Re: [volt-nuts] Fluke 845AB 1993 Modification Schematic
On 9/25/2014 12:01 PM, starb...@uplink.net wrote: I not sure this was ever used for production, no known schematic. I'm going to use the LTC1150 for my other null meter 845ar. It would be a better choice then the fet chopper you are referring to. I'll use the LTC1150 for the first stage with the over all feedback and stage two op amp to control the feedback for the switch 101b which controls the gain from 300 to 9000. will scale this gain between the two op amps. Look at the May and August threads. Randy Evans is currently designing a new chopper for his HP419. Dallas Need the schematic of the Fluke 845AB 1993 modification. Thanks, John ___ 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.
[volt-nuts] Fluke 845AB 1993 Modification Schematic
Need the schematic of the Fluke 845AB 1993 modification. Thanks, John ___ 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.
Re: [volt-nuts] 845ab Led Mod Update
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" To: "Discussion of precise voltage measurement" 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" > To: "Discussion of precise voltage measurement" > 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. ___ 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.
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" To: "Discussion of precise voltage measurement" 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.
