HP 3456A vs. 3457A - Page 1
Forum section: electronics / general

author: benj38
author_rank: Frequent Contributor
timestamp: January 28, 2025, 08:33:57 pm
content: Hi,I would appreciate any thoughts individuals who have experience with both HP 3456A and 3457A would be willing to share about how these two models compare.I do not have a specific application in mind, I am just curious and trying to solicit some thoughts and opinions, if that is OK.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 28, 2025, 10:01:37 pm
content: I have not used the 3456, but the 3457 quite a lot. The two are quite different meters. The 3456 was a precision meter and high end for it's time. However it does not have current ranges, so only voltage and resistance. The best range is 10 V.The 3457 is kind of a try to make a cheaper version - not really to replace the 3456. The best range is 3 V and already the 30 V range uses the input divider and thus no high impedance. The design with 0.3 / 3 / 30 / 300 V range and an ADC that works on 10 V is a bit odd. AFAIK the 3457 is a bit more noisy, though the comparison is not easy. The main positive things about the 3457 is that is can be obtained often relatively cheap and it uses less power - so it does not get as hot as the 3456. Some units also come with an integrated scanner (in place of the rear terminals). The LCD is often a bit hard to read in low light.

author: pqass
author_rank: Super Contributor
timestamp: January 28, 2025, 10:46:02 pm
content: I have a 3456A and love the math features. It does not have a current terminal but you can easily get around that by (4-wire) measuring an external shunt (of any value) and using the (X-Z)/Y "Scale" math function (where Z=0, Y=shunt resistance).Early 3456As have a noisy fan. Get a later version with a TO-3 regulator on the back panel instead.The 3457A uses an internal 3V lithum primary battery to maintain calibration values in RAM. I don't know if you can read them back like the3478A(of similar vintage). The 3456A has no calibration memory; just pots accessible via panel behind the front terminals.You can get 7-1/2 digits out via GPIB on the 3457A but I don't know how noisy/useful it is.Some repair pictures and write-uphere,here, andhere.3456A manual. Features/operation start on page 27.3457A manual. Features/operation start on page 57.

author: garrettm
author_rank: Frequent Contributor
timestamp: January 29, 2025, 12:26:26 am
content: I've owned both meters and the 3456A is the superior instrument if you care about measurement accuracy for DC volts and IIRC ohms. It's 100mV range is very stable. AC voltage is better on the 3457A, and, as has already been pointed out, it does current and has the option for a scanner card which could be useful. But the horrible--and I mean HORRIBLE--LCD display on the 3457A is the major deal breaker for me. It's a pain in the ass to see while working at the bench, but I suppose one could swap it out with a different, more legible display. If doing automated measurements with a PC, the 3457A isn't a bad choice.My 3456A is more stable than my Tektronix DMM4050 on the 100mV range. It's still a great 6.5 digit DMM for DC volts and ohms. It's AC voltage accuracy is pretty bad though. I have a Fluke 8506A that I use for DC current and AC volts, as well as DC volts above 100V--as that is where it is superior to the 3456A. Anyways, I wouldn't rely on a single DMM. Having two or more helps with sanity testing and for doing multiple precision measurements without requiring a scanner to multiplex measurements.

author: garrettm
author_rank: Frequent Contributor
timestamp: January 29, 2025, 12:33:11 am
content: Oh yeah, if you work out the DC specs for 90 days or a year the 3456A beats the 3457A on ALL measurement ranges. While 3000000 counts _is_ nice, only the 300mV and 3V are high impedance. But for everything else its not all that bad--just don't buy it thinking it is going to have amazing DC voltage capabilities. And the 7.5 digits over GPIB is suspect at best. Averaging the 3456A's output to get 7.5 digits is likely more trustworthy.

author: WillTurner
author_rank: Regular Contributor
timestamp: January 29, 2025, 12:39:39 am
content: The user interfaces are significantly different. The 3456A basically uses RPN, while the 3457A is algebraic.

author: srb1954
author_rank: Super Contributor
timestamp: January 29, 2025, 03:38:51 am
content: I find with my 3456A that the VDC temperature coefficient is significantly worse than for my 3457A. This is only for my sample of 2 units so I don't know how the general population compares. Whether or not this is a concern for you depends on how well controlled your environment is.The 3456A is considerably deeper (510mm) than the 3457A (290mm) so it can be difficult to find shelf space. The 3456A is also considerably heavier.

author: jfet
author_rank: Contributor
timestamp: January 29, 2025, 08:38:29 am
content: I have both. I own 3 each HP3456A and 1 each HP3457A. The 3456A is strictly a 6 digit meter. It is a low noise unit, and as mentioned, its calibrated thru pot behind the front panel of the input banana connectors. I rotate them thru calibration each year and when the 3456A comes back from cal, I use it and spot check the others. They do not seem to drift at all. The nice red LED display makes it easy to see from some distance. The 3457A uses a LCD display. There is a thread in EEVblog where it has been converted to LED if one wants. There is also a thread where a 3456A has circuitry added to get a 7th digit out. The 3457A uses a 3V lithium battery back memory for calibration constants.The 3457A can give you 7 digits on the display in DC volts. All you have to do is press the DIGITS DISP key, press 7 key, press ENT key. Its noisy, you probably want to use NPLC of 100 to clean it up.The 3456A works on a full scale of 1.2. The 3457A is a full scale of 3. The 3457A will also measure frequency and current. The 3456A will measure ac to 250 Khz, the 3457A to 1 Mhz.The 3456A is a big animal. its deep, a joke is you need to cut a hole in the wall behind it ! The 3457A is the same width, but only 11 inches deep.The elder 3456A has a 3 phase fan, that is difficult to find if it goes bad, better to get the unit that does not have the fan.HP also printed article's on their designs, the 3456A is in HP Journal April 1981 (http://hparchive.com/Journals/HPJ-1981-04.pdf), the 3457A is in HP Journal February 1986 (http://hparchive.com/Journals/HPJ-1986-02.pdf). You can find the operations and service manuals on various internet technical manual sites.The problems I have had in the past with the 3456A is the switching FETs in the analog front range will go out. Its like you need a second meter to compare to to troubleshoot. And the original HP FET is not available. But there are suitable substitutions, need to use an extremely low leakage device. Somewhere I have it wrote down what the replacement is. So far, I have not had a problem with the 3457A. I worry about its battery but when I open it up and check it, its close to its rated spec.Also 3457A is limited to a maximum of 450V. 3456A can go to 1200V.

author: guenthert
author_rank: Frequent Contributor
timestamp: January 29, 2025, 10:38:21 am
content: I also am in the fortunate situation to own one of each. A few years ago, one could get the 3456A very cheaply on the secondary market (mine seems to stem from an IBM lab). I suppose the weight, depth, small display and most importantly, inability to calibrate it using software (others mentioned the pots already) made them less desirable for professionals.To me it seems the 3456A was made with application in metrology in mind, e,g. it can determine the ratio of two DC voltages.One thing to keep in mind when importing a 3456A: it's crystal oscillator needs to be exchanged depending on whether line frequency is 50 or 60Hz for best results (it works anyway, albeit with added noise). For the 3457A, this s a NVRAM setting.

author: benj38
author_rank: Frequent Contributor
timestamp: January 30, 2025, 03:13:53 pm
content: Thanks everybody for sharing your knowledge and thoughts!

author: MadTux
author_rank: Frequent Contributor
timestamp: February 01, 2025, 04:26:32 pm
content: 3456A is great instrument, nicely build, fixable, great display, good keys, math functions...3457A, big meh, nothing great about it IMO, cheap plastics, extremely shit display and no good keyboardAbout everything is inside hybrids on 3457A, even the input switching FETs, so if one of them gets fried for whatever reason, you're screwdAnd the crazy input ranging design, had to look in the schematics:30mV/300mV/3V range => no divider, 30V/300V => 1/100 divider, noise accordingly.Then goes to "input amplifier" or whatever they thought it would be:30mV x333 amp, 300mV&30V x33.3 amp, 3V&300V x3.33ampSo the common 30V range you'd use for most stuff is what you get after 1/100 divider & 33.3x amplifier, whereas any sane instrument uses a real preamp for 100mV range and a 10/100x divider on 100/1000V ranges only.Or even a true 20V range, like in Datron 1271/1281 or Keithley 2001/2002Get a Keithley 2015/2010 or 3456A, 3457A is trash!