Any HP 3456A user? - Page 1
Forum section: electronics / general

author: nadona
author_rank: Regular Contributor
timestamp: December 20, 2012, 12:30:58 am
content: I recently bought two HP 3456A. Couple of concerns stays in my mind and doesn't go away.1) Self-test: Manual says if there's an error it will show the error number at each step and at the end if all test are successful, it will show number 100.My meter - both: When I push the GUARD button in and press the TEST button and release it. It displays "+1.8.8.8.8.8.8.+8." for 3 seconds and goes to off repeating hours. No end. No change.2) When I turn on the machine, it starts at low mV range and goes up to -8.nnnnV very slowly and floats around there. Is this normal? I have two other DMMs and they float but at very low mV near 0mV.I think they both are wrong but how two meters broke same way? If it is normal, how do you deal with floating Voltage number?Strange! Two same models show same trouble. That's why I am asking this question. Measurements themselves are good. I was using this meter fixing Fluke 8840A which has lots of pin of -8.2nnV.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 20, 2012, 03:06:00 am
content: I have a couple 3455s that might be similar. Remember that 6 1/2 digit meters are useless if they load the circuit. On the lower voltage ranges the input impedance is something huge, I forget but probably Gohms. They will float all over the place if not terminated.

author: nadona
author_rank: Regular Contributor
timestamp: December 20, 2012, 03:48:22 am
content: @Conrad Hoffman3465A has only V button, no mV button. I think default boot up put this machine in VDC mode. One machine floats around -8.7v and another one -5.6v. Not mV.For reference, I have a Chinese made DMM VC8145 which stays at -0.0003V, sometimes move down to 2 or creep up to 4. Another DMM BK Precision 2831E stay in narrow band from -0.08 mV to -0.11 mVI found out that if I short the machine's probes, it shows about 0.1x mV but it goes back to where it was slowly.

author: lowimpedance
author_rank: Super Contributor
timestamp: December 20, 2012, 04:54:48 am
content: @nadonaThe drift is normal with an open input (short the input and you will get all 0). And the test routine will cycle from all indicators on and all display digits lit to all off and then back again. This routine will carry on continuosly until you either turn the instrument off or press the Test button again, (this is when there is no errors detected with the internal diagnostics!).Note if there is a problem it will come up with the error number and not complete the routine.I dont know the condition of your machines, but they may need cleaning if there are offsets etc.CHeck out other threads regarding this meter on here (in particular check your power supply electrolytics, they could be on their last legs).

author: Unknown
author_rank: Unknown
timestamp: December 20, 2012, 05:12:16 am
content: The input impedance in VDC mode is >10 Gohm for ranges up to 10 V, so any induced current will cause an offset, especially with leads connected. Connecting even a high value resistor across the input will remove this offset, so it won't cause problems with any sane source impedance. You can put it in the 100 V range or connect a 10 Mohm resistor across the input if it bothers you, but it's perfectly normal for this class of DMM. The VC might have a lower input impedance.

author: nadona
author_rank: Regular Contributor
timestamp: December 20, 2012, 06:20:42 am
content: @alm & lowimpedance,thank you for the detailed answers. Both of you cleared of my mind a lot.My two meters are very accurate down to the last digit. Either Voltage or Resistance if I use 4 wire measurement. I really like it.Thank you again.

author: Unknown
author_rank: Unknown
timestamp: December 20, 2012, 06:32:59 am
content: Note that you can use 6 store n digits to get an extra digit of resolution. I believe it defaults to 5.5 digit mode.

author: saturation
author_rank: Super Contributor
timestamp: December 20, 2012, 02:46:21 pm
content: They are my favorite DVMs, I have 4 of them.

author: nadona
author_rank: Regular Contributor
timestamp: December 20, 2012, 08:36:56 pm
content: @alm & saturation;I searched "3456a" Whoa! Bunch of readings. Maybe I spent good 5 hours reading you guys posts. Both of you are great, lots of good, very useful information. Until I read your post I didn't know 3456a doesn't have "Current" button! Front panel has 40 buttons and I can't find "A" button. I checked the manual and the cover says, "Digital Voltmeter" Smaller surprise than when I found Fluke 8840a's AC V&A is an option. AC buttons are on the front panel, but option. Huh?Anyway, I am happy with my 3456As.I just have to find out adjustment that Voltage reading will stay at near zero mV for default.Thanks again.Regards,

author: Harvs
author_rank: Super Contributor
timestamp: December 21, 2012, 09:10:14 am
content: Don't know if you've downloaded the operators manual yet:http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDIQFjAA&url=http%3A%2F%2Fwww.ko4bb.com%2FManuals%2FHP_Agilent%2FHP_3456A_6_Digit_Bench_Multimeter%2FHP_3456A_-_service.pdf&ei=QiXUUJ3sGNGviQe1mIGgCQ&usg=AFQjCNE07a1fNh2HFRA-EwoEiw4SnFrsmg&bvm=bv.1355534169,d.aGc&cad=rjaI use this meter all the time. It's great having the 6.5 dig resolution and accuracy, but the thing I would hate to give up is the other useful functions. Like ratio measurements, the onboard maths, etc.If you haven't yet, have a good flick through the op manual and it tells you how to do it all.If you need current measurement, you can always just get a 3/4" banana shunt and plug in as required. But If you've got other meters that do current then this is probably more trouble than it's worth.QuoteIf you're talking about the floating voltage like you were earlier, my advice is to forget about it. It does that by design, anything you do to get it to read 0 with no input will substantially degrade the characteristics of the meter.

author: saturation
author_rank: Super Contributor
timestamp: December 21, 2012, 04:53:13 pm
content: You're welcome. As Harvs suggested don't adjust anything until you've downloaded and read the users manual, its very detailed and explains everything, from how to use, troubleshoot, and repair it as necessary.Its probably the best bang/buck metrology grade voltmeter for DIY owners: easy maintainability, low purchase and maintenance cost, with most of its parts not unobtanium. Its also discussed at length in other forums, I think you posted on the the hp equipment group at yahoo; but there is also much in volt nuts forum.http://tech.groups.yahoo.com/group/hp_agilent_equipment/message/31984Its well documented, a 12 year production run produced a lot of units, so eBay prices tend to be low, and should the rare unobtanium be needed [e.g., keyboard] there are cannibaliz-able machines to go for.Enjoy.Quote from: nadona on December 20, 2012, 08:36:56 pm

author: nadona
author_rank: Regular Contributor
timestamp: December 22, 2012, 12:38:32 pm
content: @Harvs, saturation;Thank you for the info. I joined the volt nuts forum already.