MicroAmps Meter Selection - Page 1
Forum section: electronics / testgear

author: sylvainssiri
author_rank: Unknown
timestamp: July 27, 2021, 11:41:59 pm
content: Hi everyone!I am looking into buying a multimeter for the microamps measurement of a flame ionization rod, and an ultra violet scanner that goes on burners. So far, the Fluke 116 seems like my best bet, since it is high impedance, which I believe is what I need because of the high voltage on those. I did notice three of Dave's meters have microamps too: the BM786, BM235, and 121GW. Would one of those be a better fit for my purpose? I was not able to answer the question by myself, hence why I decided to ask more knowledged people.Do note, that I did my research on the forum before posting. The only post I could find directly related is:https://www.eevblog.com/forum/testgear/micro-amp-meter/msg661641/#msg661641But it does not answer my question. Also note that I will be using the meter outside, summer, and winter, inside and outside, on big, and small burners. So the meter will be subject to some temperature extremes.Thanks in advance!Sylvain

author: bob91343
author_rank: Super Contributor
timestamp: July 28, 2021, 04:52:48 am
content: If you are measuring current, it's most desirable to have as low an impedance as possible for the measuring device so as not to disturb the circuit unduly.I have no idea of the parameters involved, so can't comment regarding suitability of any particular instrument. One would need to know the waveshape, frequency components, type of measurement required, etc.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 28, 2021, 06:47:46 am
content: For very small currents with not to much need for accuracy one can use the 200 mV range on a meter with 10 M input impedance. It effective acts as a 20 nA current range too. So 100 pA per mV from the 10 M input resistance used as a shunt.This may be all it takes for the low range currents if one can accept a few percent of uncertainty in the scale factor.

author: ace1903
author_rank: Regular Contributor
timestamp: July 28, 2021, 07:53:01 am
content: Most European flame checkers limit resistance of instrument to 5kohm. One can check documentation of LFL1.333 LME11 ...Don't know which controllers are used in Canada but think that similar limit can be expected.For my needs I made checker according schematic that is shown in datasheet for those controllers.Capacitor and analog meter. In systems with blowers ionization current can have changing component so analog meter smoot measurement much better.One is interested in "average" current. Some digital meters sample current in 3-5 samples per seconds and readings can look like lottery drawing.I found solution with dedicated meter only for ionization measurement most practical one.Yes scale is not directly in uA but for me if needle is in left half of the scale means that I need to do something about the electrode or to adjust air to get correct lambda.

author: Fungus
author_rank: Super Contributor
timestamp: July 28, 2021, 10:26:07 am
content: Almost any meter will be able to do this (so long as it has uA).Quote from: sylvainssiri on July 27, 2021, 11:41:59 pmVoltage doesn't matter when you're measuring current and you want the lowest possible impedance on the current range.(Ohms law...)I've measured current 21kV on a laser tube using a $13 multimeter.Quote from: sylvainssiri on July 27, 2021, 11:41:59 pmAgain, that's not really a problem. Most meters will survive bigger temperature extremes than the operator.So... pick a meter that makes you happy. Fluke 116 is good, as are the Brymens you mention.

author: David Hess
author_rank: Super Contributor
timestamp: July 28, 2021, 11:36:42 am
content: Quote from: Kleinstein on July 28, 2021, 06:47:46 amJust make sure the meter is actually 10 megohms on the 200 millivolt, or even 2 volt, range. Most modern autoranging multimeters are about 9 megohms on their most sensitive range but some are 3 megohms or 100 megohms.

author: sylvainssiri
author_rank: Unknown
timestamp: July 28, 2021, 10:25:34 pm
content: Quote from: ace1903 on July 28, 2021, 07:53:01 amThe LFL1 is actually one of several I want to measure in my day to day work. Fireyes, and Honeywells too.Thing is, unless I put the meter in low-z mode, it will be around 10 M ohm impedance. But then, it will not be in reading microamps.Ill check locally what they can have, either brand. I looked online, and so far with shipping and all, they all come close to the same price.

author: bdunham7
author_rank: Super Contributor
timestamp: July 29, 2021, 01:12:21 am
content: Quote from: sylvainssiri on July 27, 2021, 11:41:59 pmThe Fluke 116 current range is explicitly designated for measuring ion flame sensors, so it should be good. It does have an impedance of 3-4kohms, but the microamp ranges of most DMMs will be pretty high, often as much as 10k. It is also fully protected against any conceivable overload.

author: 2N3055
author_rank: Super Contributor
timestamp: July 29, 2021, 06:54:59 am
content: 8 posts and no details what exact currents are in question.. Just speculations.To me it looks like ANY meter that has 400-600uA range will do the work.Just pick a brand you trust and go with it.Fluke 116 is marketed as HVAC meter and it's 600 uA range is mentioned for flame sensor measurements.Even small Brymen 27 (pocket one) has also Lo-Z mode and 600uA range.Quote from: bdunham7 on July 29, 2021, 01:12:21 amI'm curious what might that mean: does it mean that you can put it in uA mode and try to measure 240V AC and nothing is going to happen ?

author: HKJ
author_rank: Super Contributor
timestamp: July 29, 2021, 07:12:22 am
content: Quote from: 2N3055 on July 29, 2021, 06:54:59 amProbably, in some meters with only a uA range it is using same protection as the ohms range (PTC and transistor clamp), i.e. it can handle 240VAC. This protection also means the resistance is a few kOhm instead of the more common 100ohm for the range.

author: 2N3055
author_rank: Super Contributor
timestamp: July 29, 2021, 08:18:02 am
content: Quote from: HKJ on July 29, 2021, 07:12:22 amI agree, but my problem is with the word "probably".It would be very nice to know exactly which ones are which. It would be very useful to people that work on this kind od work.

author: HKJ
author_rank: Super Contributor
timestamp: July 29, 2021, 08:37:19 am
content: Quote from: 2N3055 on July 29, 2021, 08:18:02 amThe Fluke 116 do not specify any fuse or special limits for uA range, only limit specified is 600VAC, i.e. this do also apply to the uA range (With Fluke it is safe to read the specifications that way).

author: Fungus
author_rank: Super Contributor
timestamp: July 29, 2021, 09:19:43 am
content: Quote from: 2N3055 on July 29, 2021, 06:54:59 amYou'll end up with a bill for a replacement fuse but nothing should happen apart from that.

author: HKJ
author_rank: Super Contributor
timestamp: July 29, 2021, 09:23:07 am
content: Quote from: Fungus on July 29, 2021, 09:19:43 amThere is no fuse, but a PTC.

author: Fungus
author_rank: Super Contributor
timestamp: July 29, 2021, 09:33:02 am
content: Quote from: HKJ on July 29, 2021, 09:23:07 amOh, duh! I hadn't looked at the exact model.Post edited.

author: 2N3055
author_rank: Super Contributor
timestamp: July 29, 2021, 10:17:56 am
content: Quote from: HKJ on July 29, 2021, 08:37:19 amMy experience is that EXACTLY with the likes of Fluke, it is NOT safe to read specification any other way than corporate lawyers thought when they gave final edit on the specification documents.Anything that is explicitly stated in a document will be exactly like that, or better, with some safety margin. Anything that is NOT explicitly statedis not guaranteed or implied in any way.They (being THE Fluke) will protect instruments beyond basic specifications because more robust instruments generally means less problems for the manufacturers and goodwill from users (of course, if the cost to do so is not prohibitive).But if it is not explicitly stated, i would not RELY on it. Even if you independently characterize it for higher specs and/or protection, that is only valid for current batch and current model. New batch can have any number of changes on any part of instrument and it's characteristics in all parts not strictly specified...

author: HKJ
author_rank: Super Contributor
timestamp: July 29, 2021, 10:43:31 am
content: Quote from: 2N3055 on July 29, 2021, 10:17:56 amFlukes safety information is very clear on the 116:QuoteAnd both the meter and the specifications says 600V

author: 2N3055
author_rank: Super Contributor
timestamp: July 29, 2021, 12:14:12 pm
content: Quote from: HKJ on July 29, 2021, 10:43:31 am"Caution" statement identifies conditions and actions that could damage the Meter or the equipment under test.To avoid possible electric shock or personal injury, follow these guidelines:•Use the Meter only as specified in this manual or the protection provided by the Meter mightbe impaired.• Do not use the Meter or test leads if they appear damaged, or if the Meter is not operatingproperly.•Always use proper terminals, switch position, and range for measurements.• Verify the Meter's operation by measuring a known voltage. If in doubt, have the Meterserviced.• Do not apply more than the rated voltage, as marked on Meter, between terminals orbetween any terminal and earth ground.So reading that, I can only see that youshouldn'tapplymore than600V when measuringVOLTS.So, if you connect 600V source with no current limit to the metercontraryto theproper measurement procedure in manualtoa wrong setting of uA, thenall bets are off..All they guarantee is safety according to :Complies with ANSI/ISA 82.02.01 (61010-1) 2004,CAN/CSA-C22.2 No 61010-1-04, UL 6101B (2003) andIEC/EN 61010-1 2nd Edition for measurement Category III,600 V, Pollution Degree 2, EMC EN61326-1Which mostly means it won't kill you but they don't even mention if it gets nonfunctional...Don't get me wrong, it might as well be that it would routinely survive 600V on uA range, it's just Fluke carefully avoided making any promises it would.. Which is suspicious because that would be great bragging point...

author: bdunham7
author_rank: Super Contributor
timestamp: July 29, 2021, 02:01:42 pm
content: Quote from: 2N3055 on July 29, 2021, 06:54:59 amYes. There are only two terminals, no separate current circuit, and you can put up to 600 volts on those terminals in any range--including microamps, ohms, capacitance, etc--and the meter will not be damaged. It does use the same PTC as the Lo-Z function.As for Fluke and specs, one interesting tidbit on the Fluke 116 is that it is CAT III/600V, but there is no CAT IV rating, not even for 300V as you might expect. Apparently the very first version had CAT IV/300V, or at least it appeared in some documents if not on the meters.As for what Fluke "guarantees" in their specs, I don't think many manufacturers are going to write manuals inviting wanton abuse. That said, it seems pretty clear that this meter was designed for HVAC techs so that they could use it normally without worrying that an errant probing accident would kill their meter--and it won't. I haven't yet seen a Fluke meter from the modern era that wasn't fully protected in all ranges from the voltage stated on the front panel, whether by fuses or otherwise.