Concentration measuring instrument

A concentration measuring instrument, comprising:

• a piezoelectric vibrator transmitting an ultrasonic wave into a solution contained in a cavity and detecting the ultrasonic wave reflected;
• a temperature sensor measuring a temperature of the solution in the cavity;
• a drive circuit generating a drive signal driving the piezoelectric vibrator to transmit the ultrasonic wave, the drive circuit including a capacitor cancelling a parallel capacitance component of the piezoelectric vibrator;
• a phase comparator performing a phase comparison between the drive signal and a detection signal obtained by detecting the ultrasonic wave reflected at the piezoelectric vibrator;
• a frequency setting circuit making the drive circuit generate drive signals having sequentially different frequencies and monitoring a phase comparison result from the phase comparator while the piezoelectric vibrator is driven by the drive signal to detect a resonant frequency of a resonant mode to be measured;
• a Phase Locked Loop (PLL) circuit including the drive circuit and the phase comparator, the PLL circuit making a frequency of the drive signal follow the resonant frequency detected at the frequency setting circuit;
• and
• a microcomputer determining a concentration of a solute in the solution on a basis of the frequency of the drive signal while the PLL circuit is being operated and a result of temperature measurement by the temperature sensor.

A concentration measuring instrument, comprising:

• a piezoelectric vibrator transmitting an ultrasonic wave into a solution contained in a cavity and detecting the ultrasonic wave reflected;
• a temperature sensor measuring a temperature of the solution in the cavity;
• a drive circuit generating a drive signal driving the piezoelectric vibrator to transmit the ultrasonic wave, the drive circuit including a phase inversion circuit inverting a phase of an oscillation signal, and an amplitude adjustment circuit adjusting an amplitude of the oscillation signal;
• a phase comparator performing a phase comparison between the drive signal and a detection signal obtained by detecting the ultrasonic wave reflected at the piezoelectric vibrator;
• a frequency setting circuit making the drive circuit generate drive signals having sequentially different frequencies and monitoring a phase comparison result from the phase comparator while the piezoelectric vibrator is driven by the drive signal to detect a resonant frequency of a resonant mode to be measured;
• a Phase Locked Loop (PLL) circuit including the drive circuit and the phase comparator, the PLL circuit making a frequency of the drive signal follow the resonant frequency detected at the frequency setting circuit;
• and
• a microcomputer determining a concentration of a solute in the solution on a basis of the frequency of the drive signal while the PLL circuit is being operated and a result of temperature measurement by the temperature sensor.

A concentration measuring instrument, comprising:

• a piezoelectric vibrator transmitting an ultrasonic wave into a solution contained in a cavity and detecting the ultrasonic wave reflected;
• a temperature sensor measuring a temperature of the solution in the cavity;
• a drive circuit generating a drive signal driving the piezoelectric vibrator to transmit the ultrasonic wave, the drive circuit includes a drive amplifier receiving an oscillation signal, connected to a first electrode of the piezoelectric vibrator, and driving the piezoelectric vibrator;
• a phase comparator performing a phase comparison between the drive signal and a detection signal obtained by detecting the ultrasonic wave reflected at the piezoelectric vibrator;
• a frequency setting circuit operatively connected to an output of the phase comparator, and making the drive circuit generate drive signals having sequentially different frequencies and monitoring a phase comparison result from the phase comparator while the piezoelectric vibrator is driven by the drive signal to detect a resonant frequency of a resonant mode to be measured;
• a Phase Locked Loop (PLL) circuit including the drive circuit and the phase comparator, the PLL circuit making a frequency of the drive signal follow the resonant frequency detected at the frequency setting circuit;
• and
• a microcomputer determining a concentration of a solute in the solution on a basis of the frequency of the drive signal while the PLL circuit is being operated and a result of temperature measurement by the temperature sensor.

A concentration measuring instrument, comprising:

• a piezoelectric vibrator transmitting an ultrasonic wave into a solution contained in a cavity and detecting the ultrasonic wave reflected;
• a temperature sensor measuring a temperature of the solution in the cavity;
• a drive circuit generating a drive signal driving the piezoelectric vibrator to transmit the ultrasonic wave;
• a phase comparator performing a phase comparison between the drive signal and a detection signal obtained by detecting the ultrasonic wave reflected at the piezoelectric vibrator;
• a frequency setting circuit operatively connected to an output of the phase comparator, and making the drive circuit generate drive signals having sequentially different frequencies and monitoring a phase comparison result from the phase comparator while the piezoelectric vibrator is driven by the drive signal to detect a resonant frequency of a resonant mode to be measured;
• a voltage control oscillation circuit having an input connected to an output of the frequency setting circuit and an output connected to the drive circuit;
• a Phase Locked Loop (PLL) circuit including the drive circuit and the phase comparator, the PLL circuit making a frequency of the drive signal follow the resonant frequency detected at the frequency setting circuit;
• and
• a microcomputer determining a concentration of a solute in the solution on a basis of the frequency of the drive signal while the PLL circuit is being operated and a result of temperature measurement by the temperature sensor.

A concentration measuring instrument, comprising:

• a piezoelectric vibrator transmitting an ultrasonic wave into a solution contained in a cavity and detecting the ultrasonic wave reflected;
• a temperature sensor measuring a temperature of the solution in the cavity;
• a drive circuit generating a drive signal driving the piezoelectric vibrator to transmit the ultrasonic wave;
• a phase comparator performing a phase comparison between the drive signal and a detection signal obtained by detecting the ultrasonic wave reflected at the piezoelectric vibrator;
• a frequency setting circuit operatively connected to an output of the phase comparator, and making the drive circuit generate drive signals having sequentially different frequencies and monitoring a phase comparison result from the phase comparator while the piezoelectric vibrator is driven by the drive signal to detect a resonant frequency of a resonant mode to be measured;
• a filter arranged between the phase comparator and the frequency setting circuit;
• a Phase Locked Loop (PLL) circuit including the drive circuit and the phase comparator, the PLL circuit making a frequency of the drive signal follow the resonant frequency detected at the frequency setting circuit;
• and
• a microcomputer determining a concentration of a solute in the solution on a basis of the frequency of the drive signal while the PLL circuit is being operated and a result of temperature measurement by the temperature sensor.