[volt-nuts] Fluke 893 vs 895.........or other?

[Todd Micallef]

David,

Congratulations on your new (to you) gear. I had typed a long drawn out
response that was putting me to sleep. I decided to reduce it to a "couple"
of paragraphs.

The problem with testing / calibrating standards and references is that you
need an even more accurate measurement system, a catch-22. The differential
meters called out in the procedures have to be within spec to be of any
use, especially the 931B. The only way to know this is to run their
performance test or send them to a cal lab. My thoughts are that you might
be better off getting a DMM that can give you more manageable calibrations.
It may not have the same short term accuracies, but you won't have to
adjust pots every 60 days(or less) as called out in the 895A calibration
procedure. This meter would be your home lab transfer standard.

Since you are using large rack mountable gear, I would add a good bench
meter to the calibration setup. One of my favorites is the Fluke 8506A. It
is not the smallest or newest DMM out there but it has great AC/DC specs.
It also has 7 1/2 digits on the 10V DC range. You could substitue it for
the Fluke 540B/931B, the differential voltmeters, DC Voltmeter, etc... in
the calibration procedures. I think that you would find it easier to send
to a cal lab than an older diff voltmeter. I prefer them with the
resistance option. Unfortunately, the current shunt option does not support
AC and you cannot have both resistance and current options installed. They
are mutually exclusive.

The 845AB/AR are good null meters. The AB has slightly better specs, but
the AR is rack mountable. If you haven't guessed, I have a fascination with
rack gear that goes back to my Army days. The Keithley 155 is also good,
and has a solid-state chopper as opposed to the photo choppers in the 845.
I have the 845AR and I recommend it since the other null meters seem to
typically carry a higher premium on fleabay.

I think it comes down to the level of accuracy and precision needed for
your home lab. My home lab gets a voltage reference, standard resistor, and
a couple of DMM's calibrated. The rest of the gear gets tested based on how
well I can transfer those cals to my other standards.

I am currently reading a book from Fluke called Calibration: Philosophy in
Practice. It seems to be a collection of everything I have found online
about calibration, but contained in one book. It is worth the money if you
can buy it used.

Looking back, this response is probably longer than the original.

Todd



On Tue, Nov 4, 2014 at 8:46 AM, David Garrido <d.garrido at me.com> wrote:

> Hello All,
>
> I am in the process of putting together AC/DC voltage standards in the
> home lab.  I want to add the necessary equipment to check out the gear and
> need a differential voltmeter / null detector as called out in the service
> manuals for the Fluke 5200A and 332D that I have recently acquired.   I am
> new enough to this that it would be helpful for me to have the brain trust
> here offer a little experience to my thoughts.
>
> The manual for the Fluke 332D stipulates that I need (2) 895A or
> equivalent.
>
> The Fluke 5200A manual calls for a Fluke 887A and a 931A or equivalent.
>
> And................................... I will be adding a Fluke 5205A to
> finish off the standards.
>
> There is a very nice 893A at a local shop with ALL factory new accessory
> cords and a fair price.  Will this fill the bill or should I be looking
> specifically for the 895, 887, and 931?
>
> Or................are there any others that are better suited, like the
> 845A.  Fluke has so many darn Differential Voltmeters and Null-Detectors
> that it seems a daunting task to sort it all out.
>
> Cheers,
>
> David
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