I have a newbie question.
I'm learning about electrical engineering and I bought my first multi-meter. It has a feature called "Continuity Test". I believe this test is to make sure conductors such as wires and cables are continuous and not severed or perhaps you want to find the right circuit.
When I inspect a resistor with the multi-meter probes I can find voltage and current, but when I test for continuity the meter does not beep.
It's as if the two ends of the resistor were not connected somehow. I'm sure this is a laughable question for veteran electrical engineering people but why is it that a multi-meter would not register continuity through a resistor? What goes on in the continuity test so that it registers positive for continuity? Does a certain amount of voltage, current or perhaps the frequency needs to be equal through the circuit in order for the meter to consider continuous?
Best Answer
The continuity function is designed to give an audible indication of resistance that is less than some threshold value.
To be useful, it will be designed to respond much more quickly than the display so that a tech can quickly 'buzz out' wiring and such like without waiting for the reading to settle or even taking his or her eyes off the test probes. It's specifically designed so that the voltage does not turn diodes on, it won't respond to resistors above a certain value and so on, so that it (usually) responds to just a fairly solid electrical connection.
The values will vary somewhat by manufacturer, but here is an excerpt from the Fluke 177 DMM manual:
As you can see it has hysteresis and a pulse stretcher that allows brief breaks to be detected. This is done by circuitry that is mostly operating in parallel to the main ADC function. Some crummy cheap meters have a continuity beep that is dependent on waiting for an ADC result, but they are not very useful. Avoid!