Most of the fitness trackers on the market use PPG to measure heart rate, and when we measure, there will be green flashing at the bottom of the bracelet. Why? Because in the blood of this red liquid, the absorption rate of green light is the largest, and the data is relatively accurate.
When the user’s heart beats, more blood will flow through the user’s wrist, and the amount of green light will be absorbed. In the heartbeat gap, blood flow is reduced, resulting in a decrease in green light absorption.
For example, suppose the luminescence value of the bracelet is 100, the skin muscle tissue absorbs a constant 10, the total blood absorption is 15, and the reflection is 100-10*2-15=65, then the arterial blood comes over, and the red blood cells have increased oxygen. The total blood absorption has become 2 times, then the reflection is 50, after which it will remain at 65-50-65-50-65-50-65-50-65-50…, by calculating how many pulse changes per second , you can get your heart rate.
Do you know if PPG has this way?
Its principle determines its shortcomings. If the bracelet and skin directly have a lot of sweat? That value will be inaccurate.
If your value changes like this, 65-50-65-50-65-50-66-51-62-50-65, etc., this will also make the machine obscured.
This method, measuring resting pulse and normal regular movement (running, etc.) is still relatively accurate, but for irregular movements, such as football badminton and other irregular movements, the assumed value of the example will be chaotic, will be slightly accurate Degree drops. But it is also a few different values. For non-professionals, I feel that it should be enough.