Physitemp Instruments BFS - Manual (Page 6)

OPERATING INSTRUCTIONS FOR PHYSITEMP FREEZING STAGES
1.0 INTRODUCTION
1.1 This manual gives general information and detailed operating instructions for three freezing stages
manufactured by Physitemp Instruments Inc for use in microtomes. It also cover the FRM systems which
comprise an Erma microtome complete with BFS Freezing Stage.
1.2
All stages operate in the same manner. However, they differ in several ways, namely:
1) Surface area
BFS-3 has a 3.1 x 3.8 cm stage area
BFS-5 has a 3.8 x 3.8 cm stage area
BFS-30 has a 8 x 8 cm stage area
2) Minimum operating temperature under no load conditions
(cooling water temperature 20
o C)
BFS-3 -38 o
BFS-5 -35 o
BFS-30 -40 o
1.3 This series of freezing stages includes major improvements over our earlier equipment. There is an
electronic control built into each stage which automatically closes down the equipment if the device over-
heats. Overheating never occurs during normal use, but can be caused by two abnormal conditions:
a) seriously reduced water flow to the module, see Section 5.
b) the spring-loaded FREEZE/THAW switch being held at THAW for too long (see
Section 6.8)
1.4 Every BFS stage is supplied complete with Power Supply which converts 115V AC house current
to the non-lethal low-voltage current which operates the freezing stage. The stage itself is normally supplied
with mounting hardware to fit the user’s microtome.
1.5
BFS-3 and BFS-5 are intended for use in clinical or Minot type microtomes. The larger BFS-30
stage is designed for use in sliding or sledge microtomes. Mounting hardware is available to fit Physitemp
freezing stage to almost every model of microtome.
2.0 FEATURES OF THERMOELECTRIC FREEZING
2.1 Thermoelectric cooling was discovered by Jean Peltier in 1834. However, practical uses for the
Peltier Effect had to await developent of such efficient material as bismuth telluride. These materials have
become available only in recent years as a by-product of transistor technology.
2.2
Thermoelectric freezing stages provide deep and continual cold when fed with low-voltage direct
electric current. They consume no materials, need no maintenance and require only a supply of cooling
water. Freezing at any desired temperature down to -40
o C is maintained just as long as current is supplied to
the stage. The electrical supply to the stage is perfectly safe and non-lethal, as it never exceeds 15V DC.
2.3
Thermoelectric freezing eliminates the need to use aerosol spray coolants or freon.
2.4 If the direction of current in a thermoelectric module is reversed, heat instead of cold is produced
on the top plate. All BFS units make use of this characteristic, and include a FREEZE/THAW switch, which
reverses the current. This provides a quick method of melting the stage-tissue interface, so that solid block
of frozen tissue may be quickly removed from the stage.
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