Is the heart rate measured by a smart bracelet?
First: PPG photoelectric volume pulse wave mapping principle (Photo Plethysmo Graphy)
Simply put, the smart bracelet is to take advantage of the fluctuation of the transmittance in the blood and convert it into electrical signals, corresponding to the heart rate.
When a certain wavelengths of light ray through your fingers to the skin surface, the beam will be transmitted through the way of transmission or reflection to the smart bracelet photoelectric receiver, due to that, in the process the skin muscles and blood absorption attenuation effect, detector detects the light intensity will be reduced.The absorption of light from skin and muscle tissue is constant throughout the blood circulation, while the blood in the skin is pulsating with the heart.When the systolic blood volume was the largest in the systolic blood volume, the smallest amount of light was detected.When the heart is diastolic, the intensity of the light detected is the largest, and the intensity of the light that the receiver receives is fluctuating.
Why are we always seeing green leds?
Because of the red liquid in front of the blood, the absorptivity of green light is the largest, and the data judgment is accurate.
When the user's heart beats, more blood flows through the user's wrist, and the green light absorbs more.When the heart beats, blood flow decreases, and the absorption of green light decreases.
For example, suppose that smart bracelet glow value is 100, the skin absorb constant 10 muscle tissue, blood total absorption of 15, after the reflection for the 100-10 * 2-15 = 65, then the arterial blood, red blood cell oxygen, 2 be total absorption into the blood, after the reflection of 50, after will have been in 65-50-65-50-65-50-65-50-65-50...By counting the number of pulses per second, you get your heart rate.
I don't know PPG is this way?
Its principle determines its shortcomings, if the bracelet and the skin have a lot of sweat directly?That number would be inaccurate.
If your numerical value changes in this way, 65-50-65-50-650-650-650-650-65, etc., will also make the machine be forced.
To sum up:
This method, measuring resting pulse and normal regular sports (running, etc.) or more accurate, but for the ruleless movement, sports such as football, badminton, no rules, for example say assume values will be jumping around, slightly accuracy will be reduced.But it's also a difference. For non-professionals, I think it should be enough.
Second: electrocardioelectric signal measurement, similar to ECG (ECG)
The simple point is that you go to the hospital and have an electrocardiogram, which is kind of similar.The difference is that the hospital needs to add electrodes to the heart, foot, and wrist, and more data needs to be measured, and the wrist watch doesn't need that much data, and the heart rate alone is enough.