Signal conditioning module for sensing multiform field voltage signals

摘要

A signal conditioning module for sensing multiform field signals and for providing isolated digital signals appropriate for a processing system. The present invention allows sensing of field signals which are either AC or DC and which have magnitudes ranging from zero to greater than 240 volts in the preferred embodiment. A circuit according to the present invention includes a bidirectional maximum current limiter coupled to a bidirectional isolation current sensor. The current sensor preferably includes an opto-coupler. The current limiter preferably includes cross-coupled depletion mode devices and a current limit resistor. In this manner, current flowing through the resistor develops a voltage for turning off one depletion mode device or the other depending upon the polarity of the current, so that the input current is limited to a predetermined maximum level for a wide voltage range of input signals and regardless of voltage polarity. The opto-coupler preferably includes cross-coupled LEDs for sensing current in either direction. An AC smoothing filter is provided at the output to filter AC signals for providing a smooth digital output signal.