Setting the switch points of an electric 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 particular configuration are most regularly installed in industrial applications.
Suddenly , like 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 higher 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
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 a vacuum pump, for example, 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 end of measuring range (MRE) 0 bar. This means: At 0 bar (= start of operation) the switch ought to be closed, in order to activate the vacuum pump. If the pressure drops to -0.7 bar, the switch must open and prevent 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 Conquer be set in 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 would not activate. After entering the switch points, the schematic is obtained, which shows the way the pressure switch functions in accordance with the example:
Note
Information about WIKA?s electronic pressure switches are available on the WIKA website. Do you want to buy pressure switches? In our WIKA online-shop you will find a few of our standard designs. When you have any questions, your contact will gladly help you.
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