DS1923 Maxim, DS1923 Datasheet - Page 52

• Manufacturer Part Number: DS1923
• Description: The DS1923 temperature/humidity logger iButton® is a rugged, self-sufficient system that measures temperature and/or humidity and records the result in a protected memory section
• Manufacturer: Maxim

Hygrochron Temperature/Humidity Logger
iButton with 8KB Data-Log Memory
Step 1: Preparation
For the humidity data in the calibration memory, the lower 4 bits of each low byte are set to 0. This simplifies the con-
version from the binary data format to raw %RH values to a one-line equation.
Hr1 = ((Hr1H x 256 + Hr1L) x 5.02/65536 - 0.958)/0.0307
Hr2 = ((Hr2H x 256 + Hr2L) x 5.02/65536 - 0.958)/0.0307
Hr3 = ((Hr3H x 256 + Hr3L) x 5.02/65536 - 0.958)/0.0307
Hc1 = ((Hc1H x 256 + Hc1L) x 5.02/65536 - 0.958)/0.0307
Hc2 = ((Hc2H x 256 + Hc2L) x 5.02/65536 - 0.958)/0.0307
Hc3 = ((Hc3H x 256 + Hc3L) x 5.02/65536 - 0.958)/0.0307
Err1 = Hc1 - Hr1
Err2 = Hc2 - Hr2
Err3 = Hc3 - Hr3
B = [(Hr2
A = [Err2 - Err1 + B x (Hr1 - Hr2)]/(Hr2
C = Err1 - A x Hr1
Step 2: Execution
Hc = ((HcH x 256 + HcL) x 5.02/65536 - 0.958)/0.0307
Hcorr = Hc - (A x Hc
Note: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are
found on various websites and are included in cross-compilers.
52
Hr1 = 20%RH
Hr2 = 60%RH
Hr3 = 90%RH
Hc1 = 17.65%RH
Hc2 = 56.41%RH
Hc3 = 89.57%RH
B = -0.186810
A = 0.001948%RH
C = 0.607143%RH
(Hr3
______________________________________________________________________________________
CONVERTED DATA FROM CALIBRATION MEMORY
2
2
RESULTING CORRECTION COEFFICIENTS
- Hr1
- Hr1
2
2
) x (Hr1 - Hr2)]
) x (Err3 - Err1) + Hr3
2
- B x Hr1
2
+ B x Hc + C)
2
2
- Hr1
x (Err1 - Err2) + Hr1
2
)
Numerical Humidity Correction Example
Err1 = -2.35%RH
Err2 = -3.59%RH
Err3 = -0.43%RH
Hc = 8.9%RH
Hcorr = 9.8%RH
2
(convert from binary to %RH)
(convert from binary to %RH)
(the actual correction)
x (Err2 - Err1)]/[(Hr2
APPLICATION OF CORRECTION COEFFICIENTS
TO SAMPLE READING
ERROR VALUES
2
- Hr1
2
) x (Hr3 - Hr1) +