ESI 242D and 707B - how useful? - Page 1
Forum section: electronics / general

author: Rax
author_rank: Super Contributor
timestamp: October 25, 2023, 12:35:59 pm
content: 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!

author: Rax
author_rank: Super Contributor
timestamp: October 25, 2023, 01:00:40 pm
content: 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.

author: guenthert
author_rank: Frequent Contributor
timestamp: October 25, 2023, 01:07:02 pm
content: 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)

author: Rax
author_rank: Super Contributor
timestamp: October 25, 2023, 03:05:53 pm
content: Quote from: guenthert on October 25, 2023, 01:07:02 pmOf 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.

author: manganin
author_rank: Regular Contributor
timestamp: October 25, 2023, 06:55:25 pm
content: Quote from: Rax on October 25, 2023, 12:35:59 pmhttps://www.eevblog.com/forum/metrology/esi-242d-(sp3632)-resistance-bridge-for-sr104-intercomparison/

author: alm
author_rank: Super Contributor
timestamp: October 25, 2023, 07:38:49 pm
content: 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 toits manualit'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.

author: Rax
author_rank: Super Contributor
timestamp: October 26, 2023, 02:11:31 am
content: Quote from: manganin on October 25, 2023, 06:55:25 pmFantastic, thank you. This particular unit I am contemplating is an SP3623/242D, so I guess low tempco.

author: Rax
author_rank: Super Contributor
timestamp: October 26, 2023, 02:19:38 am
content: Quote from: alm on October 25, 2023, 07:38:49 pmVery 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.Quote from: alm on October 25, 2023, 07:38:49 pmThat'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.

author: manganin
author_rank: Regular Contributor
timestamp: October 26, 2023, 06:44:35 am
content: Quote from: alm on October 25, 2023, 07:38:49 pmDespite the "mediocre" overall specifications of the bridge, the internal 1000 pF reference is an unboxed ESI SC1000 standard capacitor ...

author: alm
author_rank: Super Contributor
timestamp: October 26, 2023, 07:22:50 am
content: Quote from: Rax on October 26, 2023, 02:19:38 amThere 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'seveneither a HP419 or Keithley 155. I don't see a use for the source or the bridge outside the system.

author: ap
author_rank: Frequent Contributor
timestamp: October 26, 2023, 07:46:15 am
content: 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?

author: alm
author_rank: Super Contributor
timestamp: October 26, 2023, 10:12:44 am
content: 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.

author: manganin
author_rank: Regular Contributor
timestamp: October 26, 2023, 01:19:57 pm
content: Quote from: ap on October 26, 2023, 07:46:15 amI 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.

author: Rax
author_rank: Super Contributor
timestamp: October 26, 2023, 02:06:35 pm
content: Quote from: alm on October 26, 2023, 07:22:50 amThat'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.

author: manganin
author_rank: Regular Contributor
timestamp: October 26, 2023, 02:50:58 pm
content: Quote from: Rax on October 26, 2023, 02:06:35 pmThose are just pull-out shields. It is only the friction of the banana plugs that keeps them in place.

author: alm
author_rank: Super Contributor
timestamp: October 26, 2023, 08:47:17 pm
content: Quote from: Rax on October 26, 2023, 02:06:35 pmI 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?).

author: Rax
author_rank: Super Contributor
timestamp: October 27, 2023, 04:30:32 am
content: Quote from: alm on October 26, 2023, 08:47:17 pmI 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.

author: alm
author_rank: Super Contributor
timestamp: October 27, 2023, 06:04:14 am
content: I think that contains a HP 419A and that the K155 versionlooks like thiswith the mirrored scale and going down to 1 uV F.S.

author: donlisms
author_rank: Frequent Contributor
timestamp: October 27, 2023, 05:44:45 pm
content: 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.

author: Rax
author_rank: Super Contributor
timestamp: October 28, 2023, 01:30:21 am
content: Quote from: donlisms on October 27, 2023, 05:44:45 pmSelf deprecating humor a value you cherish?...

author: donlisms
author_rank: Frequent Contributor
timestamp: October 28, 2023, 02:30:54 am
content: I don't think much about self-deprecation one way or the other, just clarity! :-)e

author: alligatorblues
author_rank: Regular Contributor
timestamp: October 29, 2023, 07:06:53 am
content: Quote from: donlisms on October 27, 2023, 05:44:45 pmThen 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.

author: donlisms
author_rank: Frequent Contributor
timestamp: October 29, 2023, 09:43:40 am
content: Quote from: alligatorblues on October 29, 2023, 07:06:53 amI 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.

author: guenthert
author_rank: Frequent Contributor
timestamp: October 30, 2023, 08:24:01 am
content: Quote from: Rax on October 27, 2023, 04:30:32 amThe 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 ofcalibratedstandard resistors in a temperature controlled oil or air bath, the 242D is a heavy paperweight.E. Pettis was fond of his 242D iirc , but he was in the business of manufacturing small series precision resistors. I'm sure he found ituseful.https://www.eevblog.com/forum/metrology/want-to-measure-resistance-with-high-precision-what-would-be-best-to-get/msg1441690/#msg1441690

author: manganin
author_rank: Regular Contributor
timestamp: October 30, 2023, 02:37:13 pm
content: Quote from: guenthert on October 30, 2023, 08:24:01 amActually it is. The aluminium box, containing the 419A printed circuit boards, even has an HP serial number plate.

author: Rax
author_rank: Super Contributor
timestamp: October 30, 2023, 02:41:35 pm
content: Quote from: manganin on October 30, 2023, 02:37:13 pmBut no trace of (mercury) battery, correct?

author: manganin
author_rank: Regular Contributor
timestamp: October 30, 2023, 03:00:45 pm
content: Quote from: Rax on October 30, 2023, 02:41:35 pmSorry, but I can't remember. Must be ten years since last opened. (And I sold the whole bridge to a forum member earlier this year.)

author: alm
author_rank: Super Contributor
timestamp: October 30, 2023, 04:11:08 pm
content: Quote from: guenthert on October 30, 2023, 08:24:01 amFor best accuracy, you can use the 240 and 802 to compare two resistors that are close in value. Or use the 925 as tare resistor in parallel with one of the resistors, so its contribution to the uncertainty becomes much less.To measure relative differences between resistors you don't need a calibrated standard resistor. You can measure that resistor1 is resistor2 + 5 uOhm/Ohm very well without knowing the value of either resistor precisely.

author: retroware
author_rank: Contributor
timestamp: October 30, 2023, 04:51:04 pm
content: As someone who recently acquired a R925D to complete (I used to only have a the non-adjustable 925) my 242D system I have a couple of comments:First, there is no mercury battery in the 419 equivalent null detector. The battery was for nulling out the input voltage. This is not needed when used as a bridge detector.The thing I find fascinating about all of this early metrology gear is how accurate a mostly passive only system can be. The 242D specs are 10ppm from 1 ohm to 10M. This is about as good as the 90 day spec of the 3458 (and better at the high end of the scale). Furthermore, it can be self calibrated with only a single 10K standard resistor (the same as the 3458).Granted, for almost every application I can think of I would use my 3458 as opposed to the 242D. But as a collector of vintage metrology gear, I find this system fascinating (plus who doesn't love adjusting 40+ pots!).

author: Rax
author_rank: Super Contributor
timestamp: October 30, 2023, 06:00:09 pm
content: All this is so helpful, thank you all. Some conclusions:The real deal breaker may actually be the most prosaic of them all - size. I have not actually seen the instrument - just pictures from the seller, who is a very respectable dealer of sorts from this neck of the woods - so I never quite gotten a real sense. But I think I have enough now to work with, and space is not something I have an excess of. Now, I don't really have an urgent and frequent need for this (but more on this below). Frankly, one of the reasons that may have worked is if I could utilize the different parts for their separate duty, so I could replace some of my existing units with these, gain functionality, while not sacrificing space.The lack of the battery suggests the 419A within this is missing functionality the standalone has - which I haven't thought through (still far from home, with very little time and no manuals handy to map this out) - so that's much of a gain either.The overall question on "what's this good for in my activity" hits at the core of a bigger question for me, which I admit I don't have a lot of clarity. Heck, I have no answers to. Which is what do I hope to do with all this, which is essentially a (very serious) hobby. So, fair question, but I'll likely have a rather vague and wishful answer to it.

author: donlisms
author_rank: Frequent Contributor
timestamp: October 30, 2023, 06:28:42 pm
content: I am also fascinated by these early techniques. There is no question that is much more convenient to use a 3458a, but it seems like an awful lot of things have to go right for such an instrument to produce good answers. I read of the struggles in repair and calibration and cost, and I know the 3458 is not for me.I real a lot of the earlier papers from the NBS and others, Frank Wenner, James Thomas, Edwin Northrup, and others, building on the work of Jimmy Maxwell and so on. It is interesting (to me) to see how they did so much with so little, and figured out many concepts that we still rely on (and often make oh-so-much-more complicated!).Bridge techniques rely much more closely and simply on the fundamentals of physics. The behavior of current flow, and the reliance on a relatively simple and self-verifiable null detector. It's all the ratios. Direct or only-slightly-indirect comparison of a standard resistor against the unknown, where the measurement is determined by a variable resistor whose accuracy and characteristics are improved by a factor of 10,000 by putting it in the middle of a much larger fixed resistance, that sort of thing. Clever techniques based on the simple mechanisms available in the day. Measurements made at ppm's without any amplifiers. Without any amplifiers. Verifiable ratio techniques throughout, and somewhere... one (or more) calibrated standard resistor(s) to provide the absolute reference(s). Some (provable) Hamon buildups to scale the ratios up and down, verify linearity, and so on.At last for resistance. I suppose there are similar techniques for voltage measurement, but I don't pursue that at this juncture.My impression of modern test gear is that measurements pretty much always rely on internal resistors, anyway. They're inside there, and there is no normal hands-on with them; you may not think about them specifically, and just kinda trust that they're still right. It's way easier, and I don't discount that, but to my thinking, there are more assumptions involved. (And money!). You don't have to (but probably will anyway!) make a hobby of making/keeping it all working right. :-).And you probably SHOULD have at least a couple of calibrated resistance standards around your lab, anyway, no? So it seems like it sorta comes down to letting your meter make a comparison with its internal standards, or having your standards out on your bench (or in the 925D, which is not necessarily required).--It is 19.5 inches wide ((standard 19" rack), 20" tall (3sp + 3sp + 4sp) * 1.75 + filler strips), and 12.5" deep. I don't know what that is in metric inches, but I'm pretty sure it's still... big. It's liftable by one person, occasionally. I am putting mine a rolling wire-shelf cart that fits it pretty snugly, and then there's space for other gizmos on the shelves, and I can move it away when I'm not playing with it.I think I would only get one if I (1) really cared about fundamentally-implemented resistance measurements, enough to invest more time and effort in, for example, building some good Hamon standards, and working on calibration, and (2) had the space, or could make the space, and (3) had the money thing.

author: Rax
author_rank: Super Contributor
timestamp: October 30, 2023, 08:13:54 pm
content: Quote from: donlisms on October 30, 2023, 06:28:42 pmWhat I have around already providing roughly what this offers (a Prema 6048 - so 8.5 digit capabilities -, a full set of ESI SR1s, a Fluke 5450, an ESI RV722, and a bunch of other such things) has the advantage of being economical on space. I actually have a very real problem of lack of space and have to consider getting rid of some of the units I have here. And hobby budget is obviously limited, so.Some of this type of mechanical self-adjusting was replaced in newer models by all sorts of selfcal and int cal and other such ADC/data driven approaches. It's pretty interesting from a historical perspective, actually.