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Author Topic: Electronic Energy Meter in a Microwave  (Read 3792 times)

Offline port500

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Electronic Energy Meter in a Microwave
« on: 20/09/2011 06:39:02 »
Hello,

I am in a bit of sticky situation and would welcome all ideas in this regard. My client has this problem where people are, literally, frying the energy meters in their homes using apparatus that is similar to a microwave.

So, i have been given the task to find out what fault does the microwave induce in the energy meter. What i am doing i pretty simple, placing a energy meter (with battery) in a microwave for 5 seconds. What i have observed is it takes about 2-3 seconds for the meter to go dead. A spark is observed and the display goes dead after that.

After examination of the dead meter, i found out that the resistors connected with shunt and CT are fried.

I have repeated the experiment by removing the battery and the resistors, mentioned above, but the spark is still observed after 2-3 seconds and meter goes dead.

I can't seem to figure out why is the meter acting out the way it is. Any ideas?


 

Offline Geezer

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Electronic Energy Meter in a Microwave
« Reply #1 on: 20/09/2011 07:18:47 »

using apparatus that is similar to a microwave.


What would people have in their homes that is similar to a microwave but isn't a microwave? Are they beaming microwave RF signals at their neighbours?

 

Online Bored chemist

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Electronic Energy Meter in a Microwave
« Reply #2 on: 20/09/2011 20:39:52 »
The microwave will induce high voltages in and around the electronics in the meter. It wasn't designed to cope with that so it will fail.
I presume that your client is something like a landlord who needs the meters to work properly and the people frying them are trying to avoid paying the bill.

Does the meter transmit a signal to a "receiver" of some sort, or do you just go and look at it to get a reading?
If it doesn't need to receive or transmit then you can get a good degree of protection by wrapping it in metal mesh.
Incidentally, if you use a microwave oven to test this sort of thing there is a chance you will damage the oven as well as the meter. No doubt the oven came with  instructions telling you not to use it for anything but heating food.

I guess I should also point out that whoever is zappng the meters is at risk of damaging themselves too.
 

Offline Geezer

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Electronic Energy Meter in a Microwave
« Reply #3 on: 20/09/2011 22:48:43 »
Doh! Thanks to BC, I think I get it now. Presumably these meters are screwed down and attached to the power line and people are using some piece of portable equipment to "fry" them?

If that's the situation, I'd be a bit surprised if they are using microwave energy. Could they just be zapping them with a large electrostatic discharge? It's not too difficult to kill electronic equipment with the currents induced in the electronics by nearby electrostatic discharges. I'd suggest you try to get hold of an ESD (electrostatic discharge) gun, and do some tests.

Here's a link.

http://en.wikipedia.org/wiki/ESD_Simulator

 
 

Offline port500

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Electronic Energy Meter in a Microwave
« Reply #4 on: 21/09/2011 06:10:57 »
The meters do not have AMR capability. We are not looking for a solution right now, as it is highly unpractical to think that they an energy meter can survive some microwaving. All we want to understand is how are the PCB and components being affected.

As some part of the PCB is acting as internal antenna, probably some track, we want to try to identify it if possible. For that reason, we are using microwaves of different Electric field strength, ranging from 10V/m to 300 V/m.

We have bought ourselves a few microwaves that we consider expendable. We are sure that the apparatus being used is microwave based, as the reports from the field suggest this. Plus the meters that we have "fried" have the same symptoms as the ones in field.

I quite like the idea of using metal mesh shielding, as theoretically it would be a good fit. Thank you for your constructive feedback. I will keep you updated in this regard.

We have some very interesting experiments planned, and there are sure to be some booms along the way :)
 

Offline Geezer

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Electronic Energy Meter in a Microwave
« Reply #5 on: 21/09/2011 07:00:54 »
If they don't have AMR, you can immunize them against microwave energy by sticking them in a metal box. I'm sure that will work.

Please provide more details about the scientific nature of your research.
 

Offline chris

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Electronic Energy Meter in a Microwave
« Reply #6 on: 21/09/2011 09:21:10 »
Yes, I would agree that sticking the meters inside a locked metal box would be ample security against this sort of threat.
 

Offline graham.d

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Electronic Energy Meter in a Microwave
« Reply #7 on: 22/09/2011 13:48:06 »
If you put any electronic equipment in a microwave oven it is likely to zap it unless it is especially well screened. Are you suggesting trying to make these meters immune to such activity? It seems unlikely that any average person, even one bent on deliberately nobbling the energy meter, would be able to utilise a microwave oven to zap a fixed device installation. So are these parts easily detachable so that your belief is that someone is removing the meter, zapping it in a microwave oven, replacing it, and then pretending it died a "natural" death and therefore not recording the energy used? Is the object to try to make the meters immune to this or to prove that this is what is being done?

If they are dying in the field, and this is without any obvious deliberate act by anyone, then it is just possible that mobile phones that are the culprits. Field strengths of over 30V/m are not uncommon close to the antenna but even 5V/m can be generated at 1 to 2 metres. It may be enough to damage a sensitive component, though I think it unlikely that any circuit would be so highly matched so as to collect enough energy to burn out a resistor in the way described. Though it may be worth testing the resilience of the meters to transmitting with a mobile with its antenna close to the meter.
 

Offline RD

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Electronic Energy Meter in a Microwave
« Reply #8 on: 22/09/2011 18:09:44 »
There is (spray) paint for EMI shielding with metal particles (Al, Ni, Fe), which may be a cheaper alternative to making a metal casing, (i.e. spray painting the interior of the a plastic case). 


http://www.zeusinc.com/UserFiles/zeusinc/Documents/ZEUS_EMI_shieldingofplastics.pdf
« Last Edit: 22/09/2011 18:19:45 by RD »
 

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Electronic Energy Meter in a Microwave
« Reply #8 on: 22/09/2011 18:09:44 »

 

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