Regular interference impacting voltage reference every 40 seconds - Page 1
Forum section: electronics / general

author: essele
author_rank: Frequent Contributor
timestamp: May 23, 2020, 06:37:41 pm
content: I've hit a bit of a brick wall trying to locate the source of some regular interference that's impacting my experimental voltage reference.It's a parallel REF102 implementation, and I've just increased it to 10 in parallel (from 5) which I think has reduced the overall noise to a point where I can see a regular interference pattern every 40 seconds.I've attached a screenshot where you can see it ... the oven is still warming hence the gradual increase in voltage.Every 40 seconds I can see a few of uV increase, it's sits there for a few seconds, and then comes back down again. The MPU running the oven and temp controller is on a 1 second loop, with no change in behaviour every 40s. I've turned just about everything else off in the room.I'm down to two theories, but would love to hear if anyone has any experience of anything similar...1. The electricity meter (smart meter) is just the other side of the wall and I wonder if this is transmitting to the "console" every 40 seconds (although I'm pretty sure it updates much more quickly.)2. I can vaguely remember some wifi device I couldn't identify trying to join my network on a continuous loop ... I blocked it, but that could be retrying every 40 seconds?I don't recall ever seeing this on anything else, which I don't understand!Any thoughts?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 23, 2020, 08:15:53 pm
content: Some try to reconnect for Wifi / WLAN or similar is possible.There is also the possibility that not the reference is effected, but the meter.Even the meter itself could be the source, like doing an internal temperature reading every 40 seconds and this way disturbing the measurement. This effect may no happen with a short - so for a test one would need to check something like a 9 V battery.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 23, 2020, 08:20:46 pm
content: Those of us that aren't into RF don't typically have a lot of RF test equipment. Go back in time to when nobody had good RF test equipment. Build yourself a diode RF probe and maybe an amplifier. Use a germanium or schottky diode. That will give you a DC indication of RF field at frequencies your regular test equipment can't handle. Attach it to your meter or scope. Now go sniffing around for something that causes a slight jump every 40 seconds. It will probably be something with a "brain" like a smart meter, smart thermostat, some household appliance, TV related stuff or even something external to the house.

author: langwadt
author_rank: Super Contributor
timestamp: May 23, 2020, 08:35:53 pm
content: cellphone?

author: CDN_Torsten
author_rank: Regular Contributor
timestamp: May 24, 2020, 02:02:27 am
content: I've had issues with a power-line Ethernet extender. I would see very periodic bursts...scratched my head for days...

author: Andreas
author_rank: Super Contributor
timestamp: May 24, 2020, 05:26:04 am
content: Hello,really strange.What comes into my mind:- could be a outdoor unit of a thermometer (but the peaks should be smaller)- with such a long time constant it could also be something thermal (automatic ventilation)- popcorn noise of one of the "new" references in stack (but this should be more irregular).I fear you will have to put your equipment on a rolling desk and move it around to see where the jumps are increasing to locate the source.with best regardsAndreas

author: babysitter
author_rank: Frequent Contributor
timestamp: May 24, 2020, 07:58:27 am
content: Quote from: Conrad Hoffman on May 23, 2020, 08:20:46 pmAnd use the good old "turn stuff off and see if it disappears" method. I think that is what circuit breakers are really for.Get a portable AM radio, listen if you can identify some noise which coincides with the influence, walk around to locate. The usual ferrite antennas have a maximum sensitivity, typically perpendicular to the ferrite rod.

author: hwj-d
author_rank: Frequent Contributor
timestamp: May 24, 2020, 12:16:27 pm
content: - Thera are apps, they can scan the itensity of your WIFI area.- Maybe DECT interferences.- Maybe cellphone interferences.- Smartmeters use cellphone connections, i belive.- Use batteries for your reference.- Use a completely other place for your measurements.

author: The Soulman
author_rank: Super Contributor
timestamp: May 24, 2020, 12:27:09 pm
content: Use short twisted pair cable for connection between Vref and DMM?

author: martinr33
author_rank: Frequent Contributor
timestamp: May 24, 2020, 01:00:12 pm
content: I agree with langwadt. That looks like it could be a GSM TDMA contact burst. That's an older standard, but smart meters tend to use older standards. However, they have to be really close to have a noticeable effect.So I would try it a chunk further from the smart meter,see if it drops.

author: essele
author_rank: Frequent Contributor
timestamp: May 24, 2020, 05:47:29 pm
content: Thanks for all the suggestions.Once it gets to temperature it’s difficult to see if the problem still remains as there is a bit of noise, I have been concerned with what I thought was popcorn noise so started looking at each ref and found one that was three times as noisy as the others.I also found that with the PSoC programmer removed I get a load of noise when the serial is transmitting, but it’s ok if the programmer is connected - still need to figure that one out (may just be the hanging cable)I am a bit worried about the smart meter, it’s probably about 50cm away (the other side of the wall) but I’m not clear why that’s not impacting other devices??Anyway ... questionable ref102 swapped out, 2k balancing resistors swapped with 100R (felt like the right thing to do) and now up to 18 in parallel ... will run it for a while before it goes back into the oven for a heating cycle ... I’ll try to make the setup mobile so I can get it away from the smart meter.I’ll let you know how it goes.

author: Bill158
author_rank: Regular Contributor
timestamp: May 24, 2020, 08:47:15 pm
content: Just a couple of stories I have about regular noise in very sensitive measurements and hi fi equipment.A company called Qual-Tech made noise analyzers for discrete transistors (Bipolar and FETs). It had analog meters on the front which showed the noise in octaves (i.e. 10, 100, 1000, 10,000 hz). A device engineer was measuring some devices when he noticed that the 10 Hz meter would spike every so often. He tried a few more devices and the same thing. Went to another analyzer same thing. Finally he had to go to the restroom. The others trying to figure out what was happening then noticed that the spiking disappeared. When the engineer came back a few minutes later the spiking started up again. Bottom line here was he had a cell phone in his pocket. When he turned off the cell phone, I mean power down completely, the problem was gone. Cell phones "ping" once in a while to find the nearest tower and that was causing the spiking.Hi Fi system in the '70s. There was a very large radar system on top of a near by mountain, operated by the Air Force. It rotated 360 degrees in a regular cycle. Every time it was aimed at his house the phono cartridge would pick up the radar pulses and a "buzz" would come out of the speakers. I never did figure out what to do about this but all kinds of shielding got rid of most of this. The Air Force site was finally shut down and that solved the problem.So maybe some radar system ( weather doppler ) near you or your cell phone is causing the noise??? Just a few suggestions.Bill