Re: Fluke 8600A -- a new question about calibration


"Rich Koerner" <richk@xxxxxxxxxxxxx> wrote in message
news:48E89A84.7B65BC22@xxxxxxxxxxxxxxxx


"Phil S." wrote:

I put a "precision" 1 ohm resistor on both meters this morning. The
Tripplett reads 1.3 ohms and when its leads are crossed, they read 0.3
ohms,
telling me that the Tripplett doesn't correct for the inherent resistance
of
the probe leads. This is an auto ranging meter. That's also why the
Tripplett tells me the 2.7 ohm 25W sandblock is 3.0. I've been aware of
this since I got the meter.

The Fluke reads that resistor correctly at 1.0 when manually set to the
upper ranges. The low ranges (200z, 2k, auto) seem to have a problem
with
this internal resistance of the probes and possibly part of the circuit,
displaying in excess of 2 ohms. Is this an issue the calibration tech
will
consider in what he does to calibrate the meter, or what?

If this won't change, the incentive to pay for calibration goes way down.
If I am reasonably sure setting the meter to a higher range will get my
question answered with reasonable accuracy, then, I'm thinking, why
bother
and why spend the money? I don't have a burning desire to know the meter
is
99.999999% accurate.

Those of you who have any sense of my mindset must know that I'm a
bargain
hunter. It's kinda like the smoke in a tranny, once you let it out...if
I
have to spend too much to get this meter in shape, it takes the fun out
of
it. Truthfully, though, even if I spend a few bucks, it looks like I get
to
have a good pro-grade meter on my bench and I've been wanting that for a
while.

I"m on the fence with sending it for calibration. So, just taking
opinions
here a second time and just trying hard to set my expectations
appropriately..

Thanks.

--Phil

Phil, every bargain has its price.

Of course it does! I was bargain hunting!


A calabrated piece of gear has its value.


IMO, moreso to a pro tech than a casual user. Still, I agree with this.

Keep subtracting the probe resistance, and stay with the Tripplett?


No, that Tripplett has other issues, as well. I've been hankering for
something better. It will make a nice backup meter from this point forward.
Also, it measures capacitance, and, while probably not extremely accurate,
give me a decent idea of whether a cap should be tossed out, but this
diverges from the topic.

With my 8600A, I always have to account for the probe resistance in the
low range.

This is precisely my question.

Circuit contact points have to be made correctly, and the meter side plugs
have to be spun around a few times to
insure good contact.


OK, that's not in the manual <grin> and why I'm asking. I might have
figured this out and might not have.

THAT, goes with territory with any meter used in the very low resistance
ranges.

Uh, huh, I can live with that. Like I said, where should I set my
expectations? This is the answer.


When I got my 8600A, it had been cal'd, and the probes when shorted would
read zero. A few days
later, it would read .1. Twist the plug ends in the meter, and its back
to zero again.

Clip leads to the chassis from the meter ground side in low resistance
measurements are never good
practice in low resistance measurements. Very hard and extremely sharp
probe tips on the contact
side is the only way to make good probe surface contact in the low
resistance measurment game.

Your measurement technique becomes very important, even when you have the
best set of probes.


I've noticed this. There are times when it is hard to get a meter to
stabilize. Without a mentor present to show me, I've been guessing what I
should do. Believe it or not, these words are very helpful.

When you pinch the leads of a resistor to the ends of the meter probes,
did you scrape down the
resistor leads to get all the oxide off for good meter contact?


I'll plead the 5th amendment here.


Check yourself out.


I think you just did! Thanks again.

BTW, I'm in the middle of the battery replacement job. It is a PITA to
thread those leads and screw together the battery retainers. I've got one
screwed to the board, but only two of the 4 black plastic feet actually
seated properly in the holes. When I saw this, I thought I'd sleep on it.
After a decent night's sleep, I see the wisdom in pulling it off and making
it exactly as it should be and not just settling for "almost". It's one of
those jobs that would go much faster with 3 or 4 hands attached to one
brain.



Regards,

Rich Koerner,
Time Electronics.
www.timeelect.com

Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers

--Phil


.

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