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 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, 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?, depending on 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 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 a vacuum pump, for instance, which must maintain a vacuum between -0.7 bar and -0.5 bar. For the task described, we select a pressure switch with a measuring selection of -1 ? 0 bar.
The beginning 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 should be closed, in order to activate 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 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 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 activate. After entering the switch points, the schematic is obtained, which shows how the pressure switch functions relative to 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 Scornful -shop you will find a few of our standard designs. If you have any questions, your contact will gladly help you.
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