In the case of 4-wire transmitters, they usually need a power source of 120 VAC or 230 VAC to operate their internal circuitry and internal loop power supply. The term “4-wire” comes from the fact that these transmitters use two wires for the loop and two wires for power (ignoring the ground conductor for the AC power). Take a look at Figure 24 for a clearer illustration.
What is 4-Wire Transmitter?
In the realm of process control and industrial automation, 4-wire transmitters stand as a sophisticated solution, offering a distinct separation of power and signal transmission. With two wires dedicated to the loop and two for power, these transmitters provide a robust platform for applications demanding precision and reliability. Let’s delve into the fundamentals, operational principles, advantages, and applications of 4-wire transmitters.
Wiring Diagram of 4-Wire Transmitters:
Fundamentals of 4-Wire Transmitters:
The nomenclature “4-wire” signifies the dual functionalities of the wires – two for the loop current (signal transmission) and two for power supply. Unlike 2-wire or 3-wire configurations, 4-wire transmitters incorporate a separate power source for internal circuitry, decoupling it from the loop current. This design facilitates more stable and precise operation.
Working Principle
The two wires dedicated to the loop current follow the conventional path, carrying the process signal between the field device and the control system. Simultaneously, the additional pair of wires serves as the power supply for the transmitter’s internal circuitry.
For the power aspect, 4-wire transmitters typically require higher voltage alternating current (AC), such as 120 VAC or 230 VAC. This voltage powers the transmitter’s internal components and loop power supply.
Advantages of 4-Wire Transmitters:
- Enhanced Power Capacity: The dedicated power wires allow 4-wire transmitters to operate with higher voltages, ensuring ample power for internal circuitry.
- Minimized Signal Interference: Separating power and signal transmission reduces the likelihood of interference or voltage drops affecting the precision of the process signal.
- High Precision and Stability: With a stable and independent power source, 4-wire configurations contribute to higher precision and stability in transmitting process signals.
Considerations:
- Complexity and Cost: The inclusion of separate power wires increases the complexity of installation compared to 2 or 3-wire transmitters. Additionally, the cost of wiring may be higher.
- Power Source Compatibility: As 4-wire transmitters often require higher AC voltages, the availability and compatibility of power sources need careful consideration during installation.
Applications of 4-Wire Transmitters:
- High-Precision Control Systems: Industries requiring exceptionally high precision in control processes, such as aerospace or scientific research, benefit from the stability and accuracy provided by 4-wire transmitters.
- Laboratory Environments: Research laboratories and experimentation setups often employ 4-wire transmitters to ensure precise and reliable measurement and control.
- Critical Process Monitoring: Applications where signal accuracy is paramount, and any deviation can have significant consequences, find value in the precision offered by 4-wire configurations.
Loop Power Supply Terminal Designations:
The positive terminal of a 24 VDC power supply is commonly denoted as “+24VDC” or a similar designation. However, it’s important to note that the common or return terminal should not be represented as “-24VDC.” This designation is inaccurate because it suggests a 48 VDC difference between the +24VDC and -24VDC terminals, which is not the case.
In conclusion, 4-wire transmitters represent a pinnacle of precision and stability in process control. By segregating power supply and signal transmission, these transmitters excel in applications where uncompromised accuracy is non-negotiable. While introducing complexity and potentially higher costs, 4-wire configurations remain indispensable in scenarios where the highest level of control and reliability is imperative.
Read Also:
What is 2-Wire Transmitter? Wiring Diagram, Working Principle, Connection to PLC
What is 3-Wire Transmitter? Wiring Diagram, Working Principle, Connection to PLC