Kiln sitter timers

[cadenrank]

This question is not relative to an actual problem that I'm having, just something that I'm curious about from an electrical standpoint that I don't see any information about online, and I don't have a timer on my sitter kiln to do tests. 

I've noticed that the timers on kiln sitters only have the two wires coming off of them, and they're attached to the 'load' side of the kiln sitter terminals, usually just underneath the feeder wires to the switches on the same terminal. My question is, how does this actually interrupt the connection between the line and the load at the sitter? What is happening when the timer reaches zero that prevents the connection at the sitter terminals? 

I'm sure I'm missing something, and like I said, my older kiln doesn't have a timer, and my other kiln is digital so I don't have any ways to curiously test around and find out actually what's happening, so to settle my curiosity and expand my kiln electrical knowledge, I thought I'd ask here lol. 

[Bill Kielb]

The timer is powered by the load side so the sitter must be set to power it  but when time is expired it mechanically trips the sitter. Maybe think of the mechanics of setting a mouse trap, if the set lever is not just so, you can’t set the trap.

see page 8 of the manual http://www.fireright.com/docs/kilnsitter/lt3andk.pdf

Edited June 29, 2022 by Bill Kielb

[neilestrick]

When you push in the power button, you're actually pushing together contact plates, which allows the power to flow from the bottom terminals on the ceramic block to the top terminals. There are two plates, one for each side of the Sitter block (left and right). Over time these plates can become corroded and need to be cleaned up. I've seen a couple of kilns over the years where power was only flowing on one side of the Sitter due to corrosion.  When the Sitter kicks off, the plates disengage and the power flow stops. The back side of the power button has a small ridge in it. When you push in the button, a little spring loaded lever goes into the ridge and holds the button in. When the cone bends and the weight drops, the little bump on the weight hits the lever and it releases the button. The timer knob has a little bump on the back side that does the same thing. When it gets to zero, the bump hits the spring loaded lever and releases the power button, which disengages the contact plates. It's very much a Rube Goldberg machine IMO, but it works.

[cadenrank]

Ahhhh, so it's mechanical. The load side is just powering the timer, not actually having anything to do with disengaging the sitter contacts. I knew something had to be missing from the equation I was trying to figure out. 

Thank you guys!