Key Points for Selection and Deployment of MITSUBISHI FX3GE PLC

Solution: FX3GE-40MR/ES can directly use the built-in analog input to read tension, and the built-in analog output controls the frequency converter; The Ethernet port is connected to the upper computer through the MC protocol; Relay output controls the cylinder and alarm light. No additional modules are required.

7.2 Control of Small Refrigeration Units

Requirement: Monitor 2 temperature channels (PT100) and 1 pressure channel (4-20mA), read meter data through RS485, and have web remote monitoring.

Solution: FX3GE-24MR/ES+Left FX3U-4AD-PT-ADP (temperature)+Left FX3U-485ADP-MB (Modbus reading meter). Built in analog input for pressure. Publish operational parameters through Ethernet port web server. This combination is more integrated than using an independent thermostat and PLC.

7.3 Communication Upgrade of Old Equipment

Scenario: There is an old FX series PLC with only RS422 interface on site, which needs to be connected to the factory Ethernet network.

Solution: Replace directly with FX3GE and reuse most of the original program (note I/O address differences). The built-in Ethernet port of FX3GE can serve as a gateway, exposing the data of the original PLC to the upper computer through the MC protocol, reducing wiring changes.

Common Problems and Avoidance Measures in Engineering

8.1 Analog input reading jumping

Reason: There is high-frequency noise from the frequency converter or switch power supply coupled to the analog signal line on site.

Countermeasure:

The analog signal line uses twisted pair shielded cables, and the shielding layer is grounded at one end (on the FX3GE side).

Connect a capacitor of 0.1 µ F to 1 µ F in parallel at the analog input terminal (note the impact on response time).

Add 5-10 times of moving average filtering in the PLC program.

8.2 Excessive Ethernet communication delay

Phenomenon: When reading and writing data through the MC protocol, the response time is unstable, sometimes exceeding 50ms.

troubleshoot

Check for broadcast storms or IP address conflicts on the network.

Avoid using web servers, FTP, and MC protocols simultaneously for high-frequency communication on the same port.

Optimize communication request processing in PLC programs to reduce the frequency of calling Ethernet instructions in loops.

8.3 Relay output contact adhesion

Reason: No surge suppression circuit was added when driving inductive loads (relay coils, contactors).

Countermeasure: Connect a freewheeling diode (DC load) or RC absorption circuit (AC load) in parallel at the load end of each relay output (near the PLC output point). Although not mandatory in the manual, this is a standard practice for extending the lifespan of output contacts.