Meters and Microamps

[EasyGoing1]

I've been looking off and on for a meter that can read amperage from 1µA and up. And so far, the vast majority of the meters that I can find that state the ability to read at the microamp level list their range starting in the hundreds of microamps.

What gives? Why is it so difficult to find a meter that can read 1 or more microamps of current?

And does anyone have any suggestions for a meter that can do this? I love my Fluke 115 but it can't read current that small.

Thanks,

[eccerr0r]

Re: Meters and Microamps

Problem is noise. Reducing noise is expensive, and hand held units could get some noise if they are not set in an immobile position. There should be plenty of meters out there that can read microamps. Also expect to have to use bench form factor DMMs. There may be a price premium for true bench DMMs (these tend to be quite a bit larger than handheld units, usually at least 3x the volume to allow for shielding, etc.

My old ancient 4½ digit DMMs read 200.00µA, one goes down to 20mV - both are bench DMMs, not handheld - but both do have optional battery packs so they are portable.

[eccerr0r]

Re: Meters and Microamps

Just checked all my "sessile" or DMMs designed not to be moved around everywhere - they all have a 200µA scale on the 3½ or 4½ digits they have despite being 1980s ancient. All my handhelds only go to 200mA.

My Eico VOM has a 100µA range, which doesn't have the resolution of the DMMs but nevertheless a 10µA current will clearly get shown. In fact I have a few analog meters that are 50 or 100µA full scale. I have one that's 25µA full scale as well, and people talk about how delicate these (anything 50µA or lower) meters are and that you need to short out the terminals to prevent static electricity from damaging these analog meters.

[EasyGoing1]

Re: Meters and Microamps

Just checked all my "sessile" or DMMs designed not to be moved around everywhere - they all have a 200µA scale on the 3½ or 4½ digits they have despite being 1980s ancient. All my handhelds only go to 200mA.

My Eico VOM has a 100µA range, which doesn't have the resolution of the DMMs but nevertheless a 10µA current will clearly get shown. In fact I have a few analog meters that are 50 or 100µA full scale. I have one that's 25µA full scale as well, and people talk about how delicate these (anything 50µA or lower) meters are and that you need to short out the terminals to prevent static electricity from damaging these analog meters.

OK, lets take this spec from a web site selling this meter...

Is this thing saying that it can only read microamps NO LOWER than 400µA and no higher than 4000µA?

OR would it read 5µA without any problem at all?

Edit: After looking at that a little closer, what I THINK it's saying is that when the current is under 400µA, the resolution will be .1µA and when it's over 400µA, the resolution will be 1µA ... ???

[budm]

Re: Meters and Microamps

Can we see more details spec about the spec of this meter? Make and brand?
As shown, it can read down to 000.1uA on 400uA scale with one decimal point resolution.

[stj]

Re: Meters and Microamps

UT61e has a 220uA range with 0.01uA resolution.

[EasyGoing1]

Re: Meters and Microamps

Can we see more details spec about the spec of this meter? Make and brand?
As shown, it can read down to 000.1uA on 400uA scale with one decimal point resolution.

That spec came from a Fluke 17B+ ... I went ahead and ordered one. I'm pretty sure it will read µA below 10. Based on my experience with the Fluke 117, that spec suddenly made sense as there are thresholds on my 117 where the resolution changes as you get higher in a reading which makes sense since the available screen space for numbers gets crowded as you read higher values ... but to switch that up at 400 seems a bit odd to me... 999 makes more sense. ☺

[eccerr0r]

Re: Meters and Microamps

It's just marking two different microamp ranges for the 3¾-digit LCD: 0.0 to 399.9 µA and 0. to 3999. µA.
(and of course it has 40mA, 400mA, 4A, and 10A ranges... need more digits if more precision is needed...)

[EasyGoing1]

Re: Meters and Microamps

It's just marking two different microamp ranges for the 3¾-digit LCD: 0.0 to 399.9 µA and 0. to 3999. µA.
(and of course it has 40mA, 400mA, 4A, and 10A ranges... need more digits if more precision is needed...)

It would seem to me that given the VERY inexpensive cost of decent high-resolution OLED displays, this would not be an issue and they could just let the user chose their own precision...

[budm]

Re: Meters and Microamps

The type of display has nothing to do with the precision, its the circuit and the precision of the components.

[EasyGoing1]

Re: Meters and Microamps

Got the new meter ...




Even got a nice case for it - the zipper compartment was mandatory as my last one only had an open pocket and I was constantly chasing pieces that would fall out of it.



Right off the bat and I know this is probably nit-picking but the sound of the beep it makes is more pleasant than the 115. And notice the display - it's got larger numbers and more real estate all around. Also, the backlight produces a much cleaner look than the 115 has with more even light distribution.





Next, I need to test the microamp ability ... back to my ATTiny85 project and experimenting with the Tiny's sleep modes

[redwire]

Re: Meters and Microamps

That's great, you can't go wrong buying a Fluke. Buying a Uni-T however, those are true garbage multimeters, they have awful input protection circuits.

Keep in mind the uA current-shunt on the majority of multimeters large, at 1k ohm. So you get a large voltage drop or "burden voltage" across the shunt as it's called. e.g. 200uA is 0.2V loss and if your load goes well over full-scale for the uA range, the input protection diodes clamp at around ~2.4V drop across the DMM.

Schematic for Fluke 17B attached here.

P.S. I did a project with the ATtiny85 and had to shut off BOD and the A/D to get sleep current draw really low.

[EasyGoing1]

Re: Meters and Microamps

P.S. I did a project with the ATtiny85 and had to shut off BOD and the A/D to get sleep current draw really low.

Do you still have that code? And would you be willing to share it?

[stj]

Re: Meters and Microamps

That's great, you can't go wrong buying a Fluke.

the quality and support isnt what it used to be since they got taken over by a bunch of bankers.

Buying a Uni-T however, those are true garbage multimeters, they have awful input protection circuits.

dont believe everything you hear on eevblog
i had to explain to some asshole there once why a clampmeter doesnt have a fuse!!!

[redwire]

Re: Meters and Microamps

The spirit of Fluke truly ended with Fortive buying them and now it's only profit they worry about. Which is fine if you don't mind buying products designed in the 1980's

Basic multimeter input protection has a PTC, surge resistor, MOV's and anything less is a bit weak and can get blown up.
Uni-T UT61+ the German version has MOV's and was used to obtain TUV 61010 safety certificate. But the PCB everywhere else- has no MOV's. chinese scammers. Tons of posts where the multimeter died. But lotsa digits though lol.
I'm tired of cheap chinese/taiwan multimeters, the quality is just too low.

[redwire]

Re: Meters and Microamps

Do you still have that code? And would you be willing to share it?

The ATtiny85 project I did was a car key-off timer for the accessories so stereo, USB charger, dashcam keep running without killing the battery.
It was so I could charge my phone while shopping or keep the car stereo playing if working outside, without needing keys in the ignition on ACC.
With key off, or a button press, runs for 3 hours. It uses about 0.3mA sleeping.

The code is really complicated, I used a state-machine. Then I found a bug where the (key-on) wake-up interrupt can happen more than once and I forgot what I did about it. Posting the code would be confusing I think.
There are many tutorials on the Internet using the Arduino sleep library.

[stj]

Re: Meters and Microamps

The spirit of Fluke truly ended with Fortive buying them and now it's only profit they worry about. Which is fine if you don't mind buying products designed in the 1980's

Basic multimeter input protection has a PTC, surge resistor, MOV's and anything less is a bit weak and can get blown up.
Uni-T UT61+ the German version has MOV's and was used to obtain TUV 61010 safety certificate. But the PCB everywhere else- has no MOV's. chinese scammers. Tons of posts where the multimeter died. But lotsa digits though lol.
I'm tired of cheap chinese/taiwan multimeters, the quality is just too low.

i fitted my own movs - and big FF rated fuses.
i dont mind paying 45$ and adding them instead of paying $80+ to have them to begin with

[eccerr0r]

Re: Meters and Microamps

speaking of those ^*(#%$ing FF HRC fuses, where can we get (real ones) cheaply? Are there any china brands that are "acceptable" or are they all big bad fakes?

Need to get more of the 10mm type (ideally 100KV), though I think I can get by with ¼" x 1¼" (10KV is fine) since I'll make sure the meter will never touch 10KV...

[redwire]

Re: Meters and Microamps

What MOV's did you use, it's that people don't know they need them until the big IC is damaged.


HRC fuses are just silly overpriced. 10x38mm 1,000V 20kA Bussman DMM-B-11A or 44/100 (10kA) is USD $50 each
They are for people making big mistakes in Cat. III environments needing safety. Maybe a new form of currency,

People complain about the knockoffs on eBay/Amazon but they have jacked up the price too.
Important for the fuse to be sand-filled, and the cartridge can take a high heat arc without carbon tracking and shattering or burning up.

There are reviews where people weigh the counterfeit fuses and take them apart. These are a bit older 2017, #129 good take on it all:

Voltlog #105 – Multimeter HRC Fuses Price Rant
https://youtu.be/8MfFXRxBrrA

Voltlog #117 – Ebay Bussman DMM Fuses Fake or Genuine?
https://youtu.be/evKKE1rsGVQ

VoltLog #129 – Ebay Bussmann Fuse vs Genuine Bussmann Fuses DMM-B-44/100-R
https://youtu.be/mmxGX0K8JII

[stj]

Re: Meters and Microamps

the mov's are 07d751k

for the fuse it's more interesting,
if you really need a 1KV fuse then your reading current on a 1KV line - or your dumb as a brick and metering 1KV with the switch set wrong and the probes in the wrong places!!

so with that said, 600v 6.3mm fuses are much cheaper
https://www.rapidonline.com/siba-ult...ic-fuses-64639

or 1KV 6.3mm
https://www.rapidonline.com/eska-ver...m-1000v-537488

600v fat fuses are still not too bad
https://www.rapidonline.com/siba-hrc...al-fuses-35003

hell, even the fat 1KV ones are under $10 if you really need one.
https://www.rapidonline.com/siba-hrc...truments-80232