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| HP 3478A: How to read/write cal SRAM |
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| Miti:
--- Quote from: fenugrec on March 28, 2018, 02:16:06 am --- --- Quote from: Miti on March 28, 2018, 01:54:16 am ---So you say the calculations are done in BCD? Looks stupid to me... --- End quote --- Hehe, say not stupid, but rather out of fashion. --- End quote --- Sorry, I corrected it. :-DD Interesting, the offset constants seem to be BCD but the "gain" is in hex. Maybe all the calculations that involve mult/div are done in hex, then it comes the conversion to BCD and the offset is applied right at the end. |
| fenugrec:
--- Quote from: Miti on March 28, 2018, 02:20:36 am ---Interesting, the offset constants seem to be BCD but the "gain" is in hex. Maybe all the calculations that involve mult/div are done in hex, then it comes the conversion to BCD and the offset is applied right at the end. --- End quote --- Quite possible. Would you have time to run a few more tests ? As long as your 9V battery is stable (ideally to the last digit) that would be fine. Or maybe on one of the resistance scales, the readings will probably be even more stable . The test would be to modify, individually, some of the the 5 "gain" digits, by + 1 and - 1. I think that would give more insight into the math used. For example these test values for the 30V range: --- Code: ---13F1C (your initial gain) 23f1c 03f1c 14f1c (change just the second digit) 13e1c (change just the third) --- End code --- I'd do it myself, but I'm away from my gear for a few weeks ! [EDIT] Check it out, I updated the dump format : --- Code: ---# offset gain? range 00 000109 14F40 30 mV DC 01 000009 13411 300 mV DC 02 000001 134F5 3 V DC 03 999994 13F1C 30 V DC 04 999999 13FE1 300 V DC 05 000000 00000 (Not used) 06 000324 135D3 ACV 07 999977 05D30 30 Ohm 2W/4W 08 999998 04210 300 Ohm 2W/4W 09 000000 042F2 3 KOhm 2W/4W 0A 000000 04F35 30 KOhm 2W/4W 0B 999999 0403F 300 KOhm 2W/4W 0C 999999 04F0E 3 MOhm 2W/4W 0D 999999 03552 30 MOhm 2W/4W 0E 999844 2315D 300 mA DC 0F 999984 23D24 3A DC 10 000000 00000 (Not used) 11 000118 23EF1 300 mA/3A AC 12 000000 00000 (Not used) --- End code --- See how the "gain" values are similar within a same mode ! |
| Miti:
--- Quote from: fenugrec on March 28, 2018, 03:01:35 am --- Quite possible. Would you have time to run a few more tests ? As long as your 9V battery is stable (ideally to the last digit) that would be fine. Or maybe on one of the resistance scales, the readings will probably be even more stable . --- End quote --- I forgot to mention that the battery went down a bit during my experiment yesterday so for stability to the last digit I'll have to use a 3V reference that I have (a 0.02% linear regulator). Give me the values that you want to try for the 3V range. |
| fenugrec:
--- Quote from: Miti on March 28, 2018, 11:14:26 am --- I'll have to use a 3V reference that I have (a 0.02% linear regulator). Give me the values that you want to try for the 3V range. --- End quote --- Perfect ! how about --- Code: ---134F5 (orig value) 234F5 034F5 144F5 (2nd digit) 135F5 (3rd digit) optional: 134E5 (4th) 134F6 (5th) --- End code --- The last two (4th and 5th digits), not really necessary I think. I'm still not sure if that 5 digit "gain" group is actually two or more separate constants - as you know, the ranges can be calibrated either using a fullscale value or 1/3 FS (1V, 10V etc..) , maybe that makes a difference on the constants. What would be sad is if this was just a raw number/command sent to the ADC section that directly affects the conversion process, and don't really equate to a linear gain correction. |
| Miti:
Here you go. Every more significant nibble is 10 X the one before it. I would expect 16 X...or? Regarding the calibration at FS or 1/3 FS, I don't think it needs separate variables. The gain can be calculate either way, you just need to detect the level and you loose some precision at 1/3 FS. |
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