Benchtop Power Supply with 0.05 mV step resolution? - Page 1
Forum section: electronics / testgear

author: ninjanation217
author_rank: Contributor
timestamp: February 21, 2023, 12:01:32 am
content: Hi everyone,I tried to search the forums first, but couldn't find an answer.I am looking to simulate a sensor for a transmitter I am designing.I am looking for a benchtop programmable power supply that has a step resolution of 0.05mV or lower. The max voltage out I need is only ~110 mV.Very little current output is required at most 50mA.I am not worried about cost (Its for the company I work for).Thanks,- James

author: nctnico
author_rank: Super Contributor
timestamp: February 21, 2023, 12:22:28 am
content: You need a source measurement unit (SMU)

author: bdunham7
author_rank: Super Contributor
timestamp: February 21, 2023, 12:33:19 am
content: Quote from: ninjanation217 on February 21, 2023, 12:01:32 amWell, in that case...https://www.tek.com/en/products/keithley/source-measure-units/2400-graphical-series-sourcemeter

author: chilternview
author_rank: Frequent Contributor
timestamp: February 21, 2023, 12:41:15 am
content: Use a bench programmable supply with a 1mV resolution driving an opamp configured for a gain of 1/20 ?

author: alm
author_rank: Super Contributor
timestamp: February 21, 2023, 12:54:50 am
content: Unfortunately I don't know of a modern replacement other than a SMU, but the Keithley 230 voltage source would have been perfect for this: a 200 mV range with 50 uV resolution, up to 100 mA output current.When working professionally and not severely limited by budget, I wouldn't mess with building my own attenuator, but rather buy a device that can directly generate the output you need. I'm not quite sure what else, other than an SMU (which would be overkill), is available.

author: Swainster
author_rank: Frequent Contributor
timestamp: February 21, 2023, 02:57:48 am
content: I have a couple of Time Electronics Microcal 1030s which could fit your requirements. I bought them secondhand, but to be honest, I think they are way overpriced to buy new as they are basically just a 10 turn pot strapped on to an amplifier. They are actually quite useful to have knocking around on the bench.I'd guess that Time Electronics also offers a more modern (microcontroller based) version by now. My units are probably decades old (but still available new)Edit: Oops, re the Microcal 1030, I misread your requirements - it wouldn't really be practical to do 0.05mV resolution @ 110mV, but like I said, might still a useful tool, especially if you want to quickly dial up voltages in the mV range.

author: jonpaul
author_rank: Super Contributor
timestamp: February 21, 2023, 03:07:52 am
content: USB, GPIB, Ethernet DAC>>100 ma x 1 follower,opamp plus a transistor.cost just a bit of time, nice project for an intern or studentOtherwise any classic HP digital lab PSU, GPIB, USB controlj

author: dobsonr741
author_rank: Frequent Contributor
timestamp: February 21, 2023, 03:48:42 am
content: QuoteOh, then look at the Fluke 5730A - had a chance to play with it, really awesome. Goes from 10nV resolution up to the shocking 1000V max output.

author: armandine2
author_rank: Frequent Contributor
timestamp: February 21, 2023, 09:01:40 am
content: Not quite there, Time Electronics 100620mA and 100mV?

author: zrq
author_rank: Frequent Contributor
timestamp: February 21, 2023, 11:21:42 am
content: What about a SRS DC205?

author: bookaboo
author_rank: Frequent Contributor
timestamp: February 21, 2023, 11:42:55 am
content: QuoteSurely this is a better idea than spending a bunch on a SMU?OP did state a power supply, but I don't think he needs a power supply to simulate a sensor, just a reference. In fact a stable voltage reference, 10 turn pot, suitable opamp and a decent meter would suffice?

author: exe
author_rank: Unknown
timestamp: February 21, 2023, 12:18:49 pm
content: Wow, 50uV is kinda challenging because of the noise and thermocouple effect.Anyway, I'm with bookaboo. It can even be breadboarded, imho, just connect the DMM right at the load to make sure all parasitic resistances are compensated.

author: ninjanation217
author_rank: Contributor
timestamp: February 21, 2023, 01:13:50 pm
content: Thanks! I did actually look into this one prior, unfortunately the lead time is crazy.

author: ninjanation217
author_rank: Contributor
timestamp: February 21, 2023, 01:16:54 pm
content: I already use a Keithley 220 for current and it is pretty awesome. I will look into the 230"I wouldn't mess with building my own attenuator, but rather buy a device that can directly generate the output you need."I 100% agree, especially since my equipment must have a calibration associated with it and I don't want to deal with the headache.

author: ninjanation217
author_rank: Contributor
timestamp: February 21, 2023, 01:23:29 pm
content: You are not wrong. My main issue I run into is red tape. The company I work for wants the certified equipment for calibration/testing. Its hard to explain to someone that doesn't understand electronics that I verified the output myself with certified equipment. Its just easier to buy a calibrated piece of equipment unfortunately.

author: bdunham7
author_rank: Super Contributor
timestamp: February 21, 2023, 02:47:26 pm
content: Quote from: ninjanation217 on February 21, 2023, 01:13:50 pmAssuming that was directed at me, the Keithley 2450 appears sold out but the 2460 ($10K, overkill for your application but will work) seems available immediately. TEquipment says their stock is 6, for example.I've attached a screenshot of how quoting works in the forum. Just press the 'quote' button and edit your reply as needed. HTH

author: alm
author_rank: Super Contributor
timestamp: February 21, 2023, 03:20:21 pm
content: Quote from: bookaboo on February 21, 2023, 11:42:55 amThese days programmable usually means programmed from a computer, not by turning a pot. Sure you could use an Arduino with external DAC and attenuator, which is great for a hobby project. You could even build your own PWM DAC. But sending that to a cal lab might be fun, and also you may not spend your time troubleshooting your own design.

author: ninjanation217
author_rank: Contributor
timestamp: February 21, 2023, 03:27:28 pm
content: Quote from: bdunham7 on February 21, 2023, 02:47:26 pmThanks! I thought hitting the reply would include the comment I was replying to haha.I ended up going with the Keithley 230, as it does meet the requirements, though its missing some fancy features that are not really needed. More importantly, I could get one for just over $500 after certification cost.Thanks to everyone in this forum for all of the wonderful information, and thanks again for teaching me the proper way to reply to someone.

author: ninjanation217
author_rank: Contributor
timestamp: February 21, 2023, 03:48:45 pm
content: Quote from: alm on February 21, 2023, 03:20:21 pmYou are correct, programmed by a computer is much preferred over turning a pot. At the bare minimum a user interface where you can type in data at the unit.I was able to solve the issue for around $500 with a Keithley 230 (including cost for sending it in for certification). Realistically if you include time of design, troubleshooting, certification of a custom design (which would be a nightmare) it would have cost considerably more than that.If you are an home gamer, sure, build your own thing. However, in a professional setting, its probably not the best idea.Thanks to everyone on the sub for their help. Everyone had a lot of good ideas and recommendations.