Author Topic: Fluke 45 bench top DMM broken?  (Read 350 times)

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Offline newtekuserTopic starter

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Fluke 45 bench top DMM broken?
« on: June 16, 2024, 06:07:21 am »
I acquired an old Fluke 45 DMM off eBay a while back, been using it to measure voltage and resistance and recently been wanting to also measure the power draw on my circuits instead of relying on my bench top power supply.
I connect the red lead  to the red terminal on the DMM, the black lead connected to the 10A terminal instead of COM, then I push the A (DC) button and connect the black lead to ground in my circuit and the red lead to power in my circuit but the DMM does not read anything.
My circuit does draw about 1A. I took the DMM apart and all fuses read ok for continuity.

Am I using it wrong, or could there something be wrong with the instrument?



 

Offline BennoG

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Re: Fluke 45 bench top DMM broken?
« Reply #1 on: June 16, 2024, 07:29:38 am »
Yes, you do it wrong. You need to use the COM and 10A jack for current measurement.

Benno
 

Offline Gyro

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Re: Fluke 45 bench top DMM broken?
« Reply #2 on: June 16, 2024, 10:25:32 am »
I Suggest you download and fully understand the manual if you don't already have it. It's very important to understand the connections (and other stuff) if you intend to avoid damaging a good meter, it will save you time in looking for non-existent faults too...  https://www.manualslib.com/manual/52680/Fluke-45.html
Best Regards, Chris
 

Offline Stray Electron

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Re: Fluke 45 bench top DMM broken?
« Reply #3 on: June 16, 2024, 01:24:21 pm »
I acquired an old Fluke 45 DMM off eBay a while back, been using it to measure voltage and resistance and recently been wanting to also measure the power draw on my circuits instead of relying on my bench top power supply.
I connect the red lead  to the red terminal on the DMM, the black lead connected to the 10A terminal instead of COM, then I push the A (DC) button and connect the black lead to ground in my circuit and the red lead to power in my circuit but the DMM does not read anything.
My circuit does draw about 1A. I took the DMM apart and all fuses read ok for continuity.

Am I using it wrong, or could there something be wrong with the instrument?

  Your meter is probably ok but you're using it incorrectly.

  Use the Red connector (for voltage measurements) or the 10 amp connector (for high current) or the 100 Ma connector (for low current) but only use one input a  time.  The Black connector is the return connector and is used with both voltage or current measurements.   Just about every meter out there works the same way; they have separate inputs for voltage measurements and for current measurements and many also have two current inputs, one for high current and another for low current.  So three different inputs and only one return.

   Everytime that you use your meter you need to be absolutely SURE that you don't have your meter wired for current measurements and then try to measure voltage or you will probably burn something up.  When I use a meter I always start by unplugging the red lead from the meter and then setting all of the switch settings and only then do I plug the red test lead back in to the correct input.  That makes me THINK about what I'm doing and helps keep me from accidentally connecting power (particularly voltage)  to the wrong input jack or with the wrong switch settings. 

   The Fluke 45 is a good meter and can display readings that few other meters are capable of.  I have one on my desk but I only use it for special occasions.  I use a cheaper, more easily replaced meter for general purpose use.  I treat all of my GOOD meters the same way. I use a cheap, junkie meters for just about everything and I only use one of GOOD meters when I need them for their accuracy or speed or some other special feature.

   The Fluke 45 has features (display modes) that are pretty unique to it alone so my advice is to be very protective of it and take very good care of it.

   For what you're tying to do, turn on the -45 and them press the A === button to put it into the DC Amps mode. Then connect the 10 amp input of the -45 to the + output of your power supply then connect the black input of the 45 to the + input of your load. Then connect the return connection of your load to the return connection of the power supply.  The 45 should then show exactly how much current the load is drawing from the power supply.  If you load is only drawing a very small amount of current ( less than 100 Ma) then you can unplug the lead going into the 10 Amp input and plug it into the 100 Ma input to get better resolution. But I always start with the highest current range available just in case the load is shorted or there is another problem. 
« Last Edit: June 16, 2024, 01:34:24 pm by Stray Electron »
 


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