Ed, Your are right, it is quite expensive and difficult to send something to NIST. BUT all is not lost as other alternatives do exist.
Besides NIST, other cal labs referred to as type 1 and type 2 exist with more than enough capability to handle fairly strenuous requirements of most of the modern test equipment. A type 1 lab is one step below a primary lab and, obviously, a type 2 lab is under the type 1 with lessor capability. These designations are used with the military labs, but there is a relationship to the commercial labs. For instance, Fluke and Hp have (had?) both a primary capability in their respective fields and type 1 level. Most of the really major manufacturers supporting military contracts have at least a type 1 lab and some of them have primary capability in some fields. Except for Fluke and Hp, the others, above, would not take work from outside sources like you or me. There are plenty of commercial enterprises that have so called cal labs that are at least at the type 2 level. Unfortunately, also a number of them do not qualify either because they do not have the properly maintained standards or they fail due to quality of their personnel. A really decent commercial lab would be cheaper than NIST and can easily handle top of the line DVMs referred to elsewhere. It would not hurt to see what Fluke would charge to calibrate their 731 or 732 voltage reference or one of their very good DVMs. The best item for an individual to own is a truly top of the line DVM. It provides a reasonable reference for DC, AC, and Ohms that far surpasses what most hobbyist and for that matter most companies would ever need. As for the Geller unit, I have a problem with people who advertise such stuff to unsuspecting buyers with such fanfare. Too many people have no clue and develop a false sense of security relative to what they thought they purchased. Here is a good app-note from the Linear Technology that discusses the various issues about voltage references: http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1021,P1567,D4171 Although it is well worth reading, it does not cover off board issues like thermals in the hook leads or external guard circuits and 4 wire connections besides other things. One last issue, that of NIST traceability. For the largest part this statement really means that a measurement method was followed. It does not necessarily mean a direct comparison was made with NIST. Many people I have talked to have a misconception wrapped around this phrase. Bill....WB6BNQ Ed Palmer wrote: > Bill, > > I agree with the comments made by you and everyone else. That's why I said > "..if it's good enough..". But there's one thing that kind of slid by > everyone. All the other suggestions conclude with some variation of "..needs > to be calibrated..". Is there any other way to get a NIST-traceable voltage > into your shop for $35? (I'm not challenging you, I'd really like to know if > there is another alternative) Granted, it's only at the 10 uv level, but for > many applications that *is* good enough. > > Let's be honest, as time-nuts we're spoiled rotten. Almost all of us have > got rubidium standards at 10E-11 per day or better and at a ridiculously low > price. Many have got cesium standards and a few have got hydrogen masers. > We can calibrate them against GPS or Loran-C to obsessive-compulsive levels. > So far, none of the other physical standards allow that level of independence > for hobbyists. So when dealing with other measurement units (e.g. volts, > ohms, etc) we either have to ease the requirements by orders of magnitude or > increase the budget by orders of magnitude! > > If you're doing this as part of your job and can justify the need and the > expense - great! I'm a hobbyist and I won't be spending $1843 any time soon > to have NIST calibrate a DC solid-state voltage reference. For my needs > Geller Labs provides good value for the very nominal cost. > > And just to be clear, I have no relationship with Geller Labs. > > Ed > > WB6BNQ wrote: > > > No way in hell does that thing qualify as a voltage standard. It barely > > qualifies as a VERY short term transfer device assuming the temperature > > does not change. > > > > If you want a real voltage reference then buy, from eBay, a Fluke 731B > > voltage standard. You will still need to get it calibrated, but then it > > will hold under 10ppm for well over a year or > > more. Actually, if they are adjusted correctly, you can get less than 5ppm > > and it will hold it at a given temperature. These items are serious > > devices and their latest versions (very expensive) > > are better than a properly maintained and operated group of standard cells. > > > > I completely disagree with Brian about buying any standard cells. Whatever > > voltage value they had is lost upon shipment. Shaking the cells changes > > the value and it will not return to the > > original value. If you did have a set of cells, you would want at least 4 > > of them. Then study statistical math all over again because you will need > > it to use the cells. > > > > As Brian does suggest, you would be much better off picking up a hp3456A, > > 3457A, 3458A or getting one of Fluke 8500 series if it has the Ohms and AC > > options included. The basic Fluke 8500 series > > is DC only mainframe. > > > > Measuring your resistors, using one of the above DVMs, in the 4-wire mode > > is about the best you could possibly do. To do any better would require > > some very serious effort. > > > > By the way you could buy several of the latest and greatest Fluke super > > DVMs for the cost of what it would take to do a Josephson array and still > > have money left over to fund that divorce. > > > > Bill....WB6BNQ > > > > > > Ed Palmer wrote: > > > > > >> It's nowhere near the idea of a Josephson array, but if a NIST-traceable > >> 10V +-10uV reference is good enough to satisfy your voltage-nut urges, you > >> can buy it from www.gellerlabs.com for $35. > >> > >> I also have a few standard resistors (e.g. 1.000002 ohms) that I'd be > >> interested in calibrating, but I can't seem to come up with a practical > >> way of doing it. > >> > >> Frustrating, isn't it? :-) > >> > >> Ed > >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
