Abstract A simple rugged capacitive displacement transducer for use in dirty and severe shock environments has a conductive sleeve that is preferably lined on the inside and outside with an insulating material. The sleeve slides over the free end of a rod whose displacement is to be measured and as the rod moves within the sleeve, the capacitance between the sleeve and rod is changed. The change in capacitance is converted by an electronic circuit into a current signal representing the displacement of the rod. If the rod does not have a free end, the conductive portion of the sleeve is made in the form of two opposing triangular areas and a cylindrical ground plate disk is attached to the rod in the region of the conductive portion of the sleeve.
Apparatus for measuring the displacement of a moveable rod of a machine, comprising: a conductive sleeve located over at least a part of the rod; a resistance having one end connected to said conductive sleeve; an operational amplifier with its output connected to the other end of said resistance and its noninverting input connected to a reference ground; an input resistor with one end connected to the inverting input of said amplifier; a source of a.c. voltage connected to the other end of said input resistor; a feedback resistor with one end connected to the inverting input of said amplifier; means for connecting said conductive sleeve to the other end of said feedback resistor; means for coupling said rod to the reference ground; means for obtaining an a.c. signal equal to the a.c. voltage drop across said resistance; means for demodulating the a.c. signal; and means for measuring the demodulated signal.
Claim 2
Dependent Claim
151 words
Apparatus for measuring the displacement of a moveable rod of a machine, comprising: a conductive sleeve located over at least a part of the rod; a resistance having one end connected to said conductive sleeve; an operational amplifier with its output connected to the other end of said resistance and its noninverting input connected to a reference ground; an input resistor with one end connected to the inverting input of said amplifier; a source of a.c. voltage connected to the other end of said input resistor; a feedback resistor with one end connected to the inverting input of said amplifier; means for connecting said conductive sleeve to the other end of said feedback resistor; means for coupling said rod to the reference ground; means for obtaining an a.c. signal equal to the a.c. voltage drop across said resistance; means for demodulating the a.c. signal; and means for measuring the demodulated signal.