HP E3630A Amps meter displays 0.01A with no load on 6V setting

[RichardD]

Hi,

Does anyone have any experience with the HP /Agilent / Keysight E3630A Power Supply and can confirm if this model "normally" displays 0.01A on the Amps display for the 6V meter setting (no load, case cover on, some warm up time), instead of 0.00A as one would expect?

I picked up a reasonably priced unit on ebay that seemed to just needed calibration.  So I followed the meter calibration steps in the service manual, using my calibrated Fluke 87V.  Everything with the supply checks out OK (e.g., no oscillations, outputs voltages agree with the display), except the 6V output Amps meter displays 0.01 amps with no load.  The +20V and -20V meter settings display 0.00 amps with no load as expected.

The 6V output does display the correct current with various loads up to current limit, so the meter calibration appears to be OK.  But...I found the 6V and 20V Amps meter calibration steps interact with each other, so I can't zero the 6V Amps display without affecting the calibration of the 20V Amps display.

Thanks,
Richard.

[alm]

I have not used these power supplies, but meter accuracy is specified as 0.5% + 2 counts, so I would say that the reading for a 0.00A current could be anywhere between -0.02A and +0.02A. I would not worry about the reading. As long as it is still in spec for low currents (e.g. for 0.1A the reading should be between 0.08A and 0.12A). If you read the performance verification of the manual, you will probably find the voltages / currents and the allowed limits to check meter accuracy. If the units passes that, then it should be fully operational.

[RichardD]

I looked into what was going on with my power supply a bit further.  The amps meter voltage divider for the 6V current range presents about 0.8mV at no load, at the voltage divider node (measured between the junction of R64 and R65 and analog ground), to the amp meter input.  The amp meter scales this x10, so that ends up as 0.008.  And since the amp meter scale adjustment can only be adjusted for the 20V output, likely the .008 is scaled up slightly because of that -- enough to flip the display to 0.01 (on my unit).

I replaced R64 (332K) with a 221K 1% metal film resistor to lower the no-load R64/R65 node voltage to .0004.  I then re-calibrated the 6V amps meter (via R61) and voila!  The meter displays 0.00 at no load.  And displays correctly for various loads up to the maximum.

I am certain the HP engineers chose 332K for a good reason (maybe over productions runs 332K is optimal).  Anyhow, I don't recommend the change, but...if 0.01A is keeping you up at night...warm up your soldering iron!

A side note (see picture) - I ordered some replacement meter selection buttons from Keysight and clearly Keysight didn't want anyone else getting their hands on them!!

[Armadillo]

Hi,

Would it be possible to adjust R61 Trim?

[HighVoltage]

All my Agilent PSU of this series show 0.01A at idle
This is probably done, so they would not show a negative value in their allowed tolerance.

[GreyWoolfe]

I jsut checked my HP E3610 on all voltages and my current display reads zero.

[RichardD]

Armadillo - you are correct that R61 adjusts the 6V current measurement scale.  But I found (with my unit), adjusting R61 such that the amps display read 0.00 at no load, distorted the amps measurement scale.  No amount of adjusting R61 and the display board adjustment (R5) compensated for the high "idle current" (if I can call it that) through the current measurement voltage divider.

It seemed to me that the calibration arrangement favours the 20V output, and the 6V output calibration is a second cousin.