The difference between 2-wire and 4-wire transmitters lies in the number of wires used to power the transmitter and transmit the measurement signal. Here's a breakdown of each:

1. 2-Wire Transmitter:

   • Power and Signal on the Same Wires: In a 2-wire transmitter, both the power supply and the signal are carried on the same two wires. This means that the same wires used to power the transmitter also transmit the measurement signal.
   • Simplicity: 2-wire transmitters are simpler in terms of wiring, as they require fewer wires for operation. This simplicity can make them easier to install and maintain.
   • Limitations: However, 2-wire transmitters may have limitations in terms of power consumption and signal integrity due to the shared wires for power and signal transmission. The power supply must provide enough power to operate the transmitter and also maintain the signal integrity over the same wires.

2. 4-Wire Transmitter:

   • Separate Power and Signal Wires: In a 4-wire transmitter, the power supply and the signal are carried on separate sets of wires. Two wires are used for power supply (typically positive and negative), and two additional wires are used for transmitting the measurement signal.
   • Isolation: The separation of power and signal wires in 4-wire transmitters allows for better isolation between the power supply and the measurement signal. This can result in improved signal integrity and accuracy, especially over longer distances or in noisy environments.
   • Flexibility: 4-wire transmitters offer more flexibility in terms of power supply options and signal transmission, as they allow for independent power and signal wiring configurations.

In summary, the main difference between 2-wire and 4-wire transmitters is the number of wires used for power and signal transmission. While 2-wire transmitters offer simplicity in wiring, 4-wire transmitters provide better isolation and flexibility, which can be advantageous in certain applications where signal integrity and accuracy are critical. The choice between the two depends on the specific requirements of the application and the desired balance between simplicity and performance.