Setting the switch points of an electronic pressure switch for an application in the vacuum range is not a self-explanatory task. The following 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 frequently 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 regards 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 beginning of measuring range (MRS) is always smaller compared to the end of measuring range (MRE). Fantasy can be easily understood with settings for ambient air pressures.
Example: Control of vacuum pressure pump
Alternatively, 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 vacuum pressure pump, for example, which must maintain vacuum pressure between -0.7 bar and -0.5 bar. For the task described, we decide on a pressure switch with a measuring range of -1 ? 0 bar.
The beginning 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 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 again 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 both pictures and translate MRS and MRE:
Here it is clear that the ?normally open? function must be selected, otherwise the pump would not activate. After entering the switch points, the schematic is obtained, which shows the way the pressure switch functions relative to 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 find some of our standard designs. In case you have any questions, your contact will gladly help you.
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