Switch points in vacuum ranges: How are they set?

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 following article therefore explains what must 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, 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?, with regards 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 greater than the reset point (RP) and the start of measuring range (MRS) is always smaller than the end of measuring range (MRE). Forever 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 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 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 means: At 0 bar (= start of operation) the switch ought to be closed, so as to activate 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 top of the 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 within this vacuum range? Let?s take Innovative and translate MRS and MRE:
Here it really is clear that the ?normally Attractive ? function must 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 about 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 some of our standard designs. Should you have any questions, your contact will gladly assist you to.
Also read our posts
What’s meant by the switching function ?hysteresis? with electronic pressure switches?
What is the difference between the switching functions ?hysteresis? and ?window? in pressure switches?
What is meant by the ?normally open? switching function with pressure switches?g

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