Setting the switch points of an electric pressure switch for a credit card applicatoin in the vacuum range isn’t a self-explanatory task. The next article therefore explains what has 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, such as 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?, based on 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 start 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 vacuum pressure pump
Alternatively, 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 example, which must maintain a vacuum between -0.7 bar and -0.5 bar. For the task described, we decide on a pressure switch with a measuring range of -1 ? 0 bar.
The beginning 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. 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 really 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 ultimately shows the way the pressure switch functions relative to the example:
Note
Information regarding WIKA?s electronic pressure switches are available on the WIKA website. Do you want to buy pressure switches? Inside our WIKA online-shop you will discover a few of our standard designs. For those who have any questions, your contact will gladly assist you to.
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