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Setting the switch points of an electric pressure switch for an application in the vacuum range is not a self-explanatory task. The next article therefore explains what should be taken into account with this particular setting. It involves a pressure switch with a hysteresis function. Instruments with this configuration are most regularly installed in industrial applications.
Electronic pressure switches, such as the WIKA models PSD-4 and PSD-4-ECO or the A-1200 pressure sensor with IO-Link, operate as ?normally closed? or ?normally open?, with respect to the task. The next graphics illustrate both switching functions with the respective switch and reset points:
In principle, the following applies: The switch point (SP) is greater than the reset point (RP) and the start of measuring range (MRS) is definitely smaller compared to the end of measuring range (MRE). This rule could be easily understood with settings for ambient air pressures.
Example: Control of vacuum pressure pump
However, setting the switch points in the vacuum range and therefore, ultimately, the switching function, requires more attention. To illustrate this, let?s take the control of a vacuum pump, for instance, which must maintain a vacuum between -0.7 bar and -0.5 bar. For the task described, we select a pressure switch with a measuring range of -1 ? 0 bar.
The start of measuring range (MRS) is therefore -1 bar, the finish of measuring range (MRE) 0 bar. This implies: At 0 bar (= start of operation) the switch ought to be closed, to be able to activate the vacuum pump. If the pressure drops to -0.7 bar, the switch must open and stop the pump. When the pressure reaches the upper limit value of -0.5 bar, the pump should once more start and run until the pressure has again dropped to -0.7 bar.
ow must pressure gauge octa be set within this vacuum range? Let?s take both pictures and translate MRS and MRE:
Here it is clear that the ?normally open? function should be selected, otherwise the pump wouldn’t normally activate. After entering the switch points, the schematic is obtained, which ultimately shows the way the pressure switch functions in accordance with the example:
Note
Information regarding WIKA?s electronic pressure switches can be found on the WIKA website. Would you like to buy pressure switches? In our WIKA online-shop you will find some of our standard designs. If you have any questions, your contact will gladly assist you to.
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