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Thoughts on Winding Down

 

It has been great fun thinking about new projects and ways to share projects as plans and kits.

Many of you have contributed your valuable time, ideas, and expertise to further our efforts. It was a special pleasure when someone reported success with a project or good results using one of our transfer references.

The business loans are just about all paid, and we are finally near a break-even point! However, the sad truth is, our present business plan is not commercially viable. So it's not a bankruptcy, just an ideal time to make a good decision.

The present plan is to wind the current business down around the end of this year.

All copyrights remain in effect, however feel free to copy anything from the website for personal use. The website might remain up for the pre-paid plan some months out, or might come down sooner.

I will continue to support several projects in progress beyond the business wind down.

(be sure to hit refresh to see our latest changes!)

Since first offered in 2004, many hundreds of SVR boards are now in use world wide.

The SVR Series

 

Sold out (currently not in stock): $74.95 SVR-T A 10V reference board supporting a monolithic Analog Devices AD587LQ (ceramic package) voltage reference chip with a trim circuit for calibration as a transfer reference. The -T option adds a 100 kilo ohm thermistor in series with a fixed temperature compensation gain resistor for a secondary temperature compensation scheme (developed by Lars Walenius, Sweden).

Summer-time (U.S., North America) calibration is performed at 24 C. Special temperatures can be accomadated by pre-order, if received while we are preparing the secondary correction circuits, or can hold over to the next batch.

To build a SVR-T board (schematic diagram), a burned-in non-option SVR is temperature slowly cycled (about 7 hours) in the micro-Environmental Chamber (Details) to determine the value of the fixed temperature compensation gain resistor. After installation of the thermistor and gain resistor on the underside of the board, the board is re-calibrated to our 10 V reference point and then temperature cycled again (+/- 1c) to verify the operation of the secondary correction. The process takes many hours. Presently, initial tempco testing (7+ hours per board with a semi-automated test procedure). After secondary temperature compensation final testing (another 7+ hours per board) is performed before a blob of thermal epoxy is applied to a group of nearly finished boards. Each board is run once more before shipping to verify the 10 V calibration point, as well as to record the uncorrected, uncompensated output voltage with the trim jumper removed.

Short term transfer accuracy: better than +/- .0005% absolute (+/- 5 ppm), guaranteed to remain longer term (6 months) within +/- 500 uV (+/- .005%) of absolute as rated 1. {<1 ppm / ºC} (AD587LQ CERDIP)

Price Change Notice: SVR-T prices have increased to $74.95 to better reflect the tens of hours invested in each board as well as our payment for the FLUKE 732B annual calibration, which is now approaching $1,000 with insured shipping both ways. The replacement cost for the FLUKE 732B is well over $6,000 for insurance. We only learned last year that had the unit had been damaged either way without the extra shipping insurance, we would have only received about $100.

Recalibration (our boards only) has changed to $20 plus return shipping cost. Includes a 7+ hour run through our micro-environmental chamber to measure the +/-1 c temperature coefficient.

 

SVR

 

SVR: NOT AVAILABLE AT THIS TIME - $39.95 SVR A basic 10V board supporting a monolithic Analog Devices AD587LN voltage reference chip with a trim circuit for calibration as a transfer reference. Short term transfer accuracy: better than +/- .0005% absolute (+/- 5 ppm), guaranteed to remain longer term (6 months) within +/- 500 uV (+/- .005%) of absolute as rated 1. {5 ppm / ºC} (AD587LN) User specifies a desired temperature for calibration following burn-in. We set that temperature using our micro-Environmental Chamber (Details).

 

Other Voltage Reference items:

$20 Recalibration at 10 V, plus return shipping Only for our assembled 10 V products, please state what temperature you would like us to use for calibration.

$5.95 SVR Bare PCB SVR bare printed circuit board with no other parts. Up to two SVR boards can ship in an envelope ($0.50) and ship by USPS Priority Mail or USPS First Class International Mail ($1.25).

$25.95 10 V SVR kit of parts AD587LN chip (plastic), does not include solder when shipped to EU countries. Step by step SVR assembly instructions (needs more detail on the trim components for later, but you can get the idea)

 

Since first offered in 2004, many hundreds of SVR boards are now in use world wide.

SVR boards can ship in the US by USPS Priority Mail for about $6.50. International buyers please contact us or check USPS prices for 6 ounces (oz), SVR shipping box is 7"x 5" x 4" (example: $12.75 to Italy and Germany via USPS First Class International Mail). PayPal is okay for international orders; PayPal email address: joegeller at roadrunner dot com

There have been no credible reports of sensitivity to normal variation in Barometric pressure. The ceramic package LQ boards are substantially insensitive to humidty. Plastic package LN part sensitivity to humidity is not well understood, however believed to be small for the relatively large DIP 8 package.

Short term transfer accuracy applies in the short term at the reported temperature and at the specified power supply voltage (15.0V for 10V SVR references) after of warm up period of 30 to 60 minutes, <10 ppm within 5 minutes.

The SVR requires an external (not supplied) single 15 VDC power supply, preferably using a linear regulator. With no load on the SVR board, the board draws on the order of 2 mA. A 15 VDC linear power supply rated at 80 milliamps or more is recommended. For relatively low accuracy applications (.01%), two 9V batteries in series can power the board at about 18 V.2

SVR (boards only) are now RoHS compliant, and can sell again to EU countries.

SVR Specifications:

Temperature Coefficient "L" grade: 5 ppm / ºC

Short term transfer accuracy: better than +/- .0005% absolute (+/- 5 ppm).

Short term transfer accuracy applies in the short term at the reported temperature and at the specified power supply voltage (15.0V for 10V SVR references) after of warm up period of 30 to 60 minutes, <10 ppm within 5 minutes.

All reference boards and boxes are calibrated to within +/- 10 uV absolute and guaranteed to remain longer term (6 months) within +/- 500 uV (+/- .005%) of absolute as rated.

Extra trim resistors are added to narrow the trim range for easier calibration. Calibration data is reported to 10 uV resolution (.0001%).

More Details on the Micro-Environmental Chamber for Tempco testing and calibration at custom temperatures.

We try to be very clear about what this project is about. We are attempting to provide a low cost absolute voltage calibration point targeted to the amateur scientist, electronics hobbyists, consultants, and schools. Our SVR product is a high quality platform for the AD587 family (in our opinion) some of the best voltage reference chips ever made.

We call the SVR board a "transfer reference". The SVR board is a high quality platform for a monolithic reference chip, nothing more.

Our Fluke 732B, even with its FLUKE NIST traceable calibration, in the art of metrology, is generally referred to as a "transfer standard".

The SVR board is intended to give a small lab a way to verify their 10 V calibration point to better than 10 ppm (100 uV absolute). Our field tests have done considerably better, however 10 ppm is our conservative spec. Since the SVR board is rated at 5 ppm/c, the board should be used at about the same temperature as we calibrated the board (as reported) after a warm-up period and at about 15V. The reference chips we use are rated at 100 uV / V (power supply), however most perform much better.

The specifications are, for all practical purposes, the specs of the chip itself, and is not degraded below spec by our precision trim circuit which uses high quality IRC 0.1% 20 ppm/c trim resistors (the 20 ppm/c is per resistor, not tracking, and it is of the trim range, thus not deteriorating the board 5 ppm/c rating, and the 100 ppm/c trimmer is a small fraction of the IRC trim Rs). The boards are burned in for 300+ hours before final calibration. Final calibration is done with our Agilent 34410A and/or FLUKE 845AR null meter referenced to the 732B. (A "calibrated" hp or Agilent 3458A -alone- is no longer sufficient at 10 ppm absolute and below.)

The details of high precision use, 30 to 60 minute warm-up, use as close the temperature where we did the calibration, power supply voltage of 15V +/- 0.1V are all just to squeak the last ppms possible (to get as close as possible to our 732B voltage) using this relatively inexpensive method. At relatively low precision (e.g. 0.01%), these are all non-issues.

The AD587 series reference chips are rated at 15 ppm / 1,000 hours of operation. Very close inspection of most monolithic reference chip family specification sheets reveals a 1,000 hour rating generally ranging from 10 to 60 ppm / 1,000 hours. See also ADI Application Note AN-71, The Effect of Long-Term Drift on Voltage References by Colm Brazilon reference drift with time.

All checks and money orders should be made payable to "GELLER" (not Geller Labs, the name of our website). Please see our ordering page for more information.

 

Our Low Cost Voltage Transfer Project for Amateur Scientists, Electronics Hobbyists, and Schools, was Supported in Part by Analog Devices Incorporated. Please visit the Analog Devices website!

 

Need to find a page from a discontinued project? If the pages are still posted at our website server, you might find the page using the GoogleTM search bar from our home page .

 

1 By maintaining a calibrated Fluke 732B transfer standard in conjunction with our 34410A and/or FLUKE 845AR null meter referenced to the 732B we are able to offer NIST traceable references at affordable prices. Our 732B is under a Fluke calibration contract.

2 Suitable Power Supplies: Inexpensive linear "open frame" supplies can be used. For example, 15 VDC models rated at 0.4A, 0.8A, 1A, and 1.5A are generally available at surplus and auction sites. Remember to add an AC power fuse when using open frame supplies and for those less experienced, please observe standard line voltage safety practices (e.g. cover exposed AC line connections).

COPYRIGHT © 2005, 2009, 2010, 2011, 2012, 2013 JOSEPH M. GELLER, All rights reserved.

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