how to solve the problem when spo2 sensor no readings

when the spo2 sensor signal tracking to the pulse,on the patient monitor screen shows no reading,

how to slove the problem.

1,pay attention to patient conditions

2,keep the patient not moved or reduce the patient arm active,make the spo2 sensor securely test, if necessary please change a new spo2 sensor

3,if necessary, pay attention to the measured patient warm;

4,to avoild the light

5,if test too much long time please changed to use another finger 

6,try to avoid to test the arm blood pressure when use spo2 sensor to test the spo2