Reliable detection of flow limit values

SCHMIDT® Flow Switches SS 20.200

In many cases air or volume flow is process and quality related. Common flow / no flow information is mostly insufficient. In demanding applications the SCHMIDT® Flow Sensor SS 20.200 will supply a precise switching signal to defined threshold values– independent of the medium temperature.

For many applications, i.e. ambient air technical equipment in buildings, cleanroom technology, ventilation / exhaust systems and manufacturing processes, air and volume flow must be controlled. In most cases the plant operator only needs to know if the flow values are outside defined parameters. There are similar requirements for compressed air equipment where defined flow values must be maintained or for minimum flow rates in drying processes. In many cases the detection of air and volume flow is also required for equipment protection such as the control of supply air in cooling systems or filter monitoring.

For the accurate detection of limit values in such cases, common flow switches are not sufficient. They can only indicate yes/no and do not allow any limit values. The SCHMIDT®SS 20.200 Flow Switch is the ideal solution. They are based on the thermal measuring principle (thermal dispersion) i.e. the balance between heat generation and heat discharge by forced convection. If there is a heated body (“heater”) in a flowing medium it will release heat energy to the environment through its surface. This heat flow behaves proportionally to the contact surface and to the difference in temperature between heating element and medium. As the flow rate increases, so does the absorption rate. This heat transition is based on the interaction of a heat conductor and a substantial entrainment effect which is designated as convection.

The end result: The measurement of mass flow is independent of the medium pressure and temperature.

SCHMIDT® Flow Switches are engineered with the same premium technology as all SCHMIDT® Flow Sensors and can be used for process pressures up to 10 bar. However the output signal of the flow switches is different, it is a digital switching signal which is easily connectable to a SPS, DCS or PLC. The switch point can be adjusted either on site by means of a potentiometer or as customized programmed value. The latter is carried out on the calibration wind tunnel at SCHMIDT Technology and ensures a high switching threshold accuracy of ±3% of the measured value. Optionally the flow switches can be used as closing or opening contact in case of exceeding and shortfall of threshold (“fail safe”). All versions of the SS 20.200 are completely temperature compensated by means of an integrated temperature sensor. In practice that means flow detection is independent of temperature variations.

An outstanding feature of the SCHMIDT® Flow Switch SS 20.200 is the proven dumbbell sensor head technology. Thereby the elements for heating and temperature measurement are assembled over a large surface area facilitating measurement from any direction or angle(radial 360°, axial ±45°). For this reason the flow switches can be easily positioned therefore making installation very simple and fast either by means of a flange or a compression fitting. Its sleek, crevice-free design makes the dumbbell head sensors resistant to dust and contamination, this makes for ongoing accurate and repeatable measurement. If the sensor tip gets dirty it can be easily cleaned by the user. For applications in aggressive media like salt, acid, acetone and more SCHMIDT Technology manufacture the flow switches with a special protective coating.