# US 5,349,868 A · Pressure sensor including bridge circuit for detecting permeability of a magnetic layer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,349,868 A - Document ID: US5349868A - Status: Granted - Kind: A - Application number: 08/051,302 - Filed: 1993-04-23 - Granted: 1994-09-27 - Earliest claimed: 1992-04-23 - Assignees: Matsushita Electric Industries Co., Ltd. - Inventors: Rihito Shoji; Hiroyuki Hase; Masayuki Wakamiya - Web page: https://patentgrep.com/patent/US5349868A ## CPC - G01L 9/16: by making use of variations in the magnetic properties of material resulting from the application of stress - G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G) ## Abstract In a bridge circuit of a pressure sensor, resistances are connected in series to the impedances of a pressure detection coil and of a dummy coil for differential provided for deforming and non-deforming parts, and the values of the resistances are smaller than the impedances of the coils. The inductance and the internal resistance of the coils are measured under zero pressure and under the highest rating pressure. The resistance connected to the pressure detector coil is determined so that the sensor output sensitivity, represented as a difference of the sensor outputs under zero pressure and under the highest rating pressure, at the highest temperature agrees with that at the lowest temperature. The resistance connected to the dummy coil is determined so that the sensor output, represented as a difference of the sensor outputs under zero pressure, at the highest temperature agrees with that at the lowest temperature. ## Claims ### Claim 1 A pressure sensor comprising: a sensor body comprising a deforming part deformable under an applied pressure to be detected and a non-deforming part subjected to a constant pressure, the deforming part having an opening for introducing the applied pressure; a magnetic layer made of a material having large magnetostriction, which magnetic layer being fixed on the deforming part and on the non-deforming part; first and second permeability detector elements disposed to detect the permeability of the magnetic layer on the deforming part and on the non-deforming part, respectively, each of the first and second permeability detector elements having an inductance and an internal resistance, the first and second permeability detector elements being connected in series; a first resistor connected to the first permeability detector element, the resistance of the first resistor being smaller than the impedance of the first permeability detector element; and a second resistor connected to the second permeability detector element and to the first resistance, the resistance of the second resistor being smaller than the impedance of the second permeability detector element; wherein a bridge is constructed by the first and second permeability detector elements and the first and second resistors for taking out a difference of the voltages generated in the first and second permeability detector elements. ### Claim 2 (depends on 1) The pressure sensor according to claim 1, further comprising an AC voltage supplier for supplying an AC voltage to between a connection points of the first and second resistors and another connection points of the first and second permeability detector elements. ### Claim 3 (depends on 1) The pressure sensor according to claim 1, wherein said magnetic layer is made of an amorphous alloy having magnetostriction effect. ### Claim 4 (depends on 1) The pressure sensor according to claim 1, wherein the value of said first resistance satisfies the following relation: ##EQU4## wherein "V" denotes an AC voltage applied to the bridge, "f" denotes the frequency of the applied voltage (.omega.=2.pi.f); "V.sub.c " denotes a terminal voltage of the coil, "r" denotes an internal resistance of the coil, "L" denotes an inductance of the coil, and "R" denotes the resistance connected to the coil for the deforming part, further, subscript "h" denotes a value at a first temperature, subscript "1" denotes a value at a second temperature, subscript "a" denotes a value under a first applied pressure different from zero, and subscript "i" denotes a value under zero applied pressure. ### Claim 5 (depends on 4) The pressure sensor according to claim 4, wherein said first temperature is the highest operating temperature of the pressure sensor and said second temperature is the lowest operating temperature. ### Claim 6 (depends on 4) The pressure sensor according to claim 4, wherein said first pressure is the highest operating pressure of the pressure sensor. ### Claim 7 (depends on 1) The pressure sensor according to claim 1, wherein the value of said second resistance satisfies the following relation: ##EQU5## wherein "V" denotes an AC voltage applied to the bridge, "f" denotes the frequency of the applied voltage (.omega.=2.pi.f); "V.sub.c " denotes a terminal voltage of the first and second permeability detector elements, "r" denotes an internal resistance of the first and second permeability detector elements, "L" denotes an inductance of the first and second permeability detector elements, "R" denotes the resistance connected to the first permeability detector element, and "R.sub.d " denotes the resistance connected to the second permeability detector element, further, subscript "h" denotes a value at a first temperature, subscript "1" denotes a value at a second temperature different from the first temperature, subscript "a" denotes a value under the highest stress, subscript "i" denotes a value under zero pressure, and subscript "d" denotes a value for the non-deforming part. ### Claim 8 (depends on 7) The pressure sensor according to claim 7, further comprising a differential circuit for obtaining a difference of the output voltage of said bridge and an amplifier for amplifying the differential voltage obtained by the differential circuit. ### Claim 9 (depends on 7) The pressure sensor according to claim 7, wherein said first temperature is the highest operating temperature of the pressure sensor and said second temperature is the lowest operating temperature. ### Claim 10 (depends on 7) The pressure sensor according to claim 7, wherein said first pressure is the highest operating pressure of the pressure sensor. ### Claim 11 (depends on 1) The pressure sensor according to claim 1, wherein the value of said second resistance satisfies the following relation: ##EQU6## wherein "V" denotes an AC voltage applied to the bridge, "f" denotes the frequency of the applied voltage (.omega.=2.pi.f); "V.sub.c " denotes a terminal voltage of the first and second permeability detector elements, "r" denotes an internal resistance of the first and second permeability detector elements, "L" denotes an inductance of the first and second permeability detector elements, "R" denotes the resistance connected to the first permeability detector element, and "R.sub.d " denotes the resistance connected to the second permeability detector element, further, subscript "h" denotes a value at a first temperature, subscript "1" denotes a value at a second temperature different from the first temperature, subscript "a" denotes a value under the highest stress, subscript "i" denotes a value under zero pressure, and subscript "d" denotes a value for the non-deforming part. ### Claim 12 (depends on 11) The pressure sensor according to claim 11, further comprising first and second amplifiers for amplifying the output voltages of the first and second permeability detector elements and a differential circuit for obtaining a difference of the output voltage of the first and second amplifiers. ### Claim 13 (depends on 11) The pressure sensor according to claim 11, wherein said first temperature is the highest operating temperature of the pressure sensor and said second temperature is the lowest operating temperature. ### Claim 14 (depends on 11) The pressure sensor according to claim 11, wherein said first pressure is the highest operating pressure of the pressure sensor. ### Claim 15 (depends on 4) The pressure sensor according to claim 4, wherein the value of said second resistance satisfies the following relation: ##EQU7## wherein "V" denotes an AC voltage applied to the bridge, "f" denotes the frequency of the applied voltage (.omega.=2.pi.f); "V.sub.c " denotes a terminal voltage of the first and second permeability detector elements, "r" denotes an internal resistance of the first and second permeability detector elements, "L" denotes an inductance of the first and second permeability detector elements, "R" denotes the resistance connected to the first permeability detector element, and "R.sub.d " denotes the resistance connected to the second permeability detector element, further, subscript "h" denotes a value at a first temperature, subscript "1" denotes a value at a second temperature different from the first temperature, subscript "a" denotes a value under the highest stress, subscript "i" denotes a value under zero pressure, and subscript "d" denotes a value for the non-deforming part. ### Claim 16 (depends on 15) The pressure sensor according to claim 15, further comprising a differential circuit for obtaining a difference of the output voltage of said bridge and an amplifier for amplifying the differential voltage obtained by the differential circuit. ### Claim 17 (depends on 15) The pressure sensor according to claim 15, wherein said first temperature is the highest operating temperature of the pressure sensor and said second temperature is the lowest operating temperature. ### Claim 18 (depends on 15) The pressure sensor according to claim 15, wherein said first pressure is in the highest operating pressure of the pressure sensor. ### Claim 19 (depends on 4) The pressure sensor according to claim 4, wherein the value of said second resistance satisfied the following relation: ##EQU8## wherein "V" denotes an AC voltage applied to the bridge, "f" denotes the frequency of the applied voltage (.omega.=2.pi.f); "V.sub.c " denotes a terminal voltage of the first and second permeability detector elements, "r" denotes an internal resistance of the first and second permeability detector elements, "L" denotes an inductance of the first and second permeability detector elements, "R" denotes the resistance connected to the first permeability detector element, and "R.sub.d " denotes the resistance connected to the second permeability detector element, further, subscript "h" denotes a value at a first temperature, subscript "1" denotes a value at a second temperature different from the first temperature, subscript "a" denotes a value under the highest stress, subscript "i" denotes a value under zero pressure, and subscript "d" denotes a value for the non-deforming part. ### Claim 20 (depends on 19) The pressure sensor according to claim 19, further comprising first and second amplifiers for amplifying the output voltages of the first and second permeability detector elements and a differential circuit for obtaining a difference of the output voltage of the first and second amplifiers. ### Claim 21 (depends on 19) The pressure sensor according to claim 19, wherein said first temperature is the highest operating temperature of the pressure sensor and said second temperature is the lowest operating temperature. ### Claim 22 (depends on 19) The pressure sensor according to claim 19, wherein said first pressure is the highest operating pressure of the pressure sensor.