Abstract: An rms converter accommodates incoming signals of large crest factor by using an amplifier having a transfer function of non-uniform slope. The amplifier has a lower gain for larger signals. The output of the amplifier is converted to digital voltage values. The non-uniform gain of the amplifier is compensated for in digital calculations of the rms value. The invention produces accurate rms measurements by accurately measuring lower incoming signal voltages while still accommodating high peak voltages. The invention also reduces the dynamic range requirements for the analog to digital converter.

Abstract: A circuit for measuring alternating current (a.c.) and direct current (d.c.) in a conductor without breaking the conductor is provided. A modulated current source is coupled in parallel with a segment of the conductor to inject a test current. A synchronous demodulator is also coupled in parallel across the segment to separate the test voltage drop induced by the test current from the voltage drop due to the current in the conductor. The test voltage drop and the voltage drop are measured by a voltmeter and the resistance of the segment and the current flowing through the segment can then be calculated.