Searching for some precision mains power meter (0.1mA) - Page 1
Forum section: electronics / testgear

author: kripton2035
author_rank: Super Contributor
timestamp: January 01, 2023, 08:07:48 pm
content: Hi folks,I experimented some affordable power meter like a kill-a-watt or some chinese modulesthey are not precise enough for what I want to measure; some modules I make that need less than 1mA currentsome of the meter I tried had a 1mA resolution, but did not in reality measure anything below 5mA ...do you know a power meter that could measure mains (220v) at a precision of 0.1mA (or less)and that does not cost an arm ?ordo I have to make my own using some ADE77xx chip ?thanks for any hint(s)have a nice day, and an happy new year !

author: _Wim_
author_rank: Super Contributor
timestamp: January 01, 2023, 08:26:31 pm
content: Hi, what is the max current it must be able to measure? If only low max currents are required, you could just increase the current sense resistor in those power meters to a 10x value and divide the result by 10. Some power meters allow you to attach your own current sense resistor and configure its value in software (like my Voltech PM6000)

author: kripton2035
author_rank: Super Contributor
timestamp: January 01, 2023, 09:12:25 pm
content: I would like to still be able to measure up to some 1-5 A ?

author: _Wim_
author_rank: Super Contributor
timestamp: January 01, 2023, 09:26:35 pm
content: Quote from: kripton2035 on January 01, 2023, 09:12:25 pmMeasuring 0.1mA on a 5000mA range will be very hard (impossible?) for even a very very expensive power meter. Thats 50000 counts (almost 16 effective number of bits) that needs to be measured at high speed and fully isolated!I would first check to see what high end meters from Yokogawa and the likes can offer here and adjust your requirements accordingly.

author: 1audio
author_rank: Frequent Contributor
timestamp: January 02, 2023, 04:31:57 am
content: I would suggest searching for a Clark Hess 255 power meter.https://manuals.repeater-builder.com/te-files/MISCELLANEOUS/CLARKE%20HESS%20255%20Instruction.pdfIt can measure down to 5 mA full scale and has bandwidth to 300 KHz with better than 1% accuracy. Accuracy on distorted AC is a challenge and these are among the better instruments. There are several on eBay, the cheapest is around $75.

author: _Wim_
author_rank: Super Contributor
timestamp: January 02, 2023, 07:26:11 am
content: Quote from: 1audio on January 02, 2023, 04:31:57 amIf I understood the OP correctly, he is looking for a full scale range of 1...5A with a readout resolution of 0.1mA. When the full scale range can be lower, indeed units with switchable ranges (switchable current shunts) are a good option. Alternatively, this can be an easy modification to an existing meter to insert some additional shunt resistance (via relays or switches).

author: kripton2035
author_rank: Super Contributor
timestamp: January 02, 2023, 08:26:47 am
content: I'm ok to have the whole scale using different measuring ranges.I'm actually using a PZEM-022, it has 1mA resolution, but doesn't seems to measure something under 5mA...

author: _Wim_
author_rank: Super Contributor
timestamp: January 02, 2023, 10:57:05 am
content: It might be possible to modify that current sensing coil to add many additional turns to increase the sensitivity. Or buy on of these, and modify the shunt resistance to be for example 1000x larger:https://www.amazon.com/gp/product/B098B4BHN5/ref=ox_sc_act_title_1?smid=A3S807LE0L63AP&psc=1This will give you a 0-20mA range, and power in mWatt instead of Watt.

author: Kean
author_rank: Unknown
timestamp: January 02, 2023, 11:04:47 am
content: It may be out of your price range, but I use a Tonghui TH3321 AC power meter which has ranges from 1mA to 2A and up to 1uA resolution and many measurement features.There is also a TL3320 model also aimed at low current device measurements up to 5A with a simpler numeric only display, but without harmonic analysis.http://tonghui.com.cn/en/index.php?module=Product&action=ListView&search=TH33https://www.globalmediapro.com/dp/A2MYD3/Tonghui-TH3321-Digital-Power-Meter/

author: wasedadoc
author_rank: Super Contributor
timestamp: January 02, 2023, 11:14:10 am
content: If the supply is 220 volts AC then a relatively high burden voltage should not be a problem. All DMMs are essentially voltmeters and determine current by measuring the voltage drop across a known resistor. A 1k resistor will drop 5 volts if 5 mA is passing though it. 0.1 mA resolution requires only 0.1 volt resolution of the AC DMM. You can use a different resistor to meet your measurement needs and the capabilities of your DMM in AC volts mode.

author: jonpaul
author_rank: Super Contributor
timestamp: January 02, 2023, 11:41:09 am
content: We have amny Charke Hess 255 HF watmeters, and the Yokogawa WT110.None can do what the OP asks.The reason is leakage currents and stray capacitances, its not practical to get a sub milliampere 50/60 Hz mains current measurement.Read the CH 255 and Yokogawa specifications.In decades of power work I never had to measure less than a few watts load.At 120V 1 W will be 1/120 A = 0.8 ma = 800 uA.What is the OP trying to accomplish?Jon

author: kripton2035
author_rank: Super Contributor
timestamp: January 02, 2023, 12:13:22 pm
content: Quotemeasuring the consumption of small IOT devices that are mains powered.some are switching power loads like motors or heating elements, so there can be some Amps flowing through.when idle (no power element is on) they consume less than 5mA.

author: jonpaul
author_rank: Super Contributor
timestamp: January 02, 2023, 12:23:09 pm
content: bonjour cher MonsieurThe current is easy to measure with a sensitive AC ammeter, low range DVM. as the main voltage is fair stable, just multiply by 240, 120 for watts.We use Fluke or similar DVM, lowest AC current or Keysight 34465a.Alternative make a current senses series shunt, 1,10, 100 ohms.Just measure the voltage drop.Keep load off so the meter sees only the standby current.Easier to just get the spec of the deviceBon chanceAmicalementJon

author: kripton2035
author_rank: Super Contributor
timestamp: January 02, 2023, 12:40:37 pm
content: thanks, I know I can measure this with one or 2 DVM. I am searching for a small factor module (like the pzem-022 above) to do thisand installing it permanently on my bench.just for fun I asked chatgpt about this ...>Quoteimpressive ... even if not completely true...

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 02, 2023, 05:04:56 pm
content: I have a couple of meters that can measure in the 5A range with resolution of 0.1 mA but the accuracy is no where near that good. I wonder what kind of application that you would need such precision. After reading all the posts I see the OP wants to measure power consumption when the IOT device is idle. If the OP power the device by 220V mains why should a few mA matter?

author: Swainster
author_rank: Frequent Contributor
timestamp: January 03, 2023, 04:22:09 am
content: I have a RS branded GWInstek bench power meter with 100nA resolution on the 5mA range. Some numbers just to get a feel for things:With mains 115VAC/60Hz the current is about 0.06mA even with nothing plugged into the outlet. With a long IEC lead (still no load) then the current goes up by 0.012mA. With mains set to 240VAC/50Hz then this leakage current is about 0.1mA. Plugging in a few random bits of old test equipment (power supplies, electronic load) with hard on/off switches in the off position typically adds another 0.1mA (except for one which added 14mA... this I know has crispy RIFA caps inside so I guess it is trying to telling me something). A random cheap chinese phone charger uses about 2mA without any load, though to be fair this was dropping as the internal caps reformed.I bought this power meter to measure standby/idle currents according to IEC62301, which is actually something typical power meters cannot do. One of the requirements is 1mW resolution - thats under 9uA at 115VAC. My suggestion is that if you are serious about this type of measurement then you will need a proper bench type instrument. If you are only interested in current then a DMM could be good enough, but if you actually want to know power/energy used then a power meter is the most practical solution (2 DMMs will not work without a lot of extra work to extract and sync the data, even assuming they have enough bandwidth).TLDR What you want to do is non-trivial and probably the preserve of application specific bench instruments. Building a custom instrument to do it is always possible, but only practical for hobby/enthusiasts - In fact I think this kind of project would generate quite some interest on this forum. For commercial purposes it makes far more sense to just buy the proper tool for the job.