Phase angle voltmeter

[COWBOYME]

I need some eith the use of a phase angle voltmeter. I have a test set that calls for measuring between two phases of 115VAC (400Hz). We have a scope set up in conjunction with the meter. First, what exactly does the reading indicate? It is labled "Volts RMS". Does the reading indicate the difference in peak-to-peak voltage of the two signals? Or does the voltage relate to angles of phase?
Also, it is an old analog unit; how do you read the scale? we have differing opinions, help please.

 

[logbook]

Is this a two or three phase 400Hz system?

I take it that you understand the difference between a peak-to-peak reading and an RMS reading?

Two power lines could read the same voltage relative to ground/earth and yet you could still see a difference in voltage between them due to their relative phases. This difference voltage could be expressed as an RMS value or a peak-to-peak value, although the numerical values would be different (The ptp would be sqrt(2) larger than the RMS for a sinusoidal waveform.)

"Volts RMS" is not a phase difference reading. A phase difference reading would be expressed in degrees or radians.

Make sure the meter is rated for 400Hz operation rather than just 50/60Hz powerlines.

There should be at least 3 connections to the system under test from the meter. If there are only two then you cannot measure phase directly. I would think there was a switch to give you a phase reading if the meter is capable of this function.

 

[COWBOYME]

Thanks for the reply.
Yes I understand PtP vs RMS. and the meter is rated for 400Hz. We have two phases, 115VAC there are two pairs of leads one pair for each source.

The argument here was what is the dial actually indicating. By the way I argued for voltage as labled, but I am still kind of hazy about everything.

There is a knob to select 0, 90, 180 and 270 degrees. Does this mean we are measuring the difference between the amplitudes of those traces and the at those angles or is that knob used for nulling the voltages?

Thanks for any help, Tom

 

[logbook]

I'm not familiar with this type of equipment. At 400Hz it sounds like aviation stuff?

If there is a knob to select phase difference it isn't measuring the phase but using the supplied phase information (from the switch) to calculate the voltage difference. If you know measure the amplitude and are told the phase then you can do a calculation to find the difference voltage.

Sounds like you don't have a manual and have no prospect of getting one. So the answer is to "calibrate" the meter. Hook the probes up to the same phase so both amplitudes are the same. With the phase set at zero I think you should expect 0V as the answer. With the phase set to 180 degrees you should get double the phase voltage. For the 90 degree ones just use vector summation.

 

[nbucska]

If you tell us what you need, we may find a solution.
Is is lab measurement or for production?

Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[OperaHouse]

I've seen pictures of these old units and always thought you read the voltage point as you walked the degrees through. I'd be curious to know just what is the method. Some of the later "digital" phase angle meters ar pretty cheap. I have a Dranetz 305 and KH 6400. These are basically analog units with a digital voltmeter readout. Either of these units can be had for less than $75.