Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
344 words
A compensation circuit for a resistance bridge with a pair of arms, wherein each arm includes a pair of resistors, one of which increases with strain, and another of which decreases with strain comprising: a) a power input, a ground reference, a positive signal output and a negative signal output of the resistance bridge providing a response across the signal outputs as a function of pressure applied to the resistance bridge and an electrical signal applied to the power input; b) an offset reference generator to receive a fixed circuit reference voltage for generating a reference offset voltage; c) a voltage controlled current source connected across the power input and the ground reference, the voltage controlled current source having a bridge excitation output current directly proportional to the fixed circuit reference voltage; d) a buffer amplifier having a buffer input connected to the power input, the buffer amplifier configured as a voltage follower generating a buffer output voltage proportional to the power input voltage; e) an instrumentation amplifier with a positive terminal and a negative terminal connected to the positive signal output and negative signal output respectively to generate an initial output proportional to the response of the signal outputs; f) a compensation network having an offset correction part to receive the buffer output voltage and the ground reference, for generating an initial offset current wherein the buffer output voltage varies proportionately to temperature change of the resistance bridge providing a temperature dependent part of the initial offset current; g) an offset correction amplifier for receiving the initial offset current, the buffered output voltage, and the fixed circuit reference voltage, for generating a correction signal to counteract an offset error in the response of the signal outputs wherein the buffer output voltage and the initial offset current both vary proportionately to temperature change in the resistance bridge and thereby provide a temperature dependent part of the correction signal; and h) a reference input of the instrumentation amplifier connected for receiving the correction signal to modify the initial output in response to the correction signal.
Claim 2
Dependent Claim
47 words
The compensation circuit of claim 1 wherein the offset error has a fixed part and a temperature dependent part, both of the parts counteracted by the interactions of the buffer output voltage, the fixed circuit reference voltage and the initial offset current within the offset correction amplifier.
Claim 3
Dependent Claim
52 words
The compensation circuit of claim 2 wherein the offset correction part of the compensation network has a single resistor to adjust the fixed part and another single resistor to adjust the temperature dependent part so that the adjustment for the fixed part does not affect the adjustment of the temperature dependent part.
Claim 4
Dependent Claim
64 words
The compensation circuit of claim 3 wherein the offset correction amplifier include selected and configured resistors to allow the single resistor for the fixed part to adjust positive or negative values of the fixed part of the offset error and the other single resistor for the temperature dependent part to adjust positive or negative slope of the temperature dependent part of the offset error.
Claim 5
Dependent Claim
35 words
The compensation circuit of claim 4 wherein a programmable gain amplifier receives the initial output from the instrumentation amplifier and provides a compensated output which is independent of the resistance bridge response to applied pressure.
Claim 6
Dependent Claim
41 words
The compensation circuit of claim 5 wherein a gain correction part of the compensation network has a gain resistor used to adjust the gain of the programmable gain amplifier to compensate for variations in the resistance bridge response to applied pressure.
Claim 7
Independent Claim
235 words
A method for compensating temperature dependent and fixed offset errors of a resistance bridge having the following steps: a) Energize the resistance bridge with a well regulated constant current source, connected across the power input and the ground reference; b) Measure the offset and resistance of the resistance bridge after bringing the resistance bridge to a first temperature T1 and at zero pressure, and allowing the system to equilibrate; c) Measure the response of the resistance bridge at the first temperature T1, after applying a pressure P1 across the diaphragm of the resistance bridge, to determine the unit change in the output of the resistance bridge with pressure; d) Measure the offset and resistance of the resistance bridge after bringing the resistance bridge to a second temperature T2 and at zero pressure, and allowing the system to equilibrate; e) Determine the unit change in the output and resistance of the resistance bridge with temperature; f) Use the determinations and measurements of steps b through e to calculate the values for the single resistor, the other single resistor and the gain resistor, and g) Use the calculated values from step f to select and include the single resistor, the other resistor, and the gain resistor in the compensation network to correct for fixed and temperature dependent parts of the offset error and variations in resistance bridge response to applied pressure at the resistance bridge signal outputs.