Middleby Marshall PS360, PS570, PS200, PS555, PS220, PS224 PS310 manual Sequence of Operation

SECTION 1 - SEQUENCE OF OPERATION

ll.ELECTRIC OVEN SEQUENCE OF OPERATION

A.Electrical Supply

Most electrically heated ovens operate on a 208/230/ 380/440V, 3 phase, 4 wire system. The fourth wire is for a 120 V neutral ground. This 120 V neutral ground eliminates the need for a control transformer. Where a neutral is not available, a 240/110V transformer is sup- plied.

B.Door Switch

Closing the control cabinet door (or machinery com- partment door, as appropriate for the oven model) will close the door switch and allow the oven to operate.

Note that the electrical systems will still be “live” if the switch is open, although the oven cannot operate.

The door switch has a bypass position to enable ser- vice operation with the door opened. When the door is open, grasp the switch actuator and pull it out as far as possible. This will close the door switch and permit troubleshooting. Closing the control cabinet door will reset the switch.

Closing the door switch permits a circuit to go through a fuse (or circuit breaker, as appropriate for the oven model) to one side of the conveyor switch, blower mo- tor switch and to the heat switch.

C.Conveyor Switch

Closing the conveyor switch permits a circuit to go to the Conveyor Speed Control Module, which:

1.Sends power to the gear motor (conveyor drive mo- tor). The 120VAC signal to the Conveyor Speed Control Module is rectified to a 90VDC signal which is then sent to the gear motor.

2.Allows regulation of conveyor speed. Adjusting the thumbwheel (or digital pushbutton display unit, as appropriate) to the desired conveyor belt speed in- structs the Conveyor Speed Control Module to regu- late the output to the gear motor. This increases or decreases the conveyor speed as necessary to match the speed setting shown on the thumbwheel or display unit.

D.Blower Switch

Closing the blower switch energizes:

1.The cooling (axial) fan(s).

2.The blower motor contactor (s).

Closing this contactor starts the blower motor(s). When both blower motors are up to speed, centrifugal switch(es) located inside the rear end of the motor(s) (or air flow switch[es], as appropriate for the oven model) will close, setting up the heat circuit.

E.Heat Switch

Closing the heat switch completes a circuit:

1.Through the heat switch.

2.Through the blower motor centrifugal switch.

3.Through the high limit switch.

4.For ovens with on On-Off heater activation mode: To the primary relay contacts of the Temperature Controller (terminals 4 and 5 for digital controllers, terminals 5 and 6 for analog controllers).

When the temperature-sensing thermocouple(s) indicate that the oven temperature is below the set point on the Temperature Controller, the Tempera- ture Controller will energize the contactor(s) which in turn energize the heaters.

When the oven temperature reaches the set point of the Temperature Controller, the Temperature Con- troller will cut power to the heaters. When the tem- perature drops a few degrees, the Temperature Con- troller will again energize the heaters.

An indicator on the Temperature Controller will show whether the Controller is calling for heat. This indicator varies by Temperature Controller model. Refer to the instructions for the appropriate Tem- perature Controller for an illustration and descrip- tion of this indicator.

5.For ovens with a Variable Pulse heater activation system: To terminals 15 and 16 on the tempera- ture controller. In response to the signal from the thermocouple(s), Terminals 15 and 16 send a 4- 20mA signal to a controller module that contains an amplifier board and two solid state relays. The relays activate the heating elements at 100% power on a fixed cycle time, for a length of time propor- tional to the signal from the temperature controller.

A “HEAT ON” indicator on the Temperature Con- troller will light to show whether the Controller is calling for heat.

F.High Limit

NOTE: Electric oven models use a separate High Limit Control Module.

The High Limit relay will shut the oven burner OFF:

1.If the high limit thermocouple senses an oven tem- perature above 650°F.

2.If the signal from the high limit thermocouple is lost.

An indicator on the Temperature Controller will show a high limit condition. This indicator varies by Tempera- ture Controller model. Refer to the instructions for the appropriate Temperature Controller for an illustration and description of this indicator.

G. Cooldown

3. The Temperature Controller.

6

When the heat and blower switches are turned OFF the cooldown relay will allow the blowers to remain ON until the oven temperature falls to 200°F (93°C).

During cooldown, the Temperature Controller will con- tinue to show the oven temperature.