Ebay HP3478A   offset feature ??? - Page 1
Forum section: electronics / testgear

author: Homer J Simpson
author_rank: Super Contributor
timestamp: January 18, 2013, 01:11:07 am
content: Well I just won the auction on the 3478A.Looks clean. If it is as accurate at the other ranges as it is pictured on the volts range I will be happy.I have wanted to get one of these for a while. I have a Fluke 8840A now. This should compliment it well.I ended up getting it for $150 shipped.Any tips or advice from any one who already has this meter?Will post again once I receive and check out.KT

author: nukie
author_rank: Frequent Contributor
timestamp: January 18, 2013, 03:58:25 am
content: Check the date code and voltage of the backup lithium battery.

author: Homer J Simpson
author_rank: Super Contributor
timestamp: January 20, 2013, 02:52:52 pm
content: Is that a standard 2/3 A 3v lithium battery?Thanks

author: EV
author_rank: Frequent Contributor
timestamp: January 20, 2013, 03:24:55 pm
content: Quote from: Homer J Simpson on January 20, 2013, 02:52:52 pmhttp://www.ebay.co.uk/itm/1420-0278-Agilent-HP-Lithium-Battery-3V-95A-for-3478A-/350546682442?pt=LH_DefaultDomain_0&hash=item519e35e24a

author: Rick
author_rank: Frequent Contributor
timestamp: January 20, 2013, 03:30:00 pm
content: Quote from: EV on January 20, 2013, 03:24:55 pmAnd it's a used one...

author: free_electron
author_rank: Super Contributor
timestamp: January 20, 2013, 04:00:52 pm
content: 20$ for that cell ? Bloody hell ! Thats a 3$ part... Need one ?

author: vtl
author_rank: Regular Contributor
timestamp: January 20, 2013, 09:33:07 pm
content: I wonder if the CR123A cell is the same size as the backup battery? I wonder if its possible to buy a battery holder and solder it into the existing footprint to allow easy replacement of the battery.

author: Unknown
author_rank: Unknown
timestamp: January 20, 2013, 09:42:50 pm
content: CR123A cells have a slightly larger diameter, but you should be able to make it fit. If not using a battery holder, you want one with solder wires/tabs, unless you have access to spot welding equipment. A battery holder should work, as long as you can make it fit. The reliability when exposed to vibration will be worse, which is most likely why HP opted for soldering. It's not like you have to change it every few months.

author: Homer J Simpson
author_rank: Super Contributor
timestamp: January 20, 2013, 10:19:44 pm
content: That is what I had thought.A standard CR123A 2/3 a 3v lithium will work ok.I might do the setup with the battery holder.Will have the meter next week and will take a look.Has any one done the battery swap with the CR123A?

author: Homer J Simpson
author_rank: Super Contributor
timestamp: January 20, 2013, 10:24:35 pm
content: Found this.Battery Holder Case Box For CR123http://www.ebay.com/itm/Battery-Holder-Case-Box-For-CR123-CR123A-Photo-Lithium-Battery-/150849186477?pt=US_Battery_Converters&hash=item231f4feaad

author: nukie
author_rank: Frequent Contributor
timestamp: January 20, 2013, 11:09:55 pm
content: I used this a few years ago, they stock fresh cellshttp://shopping.microbattery.com/Panasonic-BR2-3AE-2SP-Lithium-with-PINS-3V-1200-mAh

author: vtl
author_rank: Regular Contributor
timestamp: January 20, 2013, 11:11:34 pm
content: I considered doing the holder swap on my 3478A, but it seems like the battery has been changed somewhat recently and the battery reads over 3.2 VoltsRegarding vibration resistance, its probably possible to loop a zip tie underneath the battery holder to keep the cell in place

author: Homer J Simpson
author_rank: Super Contributor
timestamp: January 23, 2013, 11:59:10 pm
content: I received today and have started to check it out.I have downloaded the user manual but wanted to ask a quick question for the group. Are sure many of you have this meter.On my fluke 8840 I can short the test leads and press the "offset" button and it will zero out the resistance of the test leads.Does this 3478 have the same function? At first glace I am not seeing it.Thanks

author: AlphZeta
author_rank: Regular Contributor
timestamp: January 24, 2013, 12:04:17 am
content: Be sure to keep the unit powered on (or at least keep the 3V voltage via a secondary battery) when changing the onboard battery. Otherwise the calibration information stored in RAM will be lost! Some people claim that if you swap out the battery really quickly you are OK, but I'd rather be safe then sorry...

author: Unknown
author_rank: Unknown
timestamp: January 24, 2013, 12:11:17 am
content: No offset/null feature as far as I'm aware. An odd omission, since competing models did offer it.

author: Rick
author_rank: Frequent Contributor
timestamp: January 24, 2013, 01:17:42 am
content: Quote from: AlphZeta on January 24, 2013, 12:04:17 amWhat if the soldering iron is connected to the ground? Wound't that cause any problem when soldering on a live circuit? (I am sure this is a stupid question for most of you, sorry).

author: AlphZeta
author_rank: Regular Contributor
timestamp: January 24, 2013, 01:50:52 am
content: Quote from: Rick on January 24, 2013, 01:17:42 amWell, if the tip is grounded, you will can do it one of many ways:1. unplug the iron when soldering the positive side. or2. use a butane soldering iron3. use the back up battery method (hook up one in parallel temporarily)If you are unsure, I would recommend using the last approach as it is safer when the rest of the circuit is powered off. When soldering a live circuit, you need to have very steady hand and don't want to accidentally short out anything.

author: Homer J Simpson
author_rank: Super Contributor
timestamp: January 24, 2013, 02:30:14 am
content: Well I have been doing some quick checks this evening on this meter.When I bought my 8840 it was sold as calibrated. I thought it was pretty close but I don't have a voltage standard yet to check.I guess the 8840 was calibrated after all.I do miss the offset feature on the HP though.Resistance measurement are on also but on the HP you have to read the resistance of the leads first then subtract them from your measurement.I like the HP and it is nice to have 2 meters to check accuracy but if I could only have one I would go with the Fluke. IMOKT

author: Rick
author_rank: Frequent Contributor
timestamp: January 24, 2013, 02:52:47 am
content: Quote from: AlphZeta on January 24, 2013, 01:50:52 amOk thanks. The option 1 seems difficult as the iron temperature would drop as soon as you unplug the iron. Or use an isolation transformer to power the iron?

author: c4757p
author_rank: Super Contributor
timestamp: January 24, 2013, 03:39:40 am
content: Put the isolation transformer on the meter instead, it uses less power.

author: ElektroQuark
author_rank: Unknown
timestamp: January 24, 2013, 07:30:56 am
content: Quote from: c4757p on January 24, 2013, 03:39:40 amYep, also some soldering stations will not work if they don't have proper connection to ground.

author: Unknown
author_rank: Unknown
timestamp: January 24, 2013, 08:14:11 pm
content: Quote from: Homer J Simpson on January 24, 2013, 02:30:14 amYou can also use 4-wire resistance measurement to compensate for lead resistance.

author: vtl
author_rank: Regular Contributor
timestamp: January 25, 2013, 08:34:09 am
content: What reading do you get when you short out the leads on AC current or AC volts on your 3478A? Mine reads at 0.480mV AC and 0.6802mA AC. I'm not quite sure if thats normal for this meter because the service manual does not appear to list this spec for AC current or Volts

author: ModemHead
author_rank: Frequent Contributor
timestamp: January 25, 2013, 01:56:55 pm
content: Quote from: vtl on January 25, 2013, 08:34:09 amI have two units. With shorting plug: first unit 0.433mVac and 0.565mAac, second unit 0.473mVac and 0.592mAac. Neither one really ever settled on one value, they were bobbling up and down a couple of counts.

author: Unknown
author_rank: Unknown
timestamp: January 25, 2013, 07:03:18 pm
content: True RMS meters rarely read zero when shorted. See for examplethis Keithley document. The True RMS converter is non-linear near zero, so accuracy at larger inputs would be compromised if it was calibrated to read 0 with its inputs shorted. True RMS meters are usually specified from 5% or so of full scale in AC ranges. At these values the contribution of the offset is negligible, as the Keithley document shows.The accuracy specs are listed in the manual. Its allowed about 1% + 163 counts in AC current mode for sinusoidal inputs at least 10% of full scale, so when applying a 30 mA 1 kHz input, it should read between 29.621 mA and 30.379 mA. Anything below 10% of full scale is unspecified, so a 30 A reading with shorted inputs would be in spec.

author: willb
author_rank: Regular Contributor
timestamp: January 27, 2013, 08:00:56 pm
content: What's the best way to replace the battery in the 3478A? The service manual doesn't seem to go in much detail. The battery in my unit reads 3.054V but I would like to replace it as I do not know it's age and it looks original.Would it be OK to hook up a bench power supply set to 3.0Vdc in parallel while removing the old battery? I have a Weller Pyropen so the grounded tip is not an issue for me.

author: vtl
author_rank: Regular Contributor
timestamp: January 27, 2013, 10:57:43 pm
content: I would just leave the unit powered on, that will keep power to the memory. Just be careful of the high voltage area, put some tape over where the IEC plug is soldered to the PCBTo make desoldering easier, break the spots welds on the battery and remove it. Then you have less of a thermal mass to heat up and you can remove the pins by heating up the joint and removing it with a pair of pliers.

author: MauriceS
author_rank: Contributor
timestamp: October 17, 2013, 03:46:34 am
content: While this thread is old... it deserves a warning... The - pole of the battery IS connected to AC ground. IF you use a grounded soldering iron on the plus pole, you just shorted out the battery backup and lost the cal constants!

author: echen1024
author_rank: Super Contributor
timestamp: October 17, 2013, 04:07:05 am
content: So, should I get a 3478 or a 8840. Both are around the same, generally affordable price point...

author: sync
author_rank: Frequent Contributor
timestamp: October 17, 2013, 01:34:14 pm
content: AC measurements and GPIB are optional on the 8840A. If you want them be sure the options are installed. Check that the VFD is not worn out.I have a 8840A but not a 3478A. I see following advantages of the 8840A:VFD vs. LCDCan take shrouded banana plugsHas a offset (null/delta) functionHigh impedance input up to 20V vs. 3V1000V vs. 300V max voltage rangeCalibration data in EEPROM (no battery)Advantages for the 3478A:303100 counts vs. 200000lower rages: 30mV, 30 ohm, 300mARead the manuals from both and decide yourself.

author: eurofox
author_rank: Unknown
timestamp: October 17, 2013, 02:01:16 pm
content: Quote from: Homer J Simpson on January 18, 2013, 01:11:07 amIf you scrap it I will buy the front plate, mine arrived with a cracked front plate due to shipping/packing

author: echen1024
author_rank: Super Contributor
timestamp: March 14, 2014, 08:46:14 pm
content: Sorry for digging up this ancient thread... I have just acquired one myself, however, I would like to perform a battery swap when I receive it. Since I have a floating power supply, couldn't I just parallel that and use my soldering iron to swap out the battery?

author: bingo600
author_rank: Super Contributor
timestamp: March 14, 2014, 09:32:51 pm
content: Quote from: echen1024 on March 14, 2014, 08:46:14 pmhttps://www.eevblog.com/forum/beginners/changing-battery-in-a-hp-3478a-can-i-use-a-3v-lithium//Bingo