Hi Jim,

Question..

Why put the diode in series with the pitot heater power.
(Ok, it senses that power if flowing in the heater circuit, but is that
necessary?)

Couldn't the same thing be accomplished by using the diode as a
temperture
sensor (thermometer) to decide if the pitot tube was above a certain
temperature?

No self-heating on the part of the sense diode, and no pitot heat
failure if the diode
opens up (burns up?).

Richard