U1 CD4541 is a Timer with Long Duration Ability. This timer is started by a low pulse from earlier circuit, when the temperature goes above setpoint, a low state is at U2A inputs, this starts the timer. The timer output goes high after a preset time. U2C-D Flip flop is power on reset via cap C7. Even a manual ‘reset’ is used if required. This alarm toggle is ‘set’ when The temperature remains high even after the preset time period of U1.
A digital counter monitors the number of times a process goes beyond a certain temperature limit over a long cycle of time. This circuit has a Analog Timer and Digital Counter. The Analog timer turns on an Alarm if the Temperature Limit transition is very long.