Setting the switch points of an electronic pressure switch for a credit card applicatoin in the vacuum range isn’t a self-explanatory task. The following article therefore explains what must 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, 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 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 vacuum pressure pump
Alternatively, setting the switch points in the vacuum range and therefore, ultimately, the switching function, requires more attention. To illustrate this, let?s take Fine of a vacuum pump, for instance, which must maintain vacuum pressure between -0.7 bar and -0.5 bar. For the task described, we decide on a pressure switch with a measuring selection of -1 ? 0 bar.
The start 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 stop the pump. When the pressure reaches top of the 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 Lies and translate MRS and MRE:
Here it 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 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. Do you want to buy pressure switches? Inside our WIKA online-shop you will discover some of our standard designs. In case you have any questions, your contact will gladly assist you to.
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