SCM7B34/34N Isolated Linearized 2- or 3-Wire RTD Input Modules
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Isolated Process Control Signal Conditioning Products SCM7B34/34N Isolated Linearized 2- or 3-Wire RTD Input Modules Description Each SCM7B34/34N RTD input module accepts a single channel of 100Ω Platinum (α = 0.00385) or 120Ω 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). Features • Interfaces to 100Ω Platinum or 120Ω Nickel RTDs • Provides 250µA RTD Excitation Current 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. • Linearizes RTD Signal Response In response to the low-level current excitation signal, the RTD 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. • Accuracy, ±0.05% to ±0.15% of Span Typical 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. • ANSI/IEEE C37.90.1 Transient Protection 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. • Provides High-Level Voltage Outputs • 1500Vrms Transformer Isolation • Nonconformity, ±0.025% to ±0.07% of Span Typical • Input Protected to 120Vrms Continuous • Noise, 500µVp-p (5MHz), 250µVrms (100kHz) • 160dB CMRR • 85dB NMR at 60Hz, 80dB at 50Hz • Easy DIN Rail Mounting • CSA C/US Certified • CE and ATEX Compliant Figure 1: SCM7B34/34N Block Diagram ©1995-2011 Dataforth Corporation, All Rights Reserved ISO9001:2008-Registered QMS

Isolated Process Control Signal Conditioning Products Ordering Information Module Input Signal Range Protection Continuous Transient Sensor Excitation Current(1) Lead Resistance Effect Output Signal Range(2) Effective Available Power(2) Resistance Protection Voltage/Current Limit CMV (Input-to-Output) Continuous Transient CMRR (50 or 60Hz) Accuracy(3) Nonconformity(4) Stability (–40°C to +85°C) Gain Input Offset Zero Suppression Output Offset Noise Peak at 5MHz B/W RMS at 10Hz to 100kHz B/W Peak at 0.1Hz to 10Hz B/W Open Input Response ‘+’ Lead ‘–’ Lead ‘x’ Lead Open Input Detection Time...