Maxim Integrated Page 7 of 15
2 Calibration of the SpO
2
Algorithm
2.1 Calibration of SpO
2
Coefficients for the Final Product
Due to variations in the physical design and optical shield of the final product, a calibration
procedure is required to be performed once in a controlled environment. This procedure is
important to ensure the quality of the SpO
2
calculation. This step is typically performed in a
standard lab with a reference SpO
2
device to determine three calibration coefficients: a, b, and c.
The details of the calibration procedure are described in the Guidelines for SpO2 Measurement
Using the Maxim MAX32664 Sensor Hub application note.
Once three calibration coefficients are obtained, they need to be loaded to the MAX32664A every
time prior to starting the algorithm. But first, they are required to be converted to a 32-bit integer
format using the following:
• A
int32
= round (10
5
x a)
• B
int32
= round (10
5
x b)
• C
int32
= round (10
5
x c)
For example, the default measured calibration coefficients are:
• a = 1.5958422
• b = -34.659664
• c = 112.68987
They are sent to the MAX32664A in integer format after conversion:
• A
int32
= round (10
5
x a) = 0x00026F60
• B
int32
= round (10
5
x b) = 0xFFCB1D12
• C
int32
= round (10
5
x c) = 0x00ABF37B
The calibration coefficients may be stored in the host flash separately and loaded to the
MAX32664A after every reset.
Table 4 shows the sequence of commands for the calibration process. Table 5 shows the format
of received samples. Typically, R values are needed for the calibration process, as described in
the Guidelines for SpO2 Measurement Using the Maxim MAX32664 Sensor Hub application
note.
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