I was given a Fluke 75 Series II recently. It works fine when measuring voltage, and I haven't tried measuring current.

When measuring resistances below about 100 ohms, I see it counting down slower and slower. For really low resistances (in the single digits) it can take a couple of minutes to stabilize. If I short the probes together, it just seems like it's going to count forever without ever getting to zero.

My questions:

1) Is this normal behavior?
2) Is it a common symptom of something?
3) If it's abnormal, is there anything I can do about it?
4) Or should I just not ask it to do what it doesn't like doing? Gift horse and all that.

educated opinions accepted with thanks

 

New battery?

 

New battery?

I was testing a car for parasitic drain on the battery. The way I went about it - before I knew better ways - was to watch the battery voltage as I pulled one fuse at a time. If the voltage jumped I figured that was probably the parasite. However, during the testing the indicated battery voltage started going up even when I didn't pull any fuses. It started out at 12.2V, then started climbing and climbing until the battery voltage read over 15 volts. The car was NOT running and there was NO charger connected. Then I replaced the battery in the meter and everything returned to normal. Eventually found that the electric door locks was to blame for the parasitic drain.

Yeah, you should start with a new battery. Cheap and easy fix. And I think it will likely work out well for you.

 

I could be that the lower the measured resistance the longer the meter needs to average the reading, especially in the presence of noise, but I doubt that Fluke would field a product that took more than a few seconds to register "zero ohms".

 

I know from experience that Fluke 77 has weird things happen when the battery is low, one is measuring double the voltage on the AC range.
Occurrence on more than one meter.
No "battery low" indicated.

 

I could be that the lower the measured resistance the longer the meter needs to average the reading, especially in the presence of noise, but I doubt that Fluke would field a product that took more than a few seconds to register "zero ohms".

Yes, I tried with several resistors below 200 ohms, and consistently found that the lower the resistance, the longer it would take for the count to settle down. At resistances in the single digits it never settled down before I lost patience.

 

How hard is it to put a new battery in it? Eventually it's going to need one anyway - so why not start there. Others have made the same suggestion. What's the fizzle?

 

I know from experience that Fluke 77 has weird things happen when the battery is low, one is measuring double the voltage on the AC range.
Occurrence on more than one meter.
No "battery low" indicated.

I pulled the battery out and measured it: 9.28 volts. I'll try another battery when I get out to buy one.

My other meter is an old Craftsman. I noticed that it also counts slowly on single digit resistors, but not nearly so slowly as the Fluke. Screen dims at the same time; probably the battery. Yep, new battery fixed all that. Takes a couple of seconds to settle on 1.1 ohm.

Here's something else: I've got a 100K 10-turn potentiometer that's open. The Fluke counts UP instead of down starting at about 10 meg. Counts beyond limits of my patience. The Craftsman starts at about 20 meg, jumps to 25 meg, then shows open (0.L). Disconnect and reconnect shows open. Disconnect, short terminals, reconnect does the quick count up to open again. Is this thing acting as a capacitor?

 

The Fluke counts UP instead of down

Acting like a capacitor. Could be measuring stray capacitance. Could be an anomaly of the meter or could be a host of other things.

The Craftsman starts at about 20 meg, jumps to 25 meg, then shows open (0.L).

Take a capacitor and test it for continuity. You'll see the same thing. Eventually you will go Over Limit. Reverse the leads of the cap and you'll see the numbers count down to zero then back up again til once again you are OL.

You say a battery rectified a lot of the issues? If so - great. Now you need to work on your test leads. Somehow they're finding stray capacitance (I think).

 

What I have discovered about multi-meters, both analog and digital, is that sometimes their function/range switch may need the contacts cleaned. So that may also be a possibility. Another time I was give a rather nice multimeter that had suffered the resistance check battery failing and contaminating the inside with a conductive film, but no corrosion seen. That repair required a great deal of washing the electronics with clean water, avoiding the meter movement, and then drying with an alcohol rinse.

AND, with one Beckman meter, measuring the resistance of a milliammeter movement, (100mA), the voltage generated by the movement of the coil started an oscillation that kept the pointer moving up and down the scale. That was interesting.

 

Service manual here
https://www.manualslib.com/products/Fluke-75-211535.html

Try changing the battery first..

 

Amazingly enough, when the battery voltage is outside of the specified limits for a device, the operation is also outside of the specified area. This is not a new thing, though.

 

Amazingly enough, when the batter voltage is outside of the specified limits for a device, the operation is also outside of the specified area. This is not a new thing, though.

Post #5

 

I had a reply this AM from new member steerage250 wanting to know whether I ever figured this out. His post is somehow disconnected from this thread, and I can't find a way to reply to it directly, so I'll answer it here and hope that he sees it: yes and no. Yes because the problem is fixed; no because I'm not sure what fixed it.

The new query kicked me in the right place, and got me to have another look. I cleaned the rotary switch with alcohol and some stuff in a bottle that I think is contact cleaner. Then I put in a new battery and shazam!!! I don't believe that it was the battery because I'd tried that before (got LOTS os suggestions to do that). On the other hand, I can't prove that it was the cleaning.

Best suggestion I can make is to try what I did but to use a good spray cleaner/lube. (The switch seems to have a back side that is inaccessible doing what I did today; a spray would reach it I think. I'll probably do that myself when I can get some spray.)

 

The meter uses a higher current to measure low ohms (it determines resistance by measuring the voltage drop generated by the meter's constant-current source), which likely causes a weak battery to slowly drop in voltage during the measurement, thus the meter has difficulty reaching a steady-state value.

 

When the low battery warning is active it is better to not trust the meter. The only promise is that it will meet the specifications with a good battery installed. with a weak battery "All bets are off."