Thermal Dispersion Switches

Thermal dispersion flow / level / interface switch

Thermal dispersion switches are used for flow, level, and interface detection by measuring changes in convective heat transfer within a process. This technology provides reliable switching performance across a wide range of industrial applications where flow presence, no-flow conditions, or fluid interfaces must be detected quickly and accurately.

How Thermal Dispersion Switching Works

Thermal dispersion switches operate using two temperature sensors:

• One sensor measures the process temperature
• The second sensor is heated by a constant power input

As process conditions change, heat is transferred away from the heated sensor at different rates.

• Increasing flow: Higher flow rates remove more heat, reducing the temperature difference between the sensors
• Decreasing or no flow: Lower flow rates result in less heat removal, increasing the temperature difference

A configurable set point is established so that when a specific temperature difference is reached, the switch output changes state. The relay can be configured to actuate on:

• Increasing flow
• Decreasing flow
• Flow/no-flow conditions

Level and Interface Detection Using Thermal Dispersion

When used for level or interface applications, thermal dispersion switches rely primarily on differences in thermal conductivity between fluids or between liquid and gas phases.

As the sensing element transitions between media:

• Heat transfer characteristics change
• The temperature difference between sensors shifts
• The electronics detect the interface or level condition and actuate the output

This makes thermal dispersion switches effective for detecting liquid presence, interfaces, or empty conditions without moving parts.

Common Applications for Thermal Dispersion Switches

Thermal dispersion switches are commonly used for:

• Flow and no-flow detection
• Pump protection
• Cooling and lubrication monitoring
• Level detection in tanks and vessels
• Interface detection between fluids

They are well-suited for applications where mechanical switches may be prone to wear or failure.