HP 6632B DC Power Supply Output Tolerance - Page 1
Forum section: electronics / testgear

author: Matt Hatter
author_rank: Contributor
timestamp: November 01, 2020, 06:37:32 pm
content: I recently scored a clean HP6632B for quite cheap on Ebay. Quite complete, aside from a missing foot and knob, and in very good shape overall.Pics for the interested:Please forgive the janky measuring setupNow for the purpose of this post-I took some quick output measurements and I am noticing a shockingly linear deviation from the programmed output. Check out this graph:I mean, that is almost pornographic!The measurements were taken in .500V steps. A slope of 0.0217 comes out to be nearly perfect. Ideally I wish I had a second reliable meter to double check, but I sadly do not. Currently on the hunt for a good bench-top DMM.In any case, because of the linearity, I can obviously compensate for this very easily, but I would ideally like to fix it at the source. Interestingly, the units front panel meter is displaying voltages well within tolerance of the programmed values. Due to the linearity, I am assuming that this is probably an error in calibration and not a hardware issue? I suppose it could also be the thin wires I have connected to the output terminals, but I am not experienced enough to say, and don't have anything better immediately available.Any thoughts?

author: 25 CPS
author_rank: Frequent Contributor
timestamp: November 01, 2020, 09:19:13 pm
content: Just a thought since you only took a picture ofThe front. What does the strapping on the outputs on the back look like? Are the sense (S+ and S-) connected to the output rails or are they floating? If floating, the supply might’ve been wired for remote sensing at the load and you’d have to make some jumper wires to hook up the sense terminals either at the outputs or at your meter or whatever load you’re driving with it.

author: Matt Hatter
author_rank: Contributor
timestamp: November 01, 2020, 10:11:13 pm
content: Quote from: 25 CPS on November 01, 2020, 09:19:13 pmAn accurate thought, at thatThis is a regular ol' *DOH* moment. It was indeed setup for remote sense, and jumping the appropriate terminals solved everything. It is at the low end of the tolerance, but for now I am satisfied. Once I get my scope back up to snuff I'll have to take a peak at the ripple to see if that is still in spec as well.Thanks for the assist, 25 CPS!

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: November 02, 2020, 01:13:26 am
content: Welcome to the world of system supplies. I have three system supplies, if they are properly calibrated and maintained, they are extremely accurate. For example, despite the HP 6632A being the oldest equipment in my lab, the output accuracy spec is 0.05% + 10 mV, and 0.15% + 7mA. After recap and calibration, it still performs well well within spec.Its spec is far more accurate than what the UNI-T can deliver, so I am not surprised by your finding. A healthy unit should deliver this level of performance, and you need a good, calibrated bench meter to measure the variance from programmed value. To measure output, HP specifies a 6 digit DMM with 0.005% accuracy.A few things you should always do, change out the RIFA caps, inspect and recap other caps as needed. If your unit did not come from a clean room, it can be caked with dust and dirt, and a good healthy cleaning may be required. These are left on continuously in most labs, the fan can draw in a ton of dust over its lifetime.