Lecture Notes on Sensor Output Signals

Introduction

• Sensors transmit measurements to control systems via electrical signals.
• Importance of choosing the right sensor output for applications.

Types of Sensor Output Signals

1. DC Voltage Output

• Description: Uses analog voltage to transmit measurements.
• Common Voltage Ranges: 0 to 5 volts DC and 0 to 10 volts DC.
• Connection Diagram: Sensors connected in parallel with resistors (R1, R2, R3) representing load devices (panel meter, controller, data logger).
• Advantages:
  • Simple and relatively inexpensive.
  • Compatible with most industrial meters and controllers.
• Disadvantages:
  • Voltage drop across cable runs affects accuracy.
  • Susceptible to electromagnetic noise/interference.
  • Requires three or four wires (two for supply/excitation and two for output).

2. 4 to 20 Milliamp Current Loop

• Description: Standard signal output, where 4mA indicates the lower threshold and 20mA the higher threshold.
• Troubleshooting: 0mA indicates an open circuit or lost feed.
• Advantages:
  • Easy wiring and installation (only two wires needed).
  • Not affected by electrical noise.
  • Current level remains the same, unaffected by small voltage drops across devices in the loop.
  • Limited only by the power supply voltage driving the loop.
• Disadvantages:
  • Each sensor requires its own cable run to power supply and receiver.
  • Information is one-way (either to or from the instrument).

3. Millivolt per Volt Output

• Description: Mainly used in pressure transducers or load cells.
• Output Ratio: Refers to the ratio of output voltage to excitation voltage.
• Example: 2mV/V with 5V excitation outputs 10mV; with 10V excitation outputs 20mV.
• Advantages:
  • Low cost and fast response times.
  • Smaller size.
• Disadvantages:
  • Requires regulated power supply for excitation voltage.
  • Shorter signal ranges.
  • Vulnerable to electromagnetic interference.

Conclusion

• Overview of the three most commonly used sensor output signals.
• For further questions, contact Omega's engineering experts online.
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