EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: Brittanym101 on September 06, 2010, 06:31:07 am
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I have done a test to measure resistance of two different circuits. One of them contains just the Multimeter and the other contains a Power Pack and an ammeter. I used them to measure resistance in the circuit. The circuit involving the Multimeter gave higher resistance, so my question is...
How much resistance does a Multimeter have?
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I have done a test to measure resistance of two different circuits. One of them contains just the Multimeter and the other contains a Power Pack and an ammeter. I used them to measure resistance in the circuit. The circuit involving the Multimeter gave higher resistance, so my question is...
How much resistance does a Multimeter have?
A multimeter doesn't have "resistance" as such.
It sounds like you are trying to measure the "resistance" of an active circuit across the voltage rails. Unless you have very specific reasons to measure such a thing, it is not a valid thing to measure, and you will get varying results as you have experienced.
The reason is that a circuit will typically have a "resistance" that changes with the applied voltage, and your multimeter will apply a different test voltage than your power supply, so the result will vary.
Hope that helps.
Dave.
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Dave is obviously correct that you can't measure resistance with a multimeter in a circuit with voltage or current sources connected (assuming power pack contains some sort of battery).
A DMM does have a resistance, but it depends on how you connect it and the range. When measuring current, the resistance is fairly low, but depends on the range. The higher the current range (eg. 10A vs. 400mA), the lower the resistance. It's usually somewhere between 0.1 ohm and 10 kohm. In most other modes, especially volts, the resistance is much higher, usually >1 Mohm, depending on range. You can measure both yourself if you have a second multimeter. It should also be in the manual, usually in the specifications section.
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OK we got another Hoax account ... do not reply .. check the signature of him ... and do not make him happy by clicking on it. :)
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Why hasn't his signature been removed?
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I think it is just a case of banning him when Dave gets around to it, in the mean time we will ping rubber bands at him and laugh at him (or her or it)
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Well, Dave has tried to "measure" the resistance of a 240V line with a multimeter several times...
But yeah, a multimeter has a very high resistance when measuring voltage (most are 10M, some can go higher) and a low resistance when measuring current (depends on range setting for normal type, "zero" for a Hall effect meter).
I wonder if that was the ghost of Brittany Murphy...