SCM5B47 Linearized Thermocouple Input Modules

• Interfaces to Types J, K, T, E, R, S, N and B Thermocouples
• Linearizes Thermocouple Signal
• High-Level Voltage Outputs 1500Vrms Transformer Isolation
• ANSI/IEEE C37.90.1 Transient Protection
• Input Protected to 240VAC Continuous
• 160dB CMR
• 95dB NMR at 60Hz, 90dB at 50Hz
• ±1µV/°C Drift
• ATEX Compliant

The SCM5B47 voltage input module provides a differential, isolated, analog input channel that is filtered, isolated, amplified, and converted to an analog output voltage. This voltage output is switchable via a logic input, allowing multiple of these modules to share a common analog bus without the need for external multiplexers.

In addition to the input, the output of the module is also galvanically isolated from the module supply. The galvanic isolation provides additional safety in industrial applications and reliably protects the downstream evaluation electronics.

The SCM5B47 can interface to eight industry standard thermocouple types: J, K, T, E, R, S, N, and B. Its corresponding output signal operates over a 0V to +5V range. Each module is cold-junction compensated to correct for parasitic thermocouples formed by the thermocouple wire and screw terminals on the mounting backpanel. Upscale open thermocouple detect is provided by an internal pull-up resistor. Downscale indication can be implemented by installing an external 47 MOhm resistor, ±20% tolerance, between screw terminals 1 and 3 on the SCMPB01/02/03/04/05/06/07 backpanels. Signal filtering is provided by a six-pole filter that offers 95dB suppression at 60Hz and 90dB at 50Hz. Two poles of this filter are located on the field side of the isolation barrier, the other four on the output side.

After upstream field-side filtering, the input signal is chopped by a proprietary chopper circuit. Isolation is provided by a signal transformer, with a proprietary technique for suppressing transmission of common-mode spikes or surges. The module is powered from +5VDC, ±5%. A special input circuit on the SCM5B47 modules provides protection against accidental connection of power-line voltages up to 240VAC.