Electronics > Repair
HP 3478A: How to read/write cal SRAM
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pigrew:

--- Quote from: ErnieW on September 01, 2019, 12:35:42 pm ---Thanks, this worked for me. But would be nice to see an interpretation of the cal values.  :)

--- End quote ---
I'm glad it worked. I doubt I will get around to updating the software any time soon (I don't have a business of changing 3478A batteries...). However, I would accept github pull requests.
alocam:
Hello,

I have two HP3478A meters that I purchased recently, and it looks like your program would be nice to get the cal data our for backup purposes. However, I only have access to an HP5810a GPIB ethernet gateway.

Do you know whether it would be feasible to reconfigure the program to make it work with such GPIB interface instead of the USB one?

Regards!

fenugrec:

--- Quote from: alocam on October 05, 2019, 10:10:34 pm ---HP5810a GPIB ethernet gateway
--- End quote ---

Most likely, reading cal constants is very simple ( https://github.com/fenugrec/hp3478a_utils/blob/master/hp3478util.c#L258 ) and should be easily programmed or done manually with any GPIB interface. You'll have to work out the details of how to program yours though, how to use its API etc.
lmester:
Thanks to code provided by steve1515 I've now added the ability to edit the gain and offset for each calibration entry into my HP3478A control program. This lets you "tweak" your cal without going through the full calibration procedure.

https://mesterhome.com/gpibsw/hp3478a/index.html

I have some questions that steve1515 or others on this thread may be able to answer.

What is the valid range for the gain value? It seems that Steve's algorithm (or my implementation of it) fails when the gain is outside the range of 1 to 1.055555. Have any of you seen a gain value outside of that range? If so, I'll need to do more work on the cal edit feature in my program.

fenugrec:

--- Quote from: lmester on January 19, 2020, 05:39:59 am ---It seems that Steve's algorithm (or my implementation of it) fails when the gain is outside the range of 1 to 1.055555.
--- End quote ---

It should be possible to have gains up to 1.077777, and below 1 probably from 0.911112 if my math was right ? (doubtful, I can't remember the results in MAME)

He wrote his algorithm slightly differently to mine, and I just noticed a bug in mine - with that fixed, they should now be fairly equivalent. I haven't look at the disasm in a while though; and looking at some cal dumps now I'm not sure what we're doing is correct (i.e. subtracting those negative digits >= 9 from the whole gain constant). But I have a spreadsheet and some tests that would tend to confirm that, so  whatever. Some example gain constants :


--- Code: ---gain_const gain
13F1C 1.012906
fff1c 0.988906
88888 0.911112

--- End code ---
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