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TDS8000 DC calibrator adjustment procedure

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jayw_comark
Posts: 36
Joined: June 5th, 2012, 4:45 am
Country: United States

TDS8000 DC calibrator adjustment procedure

Post by jayw_comark » August 27th, 2014, 3:07 am

Hello all,

I've just replaced the dead NVRAM batteries on the ACQ board and the NLX processor board. I've re-programmed the NLX board via the serial port interface so now the scope boots up into the oscilloscope application OK. Signal path compensation for the mainframe passes OK, but the scope application reports an error 171 NVRAM data integrity. Not surprising since the cal constants for the ACQ board were lost due to the dead battery. So, now I'm trying to run through the calibration procedure listed under the "adjustment procedures" in the service manual. This is where the problems start. I'm trying to do the DC calibrator adjust and I'm getting rather bizarre results. First off, the DC cal voltages with the default settings before calibration are pretty good - when I set the output to +1VDC the output is with 5mV or so. However when I go through the calibration procedure and save the results using the GPIB command CAL:SAVE:FACT:MAI and then SYST:PROT ON
the DC calibration output is completely screwed up! When I set the voltage output to be +1.0VDC, the output swings to -1.0VDC!

At this point I went back and went through the procedure again, thinking I made a mistake somewhere, but got the same result. I've had a talk with a T&M dealer that I know pretty well and asked them if they've ever done this procedure in the service manual and they told me that they've had the same problem when attempting this procedure on a CSA8000 and had to resort to getting a professional calibration done (possibly Tektronix factory) to correct the problem.

I am beginning to think there is an error in the service manual. Has anyone ever successfully done this procedure or know where the error in the manual lies?
Perhaps there is an error in the formula on the third page of the procedure:

9. Enter the following GPIB command to set the instrument’s
calibrator to --1.0 V:
CALIBRATE:DCCALIBRATOR --1.0
Record the DMM reading (reading2).

Calculate cal constant as follows:
(–1.0 * Reading2 + Reading1)
________________________
2

10. Enter the following GPIB command to set the instrument’s
calibrator Lsb cal constant:
CALCOMP:DOUBLE “DcCalLsbAdj”,calculated result from Step 9.

Thanks for any help!

Jay

cap
Posts: 397
Joined: May 1st, 2009, 8:16 pm

Re: TDS8000 DC calibrator adjustment procedure

Post by cap » September 1st, 2014, 5:09 pm

Hello,

Try, :calcomp:double instead of CALCOMP:DOUBLE.

The following may help. Notes and memory joggers for me to remember how to calibrate these. I do recall there was a step(s?) where the capitalization of the gpib commands had to be just right, and not as documented, looks like I changed all of the gpib commands to lower case...

Unprotect the cal memory by toggling the memory write protect swith (to the outside hole).

:syst:prot off

:calcomp:double "DcCalOffsetAdj",4.0e-4 ; this is equivilent to a positive 4mA shift.
(querry form, :calcomp:double? "DcCalOffsetAdj")

:calcomp:double "DcCalLsbAdj",0.9967 ; where 0.9966 and -0.9967 dmm values, see notes

:calcomp:double "Internal10MHzRefFreq",9.99008e6

:comp:sav:fact:all

:cal:save:fact:mai

:cal:update:all

:syst:prot on


Notes:

Use capitalization exactly as above.

I am not certain how many digits of precision are allowed. A 6.5 dmm per instructions implies, based on above, 4.00e-4 (or equiv) and 0.996700 as permissible values. Simple experimentation with the latter did not result in obvious influence on calibration. The values used in the top example were adequate to meet cal specs.

DcCalLsbAdj = this is a compromise adjustment and is dependent on offset being correct. You take a dmm measurements of the 1 volt calibrator signal, plus and minus, look at them as absolute values and - the best value in between. So, 0.9966 and -0.9967 becomes: 0.9966 and 0.9967, now - an in between value, 0.9966 or 0.9967. So, on this system you are telling it that a 1V signal is actually 0.9967, and it needs to adjust for that... This value is never negative! You could choose to use 0.9966 instead. If you see a greater spread than 2 digits your offset voltage is probably wrong.

The Internal10MHzRefFreq result that I got may have been wrong. This one is probably best left alone, or the 10e6 value. My math skill are not that great.

I replaced my batteries, so all of the above values were zeroed out already.

Menu Soft Key to get to calibrator.

-> lkup "DcC"
calCompSetDcCalibratorAdjConst 0x01000a8c text (rtlLibTarget.o)
calCompGetDcCalibratorAdjConst 0x01000a38 text (rtlLibTarget.o)
calLibGetDcCalibratorCalDefaults 0x01032ef8 text (rtlLibTarget.o)

verybigspeaker
Posts: 2
Joined: September 7th, 2019, 4:06 pm
Country: Yugoslavia

Re: TDS8000 DC calibrator adjustment procedure

Post by verybigspeaker » September 7th, 2019, 4:13 pm

Hi to all,

I acquired TDS8000, replaced all batteries and configured bios now the unit boots win98se from its original drive and brings up TFT screen and keyboard. However scope app never boots. It just shows 8000 series DSO loading screen under windows and never starts the application. I saw that you mentioned programming the board after batt replacement but I don't know how can't find info on the internet. I also can't find older app installation for win98 unit to try and reinstall the thing. Can someone help ?

Thx !
Viktor

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