I. Classification by Measured Physical Quantity

1. Pressure Transmitters

• Function: Convert pressure (absolute pressure, gauge pressure, differential pressure) into electrical signals.
• Application: Monitor pipeline pressure, hydraulic system pressure, and liquid level (via pressure conversion).
• Example: Differential pressure transmitters for measuring flow in orifice flowmeters.

2. Temperature Transmitters

• Function: Convert temperature signals (from thermocouples, RTDs, etc.) into standard signals.
• Types:
  • Direct-mounted type: Integrated with temperature sensors.
  • Remote-mounted type: Separated from sensors for flexible installation.
• Application: Industrial furnace temperature control, refrigeration system monitoring.

3. Flow Transmitters

• Function: Convert flow rate (e.g., liquid, gas, steam) into electrical signals.
• Principle-based Types:
  • Turbine flow transmitters, electromagnetic flow transmitters, vortex flow transmitters.
• Application: Water supply pipeline flow measurement, chemical raw material metering.

4. Level Transmitters

• Function: Detect liquid or solid level and convert it into signals.
• Technology-based Types:
  • Ultrasonic level transmitters, radar level transmitters, pressure-type level transmitters.
• Application: Storage tank level monitoring in oil and gas fields, water treatment pools.

5. pH Transmitters

• Function: Measure solution acidity and convert pH values into standard signals.
• Application: Wastewater treatment, chemical reaction process control.

6. Humidity Transmitters

• Function: Detect air humidity and output electrical signals.
• Application: HVAC systems, pharmaceutical workshop environment control.

II. Classification by Output Signal Type

1. Analog Signal Transmitters

• Current Signal: 4-20 mA (most common, anti-interference, suitable for long-distance transmission).
• Voltage Signal: 0-5 V, 1-5 V (short-distance use, easily affected by interference).
• Frequency Signal: Output frequency proportional to the measured value (e.g., 0-10 kHz).

2. Digital Signal Transmitters

• Fieldbus Signal: Modbus, HART, Profibus, etc. (support digital communication and multi-device networking).
• Ethernet Signal: Transmit data via IP protocol for integration with industrial networks.
• Wireless Signal: Use WiFi, LoRa, ZigBee for wireless transmission (suitable for difficult wiring scenarios).

III. Classification by Installation Method

1. In-Line Transmitters

• Feature: Directly installed in pipelines or equipment, with the measuring element in contact with the medium.
• Example: Pressure transmitters installed on pipelines, electromagnetic flow transmitters.

2. Remote-Mounted Transmitters

• Feature: The transmitter body is separated from the measuring element, connected by a capillary tube or cable.
• Application: High-temperature, high-pressure, or corrosive environments where direct installation is difficult.

3. Flange-Mounted Transmitters

• Feature: Fixed via flanges, suitable for level measurement in tanks or vessels.
• Example: Flange-mounted pressure transmitters for liquid level detection.

IV. Classification by Industry and Application Scenario

1. Industrial Process Transmitters

• Application: Petrochemical, power, metallurgy, etc.
• Requirement: High durability, resistance to harsh environments (high temperature, pressure, corrosion).

2. Environmental Monitoring Transmitters

• Application: Air quality, water quality, meteorology.
• Example: Atmospheric pressure transmitters, water quality pH transmitters.

3. Medical Transmitters

• Application: Medical equipment (e.g., blood pressure monitors, ventilators).
• Requirement: High precision and safety certification.

4. Aerospace Transmitters

• Application: Aircraft engines, fuel systems.
• Feature: Ultra-high reliability and miniaturization.

V. Classification by Working Principle

1. Capacitive Transmitters

• Principle: Convert physical quantity changes into capacitance changes (e.g., capacitive pressure transmitters).

2. Inductive Transmitters

• Principle: Use electromagnetic induction (e.g., inductive proximity switches for level detection).

3. Piezoelectric Transmitters

• Principle: Utilize the piezoelectric effect of materials (e.g., high-frequency vibration sensors).

4. Thermoelectric Transmitters

• Principle: Based on the Seebeck effect (e.g., thermocouple temperature transmitters).

VI. Special Types of Transmitters

1. Multivariable Transmitters

• Feature: Simultaneously measure multiple parameters (e.g., pressure, temperature, flow) and output integrated signals.
• Application: Complex process control to reduce installation costs.

2. Explosion-Proof Transmitters

• Feature: Designed for hazardous areas (e.g., explosive gas environments) with explosion-proof certifications (e.g., ATEX, IECEx).

3. Sanitary-Design Transmitters

• Application: Food, pharmaceutical, and beverage industries, with smooth surfaces and easy cleaning.

Summary: Key Features and Selection Considerations