Pressure detecting device
A pressure detecting device includes: a resonator whose oscillation frequency varies depending on a pressure; a first oscillation circuit that oscillates the resonator and outputs a signal of a frequency corresponding to the pressure; an AT-cut quartz crystal resonator; a second oscillation circuit that oscillates the AT-cut quartz crystal resonator and outputs a reference clock signal; a measuring unit that measures the reference clock signal by the use of a reciprocal counting method; a temperature detecting unit that detects a temperature of the resonator; and a storage unit that stores coefficients of a first approximating polynomial for calculating a first correction value used to compensate for a frequency-temperature characteristic of the measuring unit, wherein the frequency-temperature characteristic of the value measured by the measuring unit includes a frequency-temperature characteristic of the AT-cut quartz crystal resonator and a frequency-temperature characteristic of the resonator.
1. A pressure detecting device comprising:
a resonator whose oscillation frequency varies depending on a pressure;
a first oscillation circuit that oscillates the resonator and outputs a signal of a frequency corresponding to the pressure;
an AT-cut quartz crystal resonator;
a second oscillation circuit that oscillates the AT-cut quartz crystal resonator and outputs a reference clock signal;
a measuring unit that measures the reference clock signal in a gate period based on the period of the signal output from the first oscillation circuit by the use of a reciprocal counting method;
a temperature detecting unit that detects a temperature of the resonator or around the resonator; and
a storage unit that stores coefficients of a first approximating polynomial for calculating a first correction value used to compensate for a frequency-temperature characteristic of the measuring unit,
wherein the frequency-temperature characteristic of the value measured by the measuring unit includes a frequency-temperature characteristic of the AT-cut quartz crystal resonator and a frequency-temperature characteristic of the resonator.
2. The pressure detecting device according to claim 1 , wherein the first correction value is calculated on the basis of the detection result of the temperature detecting unit and the first approximating polynomial, and
the pressure detecting device further comprises a first correction unit that corrects the value measured by the measuring unit by the use of the first correction value.
3. The pressure detecting device according to claim 1 , wherein coefficients of a second approximating polynomial are stored in the storage unit,
the pressure detecting device further comprises a second correction unit that additionally corrects the measured value corrected by the use of the first correction value on the basis of the second approximating polynomial, and
the second approximating polynomial is used to additionally correct the measured value corrected by the use of the first correction value so that the resultant value corrected by the second correction unit is proportional to the pressure.
4. The pressure detecting device according to claim 1 , wherein the degree of the first approximating polynomial is three or more.
5. The pressure detecting device according to claim 1 , wherein the degree of the second approximating polynomial is three or more.
6. The pressure detecting device according to claim 1 , wherein the AT-cut quartz crystal resonator is disposed in a closed space.
7. The pressure detecting device according to claim 1 , wherein the resonator is a double-ended tuning fork type resonator.