Pressure Sensor, Transducer, and Transmitter Explained | Application of Each

Main ideas / concepts explained

Why terms get confusing

• Over time, the terms sensor, transducer, and transmitter have been used inconsistently (often as synonyms) by different vendors, leading to many conflicting definitions.
• The video also notes that organizations sometimes publish their own definitions, which increases confusion.

Working definitions used in the video

Sensor

• A device/element that performs the initial measurement by sensing changes in a physical variable.
• Typically involves physical contact with the variable.
• Produces a corresponding output signal that can be measured.

Transducer

• A device that converts one form of energy into another.
• Produces an output quantity with a specified relation to the input quantity.
• In instrumentation, the output is typically an electrical/electronic signal.
• Example: a strain gauge is a transducer whose resistance changes proportionally to strain.

Key relationship

• All sensors are transducers, but not all transducers are sensors.
• Example: a loudspeaker converts electrical signals into motion (transducer) but does not act as a sensor.

Transmitter (process control)

The video distinguishes “transmitter” in process control from telecommunications:

• Telecommunications: a transmitter sends radio waves to be received and demodulated.
• Process control: a transmitter sends a standard instrumentation signal representing a measured physical variable.

Standard signal ranges mentioned:

• 1–5 volts or 4–20 mA
• These represent 0–100% of the physical variable being measured.

How it knows what to transmit:

• A sensor and/or transducer performs the initial measurement and (if needed) converts it to an electrical signal.
• The transmitter then amplifies and standardizes that electrical signal into the 1–5 V / 4–20 mA range.

Example:

• Pressure range: 0–100 psi
• Sensor/transducer output: 0–3 mV
• Transmitter output: 1–5 V
• PLC receives it via an analog input module.

Pressure transmitter vs. pressure switch

Pressure switch

• A two-part device:
  • A sensing transducer
  • An electrical switch (contacts that open/close at a specific pressure)
• The video emphasizes they are functionally different from pressure transmitters, even though both include a sensing transducer.

Pressure transmitter

• Converts the transducer’s electrical signal into a larger analog electrical signal (typically 1–5 V or 4–20 mA, representing 0–100% pressure).

Using a pressure transmitter as a pressure switch

• Technically possible, but described as not practical because:
  • Pressure transmitters are typically larger, more expensive, and often harder to install.
  • It requires additional PLC work:
    • Analog input module setup
    • Scaling
    • PLC code to detect a threshold (e.g., 50 psi) and then trigger valve logic.

Example decision scenario (valve control at 50 psi)

• Using a pressure transmitter:
  • Requires analog module + scaling + PLC code to trigger at 50 psi.
• Using a pressure switch:
  • Easier: connects to a PLC digital input, simplifying valve control logic.

Bottom-line guideline:

• If you only need to know whether pressure crosses a specific setpoint (above/below), use a pressure switch.

Video summary / key takeaways

• Transducer: converts one form of energy into another.
• Sensor: performs the initial measurement of a physical variable.
• All sensors are transducers, but not all transducers are sensors.
• Pressure sensor/switch/transmitter all include a sensing transducer.
• Pressure switch: transducer + electrical contacts that open/close at a set pressure.
• Pressure transmitter: transducer signal → standardized analog output (1–5 V or 4–20 mA, representing 0–100%).
• A pressure transmitter can be used as a pressure switch, but it’s usually not practical.

---

Methodology / instructions presented (decision guidance)

Choose between a pressure transmitter vs. pressure switch

• If you need exact pressure measurement (continuous/analog value):
  • Use a pressure transmitter.
• If you only need a threshold event (e.g., “open valve at 50 psi” or “alarm if below/above setpoint”):
  • Use a pressure switch.
• Avoid using a pressure transmitter as a pressure switch when it creates:
  • More cost/size
  • More complex installation
  • Need for analog scaling and additional PLC code vs. simple digital input logic

---

Speakers / sources featured

• RealPars (promotional mention only; no individual speaker identified in the subtitle text)
  • Mentions a RealPars Pro membership offering:
    • Discount on Siemens PLC starter kits
    • Lifetime access to TIA Portal Basic
    • Learning platform and promotional links in the description
• Siemens (referenced as the PLC/platform vendor and related software/hardware)
• TIA Portal Basic, S7-1200 PLCs, PLC, DCS (referenced technologies/systems; no separate sources or authors identified)