24
Calibration
1. When using the FB-08 to calibrate thermal sensors such as thermocouples and platinum resistance
thermometers, it is important to ensure that the working volume of the bath is thermally stable. Use
an independent temperature sensor, such as a reference thermocouple, to check the temperature
uniformity and stability, see Specification.
2. The temperature stability of the fluidised bath at any operating temperature may be improved by tuning
the control parameters of the temperature controller to match the performance of the system under
any set conditions. Adjustment details are contained within the manufacturers instruction manual for
the Eurotherm temperature controller.
3. For precise calibration the actual temperature of the fluidised bath should be measured with an
independent calibrated reference sensor; the temperature indicated by the temperature controller
should only be used as a guide and not as an indication of absolute temperature.
4. The number of sensors calibrated in the fluidised bath at any one time should be kept to a minimum
so as not to disturb the flow pattern within the bath. Typically up to 10 sensors of approximately Ø10
mm may be calibrated without loss of performance.
5. The probe plate supplied with the FB-08 may be machined to allow the sensors being calibrated access
to the bath. This probe plate should always be positioned above the surface of the bath in the probe
plate carrier so as to inhibit the loss of fine alumina particles from the surface of the bath.
6. Techne are able to offer a work basket which ensures that the probes being calibrated are held within
the working volume of the bath, alternatively custom built probe holders are available. Probe holders
locate the sensors being calibrated at a known position within the bath and act as equalising blocks
so that the basic isothermal properties of the fluidised bath are further enhanced.
Dead Bed Calibration
1. Temperature stability during calibration may be further improved by using a dead bed calibration
technique. This technique involves heating the bath to the required calibration point, then allowing
the temperature of the bath to stabilise for a period of approximately 20 minutes, dependent upon
the actual calibration temperature and the thermal mass of the sensors being calibrated.
2. The fluidised bed is collapsed by cutting off the fluidising air to the FB-08 so that the sensors being
calibrated are surrounded by a solid bed of alumina which acts as a thermal insulator. After a period of
approximately 2 minutes at set temperature a stability of 0.01°C can be achieved for a further period of
approximately 8 minutes, dependent upon heat loss along the stem of the sensors being calibrated.
3. At the end of the required period of dead bed it is necessary to reconnect the fluidising air to the FB-
08.
Close Down
1. Turn off the mains power switch (19).
2. Close the fluidising air and nitrogen control valve (21).
3. Turn off the dust extraction system (22).
4. Disconnect the compressed air supply.
5. Disconnect the mains power.
