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Probably a dumb question

miller

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Or, why I'm not an electrician.
Kinda hope someone can give me a why on this.

Fooling with a couple fuel sending units, looking at ohms.

I have two different Fluke multimeters, one a 12, the other a 77BN. The ohms scales are different between the two. The 12's basic range starts at 400 ohms, the 77's at 320 ohms. No setting for 0-100 on either.
Just using the auto-range on both, checked ohms on the same sender at empty.

The 12 read 101 ohms, the 77 read 130 ohms. Is that because of the different basic ranges?
The test leads were hooked to same spots on same sender. Why the difference? Or is there some math involved?

Thanks, guys!
 
I use test equipment every day
Spec A's (Spectrum analyzers)
Digital O'scopes
TDRs (Time Domain Reflectometers)
Signal generators
etc.

1. It could be the test leads.
2. Calibration tolerance issues are always a factor.
3. Always use your lowest setting in this example. simply put, a 10% error at a Max resolution of 320 is significantly less than a 10% error at 400 scale.
(Typically, I would dismiss that error)
Remember in Instrumentation Test systems: there are 2 errors
A. Built in Errors (Test Sets)
B. System Errors (the fault in the system being tested)

Try at the 1K Ohm setting...
 
I love my Fluke meter because you really have to do some thing stupid to kill it
but I have other meters that are more accurate and read higher OHMs but die if hooked up wrong
 
You need to check the resistance in the leads to get an accurate reading. I use a fluke daily and there is resistance in the leads the meter will read. So if this is not recorded it will add to the value.
 
Maybe buy a resistor or two at radio shack in the range you are testing and see which one is off, resistors have an allowable variation of 5% I think.
My Fluks reads 0.1 ohms when I touch the leads together, not enough to make a difference.
 
a tenth of an ohm wouldn't make a difference on a fuel sending unit. Gotta wonder what the OP lead resistance is would at least maybe explain 29 ohms difference between the two flukes
 
Make sure the tips of your leads are clean also!!!! Dirt and other gunk that gets on them can also cause anomalies in the readings.
 
Make sure the tips of your leads are clean also!!!! Dirt and other gunk that gets on them can also cause anomalies in the readings.



I agree as the dugital Fluke meters are so accurate and sensitive it only takes some grease or dirt on the lead clips to change the reading a little. Ron
 
My Fluks reads 0.1 ohms when I touch the leads together, not enough to make a difference.

Thanks for the ideas, guys! Yes, 440+6, on both Flukes, leads together, get a 0.1 ohms reading. Also had checked both sets of leads, both showing around 0.3.

My 30+ years old analog meter finally quit on me...wouldn't zero out on any ohms setting. It's resting at the dump.
My two youngest sons are electricians, the older a master, but both wire up houses and buildings.
The 77 was loaned to me by my youngest son, the 12 a gift from the other, though just used a few times.

One problem is the Fluke 12, seems the zebra strip under the buttons went south, and don't work. Any rate, just not understanding why the big difference in the reading. I'll play with it all more.
 
For what it's worth. Both sets of leads are clean. Checked ohm loss on both sets of leads, with both Fluke meters, and got 0.3-0.4 ohms.

Remember...I'm no electrician...strictly a nuts/bolts guy. Both of these Flukes have ohms and continuinty (can't spell this morning!) checks. If I understand things right, ohms is reading either (lol) continuenty, or resistance, right?

Using the continuanty test, getting a range of 6.0 to 84.0 on the sending unit. Why the difference between the two tests, since both read ohms? Probably get a hold of son in Seattle, and see if he can tell me, since he's the master.
 
Check the battery's or test with new ones in both as that is the push for the test
 
New battery in each meter, and checked the contacts. Son couldn't give me an answer either, on the different readings.
Going to square one, since I checked the chinese sender I got, before knowing the deal. I'll figure it out, one way, or the other. Gonna re-check, though on that china sender, was getting repeat readings across the sweep.
 
If the Fluke meters have not been checked at Fluke for a long time; then you need to send them in to be calibrated and tested; I am a HVAC tech/ and a licensed contractor. I send mine in every 3 years; I have 3 meters so I am not down while waiting. You can't assume anything; Cheap meters are just that cheap. However, you can check a known value to verify accuracy.
 
Thanks, uwss! Yeah, understand. Getting believable numbers now, except the fact my old senders are way out of range.

But, on a side note...the two Flukes I'm fooling with, the 12 a gift from one of my sons, only used a few times. Other, a 77 is on loan from other son. These are the first Flukes I've ever had my hands on.

Now for the funny! The like new 12 was/is acting flaky from word go. It has four buttons on it, that switch from one thing to the other. Only bringing this up, since it might help someone else.
First time I turned on the 12, 'seemed' to work okay, except the buttons would take their time doing anything. After that, three buttons...nothing. Put new battery in, no real change.
Did a search on Fluke 12 buttons, and read about possible bad 'zebra strip' needed to be cleaned. Okay.
Busted the thing down, all the way to the buttons. No zebra strip. What I did find is a small square circuit plate under the buttons. That circuit plate (on the back side) fits against an aluminum conduit plate. Understand, just doing a simple switch to read ohms, had to play with the button nearly a minute, before it would work.

That dang aluminum plate had several long scratches, in same direction, under two of the buttons! Rubbed 'em down flush with my fingernail. Now the ohms switch button works like a champ! But, no tango on the other buttons. Gotta wonder if that small circuit plate went south.

Kinda irritating, but might have to send this like new Fluke, to get fixed. Thanks for the info!!
 
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