Calibration Of Electronic Equipment In The Home Workshop

[Jim Yanik]

Check; the neatthing is that on higher voltage scales, the input
resistance exceeds that of a DMM.
Which is why i built a voltmeter/currentmeter around a 5 microamp
movement giving 200K per volt sensitivity.

Then there's the Fluke differential voltmeters,that have nearly infinite
impedance at null. ISTR a HP diff VM that had a 100Meg Z on it's off-null
mode.Then there are Keithley hi-Z meters,with gigohm input Zs.

 

[Robert Baer]

Here's a couple of beauts:
http://www.bkprecision.com/www/np_searchmodel7.asp?lf=Analog+Multimeters

That 114B is the best one..

 

[Robert Baer]

Then there's the Fluke differential voltmeters,that have nearly infinite
impedance at null. ISTR a HP diff VM that had a 100Meg Z on it's off-null
mode.Then there are Keithley hi-Z meters,with gigohm input Zs.

Wouldn't be neat to have a handheld differential voltmeter?

 

[MassiveProng]

Wasn't it you that said that certs
were often just a check not necessarily turning screws?

NO! I said that when you get your gear calibrated, it is typically
ONLY a verification of a good instrument.

Being off cal usually means something is awry.

What you are paying for is a VERY nice standard and a comparison
check against it. Of the hundreds of calibration sessions that we
have had done IN our lab, as opposed to sending the gear out, it was
done without them ever opening a single instrument.

 

[MassiveProng]

My first meter cost five times that, was analog, and only had 20K ohms
per volt.

For those young folk who aren't familiar with that, yes, the meter input
impedance changed depending on the range you set the meter to.

Lemmie guess... An RCA Master Volt Ohmist?

I still have one of those as well.

Have a couple Heathkit MMs around too.

 

[Anthony Fremont]

NO! I said that when you get your gear calibrated, it is typically
ONLY a verification of a good instrument.

Pretty close to the same thing to me.

Being off cal usually means something is awry.

What you are paying for is a VERY nice standard and a comparison
check against it. Of the hundreds of calibration sessions that we
have had done IN our lab, as opposed to sending the gear out, it was
done without them ever opening a single instrument.

IOW you didn't turn any screws, you just checked it.

 

[Anthony Fremont]

Anthony Fremont wrote:
That 114B is the best one..

Yeah, but it's not as good looking as the other one though. I just recently
saw another really nice, big analog meter that someone sells. It wasn't
cheap either, but I can't recall where I saw it. I was thinking it was in
my Jameco catalog, but I can't seem to find it in there. It looked allot
like the older ones.

 

[MassiveProng]

Pretty close to the same thing to me.


IOW you didn't turn any screws, you just checked it.

That is 99.999% of the time ALL they do.

That would be worldwide practice.

 

[Jim Yanik]

Wouldn't be neat to have a handheld differential voltmeter?

why do you need that accuracy in a handheld instrument?

 

[Jim Yanik]

Pretty close to the same thing to me.

I would say "accurate,traceable standard".

IOW you didn't turn any screws, you just checked it.

If it meets all specs,then there is no need for adjustment.

In fact,you might make it worse by tweaking on adjustments.
(some pots or trim caps on older instruments freeze in place and turning
them breaks them or they become noisy)

Instruments that have been adjusted have to be rechecked,as some
adjustments interact with others.Trying to "optimize" a range may throw
another range or ranges out of spec.

 

[clifto]

why do you need that accuracy in a handheld instrument?

I don't *need* a Ferrari, but it would be neat to have one.

 

[MassiveProng]

I would say "accurate,traceable standard".


If it meets all specs,then there is no need for adjustment.

In fact,you might make it worse by tweaking on adjustments.
(some pots or trim caps on older instruments freeze in place and turning
them breaks them or they become noisy)

Instruments that have been adjusted have to be rechecked,as some
adjustments interact with others.Trying to "optimize" a range may throw
another range or ranges out of spec.

All great reasons to abide 100% with my original reply.

So there, Too Much Toolessness!, you fucking RETARD!.

 

[Jim Yanik]

I don't *need* a Ferrari, but it would be neat to have one.

well,precision lab instruments are used in lab conditions,with at least 15
minute warmup times to allow the unit to stabilize,and to expect that
accuracy in a handheld that would be used in non-lab conditions....it
doesn't make sense.

BTW,when calibrating precision instruments,the unit under test has to warm
up and stabilize for 20 minutes minimum,and the lab has a controlled
temperature and humidity,usually 73+/-2 degF. Of course,your lab standards
have already been powered up and stabilized for the proper time.
Insturments used outside of specified temps were derated in accuracy.

I worked in a USAF depot-level primary standards lab.(PMEL)
(before repairing and calibrating for Tektronix for 21.5 yrs.)
My lab (L.G. Hanscom Fld) did the MIT-Lincoln Labs instruments,besides the
usual USAF stuff,covered Pease,Otis,and other military bases.

 

[Robert Baer]

why do you need that accuracy in a handheld instrument?

Someone asked the same question about a pocket scope.
I guess there are times and conditions when such "esoteric" equipment
would be nice to have.

 

[Palinurus]

NO! I said that when you get your gear calibrated, it is typically
ONLY a verification of a good instrument.

Being off cal usually means something is awry.

What you are paying for is a VERY nice standard and a comparison
check against it. Of the hundreds of calibration sessions that we
have had done IN our lab, as opposed to sending the gear out, it was
done without them ever opening a single instrument.

-
Odd, I've been working in a cal lab for the last few years, and I'd say
a good 10% of what we get has something wrong with it. Some of it is
designed-in problems, but most of the rest is due to impact damage or
contamination. Our customers are largely the petrochemical industries
along the Gulf Coast, and they apparently believe that if a piece of
gear can't survive a 1 meter fall onto concrete, or being rained on and
rattling around in the back of a pickup truck for a few weeks, than
there's obviously something wrong with it anyway. It makes for a good
business in replacing switching, connectors and cracked LCDs.

 

[MassiveProng]

Someone asked the same question about a pocket scope.
I guess there are times and conditions when such "esoteric" equipment
would be nice to have.

Ahhhh... the "nice" factor.

I think it would be nice to have a nice Agilent spectrum analyser,
or network analyser, but I don't have $60+k for each right now.

Maybe after I win the lottery.

 

[MassiveProng]

-
Odd, I've been working in a cal lab for the last few years, and I'd say
a good 10% of what we get has something wrong with it. Some of it is
designed-in problems, but most of the rest is due to impact damage or
contamination. Our customers are largely the petrochemical industries
along the Gulf Coast, and they apparently believe that if a piece of
gear can't survive a 1 meter fall onto concrete, or being rained on and
rattling around in the back of a pickup truck for a few weeks, than
there's obviously something wrong with it anyway. It makes for a good
business in replacing switching, connectors and cracked LCDs.

Which distinctly falls under the category of REPAIR, NOT
calibration.