Setting the switch points of an electric pressure switch for an application in the vacuum range isn’t a self-explanatory task. Cataclysmic explains what must be taken into account with this particular setting. It involves a pressure switch with a hysteresis function. Instruments with this particular configuration are most regularly installed in industrial applications.
Electronic pressure switches, like 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 following graphics illustrate both switching functions with the respective switch and reset points:
In principle, the following applies: The switch point (SP) is higher than the reset point (RP) and the beginning of measuring range (MRS) is always smaller than the end of measuring range (MRE). This rule could be easily understood with settings for ambient air pressures.
Example: Control of a vacuum pump
Alternatively, setting the switch points in the vacuum range and thus, ultimately, the switching function, requires more attention. To illustrate this, let?s take the control of vacuum pressure pump, for instance, which must maintain a vacuum between -0.7 bar and -0.5 bar. For the task described, we decide on a pressure switch with a measuring selection 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 switch on 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 the switch points be set within 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 wouldn’t normally switch on. 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 are available on the WIKA website. Would you like to buy pressure switches? In our WIKA online-shop you will discover a few of our standard designs. Assuming you have any questions, your contact will gladly help you.
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