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 particular 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?, with respect 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 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 a vacuum pump, for instance, which must maintain vacuum pressure between -0.7 bar and -0.5 bar. For the duty described, we select a pressure switch with a measuring selection of -1 ? 0 bar.
The start 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, so that you can switch on the vacuum pump. If the pressure drops to -0.7 bar, the switch must open and prevent the pump. When the pressure reaches top of the limit value of -0.5 bar, the pump should once more 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 is clear that the ?normally Official ? function should be selected, otherwise the pump wouldn’t normally activate. After entering the switch points, the schematic is obtained, which shows how 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 some of our standard designs. For those who have any questions, your contact will gladly assist you to.
Also read Outstanding
What is meant by the switching function ? On-demand ? 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 function with pressure switches?