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Re: [Amps] Measuring filament voltage

To: jeff millar <>
Subject: Re: [Amps] Measuring filament voltage
From: Radio WC6W via Amps <>
Reply-to: Radio WC6W <>
Date: Thu, 21 Jul 2022 17:07:29 +0000 (UTC)
List-post: <>

 A while after my post on this topic, I recalled a design I created about a 
decade ago, for a RMS meter in an Audio Compressor, using a microprocessor.

 Exact accuracy was not a requirement in this instance but, for precision 
measurement a voltage reference may be added to the circuit.

 A dual op-amp absolute value circuit conditions the AC input and the 
microprocessor has an integral 10 bit A/D converter.

 The output from the micro was PWM driving an analog meter. For the HV 
application, this could drive a fiber optic transmitter.

 At the fiber optic receiver, a precision reference would also be required, and 
the recovered signal could likewise drive an analog meter.

 At single pot on the receive side would calibrate the entire system.

 For this 60Hz application, sampling at 50KHz, 833 samples would just about fit 
one cycle of the AC to be RMS'ed.

 Just for "fun", I search the 'net for an ancient fiber optic system with which 
I've had some familiarity.

 This link was returned:

 Looking at the product offered, it appears to include two receivers and no 
transmitter! Gotta love the internet!

 Marv WC6W

     On Wednesday, July 20, 2022, 06:35:54 AM PDT, jeff millar 
<> wrote:  
 Suggest adding a bluetooth link from filament to control panel to further the 
jeff, wa1hco
On Wed, Jun 22, 2022 at 10:59 AM Radio WC6W via Amps <> 

Ooops, somehow, I lost the last two "OR's" when copying this scheme into email. 
 Yahoo has a mind of its own at times.

Here's the whole idea(s):

If you want to measure the voltage at the filament on those follower triodes 
may I suggest the following scheme:

Use an AD536 to convert to RMS right at the tube.

Use a LM331 to convert the voltage to frequency.

Send the frequency out over an optical fiber and read it with a frequency 
counter or alternately convert it back to voltage with a F-V converter.

Power it with a tiny hi voltage isolation transformer. Only requires milliamps 
to run.

Or use a power over fiber cable scheme, though those are rather pricey.

Or rectify and regulate the filament voltage to power the interface.

Or eschew the RMS chip, add an absolute value circuit in front of the V-F 
converter, and then process the resulting signal down fiber.  A small 
microprocessor should be sufficient in lieu of that pricey RMS part.  There 
might be a touch of error down at the lowest transmitted frequency, though it 
should be less than .1%.

Just the complete thought,
Marv WC6W

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