Disappointing Amprobe Multimeter (false claims) - Page 1
Forum section: electronics / testgear

author: GoneTomorrow
author_rank: Regular Contributor
timestamp: April 21, 2015, 09:43:37 am
content: So, I recently purchased an Amprobe 38XR-A multimeter from Amazon; I was after a good general electrical/electronics meter, high UL certified Cat rating, good ranges etc. Ended up on this meter mainly because it was one of the few that Amazon will ship directly to New Zealand, and because Dave has a review of the 37XR-A that wasn't bad. His biggest complaint was the 10mV/mA burden voltage, which wouldn't do for me.So I checked out the data sheet on the 38XR-A, and saw the spec as 1mV/mA and thought; "great, they've fixed the burden voltage issue on the 38," and ordered it.Fast forward a couple of weeks and I'm measuring the current on an LED. When I put the meter in series with the LED on the mA range, I notice that it is incredibly dim now, barely turning on. I get my other meter and measure 500mV(!) of voltage drop across the meter with a 50mA current. Bugger, the data sheet lied and it is actually 10mV/mA (or this unit is oddly faulty to that value).As a more controlled example, see attached picture. I'm using my bench supply to source a constant 100mA, with the Amprobe in series on mA, and the crappy UNI-T on DC volts across the Amprobe.There's this, and also, the protective boot over the positive alligator clip has split, exposing the metal clip underneath, and the buzzer is very sick sounding and changes pitch at random times.Looks like it'll be going back to Amazon, hopefully they're good about it.

author: leppie
author_rank: Frequent Contributor
timestamp: April 21, 2015, 10:04:41 am
content: If there is nothing else in series with the current measurement, you are simply measuring the output voltage of the PSU, which shows 1V.I dont see anything wrong with the picture...Edit: Add 100 ohm resistor in series and see if you see a 10mV or 100mV drop.

author: ve7xen
author_rank: Super Contributor
timestamp: April 21, 2015, 10:14:23 am
content: Quote from: leppie on April 21, 2015, 10:04:41 amTest looks valid to me; there's nothing else there to drop the voltage, so it must be dropped across the current shunt (or wiring, but that seems unlikely). The power supply is running in CC mode anyway, so same conclusion.

author: Balaur
author_rank: Unknown
timestamp: April 21, 2015, 10:20:03 am
content: Quote from: leppie on April 21, 2015, 10:04:41 amIt means that the resistance of the internal shunt on this range is 10 Ohms, which means a burden voltage of 10mV/mA which is not what the user manual says:Quote

author: electr_peter
author_rank: Unknown
timestamp: April 21, 2015, 10:21:57 am
content: Looks like somebody made a mistake in datasheet. A world will not stop because of this, data sheets are full of unidentified errors.

author: Balaur
author_rank: Unknown
timestamp: April 21, 2015, 10:32:56 am
content: Quote from: electr_peter on April 21, 2015, 10:21:57 amIn this case, there is no mention of the burden voltage in the datasheet, it's in the manual.I can understand the disappointment of somebody who really needed this feature and did his homework by reading the manual before buying.

author: GoneTomorrow
author_rank: Regular Contributor
timestamp: April 21, 2015, 10:36:02 am
content: Quote from: electr_peter on April 21, 2015, 10:21:57 amSure, but the error basically turns it from a serviceable meter to an unusable one. That kind of burden voltage essentially makes the mA range useless. That, and, whether I purchased it essentially pivoted on it's ability to meet the advertised specs.(and yeah whoops, the burden voltage is in the manual, not the data sheet, not that it really matters)I work for a company designing commercial equipment, and our technical writers pore over the datasheets before they are published (sometimes going through dozens of revisions), because if there's some false info in there, the customers will have our guts for garters.I suppose if Amazon can take it back for a refund, no real harm done (only to them I guess). And on that note, anyone got any suggestions for a replacement meter in a similar price range ($100-$150 USD)?

author: leppie
author_rank: Frequent Contributor
timestamp: April 21, 2015, 10:44:00 am
content: Quote from: Balaur on April 21, 2015, 10:20:03 amMy badMakes sense now.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 21, 2015, 10:59:46 am
content: Quote from: GoneTomorrow on April 21, 2015, 10:36:02 amGoneTomorrow, at that price range the multimeter to beat is the BM257S - a regular on the forum named Frankie provides excellent service through its eBay store - checkthis post.

author: dadler
author_rank: Unknown
timestamp: April 21, 2015, 03:31:28 pm
content: TME.eu has better pricing, and And Franky seems to be on vacation for a month or so.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 21, 2015, 06:21:31 pm
content: The price is lower, but I would double-check the shipping costs from tme.eu - as far as I recall they weren't free (I ordered an item too long ago to remember).Also, some folks had issues with their customer support as reported in one thread in this forum. I had no issues at all - on the contrary, I received prompt answers to all my inquiries. But that should be taken into consideration if something goes awry.Despite I never bought anything from him (it just did not happen yet), Franky ships for free and has an excellent track record of customer support (oh, and I get no commission whatsoever...). One thing to consider is that shipping from HK may take longer than Poland.

author: Lightages
author_rank: Unknown
timestamp: April 21, 2015, 07:19:17 pm
content: I think that shipping would be around $30 to Aus from Poland. I can guarantee that Franky gives better service than tme.

author: dadler
author_rank: Unknown
timestamp: April 21, 2015, 08:03:48 pm
content: DHL shipping from Poland to California was $8, and both of my orders arrived in exactly two days.I have ordered many things from Franky now, but orders take 2-3 weeks to arrive here.

author: GoneTomorrow
author_rank: Regular Contributor
timestamp: April 29, 2015, 05:04:49 am
content: Well I've initiated a return with Amazon, hopefully it goes OK. I'll probably look at the BM257S once I get my money back, seems like a nice meter and I assume given it's popularity on here, it's not lying about any specs.

author: GoneTomorrow
author_rank: Regular Contributor
timestamp: May 14, 2015, 10:58:45 pm
content: Amazon approved a full refund (plus some as they over compensated for shipping). So I'll probably pick up that Brymen BM257s fairly shortly.TME wants a minimum of 20 Euro to ship to New Zealand, and shipments from Hong Kong actually tend to arrive fairly quickly to NZ, based on other eBay experience, so I'll go with Franky.

author: IanB
author_rank: Super Contributor
timestamp: May 14, 2015, 11:43:05 pm
content: To measure the burden voltage of a meter, don't mess around passing current through it, just measure the input resistance using the resistance range of another meter. It will be a constant. I would be surprised if it is less than a few tens of ohms on milliamp ranges.

author: Muxr
author_rank: Super Contributor
timestamp: May 14, 2015, 11:50:09 pm
content: On the topic of Amprobe meters, I have an Amprobe 34XR-A. It's a solid meter, in terms of construction it feels top notch, I bought it mainly for when I need extra protection. But in terms of features it feels a bit crude. I've often prefered my UNI-T 61E over it for electronics.I have since scored a good deal on a Fluke 87-V which is my main meter now.

author: IanB
author_rank: Super Contributor
timestamp: May 14, 2015, 11:52:19 pm
content: Quote from: GoneTomorrow on April 21, 2015, 09:43:37 amWhen you say "the mA range", what range? The meter apparently has ranges for 10 mA, 100 mA and 400 mA. They may have different input resistances.Also, the lowest DC volts range appears to be 1000 mV, which sets the DC sensitivity. So if (for example) you want to measure 100 mA it is required to drop 1000 mV. So the input resistance would most likely be 1000 mV / 100 mA = 10 ohms on that range. That seems pretty reasonable to me. If the meter had a lower input resistance the accuracy would suffer. You have to choose what you prefer, accuracy or sensitivity?It may be if you used the meter on the 400 mA range you would get a lower input resistance, and if you used the 10 A range you certainly would.

author: GoneTomorrow
author_rank: Regular Contributor
timestamp: May 15, 2015, 12:52:29 am
content: Quote from: IanB on May 14, 2015, 11:52:19 pmIt was constant across all mA ranges, using the manual range function. I also did measure the resistance, and got something like 11.7 ohms on all mA ranges.Most other meters get by with a ~1 ohm current shunt on the mA range, so there's no reason why this one should not. But my main issue is that they clearly state that it is 1mV/mA (1 ohm), which it absolutely is not.

author: IanB
author_rank: Super Contributor
timestamp: May 15, 2015, 01:04:33 am
content: Quote from: GoneTomorrow on May 15, 2015, 12:52:29 amAh, that matches the 10 ohms I estimated.QuoteThe 1 mV/mA is evidently an error in the document. Errors do creep in from time to time.If you are evaluating other meters you can do the same calculation. Look at the lowest voltage range and then look at the current range of interest. Divide one by the other to estimate the input resistance on that range.For instance if you wish the meter to have a 1 ohm input resistance on a 100 mA range, then most likely the meter will also have a 100 mV DC volts range so that it can measure the voltage drop over the 1 ohm resistor when it has 100 mA passing through it.

author: Fungus
author_rank: Super Contributor
timestamp: May 15, 2015, 08:42:12 am
content: Quote from: leppie on April 21, 2015, 10:04:41 amUmmm....there's this thing called Ohm's law:

author: LaurentR
author_rank: Frequent Contributor
timestamp: May 15, 2015, 09:00:36 pm
content: Quote from: GoneTomorrow on May 14, 2015, 10:58:45 pmAre you using the US Amazon? If so, you could grab a Greenlee DM-510A if they'd ship it to you. It's a locally-branded version of the BM257 and goes for USD125.96.

author: GoneTomorrow
author_rank: Regular Contributor
timestamp: May 19, 2015, 04:17:25 am
content: Quote from: LaurentR on May 15, 2015, 09:00:36 pmThey do ship, but it looks like it's the non-s version? Ends up about the same as Amazon shipping is quite a bit more than eBay, and that's for the improved s version.

author: GoneTomorrow
author_rank: Regular Contributor
timestamp: July 01, 2015, 02:56:21 am
content: Well I ordered a Brymen BM257s from Franky on eBay (apparently in the nick of time, before they took a 2 weeks break from eBay).Interesting to see the reports of slow shipping (3 weeks) using the standard int'l shipping. But after having ordered only 2 days ago, I checked today to see:Once it gets to that stage, it usually arrives at the door next-day, or 2 days later tops. Pretty impressed with that really, wouldn't have gotten it any quicker with the 20 euro express shipping from TME or something.