#$%& Wavetek/Fluke 9530 Heads

[Bryan]

I have a 9500 (Wavetek Branded) and 5 heads.  In Novemeber heads on Ch1 - Ch4 were due and had just been to Fluke the previous year for new connectors & some repair so testing them was a breeze, perf test & re-save the correction data to update the date stored in the heads.  Well last week the head on Channel 5 was due and I start on it, have some bad readings and notice the correction factors have all defaulted.  I go back to the others and notice that all of them except channel 4 have done the same.  Anyone else seen this happen?  It's not the first time for me but I have seen it on an individual head but not 4 out of 5.  Any ideas?
The thing does move around on a cart rather than parked in a rack.

[mdbuike]

Did you remember to set the interlock on the back of the 9500 after updating the correction factors?  If you didn't, a static charge can cause heads to reset.

Mike

[Bryan]

Thanks Mike.
Pretty surre I had the switch thrown but we were fighting with low humidity more often than not in December.
I have double checked it now.  Aligning these things makes you in to a zombie.

[mdbuike]

I can undersatand that..fortunately our invironmental system was just replaced last summer, so all goes well here (knock wood)..

One solution we've used on the heads is to ensure minimum use specs for risetime and limit them for "Displayed indication not calibrated".  I haven't found anything that actually needs the actual risetime to be known except for calibrating an SD-24, and then we use the AFPSL standard.  And the only thing I use the fast rise pulse for any ways is to trigger my digital delay sytem that goes with the fiber optic system, just for the sake of stability.

Until the USAF comes out with a step by step way to use the current sampling system to measure 9530 risetimes, they'll stay limited.

BTW    do you have a spare SD-24 you could lend me?  I still have to calibrate signal standardizers (2 of my own, and 3 other bases, just because I took care of my pick-off adapter)..I only have 1 working channel on mine, so I'm nursing a 7904 and the 7S11/7T11 sampling system until we are "granted" some money.  Tek wants $500 or so, and won't guarantee the repair (bastiges)

Hope everything works out

Mike

[Bryan]

Sorry no spare SD.
We only use the pulse for some delta time accuracy time accuracy test that tek has come up with for TDS7000 series, shoot a pulse in to a Tee connectoed to the instrument and also to a sma Tee with a couple 20 in cables w/shorts. I think it rsults in a known pulse width from the delayed reflection coming back.

[Merckx]

Did the same for some heads at the lab I worked for

. . . One solution we've used on the heads is to ensure minimum use specs for risetime and limit them for "Displayed indication not calibrated".  

[CalLabSolutions]

It sounds like you are losing the calibration factors for the delta time when you move the heads around.   I have had other customers with the same problem.

The Fluke 9500 can store a phase correction value that adjusts the output of each channel so the signal applied to the UUT is in phase with the signal applied on the other channels.   This allows the 9500 to test more function on a scope with a single connection.   The 9500 does this my storing the head's SN and the offset value in memory for that channel.   

The problem is when you change the head connection to that channel you loose your calibration data.   And now you have to recalibration the 9500's offset.   If you are on an onsite of something you are screwed because odds are you did not bring a standard accurate enough to re-align the heads.

My recommendation is simple. .  Do not use the feature.   If your automated procedures use the feature, re-write them.   Go back to the tried and true equal length cables like the manual calls for.   Yes you will have to make 4 additional connection and it will add about 2 minutes to your total calibration time. .   But it works the first time—every time.