bar graph on multimeters

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A bar graph vs a numerical readout on a meter is similar to analog automotive gauges vs those with numerical readouts. When you need a specific reading, digits are best.

But, an analog gauge, such as a tachometer or oil pressure gauge, etc., is quicker for the brain to interpret for relative readings. Imagine a race driver having to use digits for a tach.
 
I use mine all the time when you are phasing two sources at an ATS it is invaluable. easier to watch then the digital display, I also use a Simpson analog meter and a analog megger with voltage capabilities for this.

Even though both sources may have correct rotation they may not be in phase.

Connect one meter lead to A phase one source, and the other lead to A phase the second source, connect the second meter lead to B phase one source, and the other lead to B phase the second source
when the bar graph is "0" (no bar graph) on both meters you know both sources are phased properly. If one meter is "0" (no bar graph) and the other full scale then the two sources are out of phase.

Basically when the two sources are in phase the two meter match high or low or in the middle, I just always look for the no bar "0" reading..Old habit..

The reason this works better IMO is the digital display is constantly flashing and hard to get a read on.
 
please explain further. Are you syncing phases from a generator to norm power (makes no sense to me), or is this between emer. poco service and norm service ? (I think I could understand that one)
 
You can see the bar graph move up and down before the digital display will change. Rapid movement will help you decide if the min/max feature needs to be used and just how quickly, within reason, changes are taking place. You may notice that the grapic display moves at specific rate. That in turn may point you to a piece of equipment that is cycling improperly. The min/max feature will not tell the frequency of change, just the amount.
 
please explain further. Are you syncing phases from a generator to norm power (makes no sense to me), or is this between emer. poco service and norm service ? (I think I could understand that one)
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In a normal installation generator to normal power = emergency to normal service no mater what the second source is. Except with a second utility source there will be some difference due to VD on the source carrying the load. I have seen as much as 15 VAC drop between load and non-loaded utility sources on a 480/277 VAC 3 phase Wye system

When you have two sources utility to utility or utility to generator it is possible to have correct rotation A-B-C and C-A-B but the phases out out of sync. With an ATS with an in phase monitor this will not allow the ATS to transfer when both sources are available.

So to verify phasing is correct A is A, B is B, C is C (and if you get 2 of the 3 correct, well by default the 3rd phase had better durn well be right).

To check this you would 1st need to meters, then connect one meter to the A phase utility source (typically normal) and A phase generator (typically emergency), then connect one lead of the second meter to B or C phase
utility/normal and one lead to B or C phase of generator/emergency. If the meters bar graph comes and goes in sync the phasing is correct, if the bar graph is minimum scale on one meter and max scale on another you have the phases crossed. Check all 3 phases till you decide what is correct.

If it is a utility to utility one meter would work, just check for "0" volts from A phase source one to A phase source two and B phase source one to B phase source two.
 
interesting. I only ever checked rotation. why would it matter if phases "skipped a beat" on transfer ?
 
As noted with an ATS with an in-phase-monitor it won't transfer if both sources are available like on restoration of power or duirng a test utilizing the test switch on the ATS.

Besides in my opinion it is good practice..
 
nakulak said:
interesting. I only ever checked rotation. why would it matter if phases "skipped a beat" on transfer ?
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There is no problem on transfer. It's when two sources are connected together. Two different sources with the same rotation but out of phase will result in a phase to phase fault (on all three phases) if they are connected together.

You would find this situation where a a utility customer generates some or all of their own power and is also connected to the grid. When they are first connected together they are synchronized where volts equals zero from A to A, B to B and C to C.
 
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