Amprobe DMM 34XR-A Good or Bad? - Page 1
Forum section: electronics / testgear

author: alxf001
author_rank: Newbie
timestamp: February 23, 2014, 03:47:19 am
content: I just purchased an Amprobe 34XR-A from ebay as a second meter. I'm currently working on a project and noticed it read DC volts higher than my old fluke (334 clamp meter). I was checking a rated voltage supply of 115v refrigerator compressor, my Fluke read 115 vdc, but the Amprobe was reading 150-150 vdc.I installed a new battery to insure there was no low battery issues. I did a few tests after this comparing low DC voltages from both meters from AA and 9V batteries and were both within 0.1 volts. I have a 14 volt power supply and both read 13.8 volts. So at low voltage, the Amprobe seems to be fine, but double checked the 115v from the compressor and same thing, it reads 150-151 volts while fluke reads 114v.I checked AC voltage to household outlets and both meters read same at ~119volts. I checked a few capacitors and readings appear to be accurate as well, so it seems only at high dc voltage it does not seem accurate.Does this simply mean the Amprobe is bad for DC voltage?

author: Wytnucls
author_rank: Super Contributor
timestamp: February 23, 2014, 05:02:55 am
content: Difficult to say. It is unusual to have an accurate measurement at low voltages and such a high discrepancy at higher ranges. Try to find something else to measure, in the same high DC range, to confirm your readings.

author: retiredcaps
author_rank: Super Contributor
timestamp: February 23, 2014, 06:50:12 am
content: I buy used/abused meters from ebay and sometimes they work 100% and other times I have fix them despite what the seller claims.I suggest you measure the input impedance of the Amprobe in all DCV ranges. That is, put your 34XR in manual VDC range mode and measure the input impedance of each range.For example, in 4VDC mode, it might measure 11.11Mohm. In 40VDC, it might measure 10.10Mohm. In 400VDC, it might measure 10.01Mohm.Here is a sample I took a few days ago.https://www.eevblog.com/forum/testgear/fluke-87-i-repair/msg390462/#msg390462

author: WVL_KsZeN
author_rank: Regular Contributor
timestamp: February 23, 2014, 02:24:53 pm
content: hold on..The Fluke 334 is not a TRUE RMS meter, while your Amprobe is. With things like compressors, you would expect a different result!Try them both while measuring the voltage over a simple lightbulb and see if they match up.

author: alxf001
author_rank: Newbie
timestamp: February 24, 2014, 09:39:39 am
content: THanks for the replies, I did try measuring resistance as suggested, but my Fluke 334 only gave OL, I believe its resolution is only to 0.1 ohms. my other cheap (harbor freight freebie) dmm also did not measure any ohms.I didn't mention the fluke 334 was not true rms, but it did cross my mind if that would have an effect. I don't have that much knowledge of electronics, just average DIY, maybe a little below average, lol.The compressor is rated at 115 volts and supplied with power from the fridge's PC inverter board. i measured 119 volts AC with both the Fluke and Amprobe going into the inverter board and 114 volts DC going to the compressor with the Fluke and 150Volts DC with the Amprobe.I'll have to wait to get another DMM with a higher resolution for ohms and make sure its true rms as well.

author: deth502
author_rank: Frequent Contributor
timestamp: February 24, 2014, 10:32:34 am
content: as was stated, true rms has NOTHING to do with dc measurements. rms only affects ac measurements. again, are you sure the motor is running on dc?? that sounds odd to me as well.

author: ttp
author_rank: Regular Contributor
timestamp: February 24, 2014, 12:08:15 pm
content: Quote from: alxf001 on February 24, 2014, 09:39:39 amI think inverter board loaded with compressor is not the best DC source to compare your meters. Rectified and chopped sinusoid is not what they are calibrated for. I'd rectify and filter mains to compare the meters high voltage DC readings.