Well I finally got the 615nm Led's installed and the results seem so so. The zero drifted was significantly on the 1uV range. So I used two LT1634 1.25 Volt references with the current set by two 43k resistors from the ±15 volt supplies. The previous reference used came from the -0.4 volts at TP1 and +0.6 volts at TP8. Removed the 150k resistor at the positive end of the zero control and lifted the negative end from the circuit board the connected the ±1.25 ref to the zero pot. Much better stability, drifts by noise about ±.1 to ±.2uv now on 1uv range. Is this normal now? Never used a new Fluke 845ab before. The white led's seemed to filter the noise better with its persistent, may go back. The zero seems stable with ±2 F change in room temperature now.

I check my 845ab yesterday, S/N 4470002.  It still has the neon

From what I can observe the Peak to Peak noise on the 1 mv range is

Sure would love to know if the FLUKE modification to the 845ab made in

Dallas: I check my 845ab yesterday, S/N 4470002. It still has the neon bulbs/photo resistors chopper. From what I can observe the Peak to Peak noise on the 1 mv range is about +/- 0.1 mv, or a total of around 0.2 mv. As far as temperature drift I don't know. Never tried to measure that parameter. Sure would love to know if the FLUKE modification to the 845ab made in 1993, when the new circuit was put into production, makes the noise lower. Or better, if your efforts can make the noise lower on the 1 mv range. Bill ----- Original Message ----- From: "Dallas Smith" <dosmith@outlook.com> To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Sent: Wednesday, September 24, 2014 12:06 PM Subject: [volt-nuts] 845ab Led Mod Update > Well I finally got the 615nm Led's installed and the results seem so so. > The zero drifted was significantly on the 1uV range. So I used two > LT1634 1.25 Volt references with the current set by two 43k resistors > from the ±15 volt supplies. The previous reference used came from the > -0.4 volts at TP1 and +0.6 volts at TP8. Removed the 150k resistor at > the positive end of the zero control and lifted the negative end from > the circuit board the connected the ±1.25 ref to the zero pot. Much > better stability, drifts by noise about ±.1 to ±.2uv now on 1uv range. > Is this normal now? Never used a new Fluke 845ab before. The white led's > seemed to filter the noise better with its persistent, may go back. The > zero seems stable with ±2 F change in room temperature now. > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

 I check my 845ab yesterday, S/N 4470002.  It still has the neon

 From what I can observe the Peak to Peak noise on the 1 mv range is

 Sure would love to know if the FLUKE modification to the 845ab made in

Sorry I should have said "uv" where ever I said "mv". Too early in the morning where I live in the world. Bill ----- Original Message ----- From: "Bill Gold" <wpgold3637@att.net> To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Sent: Thursday, September 25, 2014 8:10 AM Subject: Re: [volt-nuts] 845ab Led Mod Update > Dallas: > > I check my 845ab yesterday, S/N 4470002. It still has the neon > bulbs/photo resistors chopper. > > From what I can observe the Peak to Peak noise on the 1 mv range is > about +/- 0.1 mv, or a total of around 0.2 mv. As far as temperature drift > I don't know. Never tried to measure that parameter. > > Sure would love to know if the FLUKE modification to the 845ab made in > 1993, when the new circuit was put into production, makes the noise lower. > Or better, if your efforts can make the noise lower on the 1 mv range. > > Bill > ----- Original Message ----- > From: "Dallas Smith" <dosmith@outlook.com> > To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> > Sent: Wednesday, September 24, 2014 12:06 PM > Subject: [volt-nuts] 845ab Led Mod Update > > > > Well I finally got the 615nm Led's installed and the results seem so so. > > The zero drifted was significantly on the 1uV range. So I used two > > LT1634 1.25 Volt references with the current set by two 43k resistors > > from the ±15 volt supplies. The previous reference used came from the > > -0.4 volts at TP1 and +0.6 volts at TP8. Removed the 150k resistor at > > the positive end of the zero control and lifted the negative end from > > the circuit board the connected the ±1.25 ref to the zero pot. Much > > better stability, drifts by noise about ±.1 to ±.2uv now on 1uv range. > > Is this normal now? Never used a new Fluke 845ab before. The white led's > > seemed to filter the noise better with its persistent, may go back. The > > zero seems stable with ±2 F change in room temperature now. > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > > and follow the instructions there. > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.