Agilent E3631A current calibration routine, CC mode not necessary?

[the Chris]

I ran the calibration routine on my newly aquired E3631A two days ago and I am still wondering about one detail:

The service manual requests the unit to be in CV mode during voltage calibration, which obvioulsy makes sense as otherwise, the unit would not be able to freely adjust it's voltage output to the value intended for each respective calibration step. As there is nothing attached to the PSU besides the DMM for calibration, CV mode is engaged naturally.

However, for the current calibration steep, the service manual does neither explicitly request the PSU to be in CC mode, nor does it forbid that. How can the PSU control its current output if not via CC mode?

I originally set my electronic load to 1.2Ohm for the 6V output and 25Ohm for the 25V outputs to replace the shunts that are specified in the service manual with respect to the maximum power capabilities (6V/5A and 25V/1A each). However, the regulation in the electronic load and in the PSU kept fighting against each other, leading to jumping values. To me, the only sensible solution was to drop the load into CV mode and choose a target voltage slightly below what would engage the CC control on the PSU in a stable manner so I could feed the PSU a stable reference value to process the calibration on.

The calibration routine passed and follow-up tests confirmed that the PSU is now in line with my DMM at various voltages and current. Questios remain: did I miss something or why is the CC mode not a requirement mentioned in the manual? And if so, couldn't the calibration routine be done with just a simple short instead of the electronic load? In the end, it seems it was only about the current set by the CC limiter.

Thanks for any explanations,
Christian

[IanJ]

For current calibration the unit just needs to deliver current (at a fixed voltage) through a fixed resistor which is then observed.
The user calculates what it should be versus what is displayed and then adjusted.
The unit doesn't need to go into CC mode, nor should it as it will affect the voltage output.
After calibration CC mode is then just a function and will base it's delivery on the previous calibrated voltage and current values.
Setting CV mode for voltage calibration just ensures the power supply is able to have the voltage output set by the user.

Ian.

[the Chris]

Hi Ian,

Thanks for your input. I repeated the current calibration. I noticed that one needs to keep the electronic load just below a certain current level that the PSU is intended to put out so it does not get into CC mode. But it seems not to make any difference if one measures and enters the current output done by the PSU voluntarily because it is still in CV mode, or the current determined by the CC limit. I am not sure what the voltage does for the current calibration.

Anyway, it sounds reasonable to prevent a voltage drop, so I will pay attention to the mode the PSU is in.

[IanJ]

Hi Ian,

Thanks for your input. I repeated the current calibration. I noticed that one needs to keep the electronic load just below a certain current level that the PSU is intended to put out so it does not get into CC mode. But it seems not to make any difference if one measures and enters the current output done by the PSU voluntarily because it is still in CV mode, or the current determined by the CC limit. I am not sure what the voltage does for the current calibration.

Anyway, it sounds reasonable to prevent a voltage drop, so I will pay attention to the mode the PSU is in.

Set the CC setting as high as it will go so it is out of the way and so that you can follow the calibration instructions.
Make sure OVP and OCP are turned off.
As long as the PSU is in CV mode throughout you are good.
I take it you are not trying to set a calibration current that is beyond the limit of the PSU.

PS. All the above from memory of calibrating a E3631A I repaired some time ago on my channel.

Ian.

[the Chris]

There is no option of adjusting the CC limit during calibration. The procedure uses the display to offer the value that the operator can adjust according to this measurements. Measuring the voltage alongside the current calibration shows that the PSU maxes out the voltage of the respektive port (e.g. ~6.3V for the 6V port) and deliveres the current demanded by the load. If one increases the load, it will raise the current up to a limit that is somewhere near the expected current value. From then on, it gets into CC mode, which is why I adjusted the load to stay just below the current that enables CC, during my last calibration.

I did not notice your videos about the PSU repair until now. I'll have a look, thanks!

[alm]

The adjustment procedure may not cover constant current, but the performance verification procedure, which should be part of every calibration, does test constant current. How can you claim it's within specifications never mind produce a report with values if you don't perform measurements? Adjustment is optional, but performance verification is critical for a calibration. And yes, HP/Agilent/Keysight are sloppy in their writing. But if you send this power supply to Keysight for calibration, then I'm sure they'll do a performance verification.

[IanJ]

There is no option of adjusting the CC limit during calibration.

I meant before you start calibration.

Ian.