[Test-Equipment] Simple DC Voltage Standard?

[jbarnes]

Group,

The LM399 is well known for its excellent temperature stability, however the initial accuracy, the factor that makes it useful as a transfer standard is 2%.

The Linear Technology LTZ1000A is a better LM399.In fact the LTZ1000a is found as the reference in the HP3458A 8.5 digit DMM. It has the same issue with initial accuracy.

The LC6655B is available in several voltages and has 0.025% initial accuracy.

Here is a link:

http://cds.linear.com/docs/Product%20Selector%20Card/2PB_6655.pdf

If you are building your own reference. You need to look at:

Temeperature coefficients in the resistors
Offset and offset drift in the op-amps
Thermocouple effects
Drift in the reference.

I have a Fluke 732A. This has been powered up for 5 years, with SLA batteries so it can be shipped under power for calibration.

If you are looking for a good working reference. Search for the Fluke 731A.

Regards,

John VE3XRY

---------- Original Message ----------------------------------
From: Bill Fuqua <wlfuqu00 at uky.edu>
Reply-To: Discussion of Electronic Test Equipment<test-equipment at mailman.qth.net>
Date:  Tue, 1 Mar 2011 10:49:44 -0500

>   Most people have access to an accurate meter via friends or
>work. They can simply check it there. If you are looking for a
>cheap and easy solution that may be it especially if you need
>a variable calibration source.
>    You can get from time to time the standard board used in
>HP's 8.5 digit meter, if you want a really precise standard. We have gotten 
>a 8 or 10 of those
>for the lab at work. They usually go for around $100 each. I think my 
>present source has dried up.
>These are often rejected by HP after calibrating due to an occasional noise 
>flicker but
>work very well 99.99% of the time.
>    You can buy a precise regulator chip but you should still verify your 
>circuit works properly somehow.
>An interesting note. The LM399 is available again. It is an active Zener 
>diode with a temperature regulator
>on the chip. Can't remember the supplier but I believe they have an 
>improved version.
>   People used to take the plastic thermo insulating shell off these and 
>attach them to
>crystals and other things to regulate their temperatures. Naturally you had 
>to surround
>the whole mess with thermo insulation.
>
>
>73
>Bill wa4lav
>
>
 




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