Need advice on my Fluke 87v

[turtle2013]

I was asked to measure the max DC input of a charging system, the DC input should be roughly 400v and no more then 800v. When I first measured the dc input it was 1265v. I tested 3 more times and the highest I recorded was 1663v.

The manufacture said there was no way it could be that high. So I bought a Fluke 87v and a 1000:1 HV probe, and measured the site again. This time the manufacture flew their tech out to measure as well.

With the 1000:1 HV probe connected to the Fluke and the settings on Auto hold and the voltage range set to 6.000v
the results I got were 0.1114v. As I understand it that with using the 1000:1 HV probe that would equate to 1114v or would I be incorrect?


Thank you for your help with this

 

[belvedere]

Wouldn't you multiply the reading by 1000? So 0.1114 = 111.4?

 

[turtle2013]

Wouldn't you multiply the reading by 1000? So 0.1114 = 111.4?

Normally I would say yes, if you did not use the manual range, so normal range would have looked like this 111.11 now manual 6v range does this 0.111l which is why I ask if 6v manual moves everything 3 to the right then 111v would read 0.111v. When you multiply that by 1000 you get 1110v dc.

or at least that is my calculation and it could be off I am new to the meter which is why i gave some field expamples

 

[mrjaw14]

You need to verify the 87v is working right. A 1000:1 probe should read 1v per 1000v. I’m assuming your dual meter shot is measuring the same 460v source right? If so the 87v isn’t reading right. Measure 460 with and without the hv probe. You should get 0.460 with the hv probe at 1000:1 if you get 460 without the probe. The 87v has a max voltage of 1000. maybe reading above 1000v blew a fuse or component?

 

[tool_scrounge]

Put in a new battery and recheck the readings

 

[APEowner]

Autohold is not the same is peak hold. Autohold just locks the current value. Since you can see the screen there's no reason to use Autohold.

With a 1000:1 HV probe you should be multiplying the measured measured volts by 1000. If you're in auto range the meter might be displaying millivolts which it will indicate by showing mV instead of V on the display. To convert from mV to V you divide by 1000. So

With the 1000:1 HV probe to get actual volts you multiply the displayed volts by 1000

0.1114 V displayed x 1000 probe correction = 111.4 V actual
111.4 mV displayed / 1000 = 0.1114 V x 1000 probe correction = 111.4 actual

If it turns out that you really are getting the large difference that it looks like you're getting between meters and the meters are determined to be good (they should be calibrated occasionally to be sure) then I'd be suspicious of the power supply having a significant amount of AC noise. Different meters will integrate the AC component differently and some HV probes will filter out a significant amount. While a good HV probe and an oscilloscope is the best way to check for this a quick and dirty test is to just put the meter in AC mode.

 

[cptn_zippy]

I’m confused by the photo. Is the 287 measuring the same source at the same time? If so, there’s either something wrong with the meter or the voltage source is not good DC. What did you originally measure the voltage with?

J

 

[cvairwerks]

Need to go back and read the instruction sheet on the probe....Some of the Fluke probes use the 10Mohm range for high voltage readings, and not the VDC....

 

[APEowner]

Need to go back and read the instruction sheet on the probe....Some of the Fluke probes use the 10Mohm range for high voltage readings, and not the VDC....

That's interesting. I've never used a Fluke HV probe and didn't know that. I wonder what the circuitry in the probe is.

 

[cvairwerks]

That's interesting. I've never used a Fluke HV probe and didn't know that. I wonder what the circuitry in the probe is.

Not sure, as I didn't look at the circuit diagram real close for the one I grabbed. That particular one was for up to 40KV, for looking at things like electrostatic cleaners. The instructions said use the particular resistance scale on the meter. I gather that when using it, the output voltage from the probe is in the milivolt range, and if you use a DC scale, it would load the probe too much...Just guessing from a 30 second look at the book for it.

 

[mrjaw14]

I thought the 10M ohm was the meter impedance the probe is calibrated for, but the instruction sheet is confusing