HP 4274A vs 4276A LCR meter

[Nevada]

Hi,

I'm curious about your thoughts about the difference between the two units.

What I see:

4274A:
- the older one
- it has one more digit (max 5.5)
- it has much wider external polarization voltage range by default (+/-200V) (yes, I know that a sepcial adapter can be used with the other one, but the 4274A can handles higher voltage without any support other than an external power supply or option card)
- the built-in bias supply cannot be adjusted from the front panel, a special remote controller is needed
- it can be used up to 100 kHz
- wider driver oscillator range (up to 5V)
- adjustable oscillator voltage
- oscillator monitor (either voltage & current)
- much heavier (~18 kg)

4276A:
- newer design
- seems to be a bit budget-oriented (LED range indication instead of dotmatrix display), a lot of Sony hybrids
- there are a lot of frequencies up to 20 kHz
- it only goes up to 20 kHz
- no oscillator monitoring
- one digit minus (max 4.5)
- it seems to be faster
- better built-in bias voltage design to +/-40V (it can be set on the front panel) (but it's optional)
- cannot handles higher voltage only with a special adapter
- there are only two test voltage settings (LOW and HIGH)
- although it has much more measuring frequencies, but the compensation is made only at some spot frequencies, and a second order interpolation is made from that measurement to the other frequencies

As far as a I know, they have a different front-end.

As I see although they're in the same accuracy range (0.1% basic error), but the 4274A looks to be more precise according to the datasheets. The 4276A can do measurements with 0.1% error only in a thinner range (e.g. caps 1nF-1uF/1kHz), the 4274A specced much nicer (the basic accuracy is valid in almost all the ranges).
The other curious thing is that although they work in the same impedance range (100 mOhm to 1 MOhm), but the 4274A can measures much wider range of the components at a given frequency (e.g. 100pF - 100mF vs 100pF-1mF at 1kHz).

So, all in all, the 4274A seems to be the "better" unit for me except the measuring frequencies selection up to 20kHz. I would choose the 4276A over the 4274A only in the case of doing impedance curves (up to 20kHz).

[TERRA Operative]

I have a 4276A and love it. It's fine for my needs (although the high voltage adapter would make it perfect).

If you search youtube, ypu'll find a video I made. I have some spare PCB's with parts to construct a +/-40V bias voltage option I can sell for a reasonable price if you end up getting one without.

[precaud]

There's one significant difference that rarely gets mentioned, which tips the scales entirely in the 4276A's favor. Even the manual is somewhat vague about it.

The 4276A is unique among LCR meters in that it can measure AC impedance with DC present, within the +/-40VDC range. That includes batteries. DC regulators/voltage sources. Power rails in active circuits. There are enough freqs available to characterize impedance in the audio spectrum really well. Just set the rear-panel switch to "Ext".

Try that with a 4274A and you will have some repair work to do.

It enables you to see stuff like this. Impedance vs freq of the ubiquitous LM317 regulator with 50mA load current, showing the change of output impedance with change in input-output voltage differential.

[TERRA Operative]

Oh, I did not know that. I think I'll hold onto mine... I'm downsizing to newer, smaller equipment, but I think this one will stay.

[Nevada]

I believe it's not true: you can measure active biased circuits with the 4274A also! Please look at the attached manual page. By the way, I can't see that this is mentioned in the 4276A manual, so I was not sure if she can do that.

Basicall you're right: only the minor part of the RLC meters can do that, but HP ones from that era (even the 4261A/4262A) can! Although the newer HP models has no this feature (e.g. 4263A/B or 4284A).

[ZGoode]

If you search youtube, ypu'll find a video I made. I have some spare PCB's with parts to construct a +/-40V bias voltage option I can sell for a reasonable price if you end up getting one without.

Hey, I found your video on YouTube a while back and was going to make my own for my 4277A.  But if you still have some spare parts to build one and the boards, how much would you charge for it shipped to the United States?
And also out of curiosity, what part did you use as the screw terminal for mounting the aluminum back plate?  It's the one part not listed in your BOM

[TERRA Operative]

I can send you a kit of parts.
PM me and I'll work out what a kit of parts is worth. IIRC I have all the bits except the aluminium plate, but you just reuse the existing dummy blanking plate from your instrument.

I'll figure out the part I used for attaching the rear bracket too (I'll include some in the kit) and update the BOM from my video.

[ZGoode]

Yo, that would be awesome.  Yeah, I'll PM you.
Also, yeah I was planning on drilling holes in the blank plate, just wasn't sure what mounting hardware was used there, especially since the part also isn't listed in the service manual, just the screw.