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Topic: Wandering John's Computerized FR [was RE: +Advise on buying a (3 msgs / 81 lines)
1) From: Tom Gramila
On Sun, 24 Nov 2002, John Abbott wrote:
<Snip>
		^
		do you mean electrically noisy?  I have tried to avoid
that problem by using solid state relays that claim to switch only when
the line voltage is zero, thus avoiding large transient signals.  This
limits the temporal resolution of switching to be 1/60 of a second (or
1/120, its not explicit from the specs).  But that can be accounted for in
the control code.  My computer control system works very well with a WBII, 
using direct dvm reading of the thermocouple voltages.
	If you are interested, the relays I use are detailed in:
	http://www.magnecraft.com/products/section2_9_13-14.pdfand they are available from Grainger for about $20.  I use the 
250V 25 A version with no additional heatsinking.
	Much more detailed info on the zero voltage switching is available 
at the Omega site, but you pay alot more for their relays....
	Tom G.
<Snip>
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2) From: Tom Gramila
Hmmm.  The computer controlled SSR was the mext step for me after a hand
controlled variac.  motor control would be very nice, but I would have
thought that it would be hard to do for twenty dollars.  You might have a
look at c and h sales which is one of the surplus houses that I have used
that has lots of unusual stuff.  A quick look shows that they sell stepper
motors.
	
http://aaaim.com/cgi-local/shop991/shop.pl/page=start_shopping.htm~~~~~
A minor correction on a detail on the relay I suggested, grainger sells it
as a dayton electric part.  I cannot remember if it was:
 Solid State Relay 25 Amp,Input 3-32 Vdc,Output 24-240Vac
DAYTON	5Z438	 $22.46
-- or --
 Solid State Relay, 25 Amp, Input 3-32 Vdc, Output 24-280 Vac, Triac
DAYTON 	5Z956 	 $20.51
But both claim to be opto-isolated and zero switching, both of which help 
keep my computer happy.  
Good luck and tell us all if you figure out a stepper motor approach!
Tom G.
On Mon, 25 Nov 2002, John Abbott 
wrote:
<Snip>
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3) From: Tom Gramila
On Mon, 25 Nov 2002, Rick Farris wrote:
<Snip>
	I continue to believe that computer control can be done with a
"junk" computer, a sound card, and a $20 solid state relay.  Of course, my
proof of principle system consists of a "junk" computer, two HP gpib
voltmeters, a gpib d/a, a gpib interface card, and a twenty dollar solid
state relay.
	Fortunately, I do work in a lab, so all the expensive gpib gear is
borrowed until I can implement the sound card approach.....
Tom G.
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