Why a 0 mA Signal is Not Practical?

Why a 0 mA Signal is Not Practical?

Why a 0 mA Signal is Not Practical and Advantages of 4-20 mA Standard: Industry Preference

Engineering Complexity and Cost:

  • Designing circuitry for 0 mA signals requires more sophisticated components.
  • Circuitry must be able to handle a wider range of signal values, adding complexity.
  • This complexity increases manufacturing costs for devices utilizing 0 mA signals.
  • 4-20 mA signals offer a simpler and more standardized design approach.

System Fault Detection:

  • 0 mA signals make it challenging to distinguish between zero readings and system failures.
  • Live zero signals (e.g., 4 mA representing 0% measurement) enable faster fault detection.
  • In case of a system fault, a live zero helps quickly identify issues such as line breaks or wiring faults.
  • This capability enhances system reliability and reduces downtime for troubleshooting.

Powering Devices:

  • 0 mA signals do not provide any current flow to power devices in the loop.
  • Loop-powered devices, such as transmitters and displays, require a minimum current to operate.
  • The 4-20 mA signal ensures a continuous flow of current, meeting the power requirements of connected devices.
  • This allows for reliable operation of instrumentation and control devices without the need for additional power sources.

Advantages of 4-20 mA Standard:

  • Easier Wiring: Standardized signal range simplifies wiring connections and configurations.
  • Cost-Effectiveness: Manufacturing costs are lower due to simpler circuitry and standardized components.
  • Long-Distance Transmission: 4-20 mA signals are less susceptible to voltage drops over long transmission distances.
  • Reduced Electrical Noise: The signal range is less affected by background electrical noise, ensuring more accurate readings.
  • Lower Risk of Electrical Shock: The low current levels of 4-20 mA signals pose minimal electrical shock hazards.
  • Safety in Hazardous Environments: The signal range is suitable for designing intrinsically safe equipment for hazardous areas.

Industry Preference:

  • The process control industry has widely adopted the 4-20 mA signal range as the standard for transmitting process data.
  • It offers a balance of efficiency, reliability, and safety, making it well-suited for various industrial applications.
  • The 4-20 mA standard has become ingrained in industry practices and is supported by regulatory standards and guidelines.