Go Down

Topic: Continuity test fail (Read 1 time) previous topic - next topic

guix

Hello :)

Sorry this is a stupid question and I probably have the answer already but I want to make sure... I try to do continuity tests on a board but I can't, I believe it's because there is a resistors between the 2 points I want to test. The resistors are of value "103" (10000 ohm, right?). Does the test fail because the resistor resists too much? If I try from one point, to resistor, then the other point to (other side of the) resistor, of course the continuity test works.

#1
Nov 06, 2012, 12:52 am Last Edit: Nov 06, 2012, 12:54 am by seanz2003 Reason: 1
It depends on what range your meter is set to, and whether your circuit is "live", (no voltage should be applied if you are measuring resistance.) if you are trying to measure a 10k resistor, your meter will register an open circuit if you have it set to something less than 10k. Also depends on the complexity of the board you are testing.

James C4S


I try to do continuity tests on a board but I can't, I believe it's because there is a resistors between the 2 points I want to test.

Continuity tells you if there is a short circuit.  If a big resistor is in the path, then you WANT the continuity test to fail.

You are attempting to measure "in-circuit" which doesn't always work.  You have to take into account everything in the circuit that touches the points you are measuring, not just the points themselves.

If you're measuring resistances in a path, you probably want to use the "resistance" function of your multimeter.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

guix

Thanks both, I didn't want to measure the resistance, just see if the 2 points were connected, using the resistance function of the multimeter proved that they are connected ;)

retrolefty

Many of the digital multimeters available today have a so called continuity test function that is very much a function of a specific meter's design. That function is usually designed as a go/no go test often with a buzzer also so you can test with eyes off the meter. However as a go/no go test there has to be some resistance value that is the decision point of it being a 'go' at or below that value or a 'no go' above that resistance value. Whatever that decision resistance value is, it will be specific to that specific model meter as there is no agreed on 'standard' continuity resistance value. Probably a good test would be to get a pot and slowly adjust the pot while performing a continuity test on it and stop when the test first says it has good continuity and then measure the pot's actual resistance with the ohm function of the meter, that way you will know what resistance value your meter uses as it's go/no go continuity value.

That make sense?

Lefty

michael_x

Quote
see if the 2 points were connected, using the resistance function of the multimeter proved that they are connected

I understand you see a short / continuity across a 10k resistor ?
If your board is not powered, and there is no other connection in parallel, there seems to be something wrong, agreed.

However, if there is anything connected in parallel, you might measure less than the 10k value.
An inductance might have a DC resistance of 0 Ohms, e.g.  (Not sure if a resistor in parallel would make sense)

guix

Lefty, yes it does make sense :)

michael_x, no I was trying to measure continuity between 2 points, board unpowered, and on the path was a resistor and I was just wondering why the continuity failed. Then, I've set my multimeter to 20kohms, measured between the same 2 points, and the multimeter showed ~10kohms so it proved that the 2 points were connected, that's all I wanted to know :)

MarkT

A useful tip:  measure the resistance twice with the leads reversed - if there's a difference then a diode or other semiconductor is involved.  If your multimeter has a diode setting then that's the best setting for this.

Continuity settings with a buzzer normally only detect low resistances (10 ohms or less) indicative of direct wiring between the test points, so
normally aren't confused by other components (other than inductors as has been mentioned)
[ I won't respond to messages, use the forum please ]

Go Up