On Friday, 13 March 2020 17:40:19 UTC, Tim+ wrote:
Anyone know how these work and why my tumble dryer has a long central
electrode in the flame path with an adjacent earth pin that is angled so
that theres a small gap between the end of the insulated electrode and the
end of the earth pin.

I ask as all the replacement ones I see for sale only have a single
insulated electrode and no earth one. Im assuming that the electronics
for these must be a bit different and a single electrode type wont work in
mine.

Its a White Knight gas tumble dryer. Only 30 years old now so Id like to
get a few more years out of it but Crosslee dont stock spares for this
machine any more and I havent seen anything similar on line.

The present earth pin has suffered some erosion/corrosion and its not
always sensing the flame.

Hopefully, heres a picture. https://photos.app.goo.gl/HGzbwdk6Lw1zMNAb9


The resistance path in a flame is very low.
The probe is measuring the absence or not of the flame by measuring resistance.

Quite often the probe is just a an ordinary spark electrode used for this purpose.