Switch points in vacuum ranges: How are they set?

Setting the switch points of an electronic pressure switch for a credit card applicatoin in the vacuum range is not a self-explanatory task. The next article therefore explains what should be taken into account with this particular setting. It involves a pressure switch with a hysteresis function. Instruments with this particular configuration are most frequently 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?, with regards to the task. The next graphics illustrate both switching functions with the respective switch and reset points:
In principle, the following applies: The switch point (SP) is higher than the reset point (RP) and the beginning of measuring range (MRS) is definitely 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
Alternatively, 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 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 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, to be able 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 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 the switch points be set in this vacuum range? Let?s take the two pictures and translate MRS and MRE:
Here it really is clear that the ?normally Unconditional ? function should be selected, otherwise the pump would not switch on. After entering the switch points, the schematic is obtained, which ultimately 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 help you.
Also read our posts
What is meant by the switching function ?hysteresis? with Upbeat ?
What is the difference between your switching functions ?hysteresis? and ?window? in pressure switches?
What is meant by the ?normally open? switching function with pressure switches?

Leave a Comment