Keysight-Agilent 427A

HP 427A Voltmeter

The HP 427A Voltmeter is really a multimeter with the ability to measure AC, DC+, DC- Volts and Ohms. It has a mirrored analog meter. The black common 5-way binding post is isolated from the instrument chassis. The AC measurements are average responding not true RMS. Specifications: AC Voltage Range 10 mV - 300 V DC Voltage Range 100 mV - 1000 V Frequency Range 10 Hz - 1 MHz Interface 10 Mohm

Before the handheld DMM this was the general purpose lab instrument used for common electrical measurements.  It can be powered from an AC line using the standard IEC power cord (110 or 220) or from an internal 22.5 Volt Battery.  There is a carrying handle on the top so it can be used in the field like the DMM is used now.  Maybe it could be called an AMM "Analog Multi Meter".

This is a solid state meter that measures AC, DC+, DC- Volts and Ohms.  It has a mirrored analog meter.  It's 1/3 Rack wide & will mount in 4 Units of height.  The black common 5-way binding post is isolated from the instrument chassis.  The AC measurements are average responding not true RMS.

The reason for the DC+ and DC- functions is because this meter reads up to 1,000 Volts on the DC range but may have a lower spec for the isolation between the black common 5-way binding post and earth ground.  Some power supplies, like ones used for small Cathode Ray Tubes (CRT) have the positive terminal connected to the chassis and the negative terminal is floated.  The 427A could measure these voltages either direction.

115/230 Volts 1 Phases 50~1000 Hzs