Patent ID: 6427540
Filing Date: 2002-08-06
Classification: G01L

Abstract:
A pressure operated switch comprising:a membrane pressure sensor, which is a variable resistor which varies in response to pressure, the variable resistor having a first end, and a second end: an operational amplifier having a positive input, a negative input, and a DC voltage output, the output being connected to the negative input and the output being connected to ground through the membrane pressure sensor; a microcontroller incorporating a timer and a voltage monitoring circuit; a plurality of switches, arranged to in a first condition, connect the first end of the membrane pressure sensor to the negative input of the operational amplifier, and the second and to ground, and alternatively to, in a second condition, connect the first end to ground and the second end to the negative input of the operational amplifier, wherein the plurality of switches are connected to the microcontroller, and the microcontroller, in response to the timer, periodically alternates the plurality of switches between the first condition and the second condition; the voltage monitoring circuit of the microcontroller being connected to the DC voltage output of the operational amplifier, the microcontroller causing at least one switch to close in response to a change in the voltage of the operational amplifier output; and wherein degradation of the membrane pressure sensor is substantially prevented by periodically reversing the flow of current through the membrane pressure sensor, and wherein a change in resistance of the membrane pressure sensor is detected by a change in the DC voltage output of the operational amplifier.