Fig. 2-Drawing showing the placement of the thermocouple and "dam" in the dryer discharge chute.
A small clearance (I" maximum) should be provided under the thermocouple so material will not be
trapped between the thermocouple and the chute Trapped material will cause a heat loss path and the
thermocouple will give erroneous readings.
The thermocouple should make good contact with the material but not be subject to severe abrasion caused by high
velocities. If the material is moving so fast that it bounces and leaves air adjacent to the thermocouple, the temperature it
senses will be lower than the material. It may be necessary to place a dam in the chute so that the thermocouple Is in a
relatively slow moving area next to the dam. The dam must only be wide enough and high enough to create a localized
area of build-up where the material loses velocity BUT DOES NOT STOP FLOWING. The thermocouple must not be
located in a stagnant zone or erroneous temperature readings will result Because of the large number of variables
involved, it is impossible to set down any exact size or location of the dam that will always work. Field experimentation will
be necessary if good results are to be obtained. It is advisable to tack weld the dam in place so that it can be easily
modified if it fails to perform satisfactorily.
During normal operation, the thermocouples should be rotated once a month to expose a different area of
its surface to the abrasive forces of the material. This procedure will Increase the effective life of the
thermocouple. If excessive wear occurs, a protective tube may be added to shield the shaft In the region
of the high velocity flow.