Fluke 3330B Calibrator

[at2marty]

Hi all, I'm new to the forum.  I've been lurking and reading for quite some time and finally decided to register and ask a question.

I recently purchased a Fluke 3330B Constant Current / Constant Voltage Calibrator off of Ebay.  Upon initial inspection and testing, everything seems to "work", but it's definitely out of Cal.  I would like to try and tweak it to get it closer to being in calibration, but the problem that I have is I need an extender card to test / make adjustments.  The service manual states that the extender card should be mounted in a plastic holder on the rear panel, but unfortunately that is not the case.

I realize that it's not going to be spot on, but for my use as a hobbyist, I would just like for it to be close.  As of now readings are roughly 500mv off when I check with my Fluke 3468B multimeter.  In order to do the alignment procedure I need the extender card.

I have tried to search on google by part number and by searching for "Fluke 3330B extender card" and have not had any success.

Any ideas regarding where I might purchase one?  Either that, or if anyone happens to have one that I could rent, I would happily pay a deposit and shipping charges to Florida plus a small fee to use the card.

My other option that I am considering is trying to find compatible pins and a receptacle to make my own.

[wn1fju]

I'm a little puzzled, first of all.  You say you are off 500mV?  At what setting?  It's one thing to be off 1/2 volt when the thing is set to 1000V, and quite another to be off 1/2 volt when the thing is set to 10V.  I would suspect that something is malfunctioning, not that the unit is simply out of calibration.  I have a similar Fluke 343A calibrator, a Rotek 320 calibrator, am EDC 501 calibrator, etc., and I don't think I could get any of them misadjusted enough to be that far off.

As far as extender boards, or lack thereof, welcome to the club.  I believe your Fluke 3330B has a nonstandard pin/socket arrangement that most likely will require you to make your own out of whatever you can find.  Fortunately, there aren't a lot of pins. 

For simple adjustments, you can always revert to the method of 1) pull the board out, make a small change, 2) plug the board back in and measure, 3) go to step 1).  Tedious, but in a pinch can be good enough.

[at2marty]

First of all, thank you for the response wn1fju.  I guess I should have been a bit more clear with what I found.

My initial tests were not done properly which is my mistake.  I didn't allow the equipment to warm up and stabilize the way that it should.  I got it out of the box, plugged it in and started fiddling with it.  My initial tests were on the 10V mode and the 1V scale gave me a reading of 1.4XXXXX on my meter.  I left it running over night while I slept, and the voltage reading was pretty close to the same.  I shut it off while I was away and recently turned it back on.

I'm following the manual which states for me to turn it on with the decade switches set to zero and allow it to operate for "at least an hour".  It currently has been on for slightly over that, and it is finally getting close to a zero reading on my meter (0.00027).  It started at a rather higher value and decreased over time.

However, when I change the decade switch to 1V I get a reading of 1.45101 on my meter that is steady (no variation on the lesser digits).  I checked it with another meter (Fluke 27) and the values agree.

I would like to do the calibration procedure on it, and see if I can get it close.  Then after that, try to troubleshoot the problem and fix it.

I can't do the procedures in the manual without an extender card.

[edavid]

However, when I change the decade switch to 1V I get a reading of 1.45101 on my meter that is steady (no variation on the lesser digits).  I checked it with another meter (Fluke 27) and the values agree.

I would like to do the calibration procedure on it, and see if I can get it close.  Then after that, try to troubleshoot the problem and fix it.

Don't touch the calibration until you fix it - after fixing it you will probably find that the calibration is still good.

[wn1fju]

As suggested earlier, there is little chance that a working unit could give >1.4V on a 1V setting due simply to misadjustment.  I suppose it is possible if Fluke made the cal pots go over a sufficient range, but I highly doubt it.  After all, when adjusting these kinds of calibrators, the cal pots are used to get things accurate to a few microvolts.  That would be harder to do if the pot could swing things 1/2 volt! 

As far as warm-up time, there certainly would be some drift from a cold start, but that again should only be microvolts, or a few millivolts at best.  My calibrators typically get used without an extended warm-up time, and I've seen very little penalty (luckily, I'm not a cal lab).   Unless you truly are a cal lab, overnight warm-up is probably overkill.

As is typical with most repairs, start with the power supply in the unit.  Perhaps there are some reference voltages lurking around that are incorrect.  As the previous post says, don't touch the calibration until you are 100% sure the thing works.  Good luck.

[Dr. Frank]

Hello,

an output of 1.4 V for a setting of 1.0V in Voltage mode refers definitely to a defective unit.
Calibration on those Fluke boxes can be done on a range of +/- 100ppm  only; 40% is completely out of range of trimming.

Do not fumble on the calibration at that point!!

If the instrument was sold as being "ok", perhaps you do not operate it correctly.
Your descriptions of your chosen settings is quite strange, and lets me assume that you are not familiar with such an instrument, yet.

Check first:

- Do you use it correctly in the constant voltage mode, or instead in the constant current mode?

- Are output +/- and sense +/- correctly connected, or are the short bars missing?

- On the front panel, is the unit eventually set to remote operation?

- If in constant voltage mode, and correctly connected output/sense connections: What are the output full scale readings at 10V, 100V, 1000V?

- What are the zero setting outputs on the 10, 100, 1000V ranges?

- Are the constant current ranges working properly at full scale?

You'll need the extender card for repair only, afaik. For calibration, all trimmers are accessible without that.
Extender cards normally are accessory, and not provided with the instrument. That's not clear to me from studying the 3330B manual.

Before you try to "repair" the unit, please read the manual completely!!

Calibration of this instruments is quite delicate, as far as I remember.

Its internal R2R ladder is quite sophisticated and requires some additional calibration equipment, as a Kelvin Varley divider, and so on..
I really doubt that you have the equipment necessary for a serious calibration.

Frank

[at2marty]

Thank you all for the responses.  I did some reading and let the unit run over night.  Dr. Frank, you touched on something that made me think... only the + output / sense shorting bar was connected.    I connected the - shorting bar and guess what?  My current readings are as follows.

1V setting = 0.99997
10V setting = 9.9996
100V setting = 99.996

For me that is close enough.  I am very happy with my Ebay purchase.  I picked this up for a bit over $100 US + shipping.  I don't plan on touching any of the settings and will use this to keep track of my meters.  Maybe one day I will send it in to a proper lab for proper calibration, but as I said, for my needs at the moment it is good enough.

Once again, thank you all for the responses and a very huge thanks to Dr. Frank for jogging my brain to realize the simple mistake that I was making.

[Dr. Frank]

Thank you all for the responses.  I did some reading and let the unit run over night.  Dr. Frank, you touched on something that made me think... only the + output / sense shorting bar was connected.    I connected the - shorting bar and guess what?  My current readings are as follows.

1V setting = 0.99997
10V setting = 9.9996
100V setting = 99.996

For me that is close enough.  I am very happy with my Ebay purchase.  I picked this up for a bit over $100 US + shipping.  I don't plan on touching any of the settings and will use this to keep track of my meters.  Maybe one day I will send it in to a proper lab for proper calibration, but as I said, for my needs at the moment it is good enough.

Once again, thank you all for the responses and a very huge thanks to Dr. Frank for jogging my brain to realize the simple mistake that I was making.

                

Well, no, that was no "simple mistake", you just have to get familiar with such precise instruments, then only you will realize ("see") such errors directly.

$100 is an extreme bargain, especially for this instrument, as it has the ultra stable / precise constant current feature.

Have fun, and welcome in the club of volt-nuts!

Frank

[cellularmitosis]

I just watched three of these go on ebay relatively cheap prices.  Did any forum members snatch one of them up?

[pelule]

Dr. Frank
You'll need the extender card for repair only, afaik. For calibration, all trimmers are accessible without that.

Dr. Frank is fully correct (as usual). I am owning a 3330B which I calibrated after repair.
1st - at the closed gear do the "performance test" as described in the service manual.
If the gear is far of:
2nd measure the 10V reference voltage (you just need to remove the top cover to measure the reference voltage.
BUT BE CAREFULL TO NOT POWER THE GEAR DURING CONNECTING THE LEADS. The tool generates high voltage !!!! and you may damage something by accident - I recommend to disconnect from power, connect the leads, than connect the power and power on.
Wait at least 30 minutes (warm up) before measuring the ref voltage. If ref voltage close to 10V (a few ppm off) you most probably you need to recap some boards (power supply, differential amplifier, chopper amplifier...) which is in most cases the reason for the problems.
/PeLuLe

[cellularmitosis]

I just watched three of these go on ebay for relatively cheap prices.  Did any forum members snatch one of them up?