Error tolerances of AC/DC mA/mV of pulsed DC using a MS8040 and the uCurrent - Page 1
Forum section: electronics / beginners

author: sourcecharge
author_rank: Regular Contributor
timestamp: August 27, 2018, 09:05:27 pm
content: I have 3 MS8040 meters, because I like the price verses the tolerances, so if you are going to talk about how crappy these are:==they seem to be within the specifice error tolerances in the manual that I have given below:link to manual:https://www.circuitspecialists.com/content/110562/csims8040_manual.pdfHere are the tolerances for DC and the AC between 1khz to 5khz with 200mA/mV setting (I'm testing at 4.5khz with about 10mA to 50mA)up to 200mA, 10uA resolution, 1khz to 5khz:AC = 1.2% +/- 30 digits(between 40mA rms and 180mA rms)DC = 0.15% +/- 15 digitsup to 200mV, 10mV resolution, 60hz to 5hz:AC = 1.5% +/- 30 digits(between 40mV rms and 200mV rms)DC = 0.05% +/- 6 digitsThese tolerances are not great but I far as I can tell, they have not been wrong using either straight DC or AC crossing zero.The uCurrent says:https://www.eevblog.com/projects/ucurrent/"Accuracy (typical): <+/-0.05% on µA and nA ranges, <+/-0.1% on mA range."Now, I am trying to measure the current of pulsed DC using 2 MS8040 for a current measurement using the mA DC setting, and 1 MS8040 for the voltage measurement using the mV DC setting from the uCurrent, which of coarse is the current from the amplified shunt.The settup I'm using is 50Vp (measured using MS8040 V setting) 90.7% dutycycle (measured using cursors on scope) pulse at 4.5khz through a 763.3 ohm resistance (error: +/- 0.1% + 10 digits, measured within 5 seconds of post test mA/mV measurement), as this includes the current meters' resistance (or burden voltage).What I'm finding is that I am getting an error of about 0.7% from the current meters, and about 0.6% from the voltage measurement off of the uCurrent.This puzzles me. It's not within any specifiec tolerances from both AC or DC from the meter's manual. The uCurrent could be very well within the 0.1% typical accuracy, but the meters seem to both agree between the current and voltage measurement.So the question is, as pulsed DC is really AC with a DC component, how would this type of input signal be compared to ANY multimeters' tolerances given, for let say some expensive 7 1/2 digit (insert your favorate meter's name here)?They all give the same error tolerances of AC and DC but not Pulsed DC, why?

author: sourcecharge
author_rank: Regular Contributor
timestamp: August 27, 2018, 10:51:29 pm
content: Multimeters : Measurement deviationhttps://meettechniek.info/multimeter-avo/measurement-deviation.html"Pulsating DC voltageIt's striking that neither of the five multimeters measures the correct RMS-value when performing a test with a rectified sine or an asymmetrical square-wave. On the other hand it's remarkable that the two True-RMS meters: the Agilent 34410A and the Fluke 177 read a value that corresponds with the standard deviation. Later on more about this in the chapter "True RMS"."<50%I think I just found the answer to my question....Very interesting article...

author: rstofer
author_rank: Super Contributor
timestamp: August 28, 2018, 06:08:05 pm
content: Don't overlook the bit about Frequency Dependency!Pulsing DC (or square waves for that matter) may have harmonics that are beyond the capability of the meter.