Each statement in Test Instrument Reference is recorded as a data record with its source, verification date, review status
and history. The index lists 9 records by subject.
IEEE 43-2013 recognizes direct-reading megohmmeters, whether hand-cranked, battery-powered or rectifier-powered, and resistance bridges as instruments for measuring insulation resistance.
IEEE 43-2013 notes that when a low insulation resistance is measured, allowance is made for the voltage drop across the protective resistor of the test set.
IEEE 43-2013 also describes obtaining insulation resistance by calculation from a separately measured voltage and current, using a regulated direct-voltage supply, a voltmeter and a microammeter.
A low-resistance ohmmeter is an instrument that measures small resistances, such as those of contacts, joints and bolted connections, by passing a known direct current through the object and measuring the voltage drop that the current produces across it.
In a four-terminal measurement the current is supplied through one pair of leads and the voltage drop is sensed through a separate pair, so that the resistance of the leads and of the current connections is kept out of the result.
A reference on impedance measurement published by the University of California, Berkeley physics laboratory describes the four-terminal technique as passing current through one pair of leads and measuring voltage on the other pair, which removes the error caused by the series impedance of the leads, and describes it as suited to low impedances.
The same reference notes that the term Kelvin connection is often used interchangeably with four-terminal, and names the Kelvin bridge as the most widely known four-terminal technique for precision direct-current resistance measurement.
