Difference between Resistance mode and Continuity mode of a multimeter ?

Thread Starter

Ravi Teja 2

Joined Dec 5, 2016
17
Hi Everyone,

I have a very basic doubt and i don't have an answer for it. I would like to know if there is any difference between resistance mode and continuity mode in a multimeter when using it to check for short circuit.

The reason i am asking this question is that, today while i was debugging a faulty board i wanted to inspect if there is any short between Vcc and GND, so for that i put my multimeter in continuity mode to check.

My mentor asked me not to do that and instead asked me to check for short circuit keeping multimeter in Resistance mode.( He says that probing the PCBA using continuity mode may cause damage to some components) . Is this a valid reason ? Please educate me.
 
Last edited:

Wolframore

Joined Jan 21, 2019
1,257
I would say that it depends on the meter. The meter injects a small voltage to determine continuity; if the meter is injecting for example 9 volts to parts that can only take 1.6, 3.3 or even 5 V... I suppose it's possible you may damage components.

I'm pretty sure mine sends about 3V through it since it will light an LED.

So if you wanted to be absolutely safe without knowing the particular meter (i can't seem to readily find this information). Yes resistance is safer to use.
 

dl324

Joined Mar 30, 2015
8,900
It depends on the meter.

These are the specs for my Simpson 467 on resistance/continuity:
upload_2019-8-6_9-5-39.png

Continuity checker uses the 2k range.
upload_2019-8-6_9-8-30.png
 

Ylli

Joined Nov 13, 2015
776
Resistance measurements generally use a fixed voltage and measure the amount of current flowing with an external resistance connected. The max current will be limited and the applied voltage is dependent on the particular meter. Read the manual.

Continuity/diode measurements use a constant current source and measure the voltage dropped across the external device. That's why you see a typical P-N junction showing about 0.65 on the continuity scale. Again, for specifics, read the manual.
 

dl324

Joined Mar 30, 2015
8,900
@Ravi Teja 2

What this boils down to is you need to check the specs for your DVM.

Here are the resistance specs for my Fluke 8010A:
upload_2019-8-6_15-42-47.png
 

MaxHeadRoom

Joined Jul 18, 2013
19,029
As noted, the continuity or Diode range, uses a voltage in order to forward bias a diode in order to check conduction, and actually indicates forward drop.
On my Fluke, there is also a beep at different levels of continuity, 0Ω-20Ω 20Ω-200Ω etc.
Max.
 

Reloadron

Joined Jan 15, 2015
4,508
This all depends on the meter as was mentioned. Just as an example the following is taken from a Fluke 87 DMM manual.

Resistance Mode:
The meter measures resistance by passing the same current through a precision reference resistor and the external circuit or component, then ratios and measures the voltage drop across each (Ω = Vunknown/ Vreference). Remember, the resistance displayed by the meter is the total resistance through all possible paths between the probes. This explains why in-circuit measurement of resistors does not often yield the ohms value indicated by the resistor’s color code.

Most meters I have used, the better ones all use this method.

Continuity Testing is a different story:
Beeper Response in Continuity Test
Input Range Beeper On If
400.0Ω < 40Ω
40.00 kΩ < 200Ω
400.0 kΩ < 2 kΩ
4.000 MΩ < 200 kΩ
40.00 MΩ < 200 kΩ

The meter will auto-range and if the value is below a given threshold it will beep. The current in the loop will vary depending on the range be it manual or auto. The Typical Ohms Short Circuit Current is all covered by range on page 37 of the user manual. So it all depends on the range and meter type but yes, generally speaking the lower ranges use a higher current so choosing a resistance range, again depending on the meter, is a logical choice. Just depends on the meter.

Ron
 

dl324

Joined Mar 30, 2015
8,900
My HP3438A uses the constant current method with an open circuit maximum of 5V :
upload_2019-8-6_16-59-6.png
 
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