[volt-nuts] Fluke 732A themistor reading

[acbern at gmx.de]

well, re. the resistor, question is how stable it is, not so much absolute value. if not very good, your 3458a may be more stable that your reference. vpg hermetic foil 4 wire resistors are very stable (1ppm pa) and are cheap (<50usd).

re the wire, you should use twisted shielded pair. there are good teflon tsp wires with kapton isolation (as used in satellites) on sale on ebay. use copper gold plated terminals, around one usd and crimp them. pure copper wire is not needed.

cheers

adrian


> Gesendet: Montag, 18. August 2014 um 01:03 Uhr
> Von: "Randy Evans" <randyevans2688 at gmail.com>
> An: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Betreff: Re: [volt-nuts] Fluke 732A themistor reading
>
> I do have an ESI SR1 10Kohm standard, but I'm not sure its accurate
> enough.......time to look around I suppose.
> 
> BTW, I understand that TV twin lead, the copper wire type, makes a good
> test lead for the 3458 measurements.  It seems reasonable, although the
> leakage resistance might be questionable.
> 
> Randy
> 
> 
> On Sun, Aug 17, 2014 at 1:36 PM, Todd Micallef <tmicallef at gmail.com> wrote:
> 
> > Randy,
> >
> > Next thing you know, you will be looking at a 10K standard resistor to go
> > with that 3458A and possible 732A.
> >
> > Todd
> >
> >
> > On Sun, Aug 17, 2014 at 3:51 PM, Randy Evans <randyevans2688 at gmail.com>
> > wrote:
> >
> > > Todd and Bill,
> > >
> > > Thanks for the input.  The 3.6 K thermistor reading seems viable and i
> > will
> > > pursue it further.
> > >
> > > I may have over committed myself to modifying the HP-419A, the Fluke
> > 845A,
> > > buying the 3458A and looking at buying a Fluke 732A.
> > >
> > > So much to do and so little time.
> > >
> > > Thanks again,
> > >
> > > Randy
> > >
> > >
> > > On Sun, Aug 17, 2014 at 11:48 AM, Bill Gold <wpgold3637 at att.net> wrote:
> > >
> > > > Randy:
> > > >
> > > >     I have 6 ea Fluke 732A instruments.  The results of being an over
> > the
> > > > edge and deeply obsessed "Volt Nut", they just kept adding
> > (reproducing?)
> > > > over the years.  My readings for the themistors range from 3.407K OHMS
> > to
> > > > 4.514K OHMS and all work just fine.  3.6K OHMS would seem just fine to
> > > me.
> > > > It really depends upon the final inside temp of the oven assembly.  The
> > > one
> > > > with 3.407K OHMS measures around 47.5 degrees C while the others are
> > > around
> > > > 45 C.  It is the stability of this reading over time that is very
> > > > important.
> > > > Fluke says that it could change as much as 10 ohms per month but mine
> > are
> > > > rock solid for years and years.
> > > >
> > > > Bill
> > > >
> > > > ----- Original Message -----
> > > > From: "Randy Evans" <randyevans2688 at gmail.com>
> > > > To: <volt-nuts at febo.com>
> > > > Sent: Sunday, August 17, 2014 11:08 AM
> > > > Subject: [volt-nuts] Fluke 732A themistor reading
> > > >
> > > >
> > > > > Can anyone tell me what value to expect for a Fluke 732A thermistor
> > > > > reading?  I am looking to get a used 732A and one of the things I was
> > > > told
> > > > > to look for is to measure the thermistor reading after the unit has
> > > > heated
> > > > > up for at least an hour.  I saw in one of the posts that a "typical"
> > > > > reading was 4950 ohms.  One vendor I asked said he measured about
> > 3600
> > > > ohms
> > > > > after a two hour warmup. I was concerned that this is too low.  What
> > do
> > > > you
> > > > > guys think?
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Randy
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