Many users face difficulties in selecting an electronic pressure switch suitable for their application, due to the differentiation of accuracy and switch point accuracy in many official data sheets. Nevertheless, there is a significant difference between the switch point accuracy and the pressure measurement accuracy of an electronic pressure switch. This should be considered when looking at the overall accuracy of a pressure switch.
Accuracy of electronic pressure switches
Under the general accuracy of an electronic pressure switch one must recognise the accuracy of the pressure measurement itself. This accuracy depends to a great extent on the pressure sensor used within the electronic switch. The maximum measured error of the pressure signal is derived from the non-linearity, zero point offset, span tolerance, hysteresis and non-repeatability of the sensor. These stated values result from the sensor and the electronics which evaluate the sensor signal. The general accuracy thus only determines how accurately the instantaneous media pressure can be measured. However, it gives no indication of the accuracy of the switching signal at the output of the pressure switch.
Switch point accuracy of electronic pressure switches
The switching signal is an output signal generated from the electronics of the pressure switch, which is realised via PNP or NPN transistor switching outputs. The electronics monitor the pressure measurement of the pressure sensor and trigger a switching output signal each time a certain limit has been exceeded. However, this switching logic is integrated as an addition to the electronics of a standard pressure sensor within the pressure switch and thus leads to a further error in addition to the standard accuracy of the sensor. The switch point accuracy is thus the cumulative accuracy of the standard accuracy and the accuracy of the switch point logic.
Conclusion
It is important to understand, when looking at the accuracy of a switch point, that there can be a difference between the actual pressure and the activated switch point. Thus, it is primarily the switch point accuracy, which represents the total accuracy, that should be used to select an electronic pressure switch suitable for your needs.
Incidentally, the distinction between general accuracy and switch point accuracy also applies to temperature, level and flow switches.
Note
Further information on our range of pressure switches can be found on the WIKA website.