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Blood pressure/pulse discrimination method:
The criterion of systolic pressure is certain: when the ratio of the amplitude Ui of a pulse wave to the maximum amplitude Um Ui/Um=Ks in the rising segment of the pulse wave amplitude envelope during inflation, the corresponding cuff pressure at this time is considered as the systolic pressure. Ps=P Å Ui=Ks · Um. The diastolic pressure criterion is determined: when the ratio of the amplitude Ui of a pulse wave to the maximum amplitude Um Ui/Um=Kd in the descending section of the pulse wave amplitude envelope, the corresponding cuff pressure at this time is considered as diastolic pressure. Namely, Pd=P Å Ui=Kd · Um. Heart rate refers to the number of beats per minute of the heart. Due to the divergence between the heartbeat and pulse, it is possible to measure heart rate while measuring blood pressure. The key to measuring heart rate is to distinguish the peak value of pulse waves, and then calculate the heart rate based on how many pulse waves there are within a certain period of time.
The pneumatic circuit consists of a cuff, an air pump, a pressure sensor, and a vent valve. The two signals output by the pressure sensor are filtered, amplified, and connected to the two A/D channels of the main controller to measure the static pressure signal and pulse signal; The air pump and vent valve are directly controlled by the main controller through the driving chip to complete the charging and discharging of the measurement time.
Pressure sensing local:
The characteristics of human physiological signals are low-frequency small signals, usually μ The V-mV level sensor has a frequency range of 0-300 Hz and a low signal-to-noise ratio. Therefore, it is very important to choose a sensor with good performance. In this plan, the US9111 sensor is selected to cooperate with two carefully designed filtering and amplification circuits to achieve high-quality signals.
Filter and amplify local:
The signal from the pressure sensor is a mixed signal of pulse signal and static pressure signal, mixed with high-frequency interference from the outside and DC or low-frequency weight. Static pressure signal belongs to low-frequency signal, with a frequency less than or equal to 0.04 Hz, and pulse signal frequency is generally about 1 Hz. Divide the mixed signal into two parts, one of which passes through a low-pass filtering circuit and is connected to an A/D converter to stop analog-to-digital conversion, obtaining static pressure signal data; The other path passes through another filtering and amplification circuit and stops analog-to-digital conversion to obtain amplified pulse signal data.