23
DEAD BED CALIBRATION
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.
The fluidized bed is collapsed by cutting off the fluidizing air to the FSB-200-P-AC 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.
At the end of the required period of dead bed it is necessary to reconnect the fluidizing air to the FSB-200-P-AC.
AUTOMATIC AIR SYSTEM
An automatic fluidizing air control system is fitted which adjusts the air flow rate accordingly to suit the set
temperature of the bath. This allows the operating temperature of the FSB-200-P-AC to be adjusted from a
remote source e.g. using the TechneWorks PC software while the bath is unsupervised. This automatic air feature
is controlled by a control system which switches five solenoid valves. These valves are opened and closed in
various combinations, providing eighteen air flow rates corresponding to eighteen different temperatures
throughout the operating range.
Temp (°C)
Temp (°F)
Flow (LPM)
25
77
23.0
50
122
22.0
75
167
21.5
100
212
20.5
125
257
20.0
150
302
18.5
175
347
18.0
200
392
17.0
225
437
16.5
250
482
15.5
280
536
15.0
310
590
14.0
340
644
13.5
370
698
11.5
430
806
11.0
490
914
10.0
550
1022
9.5
610
1130
8.5
Table 1: FSB-200-P-AC automatic air flow rate table (factory settings)
When correctly set, the fluidizing air flow rate will vary according to the above table. It should be noted that the
air flow requirements are approximate and accuracy is not critical. The air flow rates achieved will, however, vary
according to the air supply pressure and whether the extraction system is switched ON or OFF.
SHUT DOWN
1. Turn off the mains power switch (10).
2. Turn off the dust extraction system (7).
3. Disconnect the compressed air supply.
4. Disconnect the mains power.
