EM3000 Differential Pressure Gauge: RS485 Wiring and Commissioning Guide

To standardize the power wiring, RS485 communication, Modbus reading, pneumatic connection, and commissioning steps of the EM3000 differential pressure gauge, and to prevent abnormal displays or data reading failures caused by incorrect wiring, address/parity settings, or reversed air tubes, we have prepared this wiring and commissioning guide.

1. Wiring Specifications

Proper physical wiring is the prerequisite for the stable operation of the equipment. Before wiring, ensure the power is disconnected and verify there are no short circuits before powering on.

1.1 Power Wiring

• Red Wire: Power positive (+).
• Black Wire: Power negative (-).
• Observação: Connect the voltage according to the product nameplate requirements, commonly DC 24V. Reverse connection of positive and negative poles is strictly prohibited.

1.2 RS485 Communication Wiring

• Blue Wire: A (485+).
• Green Wire: B (485-).
• Método de conexão: Connect A of the gateway or PLC to the blue wire (A), and B to the green wire (B). If communication fails, power off and try swapping the A and B wires to troubleshoot.
• Anti-Interference Suggestion: It is recommended to ground the shielded cable at one end and keep it away from interference sources such as power cables, inverters, and pulse valves.

Note: Wire colors are for reference only. For the final wiring, please strictly follow the product terminal labels and the instruction manual.

2. Communication Parameters and Modbus Reading Settings

The EM3000 differential pressure gauge uses the standard Modbus RTU protocol. The specific communication and reading parameters are as follows:

• Baud Rate: 9600
• Data Bits: 8
• Stop Bits: 1
• Parity: None
• Slave Address: 01 (Subject to the actual address in the settings menu)
• Register Starting Address: 01 (Used to read the current differential pressure value)
• Read Function Code: 03H
• Read Length: 1 register
• Data Format: 16-bit signed integer (int16)

Communication Message Example:

• Send Command: 0x01 0x03 0x00 0x01 0x00 0x01 0xD5 0xCA
• Return Data: 0x01 0x03 0x02 0xFF 0xF6 0xB8 0x44

3. Pneumatic Connection Guidelines

Incorrect installation of air tubes will directly invalidate the measurement data. Please strictly follow these guidelines:

• Port Definitions: The high-pressure port (H) must be connected to the high-pressure side of the measured system; the low-pressure port (L) must be connected to the low-pressure side of the measured system.
• Connection Requirements: Connections must be made according to the label on the side of the product and the manual; do not connect based on intuition. The air tubes should be well-sealed, ensuring no air leakage, bending, or blockages, and the length should be as short as possible.
• Strict Prohibition of Reversal: Reversing the high and low-pressure air tubes is strictly prohibited. A reversed connection will result in the gauge showing no display or no value, or the reading will not match the actual differential pressure.
• Troubleshooting: The differential pressure gauge displays the difference between the high and low-pressure ends, and under normal circumstances, it does not display negative values. If no value or an abnormal value appears, prioritize checking whether the high and low-pressure tubes are reversed.

4. Standard Commissioning Steps

To ensure the device is successfully integrated into the system, it is recommended to follow these standardized commissioning steps:

1. Power-off Wiring: Disconnect the power and properly connect the power and RS485 cables according to the specifications.
2. Power-on Confirmation: Turn on the power and confirm that the gauge’s power supply is normal.
3. Parameter Configuration: Set the parameters in the PLC or serial port as: 9600, 8, N, 1, with the slave address as 01.
4. Data Reading: Use the 03H function code to read the starting address 01 with a length of 1.
5. Troubleshooting (If data cannot be read):
   • Check if the slave address is correct.
   • Check the baud rate, data bits, parity, and stop bit configurations.
   • Check if the RS485 A/B wires are reversed.
   • Check the device configuration, terminal resistance, and power supply status.
6. Final Connection: After confirming that the communication is normal, connect the high and low-pressure air tubes.