Switch points in vacuum ranges: How are they set?

Setting the switch points of an electric pressure switch for an application in the vacuum range isn’t a self-explanatory task. The following article therefore explains what should be taken into account with this particular setting. It involves a pressure switch with a hysteresis function. Instruments with this particular configuration are most frequently 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 ? Jealous closed? or ?normally open?, depending 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 greater than the reset point (RP) and the beginning of measuring range (MRS) is definitely 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
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 a vacuum pump, for example, which must maintain vacuum pressure 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 beginning of measuring range (MRS) is therefore -1 bar, the end of measuring range (MRE) 0 bar. This implies: At 0 bar (= start of operation) the switch ought to be closed, as a way to activate the vacuum pump. If the pressure drops to -0.7 bar, the switch must open and stop 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 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 in accordance with the example:
Note
Information about WIKA?s electronic pressure switches can be found on the WIKA website. Would you like to buy pressure switches? Inside Novelty -shop you will discover a few of our standard designs. If you have any questions, your contact will gladly assist you to.
Also read our posts
What is meant by the switching function ?hysteresis? with electronic pressure switches?
What is the difference between your switching functions ?hysteresis? and ?window? in pressure switches?
What is meant by the ?normally open? switching function with pressure switches?

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