A weird measurement to me

[smiles]

Use meter to measure Ohm value between 3 point, I get
Beep sound (0.000Ohm) between A and C
Beep sound (0.000Ohm) between B and C
but no beep sound (1kOhm) between A and B
Why is this ???
Thanks !!!

 

[rikie_rizza]

So, what actually is this point?
There are a thing that is called Kelvin Resistance.

Anyway, what is the case....a single wire where C is the middle and A and B is the end? Or is it a diode bridge that you measure? or a supernatural thing maybe...uuuuuuu???

 

[smiles]

Let me remember the real circuit :|
Point A placed at C terminal of P-channel IGBT
Point B placed at C terminal of N-channel IGBT
and C is the negative terminal of a capacitor.

 

[Johansen]

the capacitor has nothing to do with it.

if you reverse the polarity of the ohm meter you should read infinite ohms. the igbts are connected such that they cancel out the body diode

edit: infinite ohms: aka overload on a DMM, characterized by the number 1 on the Left most digit, or an over range indicator.

I reread you post, hsingarajah got it right. ... .
and at the same time, there is not enough info to make sense of this

 

[smiles]

"if you reverse the polarity of the ohm meter you should read infinite ohms. "
Could you explain me more, thanks !!!

 

[inverta]

can you give some picture of your circuit?

[/quote]

 

[hsingarajah]

What you basically have is a wire between A & C a wire between B & C and a 1ohm resistor between A & B

 

[FvM]

The problem is that Beep sound (0.000Ohm) can also mean a negative voltage present between the terminals. So you have to perform an additional voltage measurement to exclude this option. Would be wise anyway to avoid damaging the instrument by circuit voltage.

 

[rikie_rizza]

"The problem is that Beep sound (0.000Ohm) can also mean a negative voltage present between the terminals."

If the circuit is a live one right? assume its not, and back to its original question, measuring IGBT with continuity test is truly a mistake?

 

[barry14]

A simple circuit that could do this is two diodes in series with opposite polarity connected between A and B with C connected to their common point. With this circuit, you should also get infinite readings if you reverse the leads for the A/C and B/C readings.

 

[siongboon]

Another possibility might be the resistance between point A & C, point B & C.
If I am correct, when a multimeter beep, it does not means 0.0000 ohms.
It mights that the connection is less than certain ohms.
Some meter will beep if ohm is less than 50ohm.
For example if point A to C is 49ohm, B to C is 49ohm.
Then the weird situation you faced might be possible.

Another reason might be the diode as discussed.
When you measure the ohm, you are actually injecting
power into the circuit. You might have activated the diode (forward bias)
during the measurement resulting in the beep sound.
When you reverse the probe direction, it will not sound,
since the diode is not activated.

You can actually troubleshoot further to confirm your encounter.

Best Regards,
Siong Boon


www.siongboon.com