Mitsubishi FXo/FXon PLC Hardware Practice

3.3 Grounding Requirements

Use copper wire with an area of ≥ 2mm ² (AWG14) and a grounding resistance of<100 Ω (Class 3).

It must be grounded independently and must not share the grounding electrode with power equipment such as frequency converters and motors.

Although the manual states that it can operate without grounding, it is strongly recommended to connect the PE terminal for anti-interference purposes.

The grounding terminals of all expansion units (including FXon-40ER, etc.) should be interconnected to the same ground point.

3.4 Main circuit protection

A 3A circuit breaker or fuse (C-type trip characteristic) should be installed on the input side of the PLC power supply to protect the power lines and internal fuses. Attention: The internal fuse of the PLC cannot be replaced. Once it is blown, it needs to be returned to the factory for repair.

Input wiring and Sink/Source configuration

The DC input circuit of FXo/FXon adopts optoelectronic coupling isolation, with a default response time of 10ms (the filtering time of X0-X7 and X10-X17 can be adjusted through D8020/D8021).

4.1 Input electrical parameters

Model input current OFF → ON threshold ON → OFF threshold

FXo (X0‑X7) 7mA @24V >4.5mA <1.5mA

FXon (X0‑X7) 5mA @24V >3.5mA <1.5mA

4.2 Sink and Source Wiring (World Standard)

World standard models with S/S terminals can select input methods by changing the polarity of the S/S wiring without the need to replace hardware:

Sink input (low level valid): Connect the S/S terminal to+24V. At this time, the input common terminal is 0V, and the input switch is connected between 0V and the X terminal.

Source input (high level valid): Connect the S/S terminal to 0V. Connect the input switch between+24V and the X terminal.

Japanese specifications (such as FXo Δ△ MT-D/E) do not have S/S terminals and are fixed in Sink mode (X terminal is the input point, COM is the 0V common terminal).

4.3 Using an external 24V power supply

If there are a large number of input devices or the internal service power supply capacity is insufficient, an external 24V DC power supply can be introduced. When wiring, connect the "+" of the external power supply to the S/S terminal (Sink mode) or input switch common terminal (Source mode), and connect the "-" of the external power supply to the 0V terminal of the PLC. Please note that the external power supply must be at SELV safe voltage and must not be grounded.

4.4 Input series diode and parallel resistor

Series diode: Each input can be connected with up to 2 LEDs or diodes in series, with a total voltage drop of less than 4V.

Parallel resistor (suppressing leakage current): If the leakage current of an input device (such as a three wire sensor) exceeds 1.5mA (FXo) or 1mA (FXon) when turned off, a parallel resistor Rb must be connected. Calculation formula:

Rb=1.5k Ω/(leakage current -0.8mA) approximately.

4.5 Special precautions for AC input (FXon-40MR-UA1/UL only)

This model has a 110V AC input (non DC input) and the following characteristics:

When the input voltage is above 80V AC, it is ON; when it is below 30V, it is OFF.

The response time is fixed at 25ms, which is not suitable for high-speed counting or interrupt functions.

Temperature limit: The number of inputs connected simultaneously must not exceed half of the total number of inputs, otherwise excessive internal temperature rise may cause misoperation or damage.

Output wiring and load protection

5.1 Relay output (model including MR)

Parameter specifications

Maximum switch voltage ≤ 240V AC, ≤ 30V DC

Each point has a rated current of 2A (resistive load), with a total of 4 points sharing 8A

Maximum lamp load 100W (tungsten filament lamp)

Response time is about 10ms

Electrical lifespan: 1 million cycles under 20VA load; 200000 cycles under 80VA load

Wiring points:

Every 4 output points should be equipped with 5-10A fuses.

When driving inductive DC loads (such as solenoid valves), freewheeling diodes (such as 1N4007) must be connected in reverse parallel at both ends of the load, otherwise it will seriously reduce the contact life of the relay.

When driving inductive AC loads, RC absorption circuits (0.1 μ F+100 Ω) should be connected in parallel.

External Interlocking: For circuits that may cause mechanical damage, such as controlling the forward and reverse rotation of motors, in addition to interlocking in the PLC program, it is necessary to add contactor auxiliary contact interlocking on external hardware, and it is strictly prohibited to rely solely on software.

5.2 Transistor output (model including MT)

Parameter specifications

Switching voltage 5-30V DC

Rated current per point 0.5A (resistive), maximum 0.8A per common terminal

Maximum lamp load 1.5W (approximately 62mA at 24V)

Response time typically below 0.2ms

Isolation method optocoupler

Key points:

The output of a transistor can be classified as Source or Sink based on the suffix: DSS represents Source output (with a positive output terminal), while the Japanese specification MT-D/E represents Sink output (with a negative output terminal).

When driving inductive loads, parallel freewheeling diodes (similar to relays) are required.