The continuity shows us the shorts, but many times I guess, even if the wire has a resistance of up to 50 ohm, the continuity will beep to indicate a short.
Is it always 50 ohm, or what parameter should we look for in the manual?
Electronic – Is the continuity test limit resistance of a multimeter standard
multimeter
Related Solutions
After you run this test for 10 minutes, wipe off the water and take a close look at the copper where the water drop was. You will see some discoleration. Essentially the copper was corroded a bit where the water drop was. As you probably notice, bare copper left in the elements is no longer that bright copper color after a while. The same thing happened to your copper electrodes, except that the electric current speeded up the process.
The reason the resistance goes up is because the corrosion layer has significantly more resistivity than copper. This is one reason the mating surfaces of electrical connectors aren't made from copper. They are usually made from material that doesn't oxidize, like gold or nickel, or forms a conductive oxide, like tin.
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!
Related Topic
- Electronic – What am I doing wrong here? LED and Multimeter [Noob]
- Electronic – Why won’t this bulb light when I put the multimeter in series
- Electrical – How to test the voltage of a speed sensor and identify the +ve, ground and signal wires using a DMM
- Electrical – Manually test computer Ethernet port with a multimeter
- Electronic – Why so much variance in the continuity beeper threshold? How do these beepers work anyway
Best Answer
It is not a standard value from meter to meter. Different models will beep at different resistances.
An example in the comments were the fluke models 175,177 and 179. In the datasheet for these, you can see on page 12 that the meter beeps at <25 ohms.
The multimeter I use is a Tenma 72-7732A, and in the datasheet for this model, on page 35 it is stated that the beeper will sound for conditions less than 50 ohms.
In the popular EEVBlog multimeter, page 25 of the Datasheet states the continuity threshold is between 30 and 480 ohms.
These few examples are enough to determine that there is no standard value. If the information cannot be found in the datasheet of your particular model, then getting a few resistors between 10 - 250 ohms and measuring them should be enough to tell you the threshold.
An easier way, as pointed out by @HarrySvensson in the comments is to turn a potentiometer/rheostat until the beeping stops/starts and measure the resistance.