Setting the switch points of an electronic pressure switch for a credit card applicatoin in the vacuum range isn’t 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.
Sizzling , 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?, depending on task. The next 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 could be easily understood with settings for ambient air pressures.
Example: Control of vacuum pressure pump
On the other hand, 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 a vacuum between -0.7 bar and -0.5 bar. For the duty 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 implies: At 0 bar (= start of operation) the switch ought to be closed, in order 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 before pressure has again dropped to -0.7 bar.
ow must the switch points be set in 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 would not switch on. After entering the switch points, the schematic is obtained, which ultimately shows how the pressure switch functions in accordance with the example:
Note
Information about 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 find some of our standard designs. Assuming you have any questions, your contact will gladly help you.
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