Rigol DP-832 as a digital volt meter - Page 1
Forum section: electronics / testgear

author: drprinter
author_rank: Newbie
timestamp: June 05, 2018, 06:37:31 pm
content: OK... I am using my DP-832 as a digital volt meter... I set the voltage to 0 volts and I can take voltages up to 30 volts (too chicken to try higher voltages). My question is - is there any danger to the dp-832 doing this?? Yes I have been using this mode for over 6 months with no problems and I do test the outputs with my fluke meter just to check the calibration once a month with no problems. Has anyone else done this???

author: sdouble
author_rank: Frequent Contributor
timestamp: June 05, 2018, 09:47:23 pm
content: why don't you use a DMM for measuring low DC voltage ?it would be safer, more convenient and more reliable.

author: drprinter
author_rank: Newbie
timestamp: June 05, 2018, 10:56:51 pm
content: I do use a DMM as a matter of fact I do have a few DMM's but having a very accurate bench meter is a plus.... I can turn the voltage to 0 and I can see the progress of a battery charging, track the input voltage and see the output voltage on the same display (turn up the voltage on a buck converter and see the output on the same display. Besides I think this might be a cool feature...

author: glarsson
author_rank: Frequent Contributor
timestamp: June 06, 2018, 08:42:49 am
content: This is a bad idea.What is the input impedance of the power supply when used as a DMM? It is most likely not something reasonable as many power supplies have resistors or current shunts to keep the current flowing at all times. There will certainly be a relatively large capacitor on the output as well. How will that affect the circuit you are trying to measure? Also, some power supplies, not the DP-832, will try to keep the set output voltage by actively sinking current to force the voltage to be what was set, 0 volts in this case. Not good characteristics of a DMM...

author: bitseeker
author_rank: Super Contributor
timestamp: June 06, 2018, 06:13:15 pm
content: Although it may work, you're introducing a lot of extra "stuff" to whatever circuit you're measuring this way. Any multimeter will alter the voltage being measured due to its input impedance. Hence, you want the meter's impedance to be significantly larger than that of the circuit you're measuring. Having a disabled power supply tagging along works against you in this scenario. How bad it is depends on the design, of course.glarsson's point about the power supply's output capacitors is of particular note since they tend to be fairly large and can adversely affect your measurements, the behavior of your circuit, or damage components if they have a large residual charge (i.e., haven't yet fully drained) when you connect the 832 to your circuit.There are other possible gotchas, but generally speaking, it's best to use the built-in meter only when you're powering something with the supply so that you don't have to worry about all the different ways things might go awry.

author: drprinter
author_rank: Newbie
timestamp: June 07, 2018, 06:55:44 pm
content: ok let me find the schematics to analyze the circuit. All make good points and need to look into it some more... anybody else have any ideas??

author: apblog
author_rank: Regular Contributor
timestamp: June 07, 2018, 07:49:22 pm
content: No, you should not do this. I was surprised that the manual wasn’t explicit about it, so I checked:“Do Not Provide Power for the Active Load.In order to avoid the anti-irrigation current which leads to the power control loop out of control and damages the powered device, this power supply can only provide power for the pure load without the current output function.”I believe that lovely bit of mistranslation is advising you to not connect a power source to the terminals.Two problems that I can think of are that you may end up reverse biasing the output transistor or overheating the bleed resistor (or bleed circuit)

author: bitseeker
author_rank: Super Contributor
timestamp: June 07, 2018, 08:13:31 pm
content: Yes, there are many ways this use case can cause problems. It's a power supply and should be used accordingly.If you need a better DMM, save up for one, which will serve you better than abusing your power supply.

author: drprinter
author_rank: Newbie
timestamp: June 07, 2018, 10:36:34 pm
content: ok then the problem I might have is if you are charging a battery and reduce the voltage then the meter will show the battery voltage and not the set voltage... this gets kinda confusing to me... ok maybe I'm old but ......Anyone have a good link to the schematics

author: bitseeker
author_rank: Super Contributor
timestamp: June 07, 2018, 11:22:09 pm
content: For charging a battery, when it reaches the desired voltage, charging is complete. You'd then remove it from the supply. Lowering the voltage will cause a reverse current into the supply, effectively forcing the supply to become an electronic load, which is not desirable and could damage the supply.When charging batteries with a bench supply, it's a good safeguard to put a power diode in series so that current only flows in the correct direction (i.e., out of the supply's positive and into the battery's positive).Regarding schematics, you're unlikely to find them for modern gear unless someone reverse engineers them. It's even rare these days for A-brand companies to release schematics, although they used to back in the day. As you peruse the forums, you'll find that many of us intentionally buy older gear because of the available service information.

author: drprinter
author_rank: Newbie
timestamp: June 23, 2018, 08:49:04 pm
content: ok I have stopped doing this practice of using the dp-832 as a meter but I still wondering if the front end protection will protect the unit as a volt meter?

author: bd139
author_rank: Super Contributor
timestamp: June 23, 2018, 09:58:41 pm
content: It may do. Farnell E/L30 supplies made many years ago didn’t. When the line power failed or output voltage was too low when connected to a source such as a battery or capacitor they would blow the shit out of the pass transistor and driver. I made a small fortune over the years fixing them and reselling. Incredibly common failure mode.There’s usually a diode across the output and the pass transistor now which takes them out of circuit but there are still current sampling resistors etc and the transformer tap in that circuit.Don’t do it. Simples.