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| DIY scan card for Keysight 34970A |
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| strawberry:
I have 3 empty slots |
| voltsandjolts:
OK, my SSR scan card seems to be working nicely, for 2w and 4w measurements. I'll add some comments to the code and tidy the schematic. Note that the 34901A card allows multiple channels to be closed at the same time, my card doesn't support that mode. In 2w mode, only one of the 20 channels can be closed at any one time. In 4w mode, the channel pairing works as it should, so one channel from each 'bank' is closed. Note also my card doesn't have hardware implemented for ch21/ch22 current measurement. Neither does it have the cold junction tempertaure sensors, but you can use an RTD instead (see 34970A manual), although that uses up one channel. Scaling for the CJ measurements sent to the dmm is not yet fully understood. I think this is the first 3rd party card for the 34970A/34972A. Since the dmm and cards are obsolete, this might breathe a little more life into them. The card is SSR so nice and quiet but with the protocol documented its easy enough to make your own custom card if you prefer armature, or want to add any of the missing features. Thank you for your help H.O. :-+ |
| voltsandjolts:
--- Quote from: H.O on June 05, 2022, 05:20:46 pm ---The scaling for the reference juctions is weird. It's not the 12bit format shown in the datasheet because the card returned values where the low 4 bits are not all zeros. My initial value of 125/32000 does not quite match, neither does 125/32768. My (genuine) card returns 0x17E4 for a reported temperature of 23.0156°C but the above scale factors eqauls 23.89 or 23.33. Like you say, there does not seem to be any calibration data transfered from the card. --- End quote --- I programmed my card to return that same value 0x17E4 and expected to see the same temperature reading as you. Nope! :o I got 16.464°C from my 34972A I am confused about this, it's as if the calibration is somehow transferred to the dmm, but I still have not seen that on the uart bus. Edit: I am reading CJ temperature using these remote commands: inst.query('SENS:TEMP:RJUN? (@305)') #bank1 CJ inst.query('SENS:TEMP:RJUN? (@315)') #bank2 CJ How are you reading the CJ? Maybe you're shorting the channel input and reading temperture from the channel? |
| strawberry:
''These adjustments are plug-in module specific and only affect thermocouple measurements. The calibration constants created by these adjustments are stored in non-volatile memory on the plug-in module.'' p112-113 could see eeprom cal data while requesting temp DS75 max 2degC error |
| voltsandjolts:
--- Quote from: strawberry on June 09, 2022, 10:43:28 am ---could see eeprom cal data while requesting temp --- End quote --- I thought that any cal data would get read at power-on but don't see it there. Maybe I'll try a long one minute capture just to be sure. I also looked for it upon the first CJ reading after power-on but again I didn't see anything. But yeh, it must be there somewhere, I just need some more time on it but can't right now. |
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