. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. PRACTICAL METHODS FOR TEMPERATURE CONTROL to the required amount. Stability is of course provided by the overall negative feedback from heater to thermistor, via the air in the enclosure. The appara- tus works quite satisfactorily with power supplies merely rectified by germa- nium rectifiers and smoothed by 32 [xF. If, however, the sensitivity control is turned up so that the output stage is either turned 'on' or 'off' by movement through a small temperature excursion, then the heater can
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. PRACTICAL METHODS FOR TEMPERATURE CONTROL to the required amount. Stability is of course provided by the overall negative feedback from heater to thermistor, via the air in the enclosure. The appara- tus works quite satisfactorily with power supplies merely rectified by germa- nium rectifiers and smoothed by 32 [xF. If, however, the sensitivity control is turned up so that the output stage is either turned 'on' or 'off' by movement through a small temperature excursion, then the heater can be replaced by a + 300 2I<Q Heater. Figure Circuit for ultra-fine control of air temperature in small enclosures; the thermistor is of type 100 kQ, at 20°C. Two control ranges are available from the switch which could also incorporate a background heater on the higher range powerful relay which will control large heat loads'. With this method, con- trol of air temperature to 1/50°C in a litre of air in an uninsulated plastic box has been obtained. Hot stages The temperature control of specimens usually immersed in liquids on the microscope stage has received much attention. The greatest problem associated is that of allowing the illumination of the specimen. Stages using circulating water in a transparent cell, and electrical heating of a perforated metal block, are in regular use. The important consideration here is that of putting the specimen in contact with a large reservoir of heat so that it can readily obtain the heat it itself loses by conduction or evapora- tion. Wherever possible the specimen should be supported on the minimum of insulating material, on a thin coverglass, and the surface which heats it must be polished to ensure the maximum of contact. (page 394) means quick-make and -break, 'snap' or toggle action.—ED. 411. Please note that these images are extracted from scanned page images that may have been digitally enhanced for rea
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