Setting the switch points of an electronic pressure switch for an application in the vacuum range isn’t a self-explanatory task. The following article therefore explains what has to 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, including 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 regards to the task. The following graphics illustrate both switching functions with the respective switch and reset points:
In principle, the next applies: The switch point (SP) is greater than the reset point (RP) and the beginning of measuring range (MRS) is always smaller compared to the end of measuring range (MRE). This rule can 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 vacuum pressure 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 means: 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 again start and run until the pressure has again dropped to -0.7 bar.
ow must the switch points be set in this vacuum range? Let?s take the two pictures and translate MRS and MRE:
Here it is clear that the ?normally open? function should be selected, otherwise the pump would not switch on. After entering the switch points, the schematic is obtained, which shows how the pressure switch functions in accordance with the example:
Note
Information regarding WIKA? In The Zone can be found on the WIKA website. Would you like to buy pressure switches? Inside our WIKA online-shop you will find some of our standard designs. For those who have any questions, your contact will gladly help you.
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