Mitsubishi FXo/FXon PLC Hardware Practice

Mitsubishi FXo/FXon PLC Hardware Practice

Key points for product positioning and selection

The FXo and FXon in Mitsubishi Electric's MELSEC-F series are compact PLCs designed for small automation equipment. The most significant difference between the two is that FXo does not have scalability, and all I/O points are fixed; FXon can be expanded, with a maximum system I/O of 128 points, and supports special functional modules such as analog and communication adapters. In applications that require flexible configuration and may increase I/O in the future, FXon is the only choice.

Basic Model Identification

Based on the model string on the product nameplate, the power type, output type, and certification specifications can be quickly determined. Standard formats such as FX0-14MR-ES/UL or FXON-40MT-DSS.

Power supply and voltage: AC (100-240V) or DC (24V). The AC version provides an internal 24V service power supply (which can be used for input circuits), while the DC version requires an external 24V power supply.

Output type: R=relay output; T=transistor output.

I/O points: For example, 14 represents 8 inputs and 6 outputs, 20 represents 12 inputs and 8 outputs, and 30 represents 16 inputs and 14 outputs. FXon-24Mx actually occupies 32 points of the system (16 in and 16 out), but there are only 24 physical ports.

Terminal arrangement: World Spec S/S terminals allow for the selection of Sink or Source input modes through wiring; The Japanese specification is fixed as Sink.

When selecting, it is necessary to confirm whether expansion is needed, whether high-speed counting or pulse output (supported by transistor type) is needed, and environmental certification requirements (UL, ABS, DNV, etc.).

Installation environment and mechanical dimensions

2.1 Environmental conditions

All FXo/FXon products must be installed in control cabinets that comply with IP20 protection level and meet the following environmental parameters:

Project specifications

Working temperature 0~55 ° C

Storage temperature -20~70 ° C

Humidity 35-85% RH, no condensation

Altitude ≤ 2000m

Pollution level 2 (non-conductive dust)

Installation Category II

Anti vibration (direct installation) 10~55Hz, 0.5mm amplitude, 2G, 2h for each of the three axes

Anti vibration (DIN rail installation) 10~55Hz, 0.5mm amplitude, 0.5G, 2h for each of the three axes

Resistance to impact 10G, 3 times in each direction

Special attention: Do not install in environments with corrosive gases, conductive dust, strong impact, or condensation. Prevent conductive foreign objects such as metal shavings from falling into the interior of the casing during installation.

2.2 Mechanical installation method

There are two installation methods to choose from:

DIN rail installation (recommended): Use a 35mm wide DIN rail (EN 60715). Insert the upper part of the device into the guide rail and push the lower part forward until the spring clamp is locked. When disassembling, use a screwdriver to pull down the spring clip and lift the device up at the same time. Not suitable for strong vibration environments.

Direct screw installation: Fix with M4 screws through the mounting holes (diameter 4.5 or 5) at the four corners of the housing. The external dimensions of FXo and FXon are different, and the opening size should refer to the drawings in the manual (width: FXo-14 is 100mm, FXon-60 is 185mm, etc.).

The installation direction must be horizontal, and vertical or inverted installation is prohibited. To ensure heat dissipation, a space of ≥ 50mm should be reserved above and below the device, and there is no need for additional gaps on both sides. If using a double-layer layout (FXon only), FXon-65EC 650mm extension cable can be selected to connect to the second layer, and it should be noted that a maximum of one cable can be used per system.

Power wiring and grounding specifications

3.1 AC power supply model (ES/UL suffix)

Power terminal: L (live wire), N (neutral wire), PE (protective grounding).

Rated voltage: 100-240V AC,+10%/-15%, 50/60Hz.

Surge current: FXon maximum 50A 5ms (at 200V AC), FXo maximum 25A 2ms.

Power consumption: FXo-14MR is about 20VA, FXon-60MR is about 60VA.

Important rules:

Easy to operate circuit breakers or isolation switches must be installed outside the PLC for emergency power outages and maintenance isolation.

It is recommended to install 5-10A fuses for every 4 output points to prevent short circuits in the output circuit from damaging the circuit board.

The AC power version provides a 24V DC service power supply (located at+24V and COM terminals) with a capacity of approximately 200-400mA depending on the model, which can be used to power input switches. Do not connect external 24V power to this service terminal to avoid damaging the internal circuit.

3.2 DC power supply model (DS/DSS suffix)

Terminal:+(24V+), - (0V).

Voltage range: 24V DC+10%/-15%.

Surge current: DC type is much larger than AC type - FXo has a maximum of 60A 1.5ms, FXon has a maximum of 60A 50 μ s. When designing the system, it is necessary to ensure that the upstream DC power supply can withstand this surge.

Power consumption: FXo-14MT is about 10W, FXon-60MT is about 24W.

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.

When using Y0 as the pulse train output (PLSY command) or Y1 as the PWM output, due to the fast switching speed required by the internal circuit, an external pull-up resistor (1-2k Ω) must be connected to ensure that the output current is ≥ 0.2A, otherwise waveform distortion may cause the stepper motor to lose step.

Install 1-2A fuses every 4 output points.

Extended configuration rules (FXon only)

The FXon system connects expansion units and modules through the CPU bus and must comply with the following restrictions:

FXo is not extensible. FXon's MPU (Basic Unit) can connect up to:

Two special functional modules (such as FXon-3A analog, FXon-16NT network module), or

Expansion blocks with no more than 32 I/O points (such as two 16 point expansion blocks or four 8-point expansion blocks).

The total system I/O points (including basic units and extensions) shall not exceed 128 points.

FXon-24Mx basic unit: Physically only has 14 inputs/10 outputs, but occupies 16 inputs/16 outputs of system I/O, so when calculating the remaining expandable points, it must be deducted by 32 points.

FXon-8ER-ES/UL (4 inputs and 4 outputs) actually occupies 16 I/O points (8 inputs and 8 outputs).

The FXon-485ADP communication adapter can only be used for basic units with CPU version ≥ 1.2.

Maximum length of extension cable: When using FXon-65EC (650mm), the entire system can only use one of these cables. Can the distance between two layers exceed 650mm? It is recommended not to exceed it in practice.

Diagnosis and fault codes

There are four LEDs on the device panel: POWER (green), RUN (green), ROG. E (red), and CPU-E (red). By combining special registers and error flags, most hardware and software faults can be located.

7.1 Preliminary investigation process

Check in the following order according to the table:

Normal result of step operation

Measure the voltage of the power terminal AC or DC within the allowable range

2. Check if all wiring terminals are tightened and not loose

After powering on, if the POWER LED is on or off, check if the 24V load is too high or if the internal fuse is blown

Download the empty test program and force the RUN LED to light up. The output can be manually set

5. Observe that PROG. E/CPU. E should not be constantly on or flashing

7.2 Error Code Interpretation

ROG. E flashing: Program syntax error, parameter error, or execution error (such as watchdog timeout). Connect programming software to view error codes in D8065~D8067.

CPU. E constantly on: hardware failure or crash. Common reasons:

The FXon memory card can be unplugged and unplugged while powered on (retry after power failure to recover).

The program scanning time is too long, exceeding the watchdog setting (D8000 default 200ms). Check the maximum scanning time of D8012. If it is greater than D8000, adjust the D8000 value or optimize the program.

Error code table (D8061 hardware error, D8063 communication error):

Code meaning

6101 RAM Error

6102 operation circuit error

6301 Communication parity/overflow/frame error

6305 instruction error

6306 communication watchdog timeout

7.3 Common special relays (M) and registers (D)

Component function

M8000 RUN monitoring is always on

M8002 initial pulse

M8004 error occurred (D8004 storage error M number)

M8035~M8037 forced RUN/STOP control

M8039 Constant Scan Enable

M8061 PC hardware error flag

M8067 program execution error flag

D8000 watchdog timer setting value

D8001 PLC type version

D8012 maximum scanning time

D8067 execution error code

Battery replacement (FXon-40B, FXon only)

The FXon series can be optionally equipped with a real-time clock memory card (FX-RTC), which relies on the FXon-40B battery to maintain clock operation when the host loses power. The battery is a non rechargeable lithium battery with a lifespan of approximately 4 years (storage period of 1 year).

Replacement steps:

Cut off all power to the PLC.

Uncover the cover plate labeled "MITSUBISHI" at the top.

Expose the small circuit board socket on the left side of the memory card slot and remove the fixing clip.

Unplug the old battery and replace it with a new one within 20 seconds, otherwise the real-time clock data will be lost.

Reinstall the fixing clip and cover plate.

Attention: If the real-time clock card is not installed, this battery is useless.

Programming and Communication Ports

The basic unit comes with a programming port (RS422 round or rectangular 8-pin), which can be connected to a handheld programmer (FX-20P-E) or a computer through an SC-09 adapter.

FXon-232ADP or FXon-485ADP can be installed on the left side of the basic unit, occupying 8 I/O points and providing RS232 or RS485 communication channels for connecting to the upper computer, HMI, or frequency converter. Note: After installing the communication adapter, no other expansion blocks can be added on this side.

Common installation errors and remedies

Root cause solutions for error phenomena

After power on, the POWER light does not light up and the internal input fuse is blown; 24V service power overload, disconnect the 24V load and try again; If it still doesn't light up, return to the factory for repair

Input signal is correct but PLC cannot detect S/S terminal wiring error; Correct the S/S connection based on Sink/Source if the input response time does not match the signal pulse width; Adjust the digital filtering time to be less than the signal width

Relay output contacts are stuck and no freewheeling diode is added; Increase the freewheeling diode when the load exceeds 2A; Replace with a higher current relay or intermediate relay

The transistor output drives the stepper motor to lose step without adding a pull-up resistor; Connect a 1-2k Ω resistor in parallel between Y0 and+24V when the output current is less than 0.2A

The expansion module is not working and the expansion exceeds 32 points; FXo extension was used to check that the total I/O points were ≤ 128; Only FXon is expandable

AC input model misoperation or simultaneous heating of more than half of the inputs should be redistributed to avoid simultaneously connecting more than 50% of the input points

CPU. E light on and unable to enter RUN program watchdog timeout; Memory card poor contact, power outage retry; Check scanning time and optimize the program