On Fri, 19 Aug 2005 00:14:38 GMT, "Vaughn"
wrote:


"Robert Swinney" wrote in message
...
The point in time where a harmonic wave (can you say "sine wave") intersects
the ordinate, or "x" axis. Voltage is zero at that time thus it is desireable
for switching to occur at that time rather than earlier or later. There can be
no transient voltage at the time of zero crossing; no chance of transient
voltage damage to the switch.

I always thought the main reason for the zero switching was to reduce
generation of electrical/RF noise caused by switching. Back in my traffic
signal tech days, I used thousands of those things.

That was part of it, but the main reason was to minimize turnon
current to incandescent loads by not switching them on in mid-cycle.
Even then, loadswitches that lasted used triacs of considerably
higher ratings than seemed necessary to the designers.

I didn't design loadswitches, but I did design controllers. I'll
admit to having been the original designer of the California 170.
Ducking incoming but I think some of those are still in service 30
years later.

I designed 'em, but only a traffic engineer could program 'em to work
well. Most fully-actuated intersections are not programmed well at
all.

Harvey Goldenberg, the traffic engineer for the State of New York, was
genius good at it. (New York adopted the 170 along with CA). I saw
him tune an 8-phase dual-ring intersection of two arterials so it ran
like magic during rush hour. It's an art as much as a science.