Abstract: A vacuum pump has a housing, a pump shaft having a terminal shaft portion, a bearing member mounted in the housing and supporting the pump shaft and a rotor affixed to the pump shaft. The housing has a housing wall forming a side chamber with the bearing member. The terminal shaft portion projects through the bearing member into the side chamber. There is further provided a device for measuring the rpm of the rotor. The device comprises an inductive sensor held in the housing wall and a ferromagnetic member mounted on the terminal shaft portion for rotation in unison therewith. The ferromagnetic member induces electric pulses in the inductive sensor at a rate proprotionate to the rpm of the rotor. A non-magnetic partition separates the inductive sensor from the side chamber.

Abstract: A method and circuit for measuring and displaying a parameter, in which the parameter is sensed by means of a sensor which supplies an output voltage representative of the value of the parameter, the output voltage is compared with a comparison voltage associated with the sensor response characteristic, and a display is produced on the basis of the result of the comparing step. The comparison is effected by supplying the output voltage from the sensor to a first input of a comparator, supplying the comparison voltage to a second input of the comparator, and varying the comparison voltage between successive values extending over the output voltage range of the sensor.