ESI 242D and 707B - how useful?

[Rax]

I have the opportunity to grab those two in the subject line for a reasonable price and am wondering how useful they are at the bench.

I haven't seen them mentioned much, so I am not even really sure what they would replace in my lab. Or add functionality to. Or what exactly is their level of service (primary? transfer? "informative?..." etc.) - though the specs seem very respectable.

Thank you for your input!

[Rax]

To be more specific - duh! - I already have a Fluke 5450A, an ESI RV722, a set of ESI SR1s, and, of course, other instruments (like a Prema 6048, Fluke 5440A, etc.).

Each, I think, performing some of the functions attached to at least the 242D.

[guenthert]

Useful for what?  To impress fellow test gear aficionados?

(if I had a surplus of money and space, I'd buy them too, but I wouldn't ask how useful they might be)

[Rax]

Useful for what?  To impress fellow test gear aficionados?

(if I had a surplus of money and space, I'd buy them too, but I wouldn't ask how useful they might be)

Of course to impress them, and myself!

But OK, maybe if I flesh it out a bit more your input will switch to being helpful. I have a very humble approach and have seen tremendous experience - or just thoughtful, generous "thinking with me on challenges and issues" (and "stupid questions") - being shared here, so I do see a lot of sense asking these questions.

I mentioned some of the units I have (and I need to add a DB62 Dekabox, and there are others like that here on a downward slope of worthiness), so my question would be regarding redundancy. Do I already have units overlapping on some of the functions included in these units? (Yes). Do they exceed their performance? (not quite sure... answer would surely need various qualifications). Do I have an SR 1010? (no).

But anyone familiar with the unit would have mapped the points above before I did, be a few miles in front of me on this road.

[manganin]

I haven't seen them mentioned much, so I am not even really sure what they would replace in my lab. Or add functionality to. Or what exactly is their level of service (primary? transfer? "informative?..." etc.) - though the specs seem very respectable.

https://www.eevblog.com/forum/metrology/esi-242d-(sp3632)-resistance-bridge-for-sr104-intercomparison/

[alm]

The ESI 242D system is for comparing resistors either to another resistor that is very close in value (e.g. two 1 kOhm resistors that are within a few uOhm/Ohm), or to compare a resistor to the built-in decade resistor, with the uncertainty limited by the uncertainty of that decade resistor (its tempco is not amazing, I think). For comparing two resistors it should be quite a bit better than your P6048, but more tedious, because you have to manually balance the bridge. You can't easily use it to measure the difference over time, for example, like you could with a DMM.

I don't know the ESI 707B, but according to its manual it's a capacitance bridge that's specified to be 0.01% accurate. Which is better than the vast majority of LCR meters (even the pretty high-end GR 1689/1693 bridges which are 0.02%) if what you need is to measure capacitance accurately. It needs an external generator and detector. For best accuracy frequency is limited from 100 Hz - 1 kHz, not 100 Hz - 100 kHz like a modern LCR meter. It will also only measure capacitance, no resistance or inductance. I decided for myself that I would probably only use a manual bridge like this a few time before finding it too tedious, so I limited myself to electronic LCR bridges that might have a slightly lower accuracy. I don't need to be a capacitance / impedance nut. But that's of course up to you. For the specific function of measuring caps at the frequency and in the ranges it supports, this will likely run rings around any multimeter you might have with capacitance function and be better than LCR meter like the DE-5000 in terms of accuracy.

[Rax]

https://www.eevblog.com/forum/metrology/esi-242d-(sp3632)-resistance-bridge-for-sr104-intercomparison/

Fantastic, thank you. This particular unit I am contemplating is an SP3623/242D, so I guess low tempco.

[Rax]

The ESI 242D system is for comparing resistors either to another resistor that is very close in value (e.g. two 1 kOhm resistors that are within a few uOhm/Ohm), or to compare a resistor to the built-in decade resistor, with the uncertainty limited by the uncertainty of that decade resistor (its tempco is not amazing, I think). For comparing two resistors it should be quite a bit better than your P6048, but more tedious, because you have to manually balance the bridge. You can't easily use it to measure the difference over time, for example, like you could with a DMM.

Very helpful, thank you. I am still not sold I want (or need) this, but this gives me good food for thought. It seems this particular unit may be lower tempco than earlier ones - not sure that's closing the deal - but there's that. One thing that's not been obvious to me is, even if a pretty eclectic instrument, I don't think it's easy to use the parts for their specific role away from the overall instrument and its integrated duty.

[...] the ESI 707B [...] I limited myself to electronic LCR bridges that might have a slightly lower accuracy.

That's been my decision also this far, and I think I'll stick with it. I don't actually have an LCR instrument, but I haven't had a distinct need for it yet either, so I'll probably commit to one such instrument when time's right.

But for now I took a pass on the 707B. A friend (and a neighbor) committed to it, so I can probably just borrow it should I need it.

[manganin]

I don't know the ESI 707B, but according to its manual it's a capacitance bridge that's specified to be 0.01% accurate.

Despite the "mediocre" overall specifications of the bridge, the internal 1000 pF reference is an unboxed ESI SC1000 standard capacitor ...

[alm]

One thing that's not been obvious to me is, even if a pretty eclectic instrument, I don't think it's easy to use the parts for their specific role away from the overall instrument and its integrated duty.

There are no internal connections between the four components. Everything is via the front panel binding posts. So you can easily use components separately, but not every would be as useful. The RS925 resistance decade could be used as a high resolution resistance decade though I would be very careful not to overload it. The null meter could be used as a generic null meter. It's even either a HP419 or Keithley 155. I don't see a use for the source or the bridge outside the system.

[ap]

My experience owning (once) a 707 was bad. Not accurate. I returned it to commercial seller. No comparison to e.g. a 1620.
And for the 242, and its some time that I had looked at that, the problem seems to be to establish the mathematically correct transfer uncertainty. No worst case spec found and not enogh data to calc (at least what I found). So of what use is it other than having a nice variable resistance for lab use?

[alm]

To me the 240 is the only critical part. Isn't that just a relative adjustment, kind of similar to using a nanovoltmeter to compare voltage references where only the null is critical and the nanovoltmeter contributes very little to the uncertainty as long as the difference is small? Measuring 1 uOhm/Ohm difference with 5% uncertainty is still pretty good. Measuring say 1 mOhm/Ohm for two resistors that are further apart with 5% uncertainty is less impressive.

Obviously the RS925 has looser specs and would need to be compared and possibly adjusted to external standards. So for anything that's not comparing two resistors that are close in value the specs would depend on the uncertainty/stability of the RS925.

But I have only played with the instrument, so I may be talking nonsense.

[manganin]

And for the 242, and its some time that I had looked at that, the problem seems to be to establish the mathematically correct transfer uncertainty. No worst case spec found and not enogh data to calc (at least what I found).

I was told that (in 1:1 comparisons) the 242D shown in the teardown gave consistent results down to 0.1 ppm against a Guildline 9975 Current comparator bridge. Reading the tenths from the dial required some experience though.

But nowadays, when running a cal lab, you need to have the math done. In the past there was more room for creativity.

[Rax]

One thing that's not been obvious to me is, even if a pretty eclectic instrument, I don't think it's easy to use the parts for their specific role away from the overall instrument and its integrated duty.

There are no internal connections between the four components. Everything is via the front panel binding posts. So you can easily use components separately, but not every would be as useful. The RS925 resistance decade could be used as a high resolution resistance decade though I would be very careful not to overload it. The null meter could be used as a generic null meter. It's even a HP419 or Keithley 155. I don't see a use for the source or the bridge outside the system.

That's what I imagined, but the unit I'm looking at has most of those front posts made inaccessible with screwed on covers.

Your sentence is a little short there - did you mean to say "it's equivalent to an HP 419 or Keithley 155?" I have an ESI DCV standard with a "galvo" module but am not entirely happy with it. It's one of the reasons for considering this.

[manganin]

That's what I imagined, but the unit I'm looking at has most of those front posts made inaccessible with screwed on covers.

Those are just pull-out shields. It is only the friction of the banana plugs that keeps them in place.

[alm]

It's even either a HP419 or Keithley 155. I don't see a use for the source or the bridge outside the system.

Your sentence is a little short there - did you mean to say "it's equivalent to an HP 419 or Keithley 155?" I have an ESI DCV standard with a "galvo" module but am not entirely happy with it. It's one of the reasons for considering this.

I fixed the typo in the quote and my original post. Older units used a HP 419A and later Keithley 155 (which is more desirable). You can tell from the meter bezel. I think the one with the mirror behind the scale is the Keithley null meter. Very old units used an even older HP null meter (413A?).

[Rax]

Older units used a HP 419A and later Keithley 155 (which is more desirable). You can tell from the meter bezel. I think the one with the mirror behind the scale is the Keithley null meter. Very old units used an even older HP null meter (413A?).

I didn't realize they used actual 419s and 155s... I'd be pretty bummed to figure the one I'm looking at is using a 419A, as I returned a 419A not long ago. This was when I found its internal mercury battery leaked all over the place. I've been looking for a 155 since, but it's not easy to find affordably.

I enclose a pic with its face, if it can help determine if it uses a 419 or a 155. I have not yet purchased this.

[alm]

I think that contains a HP 419A and that the K155 version looks like this with the mirrored scale and going down to 1 uV F.S.

[donlisms]

Yes -- I think it's the 801 versus the 801b.

I've only had my 242D for a couple of weeks; it has the 801b.  (I got it because resistors are my hobby, not because I expect to impress anyone!)

I'm seeing about +/-200nV total noise; I'm not sure where it's coming from, but everything is still pretty workable at that level.

A quick check of the TC of the system, including 1k from the 925, was about 2ppm.

I like that I don't have to put all the eggs in the 925 basket, as good as I think it's going to be. The substitution method removes its calibration from the results, and you measure only the small ratio between your standard and unknown, right out in the open where you can see them.  I trust the deviation dial for that small ratio because it has such a nice wire-wound sound and feel.  I think the 0.01x, 0.10x, 10x, and 100x multiplier settings are going to need some tweaking -- they seem to be within a few ppm, but I think they could be better.

Fun.  Big.  Tedious.  Somewhat, but not excessively, needy; most of what needs doing can be done with Hamon buildups.

[Rax]

I've only had my 242D for a couple of weeks; it has the 801b.  (I got it because resistors are my hobby, not because I expect to impress anyone!)

Self deprecating humor a value you cherish?...

[donlisms]

I don't think much about self-deprecation one way or the other, just clarity!  :-)e

[alligatorblues]

Resistors are my hobby!

Then you would probably want to look at Vishay Precision Group HZ series! It can be a surprise.

Also, one type of resistor that is very useful is a ratio standard, like the Fluke 720A. 

[donlisms]

Resistors are my hobby!

Then you would probably want to look at Vishay Precision Group HZ series! It can be a surprise.

Also, one type of resistor that is very useful is a ratio standard, like the Fluke 720A.

I don't think it's going to be that difficult to make good Hammon ratios for an amount of money I actually can spend!  I could never buy a 720a.

[guenthert]

Older units used a HP 419A and later Keithley 155 (which is more desirable). You can tell from the meter bezel. I think the one with the mirror behind the scale is the Keithley null meter. Very old units used an even older HP null meter (413A?).

I didn't realize they used actual 419s and 155s... I'd be pretty bummed to figure the one I'm looking at is using a 419A, as I returned a 419A not long ago. This was when I found its internal mercury battery leaked all over the place. I've been looking for a 155 since, but it's not easy to find affordably.

I enclose a pic with its face, if it can help determine if it uses a 419 or a 155. I have not yet purchased this.

The face of the MCM doesn't look like the ones on -hp- 419As I've seen.   I'm also surprised to see a null meter MCM w/o a mirror scale.  As there is no way to set/read the bucking voltage, I'm fairly sure there is no such circuity and no mercury battery inside.  It might be 419A-like, but it ain't no 419A.

I can't help but pointing out that you still haven't told us, what the intended purpose of your potential acquisition is.  You are aware of it's size, so I suppose you have a huge bench.  Others have meanwhile stated, what the 242D was originally meant to be used for.  I'm not sure, how clear it became, how precise that instrument is (was, when new).  To make full use of its precision, the resistors (first four decades) of its rheostat need to be adjusted (over the last five decades they might well have drifted out of the adjustable range though).  For calibration of it's rheostat, ESI suggests a complete system, i.e. with a 2nd rheostat (there will be other ways to accomplish the same, but adjusting a resistor to better than 20ppm accuracy is no small task).  I'm just afraid that without a set of calibrated standard resistors in a temperature controlled oil or air bath, the 242D is a heavy paperweight.

E. Pettis was fond of his 242D iirc [1], but he was in the business of manufacturing small series precision resistors.  I'm sure he found it useful.


[1] https://www.eevblog.com/forum/metrology/want-to-measure-resistance-with-high-precision-what-would-be-best-to-get/msg1441690/#msg1441690

[manganin]

It might be 419A-like, but it ain't no 419A.

Actually it is. The aluminium box, containing the 419A printed circuit boards, even has an HP serial number plate.