Post Reply 
New (to me) HP 3421A DA/C Unit, some questions
05-11-2017, 06:52 PM
Post: #1
New (to me) HP 3421A DA/C Unit, some questions
I am in the process of familiarizing myself with the 3421A Data Acquisition/Control Unit. This is the one that was in the classifieds a week or so ago. The unit arrived in great shape and with the extras as advertised. I was surprised that on AC power the DAC exhibited no calibration or other errors on power up. It would not start up from battery power, but I expected that and I installed a new battery when I opened the case to check jumper configuration and satisfy my curiosity. "No user serviceable parts inside" - Ha!

Before I opened the case, I experimented with the Control Pac ROM module with the Front Panel program with my 82162A printer in the loop. As an example, using the DVC program, it would print voltages of several batteries as I put the leads to one battery and the next. For some reason this feature stopped working before I opened the case yesterday. The printer works with the DAC in the loop as long as I am doing something initiated from the calculator, like print a program. I have tried several configurations for the loop to no avail. I even tried using a 82134A printer (with the I-L module set to Disable) and it was a no go as well.

I have been looking in the DAC manual and the ROM manual to see if there is a setting for the DAC that I inadvertently set to "no print". Since the loop is working normally otherwise, it seems to me the problem is the DAC is not sending the appropriate I-L "print this" word to the Printer. The voltages in the 41 display are changing as I move from battery to battery, but they are not printing. Anyone encounter this before?

Now that a new battery is installed on the DAC I get one error on startup under battery power: Error 7, "Failed 10 Mohm test (not within +/- 20%)". I suspect that this might be due to calibration drift. On battery power, if I run the ROM "FP" program it reports an error and halts. Interestingly, this clears the error symbol on the DAC and I can now run the "FP" program again without the error. Is this behavior caused by an old calibration, or something else?

I tested the voltage of the calibration battery when I had the case open and it is 3.1ish volts. Lithiums drop off quickly when exhausted, I suspect this one is nearly there. I am aware of the posts here about how to change the calibration battery on the HP 3468 meter without loosing calibration. Anyone care to offer advice?

Finally, I would be interested to hear what have you done with your 3421. I had a project that involved simultaneous truthing of a batch of six oxygen cells for rebreather diving that the 3421 would have been perfect for. For that application I built a test rig using an HP 3468 meter and a CMT-200 DAC running a home made six channel switch box, so that project is done. I suppose if I could find a 4465A (Option 40) board I could use the DAC to run lawn sprinkler's at my house. ;-)

For now, I am trying to decide on a general configuration of the leads from the various channels. I am thinking about how to set up utilitarian pig tails for the actuator channels 00 and 01. Channel 02 is set up with the 10:1 divider so I am planning to use it as a AC power ON/OFF sensor for program decisions so it might just get a wall plug. I will keep at least one of the 4 T type thermocouple plugs and I want to add one or two K type plugs.

In order of appearance: HP 41CV, CMT-MCGPS, HP 41CX, DM 41, DM 42
Find all posts by this user
Quote this message in a reply
Post Reply 

Messages In This Thread
New (to me) HP 3421A DA/C Unit, some questions - 4ster - 05-11-2017 06:52 PM

User(s) browsing this thread: 1 Guest(s)