Config Modbus Register 0: Voltage (Phase A)

Technical Definition

The register Voltage (Phase A) at address 0 is used to monitor voltage (phase a) on the Config.

• Protocol: Modbus RTU
• Data Type: FP32
• Unit: V
• Access: Read Only

How to Read (Python pymodbus)

Use this code snippet to read this specific value via RS485:

from pymodbus.client.sync import ModbusSerialClient

client = ModbusSerialClient(method='rtu', port='/dev/ttyUSB0', baudrate=9600)
client.connect()

# Read Voltage (Phase A) (Address: 0)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=0, count=2, unit=1)

if not result.isError():
    print(f"Raw Value: {result.registers}")
else:
    print("Error reading register")

client.close()

Integration (Home Assistant)

Paste this into your configuration.yaml:

- platform: modbus_controller
  name: "Voltage (Phase A)"
  address: 0
  value_type: FP32
  unit_of_measurement: "V"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

graph TD
    PLC[Host Controller / Home Assistant]
    Device[Config]

    PLC -- "A+ (D+)" --> Device
    PLC -- "B- (D-)" --> Device
    PLC -- GND --> Device

💡 Engineer's Insight

Analysis: RMS voltage of Phase A relative to neutral or ground, typically in Volts (V). Essential for power calculations.

Troubleshooting: Zero value means no voltage on Phase A, indicating a power supply failure, tripped breaker, or wiring issue. Check supply source.