Control of temperature in film processor in absence of valid feedback temperature data

摘要

A temperature control system (10) of an automatic film processor (12) includes developer and fixer recirculation paths (30, 40) having thermowell heaters (34, 44) and thermistors (35, 45), and a cooling heat exchanger (37) in the developer path (30) which passes in heat exchange relationship with water in a wash tank (23). The system (10) also has a blower (48), heater (49) and thermistor (52) in an air path of a dryer (24). Heater (34, 44, 49) and cooling heat exchanger (37) operation is normally controlled on a closed loop, feedback mode basis by comparing measured current temperatures in real time with preestablished setpoint temperatures. When system errors cause an absence of current valid measured temperature data, shutdown or lockout can be overridden, and temperature control continued on an open loop basis using stored historical measurement data and on-off duty cycle profiles.