Electromagnetic disturbances

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bernardd
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by bernardd » 23/03/10, 10:44

elephant wrote:Sometimes we have very happy troubles: I remember a large installation which adjoined (30m) a tram track and another (detection of a broken fence) which adjoined a gas pipe (cathodic protection currents rectified but not filtered)


No more problem for the power supply of the house, induction is better than photovoltaic ...

By the way, I wonder if the natural compensation of houses under THT or MV cables, it would not be an "antenna" suitable for induction :-)

I remember a metal hangar roof where I took a hell of a chestnut, but it was the 400000V line above: we really wonder why pay a meter in this case ...
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elephant
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by elephant » 23/03/10, 11:14

This is exactly why the electrical regulations (at least in Belgium) provide for the earthing of all the electrical parts of the building: frames, pipes, roofing. The rails of the PV panels must also be.
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bernardd
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by bernardd » 23/03/10, 11:21

But it is identical in France, and we checked that it was well made: but with the 400000V at 20m above, the residual voltage is quite sensitive, and I especially wonder why we are not using it : with diodes in particular, and a suitable antenna, free lighting ...
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by elephant » 23/03/10, 11:30

Try: the voltage, you will have it, but the current?

(if you want to dig, create a new subject: we are seriously moving away from the temperature probe who is kidding our friend)
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nlc
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by nlc » 23/03/10, 11:44

First, I will do what I have already indicated above: replace the probes with equivalent resistances for a given temperature (for example resistors of 100r if they are pt100, to simulate 0 ° c), and connect them as close as possible to the boxes to which these probes are normally connected.

If everything is stable in this configuration, it is because the disturbances come through the lengths of wires between boxes and sensors (which is most likely given the symptoms of the installation).

It will then remain to define what type of disturbance it is, but each thing in its time, we must first locate the problem.
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elephant
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by elephant » 23/03/10, 11:51

It is also a solution. Do we know the values?
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by nlc » 23/03/10, 11:55

If the probes have 2 wires it is easy to measure by unplugging them and connecting an ohmmeter
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by elephant » 23/03/10, 12:38

where was my head! I was really taking a cannon to kill a mouse : Oops:
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by nlc » 23/03/10, 12:48

elephant wrote:where was my head! I was really taking a cannon to kill a mouse : Oops:


Poor little mouse : Mrgreen:
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dedeleco
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by dedeleco » 23/03/10, 13:19

I did not expect to excite with the earth connection, which is probably not crucial.
I give my past personal experience.
One case where the earth electrode is working, (without a 200000V line or neighboring tram) is when lightning strikes in the vicinity. It induces (inductive and capacitive) even at 100m enormous voltages and currents throughout the house, and then we can have much more than 2A in transient a few microseconds and the whole house rises in voltage with corresponding destruction, like VMC with burnt motor, (repetitive personal case) despite the 30mA which does not jump fast enough !!
Once on my house, lightning made a hole, set fire to and destroyed the meter, the circuit breaker, the fridge, the hob but not the TV, the computer which saw its socket torn off !!!! !!
The radio and microwave emissions do the same in smaller, being able to disturb, if there are defects in the shielding, the decoupling of the power supplies (bad decoupling capacitor, badly welded, or badly placed, too far from the microprocessors, etc.). )
A simple thyristor thermostat or heater (coffee maker), even at a neighbor's, poorly suppressed (even at a neighbor's) generates appalling disturbances (1KW HF transient) in the entire neighborhood and could be enough to be the cause !! A small test is to watch TV and see the disturbances on the screen (same TNT and analog) in strong form (loss of the image one second) or weak (streaks on the screen). At home I have such disturbances on the TV every 10min and I know that a neighbor has a poorly suppressed thyristor regulation surely !!!
But as I have no more problem, I support !!
Also it is necessary to pinpoint the problem by testing each single single element isolated, collect clues without preconceived ideas not proven by overlapping evidence, considering all possibilities, like a detective.
An oscilloscope can be very useful in showing the nature of the parasites, 50 or 100Hz or HF or pulses in microseconds !!
Okofen if under guarantee, must be able to provide it or take it on loan, or buy it inexpensively, a few hundred euros.
But it is necessary to know a little practical electromagnetism, because otherwise one can make a mistake by taking what is normal for a defect !!! You have to know how to explain why any 1m end of wire put in an oscilloscope gives oscillations and especially understand how they vary (a presence detector!).
I have a small thermometer at PT100 and I used it to measure the temperature of the sea, which with the salt has oxidized the contacts, so that it often measures with fluctuating errors (T increases variable with the contortions on connectors) if the connectors are not stripped of oxidation !!
In this case, I really went overboard with seawater! and therefore very unlikely for you !!
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