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 is not a self-explanatory task. The next article therefore explains what must be taken into account with this particular setting. pressure gauge 10 bar involves a pressure switch with a hysteresis function. Instruments with this 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?, depending on 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 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 a vacuum pump
However, 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 instance, 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 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 is clear that the ?normally open? function must be selected, otherwise the pump would not activate. After entering the switch points, the schematic is obtained, which 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 find 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 the switching functions ?hysteresis? and ?window? in pressure switches?
What is meant by the ?normally open? switching digital pressure gauge with pressure switches?

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