Thermal flow sensors for industrial processes and compressed air systems

The new SCHMIDT thermal flow sensors SS 20.600 excel by their measuring principle and technical characteristics.

Compared to standard differential pressure processes mainly used for flow measurement, the so called thermal flow measurement offers major benefits. It is based on the principle of heat convection. SCHMIDT flow sensors SS 20.600 use this measurement principle to determine flow velocity or volume flow.

The flow element is securely and efficiently positioned in a chamber head. The flow sensor is being heated to 40K above the medium temperature measured by the sensor. Cooling of the heated element caused by medium flow – or rather the energy required to conserve the element temperature – determines the flow velocity. The sensor outputs this value as "normal speed" (linear current/voltage/pulse signal). The higher the flow velocity, the higher the power required for heating the sensor element.

Such measurements are independent of the prevailing pressure and temperature conditions. They do not require mechanical components, thus considerably reducing maintenance costs. Moreover, the sensor is not subject to any drift during operation as a result of this measurement principle. All these benefits make the SS 20.600 flow sensors suitable for a wide range of industrial processes and compressed air systems.

The Industry Professional

The SCHMIDT Technology SS 20.600 flow sensors are designed for demanding operating conditions. They are available as compact sensors with probe tube and housing in a single unit or alternatively with separate electronics connected via cable for installation in confined areas.

Both variants are suitable for installation in small tubes starting at DN 25, and with sensor lengths from 120 to 1,000mm they are even suited for large ducts. The special chamber head can detect flow velocities from 0.2m/s to 220m/s. Each sensor will be calibrated individually in a pressure wind tunnel.

Besides the typical measurement range SCHMIDT Technology also offers application-specific ranges in 0.1m/s increments. Operators will receive an exact output signal tuned towards their application – one pulse per measured standard cubic meter air or gas.

Upon request, the sensors can be supplied with a high precision air calibration. SCHMIDT Technology carries out these calibrations in their reference wind tunnel. The attached ISO calibration protocol documents the SS 20.600's high precision in 1% increments. Alongside the standard version for operation with operating pressures of up to 16bar, a special version for high pressures of up to 40bar is also available. The flow sensors in general offer an additional temperature measurement for medium temperatures in an extended temperature range between -20 (40) °C and +120 °C.

The SS 20.600 flow sensors are available for air, various gases and gas mixtures such as pure oxygen, CO2, Methane, etc. Especially interesting: Versions for hydrogen are available as well. A further option is the so called ATEX version SS 20.600 Ex. It is designed for operation in Zone 2 potentially explosive atmospheres. An additional benefit of the ATEX option is the extended operating temperature range to -40 °C.

The SCHMIDT® flow calculator at http://schmidttechnology.de/en/sensorik/produkte/flow-sensors/flow-calculator.htm will help you with your sensor configuration.