| Electronics > Repair |
| HP 3478A: How to read/write cal SRAM |
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| lmester:
--- Quote from: fenugrec on January 22, 2020, 03:25:18 pm --- --- Quote from: lmester on January 22, 2020, 02:28:29 pm ---Would you or fenugrec be able to help me get the gain data properly re-packed? Also, let me know if I need to make changes in the unpack algorithm. --- End quote --- Sure, but as I mentioned we may be slightly wrong (or at least uncertain) about the decoding; it would be really good to do some kind of test as I described, before spending too much time on a possibly-wrong encoding implementation. --- End quote --- That sounds good. Apply a fixed input to the meter and then enter various gain values. Is this correct? The most stable reference for me would be a resistor. I assume it won't matter which function or range is used. You only want the meter response to changes in the gain value. |
| fenugrec:
--- Quote from: lmester on January 23, 2020, 12:36:13 pm ---[...] I assume it won't matter which function or range is used. You only want the meter response to changes in the gain value. --- End quote --- Correct. And to make the math easier, set the Offset for that range to 0 too. Your resistor can be fine as long as you can ensure a tight connection for the duration of the tests; in 5-digit mode the last digit(s) should be pretty stable and repeatable. If not, @Miti can probably help (again !) Gain constants: I think these should cover all edge cases: --- Code: ---00000 00700 00800 00900 00a00 00f00 90700 77777 88888 99999 --- End code --- |
| Miti:
And how do I send these raw gains? I would have to read the calibration constants, modify the gain for the 3V range, calculate the checksum, upload the new constants? |
| lmester:
--- Quote from: Miti on January 23, 2020, 10:53:37 pm ---And how do I send these raw gains? I would have to read the calibration constants, modify the gain for the 3V range, calculate the checksum, upload the new constants? --- End quote --- That's what I'm testing now. I modified my cal edit program to accept a raw gain value. I enter 0 for the offset and 5 hex digits for the gain. The program calculates the checksum and sends the new cal entry to the meter. I then log the new reading from the meter. If you're interested I can put the modified program up on my web site. I may need to hold off on this and just let the meter run overnight. It's been on for several hours. The reading started at .68324 K Ohms it's slooowly decreased to .68311. I'm assuming that the meter and the resistor that I'm measuring have not yet reached a stable temperature. Just looked over at the meter reading. It's been stable during the time I was typing this. I'll try to get some more data. |
| Miti:
--- Quote from: lmester on January 24, 2020, 12:15:48 am ---That's what I'm testing now. I modified my cal edit program to accept a raw gain value. I enter 0 for the offset and 5 hex digits for the gain. The program calculates the checksum and sends the new cal entry to the meter. I then log the new reading from the meter. If you're interested I can put the modified program up on my web site. --- End quote --- Sure I'm interested. Even if you do this experiment, I still intend to do it in the weekend. |
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