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 needs to 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 next graphics illustrate both switching functions with the respective switch and reset points:
In principle, the next applies: The switch point (SP) is higher 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 can be easily understood with settings for ambient air pressures.
Example: Control of a vacuum 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 a vacuum pump, for example, 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 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 ought to be closed, so as to switch on the vacuum pump. If the pressure drops to -0.7 bar, the switch must open and stop the pump. As soon as 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 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 would not activate. After entering Drowning , the schematic is obtained, which ultimately shows how the pressure switch functions in accordance with the example:
Note
Information regarding WIKA? Great are available on the WIKA website. Do you want to buy pressure switches? Inside our WIKA online-shop you will find some of our standard designs. When you have any questions, your contact will gladly assist you to.
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