5 ms·

Assuming the thermister isn't very close to the heating element you'll be heating air for a while and the heating element might burn out.

• michaelt 12y ago
  On a lot of consumer products there's a resettable thermal fuse built into the heating element. Burning down people's houses is bad for business :)
  • keithpeter 12y ago
    I'll put my hand up for that one. Old fashioned non-automatic electric kettles had such a device that handily pushed out the kettle lead thus disconnecting the mains. I was saved from some embarrasment and redectoration by this a third of a century ago. PS: how could you detect the presence of water? Photocell? Ultrasound? Conductivity between two small contacts 20% of the way up the jug?
    • swdunlop 12y ago
      The old way in industrial automation is a float sensor, which is basically a reed switch with some buoyancy on the end. With substances that are corrosive, or where there's a cross contamination concern, you drop down to load cells or a rangefinder, both of which are more expensive and fussy. :)
    • smcg 12y ago
      At least in my Keurig: there are 2 tanks, 1 external, 1 internal. There is a float in the external tank that detects if there is enough water in the external to fill up the internal. If so, then it brews the internal tank and then fills it up from the external after the coffee is made. If there is not enough water to fill up the tank, it won't start.