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Thermo Fisher Scientific
Operation Manual HM550
After changing the specimen or moving the knife or knife carrier, it is
necessary to adjust the knife edge to the specimen again. is can easily
be done by means of the coarse feed and the trimming function.
After the specimen and the knife are adjusted, further gradual feed for
trimming can be carried out by pressing the button for trimming. If
this function is chosen, the specimen clamping moves forwards by the
pre-selected trimming value whenever pressing the button for trimming.
e automatic approach system is used for the fast and exact approach
of the specimen towards the knife edge.
e function of the automatic approach system is limited to the tem-
perature range between -5°C and -35°C.
c
aution
In case the specimen was frozen on to the chuck with CO2 gas, liquid
nitrogen or with the Peltier element it is not guaranteed that the auto-
matic approach system functions perfectly. For the specimen tempera-
ture must not be lower than -35°C when activating the ACA.
In case the temperature is lower than -35°C, it is recommended to insert
the chuck into the specimen clamping and wait until the specimen tem-
perature has adjusted to the chamber and or set specimen temperature.
e automatic approach system uses the intrinsic capacity of the speci-
men to notice a first contact between specimen and knife edge. If speci-
men and knife edge get in contact with each other, a very low current is
measured via a pre-amplifier, which is placed directly behind the speci-
men holder. e signal form of the detected current is transferred via
the outlet of the pre-amplifier to the micro-processor. A corresponding
software recognizes the threshold value causing an immediate inter-
ruption of the horizontal drive. e threshold value is also determined
regarding the temperature.
e optimal function of the automatic approach system is based on the
fact that the knife is conductively connected with the knife carrier base,
whereas the specimen holder is separated by an isolating piece.
Specimen coarse
feed and trimming
function
Automatic approach
system
Theory of operation
Specimen coarse feed and trimming stages
