SCM7B47 modules accept a single channel of input from Type J, K, T, E, R, S, B, or N thermocouples. The signal is filtered, isolated, amplified, linearized, and converted to a high-level analog voltage for output to the process control system.
Linearization is achieved by creating a non-linear transfer function through the module itself; refer to AN505. This non-linear transfer function is configured at the factory and is designed to be equal and opposite to the thermocouple non-linearity.
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. 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.
