Rigol DP832 Volt and Current Accuracy - Page 1
Forum section: electronics / testgear

author: raptor1956
author_rank: Frequent Contributor
timestamp: September 03, 2016, 06:32:37 am
content: I watched a video where Dave checks the voltage and current accuracy of his DP832 and I thought I'd do the same with mine. I made a tables as follows:For Voltage --> 1mV, 3mV, 10mV, 30mV, 100mV, 300mV, 1V, 3V, 10V and 30V for CH1 and CH2 but on CH3 I went to 5V after the 3V setting. For Current --> 1mA, 3mA, 10mA, 30mA, 100mA, 300mA, 1A and 3A.So, using a 5.5 digit DMM as a reference I found that the max deviation between setpoint and actual reading for the voltage on CH1 was 2mv for just one setting and mostly 0mv or 1mv error for the other settings -- so, not too bad. The deviation between setpoint and DP832 reading was mostly 7mV with a couple readings that differed by 5mV. For Current CH1 was off at most 1mA difference between setpoint and actual while the readings on the DP832 were off by at most 2mA with all other readings with a 1mA error.For channel 2 things got a bit worse with the actual deviation being between 3mV and 7mV and the readings off by 1mV at best to 11mV. For current the deviation was almost all 0mA with one reading at 1mA. The current reading on the 832 was off by 1mA at all settings.Channel 3 was a max of 2mV and 2mA off between setpoint and actual while the display error was mostly 1mV with one reading of 2mV but the current was as much as 4mA off on the display.So, the question I have is ... is there any adjustments for the DP832? For CH1 the actual volts and current are within 2mV and 1mA so no worries there, but the voltage readback on the 832 was off by nominally 7mV and I'd like to be able to adjust that if I could. For CH2 the actual voltage deviated by a nominal 6mV and the readback was off, in the same direction, by an average of 8mV and I'd like to be able to adjust both the actual values as well as the readback. The current readings were all within 1mA so nothing to get upset about there. Lastly, CH3's voltage actual's and readback's were all within 2mV so nothing there, but the current readbacks were off a bit so maybe a tweak there.I attached a jpeg showing the complete table.Brian

author: _Wim_
author_rank: Super Contributor
timestamp: September 03, 2016, 06:46:02 am
content: Nice job. Look here for more info about the calibration of this power supply:https://www.eevblog.com/forum/testgear/rigol-dp832-firmware-updates-and-bug-list/

author: raptor1956
author_rank: Frequent Contributor
timestamp: September 03, 2016, 08:44:46 am
content: Quote from: _Wim_ on September 03, 2016, 06:46:02 amThank for the heads up -- my 832 is within spec but I'd like to get it a bit closer if I can. The thing is, PS's like this are almost test equipment in there own right and a PS like this can do 4-wire resistance with just another volt meter to measure the voltage drop across the DUT so getting greater confidence in the voltage and particularly the current makes it possible to use this as test equipment not just a power supply.Again, thanks for the pointers...Brian

author: kazam
author_rank: Regular Contributor
timestamp: September 04, 2016, 05:37:12 pm
content: You're in spec.What you could do is calibrate and see if that gives you better performance. I modified the cal script references above for my Keithley DMM7510 and it worked perfectly. I will be getting a DP821 soon and plan to calibrate that as well. 10mV is more than I need though so it's just peace of mind.If that's not good enough you could construct your own offset table to counter errors if they are systematic.Be aware that voltage readout is slow over SCPI and will get the screen value. It won't trigger an ADC read first. Just something I noticed.

author: raptor1956
author_rank: Frequent Contributor
timestamp: September 04, 2016, 11:53:38 pm
content: Yeah, I'm not unhappy though I would like to get it a bit closer.Brian

author: Macbeth
author_rank: Super Contributor
timestamp: September 05, 2016, 12:36:53 am
content: Despite the accuracy of the DP832 you have to bear in mind that it doesn't have sense terminals. Ok, it actually does have them but they terminate at the output jacks. So lead resistance to your DUT becomes a thing at higher currents.

author: raptor1956
author_rank: Frequent Contributor
timestamp: September 05, 2016, 04:08:24 am
content: Quote from: Macbeth on September 05, 2016, 12:36:53 amYes, certainly, and one of the reasons for perhaps using heavier leads with lower gauge wire is to reduce that voltage drop. Of course, if the current is fairly constant you can simply compensate for voltage drop in the leads by upping the setpoint a bit.In another thread on banana plugs I mentioned using stereo grade banana plugs that typically use thicker wire, on down to 8AWG, for DUT's with higher current needs. The highest current bench supply I have outputs a bit over 5A at a bit over 30V but I have batteries that can supply WAY more than that. I'm thinking about making some banana leads with 12AWG wire for the higher current work I have in mind.Brian

author: kazam
author_rank: Regular Contributor
timestamp: September 06, 2016, 09:06:17 am
content: Voltage drop will just add to your error regardless of the ADC-DAC accuracy. So yes, thicker wires are a good thing if you plan on pushing a lot of current.However, you're never going to get better than the internal calibration even then. You have a couple of options:1. Move the sense wires from inside the chassis to outside and connect them at your load. It's a physical mod so you will void warranty for use. But nice.2. Construct an offset table that corrects the systematic sense error in the ADC.3. Connect a DMM at your load and control the voltage of the DP832 from this measured voltage to eliminate error. Requires SCPI programming of both devices and some rudimentary control loop depending on your expected voltage fluctuation time constant at the load. But this negates the use of the internal "DMM" in the DP832 which is a convenience factor.