HP 3468A HP-IL Digital Multimeter

[rprosperi]

Can anyone comment or recommend (for or against) this device?

TAS has some listed at approachable prices, assuming they are truly useful and in good working order.

One listing says "May require calibration. Sold AS-IS."

Warning bells clearly went off, but is the note about calibration typical for these units? If truly required, is this an end-user thing, or only by accessing the guts?

Gotta go look on the Museum DVDs to see if this rare beast is included.

Thanks in advance for comments.

[Paul Berger (Canada)]

They are a good meter, I have one on my bench, and I like the idea that you can use it for data collection. The A/D converter seems to be similar to the one in the 3421 (I have one of those too) The calibration is stored in battery backed up RAM and if that battery goes dead you lose the calibration. The user guide and service guide are available from the Agilent web site. The calibration procedure is documented in the service guide, so you could do it yourself, but of course the quality of your calibration would depend on the accuracy of the standards you use to do it.

[Katie Wasserman]

The group over at EEVBLOG (courtesy of one of our ex members, Dave Jones) has several discussions about this meter and its calibration, here's one for example.

[BobVA]

I've had one for about a year - it's the default meter on my bench. That said, bear in mind the following:

- You'll probably have to replace the internal memory backup battery which is hard to find and will require recalibration of the meter if you use the approved procedure. A failed self-check at startup (Error 1, I think, but it's in the manual) is a good indication the battery is dead and the calibration is lost.

- Calibration of the meter is a snap, if you've got the gear specified in the service manual (primarily a calibrated meter of higher precision ) and a major pain in the neck if you don't. The problem is that you must supply specified voltages, currents, resistances (typically a value with three as the leading digit) for the meter's auto calibration routines to work. If you've got the better meter, you can use precision pots to generate the required inputs. But if, like me, you've just got some good cal sources that are at a different rating, prepare for a long day of bodging. (Hey, if I had a calibrated 15 digit DMM, I'd be using that on my bench! )

[Paul Berger (Canada)]

The original battery may be hard to find but in the forum that Katie provided the link for there are a few examples of cells that people successfully used to replace the memory backup battery, and the process they used to replace it while preserving the calibration data. There is even one example of what not to do.

According to the service guide the original battery was rated for 3V at 0.95Ah, the 3.6V Primary lithium-thionyl chloride battery will also work. I just ordered a couple Saft LS14250 cells to replace the batteries in my 3468A and 3421A. This battery is rated at 3.6V 1.2Ah you will see in the forum that Katie linked that other have used batteries that have an even high Ah rating than the ones I ordered. In theory a battery with a higher Ah ratinfg should last longer, however you do not want to wait until the end of the batteries life to replace it as they go from full to completely dead in the matter of hours.

[rprosperi]

Thanks to all who've replied!

It seems these are cheap enough and assuming it's calibrated relatively recently, that isn't a huge deal (for my needs) so it may well be worth jumping in.

I've read many threads indicating the most likely issue I'll face is the internal battery (that stores the cal data) could be near EOL, but they also include procedures in gory detail about how to connect a bypass cap during battery surgery to keep the data intact.

Bad news is most of that is over my head.

Good news is Katie lives less than an hour away

Most of the units for sale (at reasonable prices) do not include probes/leads. The sockets in the photos appear standard, but can anyone comment if I can use other normal leads (e.g. from my Fluke) with this? I've found an HP probe kit, buts its over $40, and hoping mine would work.

[rprosperi]

(05-25-2014 02:45 AM)Paul Berger (Canada) Wrote:  The original battery may be hard to find but in the forum that Katie provided the link for there are a few examples of cells that people successfully used to replace the memory backup battery, and the process they used to replace it while preserving the calibration data. There is even one example of what not to do.

According to the service guide the original battery was rated for 3V at 0.95Ah, the 3.6V Primary lithium-thionyl chloride battery will also work. I just ordered a couple Saft LS14250 cells to replace the batteries in my 3468A and 3421A. This battery is rated at 3.6V 1.2Ah you will see in the forum that Katie linked that other have used batteries that have an even high Ah rating than the ones I ordered. In theory a battery with a higher Ah ratinfg should last longer, however you do not want to wait until the end of the batteries life to replace it as they go from full to completely dead in the matter of hours.

Thanks for the info Paul. What is the best way to tell if the battery is nearing EOL? With the near-90 degree drop-off curve (all lithiums are steep, but I've never seen one quite so 'cliff-like') it doesn't appear any measurement would help; perhaps it's best to just do it, assuming at this age it's likely close to the end?

[Paul Berger (Canada)]

From what I have read the consensus is when you buy one used you have no idea how old the battery is so it is best to change it to be sure, its better than having to recalibrate, but I have to admit I have had been pushing my luck, I have had my 3468A a couple years now and I am just getting around to replacing the battery. It would teach me not tio procrastinate, if it where to fall off that cliff in the next couple days.

[Dave Frederickson]

(05-27-2014 11:13 PM)rprosperi Wrote:  The sockets in the photos appear standard, but can anyone comment if I can use other normal leads (e.g. from my Fluke) with this?

Avoid the Fluke probes as they have boots over the plugs which will prevent them from being plugged into the 3468A. Or you can cut the boots off.

That being said, I have a couple of sets of the Fluke TL910 which I really like.

Dave

[Katie Wasserman]

Quote:Bad news is most of that is over my head.

Good news is Katie lives less than an hour away Wink

Wink acknowledged!

I'd be happy to help you replace the battery and/or calibrate it. While I don't have a calibrated voltage/current source I do have a stable power supply and couple of 6.5 digit DMM's (one Fluke one HP) that are more than adequate to calibrate against.