Pressure Switch | Pressure Transmitter

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Pressure Switch

A pressure switch is an ON/OFF device that activates (changes electrical contact) when the pressure reaches a preset setpoint. A pressure switch is a simple device that monitors pressure and turns ON/OFF a circuit when pressure reaches a set value.

How it Works

Pressure acts on a diaphragm or piston. When pressure crosses the setpoint, the internal NO/NC contact changes state.
  • You set a pressure value (Setpoint).
  • When the process pressure rises above or falls below that setpoint, the switch contacts change state (NO→NC or NC→NO).
  • It gives only ON/OFF output.

Output Type

  • NO/NC Contact
  • Relay Output

Applications

  • Pump start/stop (flow detection)
  • High/low pressure alarm 
  • Compressor control (gas pressure checking)
  • Safety interlock (line pressure checking)

Pressure Transmitter

A pressure transmitter measures pressure continuously and sends an analog signal (like 4–20 mA) to PLC/DCS.

How it Works

Pressure deflects a sensing element (strain gauge/capacitive). Electronics convert this into a linear electrical signal.

Output Type

  • 4–20 mA
  • 0–10 V
  • HART / Fieldbus / Modbus

Applications

  • Continuous pressure monitoring
  • Process control (PID)
  • SCADA trending & logging
  • Automation systems

Difference Between Pressure Switch and Pressure Transmitter

Feature Pressure Switch Pressure Transmitter
Output ON/OFF Continuous (4–20 mA)
Accuracy Low High
Function Alarm / Control Measurement
PLC/DCS Input Digital Input Analog Input
PLC/DCS Used Needs only digital input Needs analog input
Cost Low Higher
Output Type ON/OFF (Digital Contact) Continuous Signal (4–20 mA / 0–10 V / HART)
Measurement Type Discrete / Binary Analog / Continuous
Safety Low High
Interlock Protection, Alarm, Simple Control Monitoring, Precise Measurement, Control
PLC Input Required Digital Input (DI) Analog Input (AI)
Signal Type NO/NC Contact Current/Voltage Signal
Applications Pumps, Compressors, Safety Interlocks Process Control, SCADA, Monitoring
Maintenance Very Low Needs calibration periodically

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