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

[Dallas Smith]

Thank you Chuck,

I think you have something there, that is probably driving the choppers.
The meter had a little more jitter than before after the mod, that is why I modified the integration filter caps.
I like the slower response anyway. 
 
When I have time I'll share my mods for the Fluke 540b, Much better than before, can transfer at lightning speed.
The suggestion of using a voltage regulator (LM1117) for the 1.35v mercury battery from the EEV Blogs
Didn’t pan out. Its not a reference, it’s a voltage regulator. You don't need accuracy but stability.

Dallas

 
 
> Date: Tue, 9 Sep 2014 20:30:30 -0400
> From: cfharris at erols.com
> To: volt-nuts at febo.com
> Subject: Re: [volt-nuts] Finally got around to modifying my Fluke 845ab with LED's
> 
> Hi Mark,
> 
> I have an itty bitty white led, probably called a T-1 size, and it
> glows dimly for a long time after you shut it down.  They all pretty
> well have to.
> 
> I think what you are seeing with your analyzer is the blue/UV component
> that drives the phosphor element.  It will run just as fast as any old
> style LED.
> 
> I also think that the blue/UV component, which is very bright, is what
> is driving Dallas's chopper.
> 
> But enough on that.  I wasn't trying to criticize, just make mention of
> something I noticed in my own work.
> Where I got to thinking of this is when I burned out the strobe tube
> in my G-R strobotach.  Replacement tubes were in the $300 range, so I
> knew that would never happen, so I was thinking of making a solid state
> replacement using a handful of those wonderful little white LED's.
> They would certainly be bright enough, but I'm pretty sure the phosphor
> hang would make them unsuitable for stopping motion... your eye would
> see a blur instead of the razor sharp image you get with the strobe tube.
> 
> -Chuck Harris
> 
> 
> 
> Mark Sims wrote:
> > I would probably use green or yellow LEDs,  but the white ones should not be a
> > problem. I built an LED analyzer/integrating sphere and one of the features is a
> > circuit that optically measures the LED driver PWM frequency.  It can also detect
> > the minute variance in LED intensity from an LED driven by a 950 kHz boost
> > converter.  It also had no problems with a white LED driven at 4 MHz from a signal
> > generator.  You see the long persistence phosphors mainly in large lighting LEDs
> > and not in small indicator LEDs. _______________________________________________
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