HP 3456A vs 3457A vs 3478A

[Droid42]

Hello,
So i was wondering if anyone could help me decide which one is best!
They are all in the general price range of $150 to $350 and I know the 56 and 57 have more resolution than the 78.
But would buying the 56 be a bad purchase? It seems to be the same as the 57 (though the 56's math functionality isn't quite as good).
Anyways, any thoughts or advice would be helpful.
Thanks. 

[lewis]

Hi, I've got a 3456, a 3457 and a 3468 (not the 78). The 3456 has one fewer digit of resolution than the 3457, and doesn't measure frequency or current, but it's probably my favourite meter. It has an LED display which is really easy to see compared to the LCDs on the other two, and it seems to capture faster than the 3457 for a given NPLC and resolution. But it's also about 47 miles deep from front to back, so you need one hell of a bench to use it on. The 3457 is a much more sensible depth.

There are minor differences in the math functions too, but I never use these so that doesn't bother me.

Needless to say, all the meters ware bang on accurate (compared with each other!) when I bought them (and they still are).

I hardly ever use the 3468, but it's significantly smaller than the other two and can measure up to 3A (1.5A on the 3457). I love the 3456 because it's big, clunky, heavy and complex when you open the lid, and it has LEDs and big clunky switches on the front. But you'd probably be better off with a 3457 - it's smaller, has more functions, extra resolution and is better on paper in almost every respect. Don't bother with a 3478 if you can afford a 3457.

[saturation]

The 3456,7, and 8 were the top line DMM of Agilent through the 1990s.  They all support the then patented multislope II conversion for high DC accuracy.  The 6 has no amps mode.

The 7 has an extra digit that is only available through the GPIB, otherwise it shows the same 6.5 digit as the 6.  Supposedly 7 is easier to get in the EU while the 6 is equally as easy to obtain in the USA.  The 6 can be bid on the low end from $50-100, while the 7 goes between $200-300.

For more technical info, see the thread on Dave's review on the 3457a.

If you need a full bench DMM, the 3457a fits the bill, however, many of its chips have custom part numbers and could be difficult to replace if it fails; the 3456a is more 'generic' and very few unobtanium, which mostly is the keyboard and the CPU.  If you don't need amp mode, the DC accuracy can be much higher on the 3456a that the manual states.

The 3478a is not of the same class as these DMM in accuracy.

[EEVblog]

The 3478A is great if you value bench space, but no uA current measurment range.
If you don't care about bench space get the 3457A.
If you need the absolute best accuracy spec, get the HP 3456A, but few people really need this, so other more practical things come into play.

Dave.

[PaulAm]

I have a 56a, it's a big sucker but it's reliable.  I was using the resistance function the other day to track down a shorted cap on a board.  Amazing what you can do when you can measure down to 0.001 ohm.

Personally, I prefer the LEDs, they're a bit easier to read, but that's just my preference.

I've acquired a few pieces of HP gear from that genre; I'm having to think about some kind of rack to mount it in so it's accessible.  Leaving it piled up on top of a half height cabinet is getting old.

[Droid42]

Thanks for the help