DMM isn't working right...

[Klutch9]

I recently blew a 250mA fuse in my DMM. No biggie, I thought, I'll just buy another fuse. In case you were wondering, 250mA fast-acting 5x20mm fuses are nearly impossible to find in my neck of the woods. So I ordered some online. Anyway... ever since that fuse blew, my DMM will not measure resistance properly. Using resistors of known value, the meter always comes up with an extremely low number. For example, I measured several 680 ohm resistors, and for each one the meter read 4.2 ohms... huh? The meter still reads AC and DC voltage fine, continuity and the high-amperage measurement setting are all fine, too. Could the 250mA blown fuse somehow affect the resistance readings? I know that the resistance measurement works by passing a small amount of known current through the resistor, but if the fuse is blown, and the meter IS using the fuse for this function, I shouldn't be getting a measurement at all. Any ideas? The meter is of decent quality and only 6 months old.

 

[Donald]

What did you do to blow the fuse? Measure voltage using ohms? Sounds to me the fuse did not blow fast enough to protect things.

Is it under warranty?

 

[Chris142]

Battery ok?

 

[Quest]

sounds like your meter is damaged.

If it's under warranty, get it serviced.

Otherwise: buy yourself a new one instead.

(through the years I have quite a few bad DMMs and the only ones that I would seriously bother to send back for servicing would be my Fluke meters). All other cheepy DMMs not worth fixing IMO. Just go buy a new replacement instead.)


Q.

 

[Klutch9]

Originally Posted By: Donald
What did you do to blow the fuse? Measure voltage using ohms? Sounds to me the fuse did not blow fast enough to protect things.

Is it under warranty?


I blew the fuse on the 250mA setting, measuring a current that was higher than 250mA.

 

[edhackett]

That's typical of "cheap" meters, even from known brands. It's common for the meter to be damaged if the fuse equals the measurement rating, either in an over-range or trying to measure voltage in the ohms setting.

My Fluke is fused with a 1A fuse on the 40 mA setting and the 10A circuit uses a 15A slow blow that allows for 20A readings for up to 30 seconds. I also know from experience that the 15A fuse fully protects the meter in a cross measurement situation.

When purchasing your next meter, look for one that has some overhead in the fuse ratings.

Ed