M970-07/04
PAGE 18
12.Calibration Performance Optimization
The horizontal profile of the furnace should be carefully monitored over the length of any
equalization blocks under the standard test conditions for the probes used and the end
zone insulation. Short probes calibrated using the equalization blocks closer to the
furnace end, will need more care to obtain the maximum insulation / lowest end loss with
adjustment of the particular furnace end controller used to obtain the lowest gradient.
When using the equalization block in the centre of the furnace with long probes, additional
Kaowool insulation can be used at each end of the furnace to reduce heat loss and
improve the gradient in conjunction with the end zone controller differential “offset
adjustment”.
To establish radial uniformities use two identical size and thermal properties probe which
closely fit (within 0.4 mm. approx.) 2 diagonally opposite holes A and B. Make comparison
measurements in these two hole positions measuring test probe TP in position A and the
reference probe RP in position B.
Error test probe TPE = 0.5 [ (PosA. TP – Pos B.TS )+(Pos B.TP-Pos.A.TS) ]
When mounting probes in metal block, holes used should be on the same P.C.D. for best
radial uniformity.
It is important all probes use close fitting holes and are inserted to the same depth to
reduce thermal immersion errors. In 3 zone horizontal tube furnaces with blocks mounted
closer to the furnace centre immersion depth errors are considerably lower compared to
alternative systems and designs because of the additional heat area in front of each probe
or block before the furnace end and room temperature.
