[GreenKeys] Machine speed and VFDs

[Jeffrey Angus]

On 9/3/18 9:53 AM, Ralph Mowery wrote:
> I don't recall where I saw it, probably in a back issue of the
> RTTY Journal but someone had made an optical interrupter for
> feedback and made something similar to a VFD.
> Supposed to have worked well.
There's an article in the 1973 RSGB Teleprinter Handbook.
It uses a pulse width comparitor made with DTL logic. It was
designed to work with the centrifugal switch governed motors.

About 3 years ago, I designed one using a divide by N counter
and a crystal reference. My reason being I wanted something
I didn't have to adjust, and I could switch between two different
speeds.

It's mounted in my Lorenz Lo-15c. It works great. 60 or 66 WPM
at the "flick of a switch."

But the Dovetron was designed for synchronous motors. And
changed speeds by changing the apparent line frequency.
Basic design was a power inverter with a switch that changed
capacitors to change the output frequency.

If it was set to 100 WPM, the output was set to 60 Hz and the
machine (typically a 28) would run at 100 WPM with the correct
gear set installed.

Dropping the output frequency of the Dovetron would slow
the motor appropriately. For example: dropping the source to
the motor from 60 Hz to 36 Hz would slow the motor down that
with the original 100 WPM gearing it would now operate at 60
WPM.



-- 
"I am a river to my people."
Jeff-1.0
WA6FWI
www.foxsmercantile.com