Engineering · PLC · Project 11 of 15 · Process and level · Level 3

Oven temperature on / off control

Keep an oven near 60 °C using a heater, a cooling fan and an analog temperature input.

Learning model only. This page teaches the program logic. A real machine needs a proper control panel with an isolator, fuses, motor protection and a hard-wired emergency stop. Mains and motor wiring is for qualified electricians. A PLC output never drives a motor directly.

You will learn

On / off control with a dead band: the heater turns on at 55 °C and holds on until 65 °C. The comparison blocks (TEMP < 55) read an analog value as a true / false contact. The dead band stops the heater clicking on and off.

How it works

Flip Control ON. The heater warms the oven from room temperature.
At 65 °C the heater stops and the oven cools slowly.
At 55 °C it starts again. Open the door slider to lose heat faster.

In real life

Ovens, incubators, water heaters, kilns. Precise jobs use PID instead of on / off.

Inputs, outputs and addresses

The same signals on seven PLC brands. Inputs and outputs are numbered in order; check your own hardware and software, because addresses depend on the model and module position.

Name	What it is	Type	Siemens S7-1200	Allen-Bradley CompactLogix	Mitsubishi iQ-F FX5U	Delta DVP / AS	Omron CP2E	Schneider M241	Inovance H5U
ENABLE	Control enable switch	Input	`%I0.0`	`Local:1:I.Data.0`	`X0`	`X0`	`0.00`	`%IX0.0`	`X0`
HEATER	Heater contactor	Output	`%Q0.0`	`Local:2:O.Data.0`	`Y0`	`Y0`	`100.00`	`%QX0.0`	`Y0`
FAN	Cooling fan	Output	`%Q0.1`	`Local:2:O.Data.1`	`Y1`	`Y1`	`100.01`	`%QX0.1`	`Y1`
TEMP	Oven temperature	Analog input	`%IW64`	`Local:3:I.Ch0Data`	`D100`	`D100`	`D100`	`%IW0`	`D100`

Ladder diagram (shown for Siemens, live state)

Green wires carry power in the moment captured below. Switch the brand and the language in the simulator.

Structured text, Siemens SCL

(* Siemens S7-1200, CPU 1214C DC/DC/DC - TIA Portal - SCL *)
(* Rung 1: Heater on below 55, off above 65 *)
"HEATER" := ("TEMP" < 55 OR "HEATER") AND "TEMP" < 65 AND "ENABLE";
(* Rung 2: Fan on above 70 *)
"FAN" := "TEMP" >= 70;

Structured text, Allen-Bradley

(* Allen-Bradley CompactLogix 5069 (L306ER) - Studio 5000 Logix Designer - Structured Text *)
(* Rung 1: Heater on below 55, off above 65 *)
HEATER := (TEMP < 55 OR HEATER) AND TEMP < 65 AND ENABLE;
(* Rung 2: Fan on above 70 *)
FAN := TEMP >= 70;

Try this

Change 55 and 65 to 45 and 50.
Raise the door slider and see the heater stay on longer.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.

#	Item	Buy / compare
1	PLC with analog input	Amazon.in · IndiaMART · Robu.in
2	PT100 or thermocouple with transmitter	Amazon.in · IndiaMART · Robu.in
3	Heater contactor	Amazon.in · IndiaMART · Robu.in
4	Cooling fan	Amazon.in · IndiaMART · Robu.in

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This is a learning tool. It teaches the logic, not the exact keystrokes of each vendor’s software. Check the manual of your own PLC.