[volt-nuts] Finally got around to modifying my Fluke 845ab with LED's

Chuck Harris cfharris at erols.com
Tue Sep 9 16:42:30 EDT 2014

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

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