Amprobe DM-II PLUS readings

[steve66]

I had a contractor monitor the load on an ATS. They sent me the data, but there are a couple of things I don't understand.

Each voltage and current has three graphs. One labeled "high", one labeled "mid", and one labeled "low". For example, there are three graphs for the Phase 2 current - high, mid, and low. Are these just differences in how the meter averages the input?

The contractor had the meter set up for a delta system, even though this was a 3 wire wye system. Would that affect the current readings in any way? A 400 amp reading on the meter should still mean 400 amps, correct?

Finally, for some reason, the meter didn't record the 3rd phase voltage or current. Could this be because the meter was set for a delta system?

Thanks.

 

[steve66]

Any comments??

 

[GoldDigger]

Any comments??

For delta system, there are three possible current measurements, but if you know any two you can calculate the third.

For a wye with some line to neutral loads you must measure any three current values to be able to calculate the fourth.

Sounds like the meter was too clever.

 

[iceworm]

I don't have any experience with an Amprobe DM-II, so I can't tell
you about that.

Drawing on what I have seen using a PX-5:

The high, medium, and low comes from the different values the instrument sees during each measurement period.

As for the metering connection being set up for a Delta, if they used a 2 wattmeter connection, you only get two voltages and two currents. One of the phases is used as a common. So the two currents are correct, as long as there is no neutral current. The third current can be calculated, again, as long as there is no neutral current. The two voltages are phase to phase, the third voltage is zero.

As long as there is no neutral current, the power readings are correct. If you were looking for voltage transients, sags, swells I don't know what the data means.

ice