Setting the switch points of an electronic pressure switch for a credit card applicatoin in the vacuum range is not 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 configuration are most regularly installed in industrial applications.
Actionable , 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 higher than the reset point (RP) and the start of measuring range (MRS) is definitely smaller than the end of measuring range (MRE). This rule can be easily understood with settings for ambient air pressures.
Example: Control of a vacuum pump
On the other hand, 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 a vacuum between -0.7 bar and -0.5 bar. For the duty described, we select 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, as a way to switch on the vacuum pump. If the pressure drops to -0.7 bar, the switch must open and prevent the pump. As soon as 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 in this vacuum range? Let?s take both pictures and translate MRS and MRE:
Here it really is clear that the ?normally open? function should be selected, otherwise the pump would not activate. After entering the switch points, the schematic is obtained, which ultimately shows how the pressure switch functions in accordance with the example:
Note
Information regarding WIKA?s electronic pressure switches are available on the WIKA website. Would you like to buy pressure switches? Inside Spontaneous -shop you will find some of our standard designs. Should you have any questions, your contact will gladly assist you to.
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