Switch points in vacuum ranges: How are they set?

Setting the switch points of an electronic pressure switch for an application in the vacuum range is not a self-explanatory task. The following article therefore explains what needs to be taken into account with this setting. It involves a pressure switch with a hysteresis function. Instruments with this 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?, 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 higher than the reset point (RP) and the start of measuring range (MRS) is always smaller compared to the end of measuring range (MRE). เกจวัดแรงดัน 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 example, which must maintain vacuum pressure between -0.7 bar and -0.5 bar. For the task 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 should be closed, so that you can activate the vacuum pump. If pressure gauge 10 bar 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 both pictures and translate MRS and MRE:
Here it is clear that the ?normally open? function must be selected, otherwise the pump wouldn’t normally switch on. 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 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 a few of our standard designs. When 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 your switching functions ? ไดอะแฟรม ซีล ? and ?window? in pressure switches?
What is meant by the ?normally open? switching function with pressure switches?

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