OperatIOn
The FB-08 calibration Fluidised Bath is capable of precise performance, but for reliable and consistent
results it must be used by personnel conversant with its operation.
For temperature stability the heat input to the bath must exactly equal heat losses; the heat input from
the immersed heaters is varied by the controller which has a characteristic time constant for its response
to a change in demand. The heat losses from the bath are due to:
heating fluidising air
1.
radiation from the top of the bath
2.
conduction through the insulation
3.
conduction along loads inserted into the bath
4.
heating the mass of cold objects placed in the bath.
5.
Changing any of these will affect the temperature of the bath, but it will
recover under the controller's influence; this does mean, however, that after any
parameter is changed or the load in the bath is changed, there is a delay before the
bath temperature re-stabilises.
start-up
1. Check that the unit has been set up as described earlier and that required services are available.
2. Check that alumina level is correct and adjust if necessary. Never add new, cold alumina (which may
contain moisture) to a hot bath. Should the fluidised bath be stored for long periods of time under
damp or humid conditions, moisture may be absorbed by the alumina which is hydroscopic. To avoid
violent fluidisation which occurs when damp alumina is heated above 100°C, operate the bath for a
period of approximately 8 hours at 90°C prior to operation at elevated temperatures.
3. Check that fluidising air control valve and dust extraction control valve are both closed.
4. Connect bath to the electrical, and compressed air supplies.
5. Turn on mains power switch (19). The internal neon should illuminate.
6. Turn on dust extraction system switch (22), and the green lamp (20) should illuminate.
7. Open the fluidising air control valve (21) until the surface of the alumina rises and then starts to
move with a gentle flowing action, like boiling cream. The amber heater light (20) should illuminate
as should the controller when the fluidising air exceeds a preset pressure.
8. Set the desired operating temperature on the controller (16).
9. As the bath heats up, the indicated air flow for adequate fluidisation can be reduced - excess fluidising
air does not improve performance, but does increase the risk of dust emission from the bath.
10. When the bath is at operating temperature, the controls should not be adjusted without good
cause.
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