Flow Sensor - Jenn-Air JDB9600AW Technical Education

3.8

Flow sensor

3.8.1 Function
The flow sensor is attached in the water channel of the heat ex-
changer (impeller wheel counter). The impeller wheel rotates as water
flows through the channel.
A small permanent magnet attached to the impeller wheel switches
both contacts of a magnetic switch (Reed switch). As a result, elec-
trical pulses are generated.
These pulses are counted by the electronics. The electronics use
these pulses to calculate the amount of water which flows into the
appliance.
1 PCB with Reed contact switch
2 Permanent magnet
3 Impeller wheel
3.8.2 Design of mechanical reed contact
PCB with reed contact switch
1
2 Glass flask
Reed contact switches switch or interrupt circuits. They are contact
tongues fused in a glass flask in a vacuum or an inert gas and which
simultaneously form the contact spring and the armature.
The name derives from the reed of woodwind instruments as it
resembles the oscillating contact tongues. The contact tongues are
manufactured from a ferromagnetic material (e.g. soft iron) coated
with a noble metal. The contacts are actuated by an externally acting
magnetic field which is generated electrically by an approaching
permanent magnet or in an appropriate magnetic coil. The magnetic
field activates the two contact tongues which then close the circuit. As
soon as the magnetic field declines or a certain force drops below
a minimum value, the spring effect opens the contact again.
Reed contact switches are very sensitive to mechanical effects such
as distortion.
Contact tongues
3