GOOD hamfest!

From: cem14_at_cornell.edu <(cem14_at_cornell.edu)>
Date: Mon Sep 13 20:31:13 1999

On Mon, 13 Sep 1999, Tony Duell wrote:

> > FWo [channel list] Four-wire ohms; needs special connections and two
> > multiplexer assemblies.
>
> Or from the 4 sockets on the front panel if you don't need multiple
> channels ?

Yes.

> > One thing _not_ to do with an HP3421: if you remove a
> > multiplexer assembly and turn the thing on, it will notice
> > that it is missing, and the next time you plug it in, it
> > will label the assembly as "uncalibrated", requiring you to complete
> > the calibration procedure (all calibration is done in software).
>
> Uh-Oh... I am _sure_ I've done this to mine. If it's uncalibrated, does
> it just not work until it's recalibrated, or does it give suspect
> readings, or what. How hard is it to calibrate one?

If it's uncalibrated, it will report a "calibration RAM checksum error"
in the POST (more later). The first reading taken from it will be an error,
then it will continue to work fine.

The reason why these assemblies even have to do with the calibration
constants is that a temperature reading is taken from the assembly's
sensor for the purpose of cold junction compensation, and this reading
must be calibrated.

It is not hard to calibrate an HP3421 with the right equipment. You
need a voltage standard capable of supplying 0.3V, 3V, 30V, 300V,
and 3Vrms at 100Hz, a 6.5 digit multimeter, a thermometer with 0.1C or
better accuracy (HP wanted you to buy a special part #, (a thermistor)
that you would use with the temperature function of the 3456A, just for
this), and the following resistors: 100 +/- 0.0005%, 1K +/- 0.0005%,
 10K +/- 0.001%, 1M +/- 0.002%, 10M +/- 0.01% .
Basically, you turn off the power first (never power down
the 3421 with the calibration enable switch enabled! cal. RAM corruption
may result), set the calibration switch to "enable", power up,
clear any error conditions from the status, set the appropriate range
and function to calibrate, feed test voltages to it while you tell it
to compute the calibration constants. Then you disable the calibration
switch, power off, power on back again and that's it. I can give more
details on request. Just let me write something more about the POST:
the LCD shows the results of some tests. If something is wrong,
the arrow next to the "error" sign will light up, and the error numbers
will appear for about 1 1/2 seconds before the LCD returns to its
normal function of displaying which channels are closed.
The error # 's are as follows:

    0 Calibration RAM checksum error
    1 ROM 1 bad
    2 ROM 2 bad
    3 A/D slope error
    4 uP RAM bad
    5 Internal RAM 1 bad
    6 Internal RAM 2 bad
    7 Failed 10Mohm test (not within 20%)
   27 Low battery, unit will shut off in 3 seconds.


> Thanks for the info!
>
> -tony

You're welcome.
Received on Mon Sep 13 1999 - 20:31:13 BST