Setting the switch points of an electric pressure switch for an application in the vacuum range isn’t a self-explanatory task. The next article therefore explains what should be taken into account with this setting. It involves a pressure switch with a hysteresis function. Instruments with this particular 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 respect 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 definitely smaller than 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 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 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.
Shocking of measuring range (MRS) is therefore -1 bar, the end 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 prevent the pump. When the pressure reaches the upper limit value of -0.5 bar, the pump should once again start and run before 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 really 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 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. Do you want to buy pressure switches? Inside our WIKA online-shop you will discover some of our standard designs. For those who have any questions, your contact will gladly help you.
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