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 next article therefore explains what has to be taken into account with this 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 ?normally closed? or ?normally open?, according to the task. The following 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 always smaller than the end of measuring range (MRE). This rule could be easily understood with settings for ambient air pressures.
Example: Control of vacuum pressure pump
However, 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 vacuum pressure between -0.7 bar and -0.5 bar. For the duty described, we decide on a pressure switch with a measuring range of -1 ? 0 bar.
Jumpstart 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 should be closed, in order 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 the upper limit value of -0.5 bar, the pump should once again start and run until the 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 really is clear that the ?normally open? function should be selected, otherwise the pump would not switch on. 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 can be found on the WIKA website. Would you like to buy pressure switches? In our WIKA online-shop you will discover some of our standard designs. Assuming 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’s meant by the ?normally open? switching function with pressure switches?

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