Impulse SCM7B34_34N - Manual

Isolated Process Control Signal Conditioning Products SCM7B
For information call 800-444-7644 72
SCM7B34/34N
Isolated Linearized 2- or 3-Wire RTD Input Modules
Description
Each SCM7B34/34N RTD input module accepts a single channel of 100 Ω
Platinum ( α = 0.00385) or 120 Ω Nickel ( α = 0.00672) RTD input and produces
an input voltage in response to a low level current excitation. The input signal
is filtered, isolated, amplified, linearized, and converted to a high level analog
voltage for output to the process control system (Figure 1).
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.
In response to the low level current excitation signal, the RTD 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
output.
Linearization is achieved by creating a non-linear transfer function through the
module itself. This non-linear transfer function is configured at the factory and
is designed to be equal and opposite to the specific RTD non-linearity. Lead
compensation is achieved by matching two current paths thus cancelling the
effects of lead resistance.
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: SCM7B34/34N Block Diagram
▲
Features
• Interfaces to 100 Ω Platinum or 120 Ω
Nickel RTDS
• Provides 250µA RTD Excitation Current
• Linearizes RTD Signal Response
• Provides High Level Voltage Outputs
• 1500Vrms Transformer Isolation
• Accuracy, ±0.05% to ±0.15% of
Span Typical
• Nonconformity, ±0.025% to ±0.07% of
Span Typical
• ANSI/IEEE C37.90.1 Transient Protection
• Input Protected to 120Vrms Continuous
• Noise, 500µV Peak (5MHz), 250µV RMS
(100kHz)
• CMRR, up to 160dB
• NMR, up to 85dB
• Easy DIN Rail Mounting
• CSA Certified, FM Approved
• CE and ATEX Compliant