function of the flow controller is based on the thermodynamic principle. The
sensor is heated internally a few degrees °C compared to the medium into which
it projects. When the medium flows, the heat generated in the sensor is
conducted away by the medium, i. e. the sensor cools down. The temperature
within the sensor is measured and compared to the temperature of the medium.
The state of flow can be derived for each medium by the temperature difference
Function of thermodynamic flow controllers
On the basis of this functional principle EGE manufactures flow monitors for liquid and gaseous media.
The sensitivity of thermodynamic flow monitors depends on the thermal characteristics of a medium. The detection range of a standard sensor for oil, for example, is three times as great than for water and for air is approx. 30 times greater than for water due to the reduced heat conductivity.Unless stated otherwise, the technical sensor data are specified for water.
Areas of application for flow monitors
Thermodynamic flow monitors function without any moving parts, therefore they are not subject to failure due to corroded bearings, torn impellers or deflector deformation. This reliability is highly valued in many industries. Today, flow monitors are used both in liquids and in air, and are employed even in explosion hazardous environments.
Monitoring of cooling
The cooling water on welding machinery is monitored using compact stainless steel devices. This ensures sufficient cooling even for rapid cycles, otherwise the welding robot will be switched off by the sensor.
The cooling lubricant flow is monitored continuously in processing centres. The tools are protected and have a greater service life.
In metal processing, e.g. rolling mills and wire drawing machines, the rolls and coils will be cooled continually. This is monitored by thermodynamic sensors. Due to the rough environmental conditions the sensors are designed for up to 160 °C and settings are made away from the heat with special amplifiers.
Monitoring of flow medium
The run-dry protection of pumps is a frequent application, which often uses compact sensors with time delay.
In dosing technology the aggregate, usually small flow quantities, is measured exactly by means of inline sensors. These sensors are inserted like a pipe into the line.
of filters and sieves can be ensured by medium flow control; if the flow is
progressively reduced, the filter must be renewed. Where this is not carried
out, the pump is switched off in a second stage should the medium flow drop
further. This uses a sensor with two switching points.
Run-dry protection of a feed pump
Monitoring of process flow
The monitoring of cleaning processes using aggressive media at times is often only possible with special materials, e.g. hastelloy or tantalum.
Extraction systems for hazardous vapours at laboratory workstations as well as the hall ventilation in the hexane processing industry are monitored using airflow sensors.
CIP/SIP processes can be monitored and documented with flow monitors.