The English word "Photoplethysmography" is difficult to read, abbreviated as PPG, but the principle is simple: blood is red, reflecting red light and absorbing green light. Apple Watch combines a green LED light and a photosensitive photodiode to detect the blood circulation of the wrist at a specific time.
At the moment when the heart beats, the blood circulation at the wrist increases and absorbs more green light; Between heartbeats, less green light is absorbed. The LED light on the Apple Watch flashes hundreds of times per second to calculate the number of heartbeats per minute, which is the heart rate.
Apple Watch uses LED green light and infrared light, and two light sensors to detect heart rate. When it is at a low temperature below 15 degrees Celsius (59 degrees Fahrenheit), more accurate data can be obtained by measuring the absorption of green light.
In a high temperature environment, for example, when a user sweats in a gym, the moisture on the skin surface increases. Because more green light is absorbed, it is difficult to detect the green light reflected under the skin. At this point, Apple Watch switches to infrared mode.
Extended data:
At Apple? Open the "Fitness Record" App on your watch at any time to check your fitness status. The workout recording application will display three rings.
The red "activity" circle indicates the calories you burn when you are active.
The green "exercise" circle indicates how long you have been doing a certain intensity of fitness exercise.
The blue "standing" circle indicates the number of times you stand and move for at least one minute every hour in a day.
If a wheelchair is set up, the blue "standing" circle will turn into a "turning" circle to show the number of times to turn at least one minute per hour in a day.
Turn the digital crown to see your current total, and continue to scroll to see the graphic progress, total steps, total distance, physical training data and floors climbed.
The overlapping of the circular parts indicates that the target has been exceeded. Press the screen hard to view the weekly summary or change the activity goal.
Apple official website-Use Apple Watch to record daily fitness records.
Baidu encyclopedia-iWatch