Abstract
In this paper, a new design of pneumatic band reject filter based on the characteristics of pneumatic coupling condenser circuits1) is described. The coupling condenser circuit has the character of a high pass filter essentially.
A pneumatic band reject filter is constructed by combining two coupling condenser circuits and the two restrictor-capacitor circuits. Features of this device are as follows.
1) The central frequency of the band reject filter can be chosen by changing resistances in the coupling condenser circuits and the restrictor-capacitor circuits.
2) Low central frequency filters having, for instance a corner frequency lower than 1Hz, can be realized.
The gain characteristics of pneumatic band reject filters were tested in the range of stop frequencies 0.7∼5Hz. As a result, it was shown that the band reject filters reduce the signal levels of stop frequencies by more than 15dB in comparison with the signal levels of distant frequencies.
Theoretical values of the gain characteristics of band reject filters were derived from the time constants and amplitudes of the coupling condenser circuits, and the time constants of the restrictor-capacitor circuits. These calculated values and the experimental data show good agreement.
The effects of these time constants and amplitudes on the characteristics of a pneumatic band reject filter are discussed theoretically.
