for consistent and reproducible results.
The developer is the most critical
solution and should be held within 1/4 to 1/2F ( 0.1 to 0.25C).
Other
solution temperatures are less critical, but should be controlled to within 2F
(l.1C) of the developer temperature. In black and white film processing the
temperature of the developer is not as critical as in color processing. The
temperature can range from 65F to 75F and the other solution temperatures
should be controlled to within 2F of the developer temperature.
d. Heat Exchanger.
The heat exchanger incorporates refrigeration coils
and electrical heating elements. The developer and fixer solutions are pumped
through separate exchangers.
The chemicals are adjusted to the proper
temperature, and reintroduced into the processing machine.
A temperature
sensing probe, located within the processing machine tank, monitors solution
temperatures and transmits this information to the solution thermostats.
If
solution temperature is too high, the refrigeration compressor is turned on.
This drives the refrigerant through coils within the heat exchanger and cools
the solution. If the solution in the tank is too cold, the heaters located in
the heat exchanger are turned on. This heats the solution. The operator sets
the solution thermostats at the desired temperature and the solution
temperature is automatically controlled.
e. Replenishment.
Replenisher is generally introduced to existing
solutions in the recirculation system.
It is mixed with the partially
exhausted solutions and, therefore, does not enter the machine in its raw,
undiluted state.
If raw replenisher were added directly into the solution
tanks, uneven development and/or fixation could occur before the replenisher
mixed with the solutions already present.
f. Agitation.
The agitation systems used in continuous processors have
already been discussed at length.
Some of these systems, specifically the
turbulation method, the spray-immersion method, and the spray method in which
the solution is reused, rely on the processor's recirculation system to pump
the solution out of the tank, treat it (filter, heat/cool, and replenish), and
pump it back in.
5. Replenishment System.
The purpose of replenishment is to maintain the
activity of the solution at a constant level throughout processing operation.
This becomes necessary due to the fact that as solutions are used their
activity decreases. Replenisher may be added to solutions in one of two ways.
a. Topping off.
(1) After a certain amount of film is processed, a quantity of solution
is removed and another quantity of replenisher is added.
The quantity of
replenisher is usually greater to allow for carryover and evaporation.
For
example, a processing tank holds 8 gallons of developer.
After processing a
roll of film, only 7.8 gallons remain, the .2 gallon has been carried out by
the film or has evaporated.
Additionally, the remaining 7.8 gallons is
partially exhausted.
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