Finally got around to modify my Fluke 845ab with LED 's for the chopper circuit. Used the 17 volt windings for LED's (Mouser 941-C513AMSNCW0Y0511 Warm White Round LED) instead of the 130 volt, move red wire on transformer pin 9 to pin 7.This winding is 180 degrees out of phase, so I reversed the steering diodes (CR106 & CR107) I left in to help make sure the phase was correct for the LED's when connecting. Change R154 to 6K to set the brightness, selected for good operation of the zero control. Then install jumper to replace C119. Also changed the filter integration response caps C111 to .022uF and C116 to 47uF, this stabilized the jitter to a manageable mode of operation. Meter now works as well or better when the original neon's worked. As the meter originally had this problem, why is the offset reading different when polarity is reversed at the meter input? About 10uV's. Lamp Blocks.

One thing that might be hosing things up a bit is white led's don't switch quickly. They are really UV LED's with a bit of fluorescent material between the LED and the world. The fluorescent material will also luminesce for hours after the LED is turned off. Perhaps because the led never shuts off completely, it is biasing the meter up a few tens of microvolts? -Chuck Harris Dallas Smith wrote: > Finally got around to modify my Fluke 845ab with LED 's for the chopper circuit. Used > the 17 volt windings for LED's (Mouser 941-C513AMSNCW0Y0511 Warm White Round LED) > instead of the 130 volt, move red wire on transformer pin 9 to pin 7.This winding is > 180 degrees out of phase, so I reversed the steering diodes (CR106 & CR107) I left in > to help make sure the phase was correct for the LED's when connecting. Change R154 to > 6K to set the brightness, selected for good operation of the zero control. Then > install jumper to replace C119. Also changed the filter integration response caps > C111 to .022uF and C116 to 47uF, this stabilized the jitter to a manageable mode of > operation. Meter now works as well or better when the original neon's worked. > > As the meter originally had this problem, why is the offset reading different when > polarity is reversed at the meter input? About 10uV's. > > Lamp Blocks. > > _______________________________________________ > 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.

Hi Chuck, Its only 84Hz, It had the offset problem long before I made this mod. The new meter at work many decades ago also had this problem. I pick white so the full spectrum would be covered by the Csd's. Checked waveforms with scope, has sharp rising and falling edges. This mod may not be as elegant as a Linear Devices copper mod, but at lest I will not have to mess with the shielded front end. The offset may be due to the bias current in the front end reacting with the different polarities. Dallas > Date: Tue, 9 Sep 2014 15:48:01 -0400 > From: cfharris@erols.com > To: volt-nuts@febo.com > Subject: Re: [volt-nuts] Finally got around to modifying my Fluke 845ab with LED's > > One thing that might be hosing things up a bit is white led's don't > switch quickly. They are really UV LED's with a bit of fluorescent > material between the LED and the world. The fluorescent material will > also luminesce for hours after the LED is turned off. Perhaps because > the led never shuts off completely, it is biasing the meter up a few > tens of microvolts? > > -Chuck Harris > > Dallas Smith wrote: > > Finally got around to modify my Fluke 845ab with LED 's for the chopper circuit. Used > > the 17 volt windings for LED's (Mouser 941-C513AMSNCW0Y0511 Warm White Round LED) > > instead of the 130 volt, move red wire on transformer pin 9 to pin 7.This winding is > > 180 degrees out of phase, so I reversed the steering diodes (CR106 & CR107) I left in > > to help make sure the phase was correct for the LED's when connecting. Change R154 to > > 6K to set the brightness, selected for good operation of the zero control. Then > > install jumper to replace C119. Also changed the filter integration response caps > > C111 to .022uF and C116 to 47uF, this stabilized the jitter to a manageable mode of > > operation. Meter now works as well or better when the original neon's worked. > > > > As the meter originally had this problem, why is the offset reading different when > > polarity is reversed at the meter input? About 10uV's. > > > > Lamp Blocks. > > > > _______________________________________________ > > 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.

Hi Dallas, The thing is, CdS cells peak sharply at about 560nm, which is green/yellow. They are blind to most of white light... especially to the blues which are prominent in white LED's. White LED's are designed purely for bulk illumination. They have a very slow response so that they won't flicker when used for domestic lighting off of a 50/60Hz power source. There are also green yellow and red LED's that are designed the same way, but there are many that switch quickly too. -Chuck Harris Dallas Smith wrote: > > > > Hi Chuck, > > > Its only 84Hz, It had the offset > problem long before I made this mod. The new meter at work many decades ago > also had this problem. > > > I pick white so the full spectrum would > be covered by the Csd's. Checked waveforms with scope, has sharp rising and > falling edges. This mod may not be as elegant as a Linear Devices copper mod, > but at lest I will not have to mess with the shielded front end. > > > The > offset may be due to the bias current in the front end reacting with the different > polarities. > > > Dallas

My scope shows that the copper is working ok. May try amber or yellow to see if the performance is better. See page 13: http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/HB/Data%20Sheets/C513A%20WSN%20WSS%20MSN%20MSS%201042.pdf > Date: Tue, 9 Sep 2014 16:42:30 -0400 > From: cfharris@erols.com > To: volt-nuts@febo.com > Subject: Re: [volt-nuts] Finally got around to modifying my Fluke 845ab with LED's > > Hi Dallas, > > The thing is, CdS cells peak sharply at about 560nm, which is green/yellow. > They are blind to most of white light... especially to the blues which are > prominent in white LED's. > > White LED's are designed purely for bulk illumination. They have a very > slow response so that they won't flicker when used for domestic lighting > off of a 50/60Hz power source. > > There are also green yellow and red LED's that are designed the same way, > but there are many that switch quickly too. > > -Chuck Harris > > Dallas Smith wrote: > > > > > > > > Hi Chuck, > > > > > > Its only 84Hz, It had the offset > > problem long before I made this mod. The new meter at work many decades ago > > also had this problem. > > > > > > I pick white so the full spectrum would > > be covered by the Csd's. Checked waveforms with scope, has sharp rising and > > falling edges. This mod may not be as elegant as a Linear Devices copper mod, > > but at lest I will not have to mess with the shielded front end. > > > > > > The > > offset may be due to the bias current in the front end reacting with the different > > polarities. > > > > > > Dallas > _______________________________________________ > 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.

Some like the qrp12 peak around 610 nm. Anyone know who made the sensor ? On Tue, Sep 9, 2014 at 1:42 PM, Chuck Harris <cfharris@erols.com> wrote: > Hi Dallas, > > The thing is, CdS cells peak sharply at about 560nm, which is green/yellow. > They are blind to most of white light... especially to the blues which are > prominent in white LED's. > > White LED's are designed purely for bulk illumination. They have a very > slow response so that they won't flicker when used for domestic lighting > off of a 50/60Hz power source. > > There are also green yellow and red LED's that are designed the same way, > but there are many that switch quickly too. > > -Chuck Harris > > Dallas Smith wrote: > >> >> >> >> Hi Chuck, >> >> >> Its only 84Hz, It had the offset >> problem long before I made this mod. The new meter at work many decades >> ago >> also had this problem. >> >> >> I pick white so the full spectrum would >> be covered by the Csd's. Checked waveforms with scope, has sharp rising >> and >> falling edges. This mod may not be as elegant as a Linear Devices copper >> mod, >> but at lest I will not have to mess with the shielded front end. >> >> >> The >> offset may be due to the bias current in the front end reacting with the >> different >> polarities. >> >> >> Dallas >> > _______________________________________________ > 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. >

Pretty sure it would be Clarex. -Chuck Harris Pete Lancashire wrote: > Some like the qrp12 peak around 610 nm. > > Anyone know who made the sensor ?