Electronic sphygmomanometer
A first oscillation circuit and a second oscillation circuit are connected to a first pressure sensor and a second pressure sensor, respectively, and oscillate based on the capacity values of the corresponding pressure sensors. The first oscillation circuit and the second oscillation circuit operate in response to instruction from a CPU. The one of the first oscillation circuit and the second oscillation circuit that has received an activation signal from the CPU outputs a signal having a frequency that corresponds to the capacity value of the corresponding pressure sensor. An adjustment circuit is connected to the first oscillation circuit and the second oscillation circuit, and allows one of the frequency signals to pass therethrough, outputting the signal to the CPU.
1. An electronic sphygmomanometer comprising:
a cuff that is worn on a measurement area;
an inflation and deflation unit that adjusts a pressure applied to the cuff;
a plurality of pressure sensors connected to the cuff;
a plurality of oscillation circuits, provided in correspondence to the respective plurality of pressure sensors, that output a square wave signal of a frequency based on pressures;
an oscillation circuit adjustment circuit having a plurality of input terminals to receive signals from the plurality of oscillation circuits, and having only one output terminal that allows the output of the square wave signal from one of the plurality of oscillation circuits to pass; and
a CPU having only one analog input terminal that is configured to accept an input of the square wave signal from the one output terminal of the oscillation circuit adjustment circuit and configured to calculate a blood pressure from the frequency of the square wave signal,
wherein the CPU comprises a switching unit that outputs an activation signal that is applied selectively to one of the plurality of oscillation circuits so that when one oscillation circuit is activated by the activation signal, the remaining oscillation circuits are not activated, and
wherein the CPU is further configured to determine whether or not an abnormality has occurred in the plurality of pressure sensors, upon comparing the blood pressures obtained from the plurality of oscillation circuits associated with the plurality of pressure sensors, respectively.
2. The electronic sphygmomanometer according to claim 1 ,
wherein the oscillation circuit adjustment circuit comprises a logic circuit, comprising a plurality of input nodes that accept signals input from the respective plurality of oscillation circuits, that outputs one signal based on a result of a logic process performed on the signals inputted into the plurality of input nodes.
3. The electronic sphygmomanometer according to claim 2 ,
wherein each of the oscillation circuits outputs a square wave signal of a frequency based on the pressure when the oscillation circuit has been activated in accordance with an instruction, and outputs a fixed voltage signal when the oscillation circuit has not been activated.
4. The electronic sphygmomanometer according to claim 1 ,
wherein the CPU is configured to output a first activation signal to a first oscillation circuit among the plurality of oscillation circuits and detects a first cuff pressure based on a frequency of a first square wave signal outputted from the first oscillation circuit,
wherein the CPU is configured to output a second activation signal to a second oscillation circuit among the plurality of oscillation circuits and detects a second cuff pressure based on a frequency of a second square wave signal outputted from the second oscillation circuit, and
wherein the CPU is configured to determine whether or not an abnormality has occurred in the plurality of pressure sensors based on a difference between the first cuff pressure and the second cuff pressure.
5. The electronic sphygmomanometer according to claim 4 ,
wherein the controller CPU is configured to output a third activation signal to the first oscillation circuit among the plurality of oscillation circuits after outputting the first activation signal and the second activation signal, and detects a third cuff pressure based on the frequency of the first square wave signal outputted from the first oscillation circuit, and
wherein the CPU is configured to determine whether or not an abnormality has occurred in the plurality of pressure sensors based on a difference between an average of the first and third cuff pressures and the second cuff pressure.