provides High-Level Voltage Outputs
• 1500Vrms Transformer Isolation
• Accuracy, ±0.03% of Span Typical,
• ANSI/IEEE C37.90.1 Transient Protection
• Input Protected to 120Vrms Continuous
• Noise, 500µVp-p (5MHz), 300µVrms
• 105dB CMRR
• Easy DIN Rail Mounting
• CSA C/US Certified
• CE and ATEX Compliant
Figure 1: SCM7B32/33 Block Diagram
72 For information call 800-444-7644
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