Hey there guys
Had a question, I was using my 123 scope meter to take some readings on the output of a drive..........small one and the amps didn't really add up. I haven't used another meter to confirm. I know for voltage you used the filter, but any thing for amps?
THANKS GUYS

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MIKE
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Current has a frequeny also. I have one current probe meter that has a low pass filter. Doesn't your 345 have a low pass filter too? Interesting though! Yes,what about using a scope?

There are two bandwidth settings but I doubt if that would help. I can't find the specs but I "think" that the Low Pass filter used in the 289/87V is <1kHz.

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Bill

Hey Bill
Yes the 345 has a low pass filter, but at the time I was using 123 and using my BNC 400s with "BB120" on Ch.A and on Ch.B was the voltage. Voltage seem ok(however, didn't cross check with 345) but the amps was going all crazy..........I tryed going up and down with range, but didn't seem to matter. BUT I only tryed the once, just posted to see any insight!

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MIKE
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Mike:

The 345 manual doesn't say much about the low pass filter other than it has one. The 87V it's only for ACV but if your current probe is of the type that the output is mv/A, it should work. Not sure if there is some sort-of external line filter that can be used with a scope for that purpose? I'll try to search for something like that.

There is a noise filter in either/both the 123 and 199B.

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Bill

Thanks Bill
Yeah I am going to try again-I think that the current was too low to read.
I'll try the range, see if I had it to high.

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MIKE
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I know this is a old thread but, I could be wrong, I was thinking that when using the 120 series scopes that if measureing volts and amps, A had to be for volts and B for amps. I'm saying this off the top of my head without looking it up, so I might be wrong. Just didnt think 120's had any problem with measureing amp on a VFD.

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DavisIME

Ok, just read the 125 manual, it says when makeing power or harmonic measurements connect volts to A and amps to B. I dont know it this was just an example or this is the protocal for these measurements. It didn't say either way. Probably ok either way. Its just thats the way I always hook them up, the way the manual said to. I know you Canadians are a little bassakwards sometimes. lol, You know I'm just kidding Mike.

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DavisIME

Yeah for a 125, 43B and 190 Series also. It expects voltage on A channel and current on B channel because of the shift in phase angle of the two. You could end up with a negative PF and miscalculated power. It won't matter on a 123/124 unless your measuring phase angle. You must have the current clamp's flow directional arrow pointing the right way too but that goes for the 123/124 too!

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Bill

Hey Mike. Hey Fella's.

I'm wondering what kind of a drive your working with. It's been my experience that most VFD's have an interface where you can access these readings. What I have done in the past is to record the internal readings, use my Dmm with the low pass filter, and a true RMS reading snap around meter. All my readings were in line with the drives internal readings... The problem turned out to be a mechanical binding in the machine....

Sometimes the old ways are the best.

WORK SAFE !!!!

Glenn D.