Pressure switch
Pressure switches are mechanical or electronic switches that are activated by pressure changes in a gaseous or liquid medium, e.g. B. air or hydraulic oil are operated.
Among other things, they are used to switch pumps, valves or compressors so that the pressure or level of the medium in a pressure accumulator or tank does not exceed an upper value and does not fall below a lower value.
The simplest and most widespread principle of a mechanical pressure switch was registered for a patent in 1935 by August Frede Maschinenfabrik Westkirchen and is based on a membrane that expands with increasing pressure and opens the switching contacts through this movement. A pump switched via the pressure switch switches off at a defined pressure. Counterpressure is applied to the membrane via a helical spring; when the pressure drops, the expansion decreases and the switching contacts are closed (pump switches on, container is filled). The spring is often adjustable in its preload, which can be used to set the switch-on and switch-off pressure. In most cases, the difference between switch-on and switch-off pressure (the hysteresis ) remains constant.
Mechanical pressure switches have a relatively large difference (hysteresis) between the upper switching point and the lower reset point. This is partly desirable because it allows simple two-point controls to be set up without a controller . In the case of mechanical pressure switches, the size of the hysteresis (ΔP) can usually be set using an additional spring mechanism. While the adjustment of the main compression spring affects both the switch-off and switch-on pressure, an adjustment of the differential pressure spring only changes the switch-off pressure or the switch-on pressure, depending on the design, while the other characteristic value remains unchanged.
Using electronic pressure switches, it is possible to achieve a very high level of precision at the required switching points. Very small hysteresis ranges can also be realized with it. It is also possible to carry out switching tasks in very dynamic printing systems. The limit frequency with electronic pressure switches is approx. 1 kHz.
Mechanical pressure switch with integrated plug
Mechanical pressure switch with plug connection
Mechanical power pressure switch with two main compression springs and a smaller spring for adjusting the pressure difference (hysteresis)
Metal diaphragm in a mechanical power pressure switch
Electronic pressure switch with LED display
Electronic pressure switch
See also
literature
- Theodor Schmelcher: Handbook of low voltage. Siemens Aktiengesellschaft, Berlin and Munich, ISBN 3-8009-1358-5
Individual evidence
- ↑ Patent 654 404 of December 2, 1937 (accessed via DEPATISNET on August 16, 2019)
- ↑ a b Pressure switch information from Condor (accessed on August 9, 2019)
- ↑ M2. (No longer available online.) Archived from the original on August 17, 2017 ; Retrieved December 5, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ M3. (No longer available online.) Archived from the original on December 6, 2017 ; accessed on August 17, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Information on electronic pressure switches from ADZ NAGANO (accessed on March 27, 2020)
