Old aquarium thermostat.. How does it work?

[turgut kalfaoglu]

Hi. I have a very old aquarium thermostat - but it still works. I'm trying to figure out HOW it works

It has a female plug midway, and you plug an aquarium heater there. then you turn the yellow rod to adjust the temperature. When the temperature is reached, the light comes on. When the temp is too low and the heater is working, the light is off. How the heck does this thing work..The way it works seems counter-intuitive -- the metal coil expands when it's too hot, touches the rod, and that stops the current flowing. However that should CLOSE the circuit and actually make the current flow, no?

Attaching some photos..

 

[Bluejets]

Photos too blurry to make out any detail.

 

[turgut kalfaoglu]

Photos too blurry to make out any detail.

Thanks for the feedback! The system said the originals were too big for upload so I resized them to 1024x768. But did you try clicking on the plus sign while viewing the photos? I'd be happy to upload more..
I just added a 4th photo.. That's hopefully better.

 

[Bluejets]

Thanks for the feedback! The system said the originals were too big for upload so I resized them to 1024x768. But did you try clicking on the plus sign while viewing the photos? I'd be happy to upload more..
I just added a 4th photo.. That's hopefully better.

Ah yes, followed your instruction and can see now...
Way it works is the neon light gets it's path through the heater element when the heater is off and therefore neon is on.
When the sensor switches the heater on, the sensor shorts the neon and hence it ( the neon) goes off.
The neon draws very little current and it's "on" path through the element has no effect on the element.

 

[turgut kalfaoglu]

Ah yes, followed your instruction and can see now...
Way it works is the neon light gets it's path through the heater element when the heater is off and therefore neon is on.
When the sensor switches the heater on, the sensor shorts the neon and hence it ( the neon) goes off.
The neon draws very little current and it's "on" path through the element has no effect on the element.

Many thanks for your reply
I understand it now.

 

[bertus]

Hello,

The sensor seems to be a bi-metal strip.
It changes shape when heated.

Bimetallic strip - Wikipedia

en.wikipedia.org

The screw near the strip sets the temperature.

Bertus

 

[juliasmith]

The working procedure is quit simple ,the neon light gets it's path through the heaters element when the heater is off and therefore neon is on. When the sensor switches the heater on, the sensor shorts the neon and the neon goes off.

 

[Bluejets]

The working procedure is quit simple ,the neon light gets it's path through the heaters element when the heater is off and therefore neon is on. When the sensor switches the heater on, the sensor shorts the neon and the neon goes off.

Yup, that's what I said in #4 above.....