Siemens LOGO! 0BA7 Tunnel Ventilation Control with Danfoss FC302 VFD

Tunnel ventilation is a multi-discipline automation problem that combines motor control, sensor feedback, time-of-day scheduling, and fail-safe emergency logic. For a school project or pilot installation, the Siemens LOGO! 0BA7 (LOGO! 8 generation, also called LOGO! 8.1/8.2 depending on the FS level) paired with a Danfoss VLT AutomationDrive FC 302 is a credible, low-cost solution. This article walks through the full engineering path: hardware selection, I/O mapping, the weekly time program, analog reference scaling into the VFD, the smoke detector emergency stop chain, and the final commissioning verification.

1. Functional Requirements Summary

The student specification defines four speed levels, automatically selected by a weekly time-of-day schedule, with manual override pushbuttons and a smoke-detector-driven emergency stop.

The motor is assumed to be a three-phase induction motor (typical ratings 1.5 kW to 7.5 kW for a small traffic/service tunnel or model tunnel). The VFD will operate in open-loop VVC+ mode and accept a 0–10 V speed reference from the LOGO!.

2. System Topology

The complete control loop is short and easy to draw because the LOGO! acts as both the scheduler and the analog reference source. The diagram below summarises the signal flow.

3. Prerequisites

• LOGO! Soft Comfort V8.2 or later (programming environment). Download from the Siemens LOGO! product support page.
• MCT 10 Set-up Software for the FC 302, available from the Danfoss Drives support portal.
• LOGO! 0BA7 base module (e.g. 6ED1052-1MD08-0BA1 for the 24 V DC variant with relay outputs) plus one DM8 extension (e.g. 6ED1055-1MB00-0BA2 for additional digital I/O).
• Danfoss FC 302 frame size matched to motor (e.g. 132F0043 for 1.5 kW 400 V three-phase).
• 24 V DC power supply sized for LOGO!, smoke detector, and contactor coils. A 60 W DIN-rail PSU (e.g. Phoenix Contact QUINT) is comfortable for one fan contactor.
• 24 V DC contactor (e.g. Eaton DILM7-01(24VDC)) and matching thermal overload relay.
• Smoke detector with 24 V DC relay output (e.g. Siemens FDOOT241-A4 or equivalent addressable point with a single-pole NC relay contact).
• Three momentary pushbuttons (Stop, Auto, Manual) and a level-selector rotary switch (4 positions) or four individual pushbuttons.
• Shielded twisted-pair cable for the 0–10 V analog run, kept physically separated from the 400 V motor cabling.

4. Hardware Sizing and Ratings

4.1 Motor and VFD

For a small service tunnel or model build, a 1.5 kW three-phase 400 V motor is typical. Using the standard induction motor sizing formula:

kVA = √3 × VLL × Iline / 1000

For a 1.5 kW four-pole motor running near full load at 0.85 power factor:

• I_line ≈ 3.3 A at 400 V
• kVA = 1.732 × 400 × 3.3 / 1000 ≈ 2.29 kVA
• The VFD must be sized at or above the motor full-load current; an FC 302 with 5.6 A continuous rating (frame size A2) is the usual match.

The student should verify the motor's actual nameplate FLC and not use the kW rating alone, because motors from different manufacturers draw different currents at the same power. Always program par 1-30 (Stator Resistance), par 1-31 (Rotor Resistance) and par 1-33 (Stator Leakage Reactance) using an Automatic Motor Adaptation (AMA) run on first power-up. Refer to the FC 302 Design Guide MG33BC02 for the parameter map.

4.2 LOGO! 0BA7 I/O Budget

If more digital inputs are needed for the level selector, the DM8 extension adds I9–I16. The 0BA7 base also includes AI1–AI4 (0–10 V) on terminals I7/I8 and on AI1/AI2 of the AM2 module if fitted. For the simple 4-level selector, four discrete inputs are sufficient and avoid the cost of an analog selector.

5. LOGO! Program Design

5.1 Weekly Timer Block (B016)

The 0BA7 firmware supports a Weekly Timer with up to three ON/OFF cam pairs per block. Four blocks are cascaded to cover the four time windows described in the spec. Configure each Weekly Timer in LOGO!Soft Comfort as follows:

Time windows that cross midnight (20:00 → 03:00) require the Weekly Timer to be set to span two days, or the use of an additional Astronomical Timer block (B018) for sunrise/sunset alternatives. In LOGO!Soft Comfort, configure the cam with separate ON and OFF entries rather than relying on a single cam, otherwise the OFF action triggers the same day. The verified method is to use a Night timer with two cams: Cam 1 ON at 20:00 Mo–Su, Cam 2 OFF at 03:00 Mo–Su.

5.2 Reference Value Selection (B007 Analog Multiplexer)

The Analog Multiplexer block (B007) selects between the auto-schedule value and the manual override value. Connect the four Weekly Timer outputs through a priority encoder built from AND/OR gates to a single "Auto Value" integer (0–1000, representing 0–100.0 % scaled by 10 for the LOGO! 0–10 V output resolution).

Manual mode logic (pseudocode in Structured Text form to be entered as an FBD diagram):

// Manual level selection: I5..I8 → reference
IF Manual_Button AND NOT Stop_Button AND NOT Smoke_Alarm THEN
    IF I5 THEN Reference := 150  // 15.0 %
    ELSIF I6 THEN Reference := 450
    ELSIF I7 THEN Reference := 900
    ELSIF I8 THEN Reference := 1000
    END_IF
ELSE
    // Auto mode
    IF Level1_Timer THEN Reference := 150
    ELSIF Level2_Timer THEN Reference := 450
    ELSIF Level3_Timer THEN Reference := 900
    ELSIF Level4_Timer THEN Reference := 1000
    ELSE Reference := 0
    END_IF
END_IF

// Smoke alarm forces zero and latches fault
IF Smoke_Alarm OR Stop_Button THEN
    Reference := 0
    Fault_Latch := 1
END_IF

5.3 Analog Output Scaling

The 0BA7 base analog output (AM2 optional or integrated on the 0BA8) produces 0–10 V proportional to 0–1000 internal units. The B025 Analog Ramp block is used to apply a 5-second ramp-up and a 3-second ramp-down so that the VFD does not see a step change from 0 % to 100 % in one program cycle. Connect the ramp output to the physical AQ. The corresponding VFD parameter is par 3-02 Minimum Reference = 0 % and par 3-03 Maximum Reference = 100 % to match the 0–10 V span.

6. Danfoss FC 302 VFD Configuration

6.1 Terminal Wiring

The FC 302 control terminals relevant to this project are listed in the table below. Reference the VLT AutomationDrive FC 302 Design Guide MG33BC02.

6.2 Essential Parameter Settings

6.3 Acceleration / Deceleration Ramps

Set par 3-41 (Ramp 1 Ramp-up Time) to 30 s and par 3-42 (Ramp 1 Ramp-down Time) to 30 s. Tunnel fans have large rotating-mass inertia; a step change from 0 to 50 Hz on a 7.5 kW fan will trip the VFD on DC-link overcurrent if the ramp is too short. A 30-second ramp matches the LOGO! Analog Ramp duration for a smooth handover.

7. Smoke Detector and Emergency-Stop Chain

The smoke detector is wired in a fail-safe loop: its normally-closed (NC) contact is in series with the LOGO! Stop pushbutton and the VFD's Safe Stop input (terminal 37 on the FC 302, which is a hardware-based STO function). The wiring must be sized so that any single break in the loop drops out the contactor K1 and inhibits the VFD.

7.1 LOGO! ESD Logic

Wire the smoke detector NC contact into input I4. In the LOGO! program, I4 is monitored by a negation input on the master enable latch. The logic is:

// ESD latch — any condition clears the latch
SD := NOT I4     // Smoke detector NC inverted
ESD := Stop_PB OR SD OR VFD_Fault_ACK
Run_Enable := Auto_OR_Manual AND NOT ESD

Once triggered, ESD latches the contactor off and forces the analog reference to 0 V. The reset is a deliberate operator action (Stop pushbutton released, Auto pushbutton pressed) — never an automatic reset. This matches the Phoenix Contact reference design for tunnel ventilation control, which recommends manual reset of fire interlocks.

7.2 VFD STO Wiring (FC 302 Terminal 37)

Terminal 37 is a Safe Torque Off input. It must be tied to 24 V to allow the drive to produce torque; removing 24 V from terminal 37 puts the drive into the STO state in < 20 ms. Route the contactor K1 aux-NO contact in series with the LOGO! Q2 output to terminal 37. This is a hardware interlock, completely independent of the LOGO! program and the analog reference — the safest possible architecture for a fire-mode shutdown.

8. Wiring Diagram (Detailed)

9. Step-by-Step Commissioning Procedure

1. Mechanical and power pre-checks. Verify the motor is uncoupled, the fan impeller rotates freely, and the earthing conductor is connected at every enclosure. Measure the insulation resistance (≥ 1 MΩ at 500 V) between phases and from each phase to earth.
2. Power up the LOGO! and PSU only. Leave the VFD disconnected from the motor (U, V, W floating). Confirm the LOGO! runs its self-test, the time-of-day clock keeps time, and the menu appears in English. Use the LOGO!'s built-in display to navigate to Card → Program → Copy from LOGO! Soft Comfort if you programmed it offline.
3. Verify the weekly timers. Manually set the LOGO! clock to a time inside each window (e.g. 22:00 for Level 1, 04:00 for Level 2, 12:00 for Level 3, 17:00 for Level 4). Read the value of the analog output AQ with a multimeter. Expected voltages: 1.5 V, 4.5 V, 9.0 V, 10.0 V respectively (±0.1 V).
4. Verify the manual override. With the LOGO! in Manual mode, press I5 → AQ = 1.5 V, I6 → 4.5 V, I7 → 9.0 V, I8 → 10.0 V. The transition between positions must be smooth thanks to the Analog Ramp block.
5. Power up the VFD without motor. Apply 400 V to the FC 302 input. Confirm display is normal and no alarm is present. Navigate to par 1-29 and run AMA (Automatic Motor Adaptation) with the motor uncoupled but the motor cable connected. The VFD will measure stator resistance and leakage reactance; this takes about 60 s.
6. Verify the analog reference at the VFD. With the LOGO! outputting 5.0 V, measure the voltage between FC 302 terminals 53 and 55. Read par 16-01 (Frequency) — it should display approximately 25 Hz. Read par 16-09 (Custom Readout) for the actual reference in %.
7. First motor run (open tunnel). Re-couple the motor to the fan. Press Auto. The fan should ramp from 0 Hz to 7.5 Hz (15 % of 50 Hz) over 30 s. Listen for abnormal noise. Touch the motor frame to check for excessive vibration. Log the motor current at par 16-11; it should be well below the nameplate FLC.
8. Step through the four levels. Force each level manually and verify the speed is correct and the current is stable.
9. Test the smoke ESD. Trigger the smoke detector (use the test button on the device). Within 1 s, the LOGO! should de-energise Q1, the contactor K1 should drop out, the VFD should display alarm 8 (DC-link undervoltage) or 60 (External interlock), and the analog reference should fall to 0 V.
10. Reset sequence. Restore the smoke detector, press Stop, wait 10 s, press Auto. The system must not restart automatically; the operator must press Auto again.
11. Endurance test. Leave the system on Level 4 (100 %) for at least one hour. Monitor the VFD heatsink temperature (par 16-34) and the motor winding temperature (if a PTC is fitted, par 1-93). Both must remain within nameplate rating.

10. Verification Checklist

11. Troubleshooting Matrix

12. Engineering References and Standards to Verify Against

Although the student project is not a certified installation, the following standards documents are worth a one-line look so the design choices are not arbitrary:

• EN 12101-3: Smoke and heat control systems — Part 3: Specification for powered smoke and heat exhaust ventilators.
• NFPA 502: Standard for road tunnels, bridges, and other limited access highways.
• EU Directive 2004/54/EC: Minimum safety requirements for tunnels in the Trans-European Road Network.
• PIARC Road Tunnels Manual: Best-practice guidance from the World Road Association.

For the academic dimension of tunnel fire ventilation control, the review article in Tunnelling and Underground Space Technology — "On the problem of ventilation control in case of a tunnel fire event" provides the fire-engineering background. The Phoenix Contact tunnel ventilation reference architecture illustrates how the same control philosophy is implemented in industrial systems with redundant PLCs. The IEEE paper on Lévy-Flight-Dynamics optimisation for tunnel ventilator control shows where research on intelligent scheduling is heading.