The output signal of a transmitter is the electrical signal generated by the device to convey the measured parameter (e.g., pressure, temperature, flow, or level) to a control or monitoring system. The most common types of output signals include:
Common Types of Transmitter Output Signals
4–20 mA Current Signal:
Description: The most widely used standard in industrial applications. The signal ranges from 4 mA (minimum measured value) to 20 mA (maximum measured value).
Advantages:
Immune to electrical noise.
Can be transmitted over long distances without signal degradation.
Allows for power supply to the transmitter via the same two wires (loop-powered devices).
Example Use:
Pressure transmitters like the PT600 series from Pondus Instruments often utilize 4–20 mA for transmitting measurements.
Digital Signals:
HART (Highway Addressable Remote Transducer):
Combines a 4–20 mA signal with digital data overlaid on the same wires.
Allows remote communication for configuration, diagnostics, and calibration.
MODBUS:
A digital communication protocol used in industrial automation.
Transmits measurement values and additional diagnostics via RS485 or similar interfaces.
PROFIBUS:
Used for advanced control systems, especially in large industrial networks.
Voltage Signals:
Description: Analog voltage outputs (e.g., 0–5 V, 0–10 V) are less common in industrial environments but may be used in specific applications.
Drawbacks:
Susceptible to signal degradation over long distances.
Sensitive to electrical interference.
Pulse or Frequency Signals:
Description: Often used in flow meters to represent the rate of flow. The frequency of pulses correlates with the measured flow rate.
Use Case: Monitoring flow rates in utility or production systems.
Why 4–20 mA is Commonly Used
Zero Signal Indication: A 4 mA baseline indicates the transmitter is powered and operational, distinguishing it from a 0 mA reading (which might indicate a fault or power failure).
Interference Resistance: Current signals are less affected by electrical noise compared to voltage signals.
Long Distance Capability: Maintains signal integrity over distances of hundreds of meters.
PT600 Series Transmitters
The PT600 series provides:
A 4–20 mA output signal for reliable analog communication.
Advanced options like HART and MODBUS communication for enhanced monitoring and remote configuration.
Conclusion
The output signal of a transmitter is critical for integrating measurements into control systems. While 4–20 mA is the industry standard, advanced protocols like HART and MODBUS offer enhanced flexibility for modern industrial automation.
For assistance in selecting the best transmitter for your application, contact Pondus Instruments for expert advice and solutions tailored to your needs.
