ESI 1040A Guarded Volt Box - Page 1
Forum section: electronics / general

author: vsmith
author_rank: Regular Contributor
timestamp: March 13, 2019, 08:00:35 pm
content: Hi fellow measurement geeks,I am a long time lurker, first time poster, hoping that someone reading this forum can help me (and am willing to help others with similar requests!)I recently acquired an Electro Scientific Industries model 1040A Guarded Ab solute Volt Box. It is basically a precision guarded voltage divider, with a built in Wheatstone bridge type circuit which allows "on the bench" calibration of the measurement ratios (.01 or 0.1) through inter comparison of the divider resistors.(Picture attached)The unit is in good shape, nice and clean inside, and all resistors appear to be intact. What I need is an operator's manual so that I can be sure I am using it correctly. (My goal is to use it as a means of calibrating 1000 and 100 volt sources using a 10 volt reference and comparing the reference and divided source voltages using an 8 digit (Datron 1082) DMM.)I do have some ESI sales brochure type info for a similar unit (Model PC 1040) which was a guarded volt box used as part of their model 731 DC Ratio and Voltage Calibration System. Unfortunately, there is no detailed user info or schematics/parts lists in what I have.Searches on Google have not yielded any info at all.So if anyone here has any info for this unit (or knows of a source for ESI documentation) I would very much appreciate your help! I really like ESI equipment and have ended up with quite a few pieces and do have some documentation for a few of their products (as well as said sales info ca 1964), please let me know if I can help any of you with ESI info. I am happy to pay for duplication costs for manuals. Thanks!

author: Echo88
author_rank: Frequent Contributor
timestamp: March 13, 2019, 08:42:05 pm
content: Welcome aboard!I also couldnt find the manual when i looked at this baby on ebay a few days ago and therefore lost interest. Good to see its got a good new owner.If possible could you make a few photos of the inside, so we can enjoy the build-quality?Which ESI-equipment do you own? Maybe theres some device who also isnt documented/doesnt have a teardown yet on the internet and would be of interest here.

author: vsmith
author_rank: Regular Contributor
timestamp: March 14, 2019, 12:40:29 am
content: Thanks for your interest. I decided to go ahead and buy it because the concept of a self-calibrated voltage divider (similar to that same feature used in the Fluke 720a) seemed like a winner. And I did have the sales info which described it's accuracy and utility.My tests indicate that it is within 2-3 ppm of my Fluke 720a for both the 0.1 ands .01 ratios. I think I have figured out the self calibrating procedure, but also feel that I am missing something important (for example: there are 4 adjustable resistances and 2 ratio comparisons, which tends to lead to multiple "correct" balances) My solution for that until I get further info is to arbitrarily set one of the trimmers to it's index mark (100 on a 0-100 scale) and balance the other two against it. Suffice it to say, I am definitely shooting in the dark at the moment, and it's nothing you could use for certification of calibration! It does show everything seems to be working though.Here are a few photos of pages of the sales info I have on the 1040A. I will take more comprehensive (interior) photos and post them in a day or two.As far as other ESI equipment, I own:(2) RV-722 7 decade Kelvin-Varley dividers290A Impedance Bridge865A AC/DC Generator Detector(2) DB62 Decade Boxes (overlapping ranges)SV94B Voltage Calibratorand a few SR1 standard resistancesI love their stuff because of the engineering and design as well as the "look" of it. I feel that there must be documentation out there, since their stuff appears so often on eBay. I hope this post will help me find more of it. In a later post I will try to list the documentation I do have, which may be of interest to others.

author: Kosmic
author_rank: Super Contributor
timestamp: March 14, 2019, 02:07:32 am
content: Hehe I was also watching this nice instrument when it was getting sold on ebayShipping was just too much for me.Do you, by any chance, have the manual for the SV94B Voltage Calibrator and the RA79 Quadrature voltage generator ?I also have a collection of my own here:ESI RV722 Kelvin-Varley voltage dividerESI DT72A Standard Decade TransformerESI 240 Kelvin Ratio BridgeESI RA79 Quadrature voltage generatorESI SV94B Voltage Calibrator

author: CalMachine
author_rank: Frequent Contributor
timestamp: March 14, 2019, 03:54:18 am
content: Looks like a rather nice piece of equipment you found hereI've always loved ESI gear and I've not seen much in regards to this particular one.I've got an ESI RV726A, a 242A setup, as well as an oddity volt-ohm box (I'll have to retrieve the model number when I get a chance).

author: vsmith
author_rank: Regular Contributor
timestamp: March 14, 2019, 07:44:48 pm
content: Here are a few more pictures of the unit. The circular orange stickers on three of the wires are to help me remember the connection points for each of the decade sections. As you can see, the unit has 4 D cells (which power the internal bridge detector). These were dated "use before 2024", so fairly recently installed. Also, you may notice a blue 1% resistor soldered across one of the precision resistance elements. I am pretty sure this was added by an owner. It is an element in the bridge section, and I am leaving it there for now, until I am sure what it's purpose was. The value is 120K, and the resistance it parallels is in the order of 5K, so evidently it servers to trim that value.The resistances are arranged in two sets, one for the working divider, and one for the "shadow" guard circuit. That's right, each and every resistance in the divider strings has a twin in the guard circuit. The high side connectors all have a guard ring, and as you can see, each connection point for an element in the divider has a guard ring as well. Pretty fancy.Please let me know your thoughts and questions if you have any!

author: vsmith
author_rank: Regular Contributor
timestamp: March 14, 2019, 08:11:19 pm
content: I do not have the manual for the SV 94B, but I do have some sales info that mentions it, and includes a schematic. (attached) I assume you know what it's design purpose was. I have used it to calibrate 100 and 1000 volt sources using a DMM on it's 1 volt range. Works great.

author: Kosmic
author_rank: Super Contributor
timestamp: March 14, 2019, 11:06:43 pm
content: Thank you for the info. much appreciated!I didn't open mine yet, but looking at the schematic make me realize it could maybe be rewire to support 10v on the calibration port.

author: mvanocht
author_rank: Contributor
timestamp: March 15, 2019, 01:57:42 pm
content: So which came first, the ESI 1040A or the Fluke 752A?

author: Bill158
author_rank: Regular Contributor
timestamp: March 15, 2019, 04:54:10 pm
content: Quote from: mvanocht on March 15, 2019, 01:57:42 pmThe 1040A was first by many years. Around 1964 was the first production. AFAIK. You needed a RV622 or RV722 KVD to extend the output down to 1.018xxx V or 1.019xxx V standard cells. The 1040A had a basic accuracy of 10:1 of 2ppm and 100:1 of 4ppm. The 1040A had a built in null detector.Fluke had the 750A around 1968. It had a basic KVD built in, so to speak. At least you could compare various input voltages between 1.1 to 1000VDC (in specified steps) to 1.018xxx or 1.019xxx standard cells. Standard cells were the DC Volt standards of the day. The 750A was speced at +/- 10ppm transfer accuracy to the 1.01xxxx outputs.The 752A was around 1984 and had a basic 10:1 accuracy of 0.2ppm and 100:1 accuracy of 0.5ppm and then could be used with the 720A KVD to extend the output to the 1.01xxx of standard cells.You needed a Fluke 845 null detector for the 750A, 752A and 720A to make the necessary adjustments and measurements.All of the above had adjustments for corrections for resistor drifts and temperature drifts.Bill

author: vsmith
author_rank: Regular Contributor
timestamp: March 15, 2019, 09:31:31 pm
content: Many thanks to Bill for supplying me with a (faded but still readable) copy of the owners manual for the 1040A.While I was on the right track in terms of how to use and self-calibrate the dividers, I would never have known some of the caveats and order of operation steps required. With the manual, I was able to calibrate my 1040A (so it seems to be working properly in all respects) and came up with divider ratios that meet the advertised specs (at least according to my Fluke 720A KVD) Now I know what all of the control labels mean! It is a very good design. and now a permanent member of the cal collection.By the way, just as a footnote to Bill's history lesson above, I believe the Fluke 720A to have been a functional predecessor to the 752A. It is a 1100 volt capable 7 section KVD with self-calibration features, providing a fractional ppm linearity at calibration. And had the KVD advantage of 7 digit ratio settings too! The ESI RV622 and RV722 were the same idea, but the 720A allowed a higher voltage input and had self-calibration. A true top shelf design, IMO.My next experiment is going to be an attempt to find out how well (or poorly) the 1040A does with ac voltages in the order of 60 and 400 Hz. I want to compare it with my Gertsch Ratio Standard (which will not allow voltages anywhere near as high as 1KV)Has anyone experimented with using dc dividers at ac powerline frequencies?Vic

author: GEOelectronics
author_rank: Regular Contributor
timestamp: July 15, 2019, 06:11:07 pm
content: If possible would you please forward a copy o9f the manual to me at:GEOelectronics@Rallstech.netThanksGeorge Dowell

author: texaspyro
author_rank: Super Contributor
timestamp: July 16, 2019, 02:07:26 am
content: Also send it to ko4bb.com for the world to enjoy...