My 731A also drifts all over the place. The LM399 I am making was first ment to become a replacement for use in the 731A, and like you, use the diverder. But not any more, I have a LT1027B reference that is on 24/7 for about a year and nice behaving. The 1027 behaves better as my 731A and delivers 10V . Weak point is the resitors i used to adjust it to 10V. ( I was young and.... ;-) ) I plan to change that using better ones and a better construction and after that, use that to feed the divider of the 731A. Also replaced the opamp of the 731A for a better one but that improved only a little. Then use a chopper opamp with LM10 as buffer on the output of the 731A so its output impedance will be lower and it will be able to be used direct without a null detector, or before a KV devider without collapsing.
Fred PA4TIM Op 17 sep. 2012 om 14:38 heeft "J. L. Trantham" <[email protected]> het volgende geschreven: > Pete, > > As far as the connection goes, the current resistor wire appears to be > 'soldered' to what appear to be gold plated steel wires (very stiff yet > bendable). If the temperature is relatively stable, it should not be too > bad a problem as far as the repair goes. However, it seems to drift all > over the place. > > I changed the Op Amp to no benefit. > > I am leaning to switching to a different voltage reference. I have a > 'spare' reference board from an HP 3458A and it would make a good project to > install this, change the wiring to the Op Amp to adjust the 'other side' of > the Op Amp input to adjust to 10.000000 VDC and still be able to use the > output divider in the 731A to get the rest of the voltages offered by the > 731A. > > Joe > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Pete Lancashire > Sent: Sunday, September 16, 2012 4:03 PM > To: Discussion of precise voltage measurement > Subject: Re: [volt-nuts] Fluke 731A Transfer Standard and Fluke Wire > WoundResistors > > > There is a good chance the wire is Manganin or an allow that is similar. > > If what you use to connect to the resistance wire is not the same you run > into things like EMF (think thermocouple) being created at the repair. > > -pete > > On Sun, Sep 16, 2012 at 1:36 PM, J. L. Trantham <[email protected]> wrote: >> I have been following the discussion about the LM399 heater, noting >> mention of the Fluke Wire Wound resistors used often in Fluke >> precision equipment. >> >> >> >> I have a 731A that I have been resuscitating and have found that the >> R8A R8B wire wound resistor is failing. Initially, the source was >> very unstable then went to about 8 VDC. This led me to an open R8B. >> I was able to ‘reconnect’ the broken ends, loosing about half a turn >> of wire. Then, again, unstable and went to about 13 VDC. This led me >> to an open R8A. Again, able to reconnect, and, again, loosing about ½ >> turn. >> >> >> >> It appears that the wire is corroded with corrosion leading to >> failure. This brings up several questions. >> >> >> >> 1. What are the benefits of these wire wound resistors? Tempco? >> Ability to construct precise resistance? >> 2. Is there a source of the resistance wire used in these resistors > so >> that the resistor can be reconstructed? I think the resistance is in >> the 30 to 40 ohms per foot range. Something like 36 to 38 gauge >> Nichrome 60 would work but it has to be insulated. >> 3. Would it be better to look for a collection of commercial > resistors >> to ‘replace’ R8A, R8B? If so, what? The manual states that IC2, the >> voltage reference, R6, R7, R9, and R10, are ‘factory selected’ and all >> appear to be OK. >> 4. Would it be better to completely abandon the voltage reference >> section of the 731A in favor of a ‘new’ (perhaps LM399, LTZ1000A, >> etc., >> based) reference to generate 10 VDC and still use the output divider of > the >> 731A to generate the remaining voltages? >> >> >> >> The 731A manual and schematic are here: >> >> >> >> http://www.ko4bb.com/Manuals/Fluke/Fluke_731A_Transfer_Standard_Instru >> ction_ >> Manual.pdf >> >> >> >> R8A is the ‘high’ side of a voltage divider with R8B, R9, R10 and R11 >> (a 10 ohm, 20 turn pot) forming the ‘low’ side, dividing 10 VDC to >> feed the voltage reference, IC2, a DH80417B. The op amp, IC1, used to >> generate the 10 VDC is an LM301AH. >> >> >> >> R8A measures about 5903 ohms, R8B measures about 11558 ohms, R9 >> measures about 78.02 ohms, and R10 measures about 399.8 ohms. >> >> >> >> Thanks in advance for any and all information and suggestions. >> >> >> >> Joe >> >> _______________________________________________ >> volt-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
