DS1923 Maxim, DS1923 Datasheet - Page 50

• 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
The accuracy of high-resolution temperature conver-
sion results (forced conversion as well as temperature
logs) can be improved through a correction algorithm.
The data needed for this software correction is stored in
the calibration memory (memory page 18). It consists of
reference temperature (Tr) and conversion result (Tc)
for two different temperatures, as shown below. See the
Temperature Conversion section for the binary number
format.
Step 1: Preparation
Tr1 = 60
Offset = 41
Tr2 = Tr2H/2 + Tr2L/512 - Offset
Tr3 = Tr3H/2 + Tr3L/512 - Offset
Tc2 = Tc2H/2 + Tc2L/512 - Offset
Tc3 = Tc3H/2 + Tc3L/512 - Offset
Err2 = Tc2 - Tr2
Err3 = Tc3 - Tr3
Err1 = Err2
B = (Tr2
A = B x (Tr1 - Tr2)/(Tr2
C = Err1 - A x Tr1
Step 2: Execution
Tc = TcH/2 + TcL/512 - Offset
Tcorr = Tc - (A x Tc
50
______________________________________________________________________________________
Software Correction Algorithm
2
- Tr1
ADDRESS
0240h
0241h
0242h
0243h
0244h
0245h
0246h
0247h
2
) x (Err3 - Err1)/[(Tr2
2
- B x Tr1
2
+ B x Tc + C)
2
- Tr1
2
for Temperature
)
2
- Tr1
DESIGNATOR
(convert from binary to °C)
(convert from binary to °C)
(convert from binary to °C)
(convert from binary to °C)
(convert from binary to °C)
(the actual correction)
2
Tc2H
Tc3H
Tc2L
Tc3L
Tr2H
Tr3H
Tr2L
Tr3L
) x (Tr3 - Tr1) + (Tr3
The software correction algorithm requires two addition-
al values, which are not stored in the device. For the
DS1923 these values are Tr1 = 60°C and Offset = 41.
The correction algorithm consists of two steps, prepara-
tion and execution. The preparation step first converts
temperature data from binary to decimal °C format.
Next, three coefficients A, B, and C are computed. In
the execution step, the temperature reading as deliv-
ered by the DS1923 is first converted from the low/high-
byte format (TcL, TcH) to °C (Tc) and then corrected to
Tcorr. Once step 1 is performed, the three coefficients
can be used repeatedly to correct any temperature
reading and temperature log of the same device .
Cold reference temperature, high-byte.
Cold reference temperature, low-byte.
Conversion result at cold reference temperature, high-byte.
Conversion result at cold reference temperature, low-byte.
Hot reference temperature, high-byte.
Hot reference temperature, low-byte.
Conversion result at hot reference temperature, high-byte.
Conversion result at hot reference temperature, low-byte.
2
- Tr1
2
) x (Tr1 - Tr2)]
DESCRIPTION