Best multimeter for low currents measurment - Page 1
Forum section: electronics / projects

author: senso
author_rank: Frequent Contributor
timestamp: August 13, 2015, 10:46:03 am
content: Good morning, I'm looking for a multi-meter or a dedicated current meter that can read at least in the micro-amps scale, its for a friend that works with watches, I still don't know what are the lowest currents that he needs to measure, but at least micro-amps is needed, any suggestions?No price limitations.Best regards.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 13, 2015, 11:20:32 am
content: I would suggest getting a nice old mechanical movement and having it calibrated.You'd want a current reference source, which is not as common as voltage reference sources (about $3). You might make up a reference just to calibrate meters, even little 'oven's' which compensate for temperature changes, (a tiny handmade box from metal with a thermostat and resistor in it). I guess it depends on what you'd like to learn to do, and what you'd rather for out to avoid making something simple and understanding it.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 13, 2015, 11:31:19 am
content: Quote from: TheElectricChicken on August 13, 2015, 11:20:32 amWhat is the logic behind this suggestion? If the watchmaker intends to use the microammeter to check for excessive battery drain in a quartz movement, then I'd think an old school mechanical meter is the worst possible solution. You want a really low burden voltage to start with, autoranging and a reasonable dynamic range.Curiously I was of the impression that watchmakers mostly use dedicated electronic test equipment for this particular task, but maybe I am mistaken on that account.

author: senso
author_rank: Frequent Contributor
timestamp: August 13, 2015, 11:39:02 am
content: Not a watchmaker, into the repair world, mostly digital Casio's, people just seem to love them, but they are a bit of a pain to work with, parts only from Germany in 2-3 days or from Tokyo in 3-4 weeks, lots of discontinued models without support that are still on saleThere is no need to measure with 7 digits, its more for a sanity check that the watch module is OK, he as been receiving some watches were the "problem" is fast battery drain, my hunch is that the stores are just using old stock batteries, he thinks the same, but having a multi-meter/current measurement to assure that there is no problem with the module is the best proof to be relieved that the same client wont be knocking down the door 3 months lather because he got bad batteries again.There is dedicated equipment($$$), with 2 leds, good battery, bad battery, its very crude to say the least.

author: FrankBuss
author_rank: Unknown
timestamp: August 13, 2015, 11:41:54 am
content: Use any cheap multimeter, in combination with theuCurrent.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 13, 2015, 11:50:01 am
content: one like this is about $6fromhttp://www.electroschematics.com/6537/simple-microampere-meter-circuit/fromhttp://www.electronicecircuits.com/electronic-circuits/micro-ampere-meterhttp://www.ebay.com.au/itm/GE-General-Electric-Model-AY278-DC-Microamperes-Analog-Panel-Meter-40-0-40-A-/181770375541still, calibration is key. I guess you could use a resistor network, as very cheap accurate resistors don't cost much and working the math, it would be well within 1% accurate.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 13, 2015, 11:51:01 am
content: Quote from: senso on August 13, 2015, 11:39:02 amOK, but Casio is not really a top tier supplier of tools in the watch world. When it comes to dedicated watch tools: If it isn't coming out of Switzerland, then you don't want it.My suspicion is that any one of the better high end desktop DMMs will do quite nicely, depending on the burden voltage requirement. So Keysight 3446xA/34470A series or the equivalent models from Keithley. In fact all of these will probably be mad, mad overkill for a task like this.Quote from: FrankBuss on August 13, 2015, 11:41:54 amIf the person in question is anything like the watchmakers I know, then he may not want to fuzz around with multiple boxes, wires all over the place and battery issues. Some form of mains powered desktop DMM may be preferred.

author: TheElectricChicken
author_rank: Frequent Contributor
timestamp: August 13, 2015, 11:52:27 am
content: Quote from: FrankBuss on August 13, 2015, 11:41:54 amwell what do you know this place has everything. Must apologize I only just arrived.Price is $90 btw.

author: FrankBuss
author_rank: Unknown
timestamp: August 13, 2015, 11:58:24 am
content: Quote from: ElectroIrradiator on August 13, 2015, 11:51:01 amWith no price limitations, I would be glad to put it all in a nice shiny box for him/her, using one of these fixed voltage voltmeters from eBay, and extending the uCurrent range switch, and integrating a mains power supply.

author: Kalvin
author_rank: Super Contributor
timestamp: August 13, 2015, 11:58:52 am
content: If one needs to just measure overall current consumption of a watch with 10nA resolution up to tens of microamperes, any decent digital multimeter with 20 000 counts or better should do. One needs to check that the burden voltage doesn't affect the watch too much: If there are current spikes that causes overrange, the battery voltage seen by the watch may dip too low and cause problems in watch operation and/or produce invalid measurement results.It is not difficult to build a decent transimpedance amplifier (ie. current-to-voltage converter) from a low-noise op amp. Manual range selection is not complicated either. But, buying a good multimeter might be the best option.If one needs to really measure tiny quartz crystal currrents, here is one article worth reading:http://cds.linear.com/docs/en/lt-journal/LTMag-V17N02-15-SubMicroAmpCurrentMeasurement-Williams.pdfGeneral article about low current measurements (incl. comments about the Jim William's paper above):http://www.edn.com/design/analog/4315417/Measuring-nanoamperes

author: babysitter
author_rank: Frequent Contributor
timestamp: August 13, 2015, 12:12:11 pm
content: HP6632B comes to mind, as supply with current display... or a 66332b.

author: Wytnucls
author_rank: Super Contributor
timestamp: August 13, 2015, 12:38:36 pm
content: You said no price limitations:Gossen MetraHit 30M (100pA best resolution on 100uA scale)Burden voltage 15uV/uA on the 10mA scale, with a 10nA resolution.Delivered with calibration certificate.

author: rastro
author_rank: Frequent Contributor
timestamp: August 13, 2015, 12:49:39 pm
content: Keithley electrometer or picoamp meter.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: August 13, 2015, 01:39:39 pm
content: There is device named uCurrent designed by Dave J of EevBlog. This is an independent reviewhttp://www.embedded.com/electrical-engineer-community/industry-blog/4406380/1/The--CurrentYou can choose buying it because it will support this site