Plexlog Plexlog (pv)
Plexlog is a PV data-logger and monitoring platform used to aggregate output from inverters of many manufacturers into a single portal. The Plexlog (pv) template connects to the device's Modbus TCP interface, reading the total PV generation power register at address 0 via function code 4. With this single register in your ModbusCloud portal, you can trend solar production in real time, build historical yield charts, and trigger alerts when output drops unexpectedly. It is a compact, practical integration for any site where a Plexlog data-logger is already the on-site aggregator.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 1, read only
- Brand
- Plexlog
- Last updated
Registers (1)
1 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power | W | Read |
Loading registers…
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Use cases
- Monitor real-time PV generation power to confirm the system is producing at expected levels.
- Track daily and seasonal production trends to identify yield degradation over time.
- Alert on a sustained power drop during daylight hours to detect inverter faults quickly.
- Compare logged generation power against energy-billing data to verify metering accuracy.
- Verify PV output after inverter replacement or firmware update to confirm successful commissioning.
Installation
Enable Modbus TCP on the Plexlog data-logger by opening the device's web interface, navigating to the communication or Modbus section, and confirming the Modbus TCP server is active on port 502 (or 503 depending on your firmware version).
Connect the Plexlog data-logger to the same LAN as the ModbusCloud Gateway, ensuring both devices share IP reachability and that no firewall blocks the configured Modbus TCP port.
In the ModbusCloud portal, add your Gateway, then import the Plexlog (pv) template and assign unit ID 1 (default); enter the data-logger's IP address and the port confirmed in step 1.
Perform a live read of the power register (address 0, FC4, int32) in the portal's register inspector and verify the value matches the current PV output shown on the Plexlog web interface.
Things to watch for
Why does the gateway return an 'illegal function' error for the power register?
The Plexlog data-logger exposes the PV power register via function code 4 (Read Input Registers). Using function code 3 (Read Holding Registers) against the same address causes exception code 1. Confirm the template is using FC4 and that your Modbus TCP port matches the one enabled in the logger's communication settings.
The gateway connects but the power value reads zero or null. What now?
First check that the Modbus TCP server is enabled on the Plexlog device, not just the API. Then confirm the unit ID is set to 1. If it still reads zero, verify that at least one inverter is actively reporting to the logger; the logger will not forward data from inverters it has lost contact with.
Which TCP port does the Plexlog data-logger use for Modbus?
Plexlog documents both port 502 (standard Modbus TCP) and port 503 depending on logger model and firmware configuration. Check the communication settings in the Plexlog web interface and ensure the same port is entered in the ModbusCloud portal. Mismatched ports cause silent connection failures.
The power register returns an unexpectedly large or negative value. What could cause this?
The register is typed as int32 and spans two consecutive 16-bit Modbus words. If the client reads only one word or reverses word order, the decoded value will be incorrect. Confirm the template is decoding both words as a big-endian int32, and check that no scaling factor has been applied accidentally in the portal configuration.
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