Hardware Quiz #7: Ohmmeter Function - Techist - Tech Forum

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Old 03-27-2004, 03:01 PM   #1 (permalink)
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Default Core Hardware Quiz #7

When using the ohmmeter function of a DMM to perform tests, you must always ______.

Answer: D - open the circuit that contains the device being tested

Explanation: To be perfectly honest, I want to get a good meter question in so I took this one directly from a solid source and a good quiz site. I received a PM saying that there could be 2 possible answers but I don't think that is accurate given the following explanation stright from the source. But, please, let me know if this is inaccurate.

"The ohmmeter function uses an internal battery to control the environment being checked. Therefore, it is very important that power in the circuit being tested be removed. In addition, at least one end of the component being tested must be disconnected from the system. This prevents any of the control current from the battery from being directed away through other circuits to which the device may be connected, which would cause the reading taken to be inaccurate."

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Old 03-28-2004, 02:19 AM   #2 (permalink)
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Love the results so far...hehehe

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Old 03-29-2004, 03:59 AM   #3 (permalink)
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I know this from Skool
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Old 03-30-2004, 03:08 PM   #4 (permalink)
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mikegroovin, the explanation is right. Had a friend in high school, we didn't know what the ohmmeter did, and he took and plugged it into a live outlet. Meter started smoking!

Talked to a former electrician here at work, and he said that in series could also be the answer.
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Old 03-31-2004, 12:08 AM   #5 (permalink)
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When using the ohmmeter function of a DMM to perform tests, you must always
You said Ohmmeter function. The Ohmmeter function is used to measure resistance. i.e. the value of a resistor when you are talking about components in a circuit.

To measure the value of a resistor, you MUST connect the voltmeter leads across the resistor, which means that the Ohmmeter is in parallel with the resistor. You don't measure resistance with the meter in series with the resistor...you can't.

Obviously, as you have quoted, at least one end of the resistor must be removed from the circuit. If you don't do that you could measure the combined resistance of another or several other components in the circuit. For example if you have another resistor in parallel with the resistor that you are measuring and they are both 10K resistors, the resistance you measure will be 5K (Ohms).

The above two reasons are why I said that there could be two correct answers to your quiz.

I chose the most obvious one "meter connected in parallel". If you don't connect the meter in parallel, you aren't going to measure the resistance of the component whether you take it out of the circuit or not.

Your electrician friend must have misunderstood the question that you put to him. There is no way you are going to measure resistance of a resistor with an Ohmmeter if you hook it up in series with the resistor. Any first year Electronics student will be able to tell you that.

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