Programming Siemens LOGO! 230RCE for Powder Coating Oven Control

This reference designs a complete control program for an electrically heated powder coating cure oven using a Siemens LOGO! 230RCE logic module. The sequence covers a fan purge, burner enable, temperature-confirmed cure timer, finish indicator, and post-cure cool-down purge, with explicit I/O mapping, ladder/FBD logic, hardware wiring, and a commissioning checklist.

1. Overview

The powder coating oven described in the field report has four power outputs and three or four operator inputs. A complete cycle is:

1. Operator presses START; circulation fan Q1 energises immediately.
2. Fan runs for 1 minute (purge) to clear combustible residues from the cabinet.
3. Burner contactor Q2 closes; cabinet temperature ramps toward 185 °C.
4. An external temperature controller (or onboard analog threshold) closes a "temperature reached" signal to input I3; the LOGO! starts a 15 minute cure timer and energises the timer-running lamp Q4.
5. When the cure timer expires, the finish lamp Q3 turns on, the burner Q2 drops out, and the fan Q1 continues.
6. After a 5 minute cool-down purge, Q1 drops out and the system returns to idle, ready for the next START.

A STOP input must reset every output unconditionally. A MANUAL mode is required to drive the fan alone for maintenance or for loading/unloading without firing the burner.

2. Prerequisites

3. Hardware Identification and I/O Map

Before writing a single function block, every wire on the original diagram must be assigned to a physical LOGO! terminal. The mapping below is consistent with the LOGO! 8 wiring diagram in the Siemens LOGO! 8 system manual (article 109751604).

3.1 Digital inputs (230 V AC, referenced to N)

3.2 Relay outputs (Q1–Q4)

4. Process Sequence Specification

The cycle is best modelled as a 5-step state machine. Each step latches a flag and times the next transition.

Manual mode (I4 = 1) overrides the state machine: Q1 is energised unconditionally, Q2 is forced off, and the state machine is held in S0 so that toggling back to AUTO does not auto-start a cycle.

5. LOGO! Soft Comfort Program Design

The program is structured in seven function blocks so that any future change (e.g. timer values) touches exactly one block. Open LOGO! Soft Comfort, create a new project, and set the target device to LOGO! 230RCE (6ED1052-3HB08-0BA1).

5.1 Block list

5.2 Ladder text view (FBD equivalent, exported from Soft Comfort)

; -- State S0 IDLE: no output active ---
; RS1.SET  = I1 AND NOT(I2) AND NOT(RS4.Q) AND NOT(I4)
; RS1.RESET= I2 OR ESTOP
; 
; RS2.SET  = RS1.Q AND TA1.Q
; RS2.RESET= I2 OR ESTOP
; 
; RS3.SET  = RS2.Q AND I3
; RS3.RESET= I2 OR ESTOP
; 
; RS4.SET  = RS3.Q AND TA2.Q
; RS4.RESET= I2 OR ESTOP OR TA3.Q
; 
; Q1 = (RS1 OR RS2 OR RS3 OR RS4) AND NOT(I2) AND NOT(ESTOP)
;     OR (I4)         ; manual fan
; 
; Q2 = (RS2 OR RS3) AND NOT(I2) AND NOT(ESTOP) AND I5 ; door closed
; 
; Q3 = RS4 AND NOT(I2) AND NOT(ESTOP)
; 
; Q4 = RS3 AND NOT(I2) AND NOT(ESTOP)
; 
; TA1 = RS1.Q          ; 1 min
; TA2 = RS3.Q          ; 15 min
; TA3 = RS4.Q          ; 5 min

All RS flip-flops share a common RESET bus wired from I2 (STOP) and the ESTOP loop. The STOP button is normally closed, so its inverted logic is used in the SET equations; the SET line only energises when STOP is released (i.e. the button is not pressed). This pattern matches the convention in the LOGO! 8 system manual, section "RS flip-flop (relay contactor)".

5.3 Timer parameter values

For longer life accuracy, use the LOGO! 8's offline retention feature: the real-time clock (RTC) blocks B001–B004 and the battery-buffered RTC let the controller track the cycle even after a brief power loss. The RS flip-flops must be declared retentive in the program properties so the state survives a power dip.

6. Wiring Diagram Reference

The original drawing the user attached was for an older controller; the diagram below substitutes the LOGO! 230RCE terminal block.

                                  L  N   PE
                                  |  |    |
                              [MCB 6 A]  |
                                  |       |
                     +------------+-------+--- 230 V AC supply to LOGO! L, N
                     |
                  [LOGO! 230RCE]
       I1 -------[ START NO ]----+--- L
       I2 -------[ STOP  NC ]----+--- L
       I3 -------[ AT-TEMP ]-----+--- L (from external PID relay)
       I4 -------[ AUTO/MAN ]----+--- L
       I5 -------[ DOOR  NC ]----+--- L
       I6 -------[ ESTOP NC ]----+--- L
       
       Q1 ---+--- KM1 coil A1 (fan contactor)
       Q2 ---+--- K2 coil A1 (burner enable relay, series with ESTOP NC loop)
       Q3 ---+--- Green finish beacon
       Q4 ---+--- Amber timer-running beacon

7. Temperature Acquisition Alternatives

The 230RCE has no onboard thermocouple input. Three practical alternatives exist.

For 185 °C control with a gas burner, the first option is recommended: the burner controller handles flame safeguard, high-temperature cut-out, and modulation, while the LOGO! sequences the cabinet and the cure timer.

8. Safety Interlocks and Stop Categories

Every industrial oven control program must implement at least these interlocks in addition to the timed sequence:

1. Door interlock (I5) — Q2 is AND-gated with I5 (door closed). If the operator opens the door mid-cure, the burner drops out, but the fan continues to clear fumes.
2. Emergency stop (I6, hard-wired) — A normally closed mushroom button in series with the burner enable relay coil and in parallel with a soft-reset input to all RS flip-flops.
3. Burner controller fault (I3 going low unexpectedly) — A falling edge on I3 during state S3 resets RS3 to S4 early (cool-down), but does not drop the fan. The fault can be flagged with a message text M001 on the LOGO! display.
4. Fan airflow proof (spares, e.g. differential pressure switch on I7) — Q2 cannot be energised unless the airflow switch confirms the fan is running. Wire via a normally open contact; invert in the program if needed.
5. High-temperature alarm (analog) — Use the LOGO! 8 analog threshold (TH) block on I7/I8. If the scaled value exceeds 195 °C, drop Q2 immediately and write the message "OVEN OVERTEMP" to the display.

These interlocks give a layered response: soft stop (STOP button) cancels the sequence gracefully, while hard stop (ESTOP) removes power from the gas train directly.

9. Commissioning Procedure

1. Static check. With the LOGO! unpowered, verify with a multimeter that every input (I1–I6) reads 230 V AC to N when its field device is activated, and that Q1–Q4 contacts are open.
2. Download program. Connect the Ethernet cable from the PC to the LOGO! 230RCE RJ45. In LOGO! Soft Comfort, choose PC → LOGO! and transfer oven.lsc. The LOGO! will restart automatically.
3. Online monitor. Switch Soft Comfort to Online → Monitor. Each input should turn green when its field contact closes; each output should be observable in the relays themselves.
4. Manual mode test. Set the selector to MANUAL (I4 = 1). Confirm Q1 closes and Q2 stays open. Run the fan for 30 s to verify direction and amperage.
5. Auto mode dry run. With the burner gas isolated, press START. The sequence should be: fan on, 1 min, Q2 attempts to close (no gas, no flame), I3 stays low, so the cure timer never starts. Press STOP to reset.
6. Auto mode with burner. Re-enable the gas. Press START. Watch the burner controller ramp to 185 °C. When I3 closes, the 15 min cure timer must start and Q4 must light.
7. Door interlock test. Open the door during S2 or S3. The burner must drop out within one LOGO! cycle (≤ 100 ms). The fan should keep running.
8. ESTOP test. Press the ESTOP button. The gas valve must close and the burner controller must see a flame failure. The LOGO! should reset to S0.
9. Backup the program. In Soft Comfort, choose LOGO! → Memory Card and write the program to a micro SD. The LOGO! 230RCE auto-loads on power-up if the card is left in.
10. Document. Save the .lsc file to a versioned network share with the date and oven serial in the filename (e.g. oven_03_logo230rce_2025-03-04.lsc).

10. Verification Checklist

11. Troubleshooting Matrix

12. Spare Capacity and Expansion

The LOGO! 230RCE has unused capacity that the program can be extended into without adding hardware:

• Inputs I7, I8 — free for an airflow proof switch and a high-temperature alarm transmitter.
• Analog threshold (TH) blocks — use the onboard 0–10 V analog on I7/I8 for a cabinet overtemperature alarm at, say, 195 °C. Drive a message text to the LOGO! display and a flashing Q4 if triggered.
• Shift register blocks — count completed cure cycles; trigger a maintenance reminder on the 500th cycle (e.g. "CHECK BURNER NOZZLE").
• Web server (LOGO! 8) — the Ethernet port exposes a built-in web page with up to 8 user-defined variables. Map RS1.Q, RS2.Q, RS3.Q, RS4.Q, TA1.ET, TA2.ET, TA3.ET, and I3 for remote monitoring on the factory floor.

13. Field Notes

Always keep a current .lsc file off the oven, e.g. on the factory MES or in a labelled folder on the maintenance engineer's laptop. Treat the LOGO! program like any other piece of controlled documentation: revision history, signed-off parameter changes, and a backup SD card stored in the oven's control cabinet.