- Interfaces to 100 Ohm Platinum, 10 Ohm Copper, or 120 Ohm Nickel RTDs
- Linearizes RTD 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
- ATEX Compliant
The SCM5B34 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.
RTD excitation is provided from the module by two matched current sources. When using a three-wire RTD, this method allows an equal current to flow in each RTD lead, which cancels the effects of lead resistances. The excitation currents are very small (0.25mA for 100 Ohm Pt and 120 Ohm Ni, and 1.0mA for 10 Ohm Cu) which minimizes self-heating of the RTD. 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 SCM5B34 modules provides protection against accidental connection of power-line voltages up to 240VAC.