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 -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
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