Apogee SI-421 Benutzerhandbuch - Seite 14
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sensors with the factory address of 0 requires changing the address on one of the sensors to a non-zero
value in order for both sensors to communicate properly on the same channel:
Command
aAn!
where a is the current (old) sensor address ("0-9", "A-Z"), A is an upper-case ASCII character denoting the
instruction for changing the address, n is the new sensor address to be programmed ("0-9", "A-Z"), and !
is the standard character to execute the command. If the address change is successful, the datalogger
will respond with the new address and a <cr><lf>.
Send Identification Command: aI!
The send identification command responds with sensor vendor, model, and version data. Any
measurement data in the sensor's buffer is not disturbed:
Command
"aI!"
where a is the sensor address ("0-9", "A-Z", "a-z", "*", "?"), mm is a the sensor model number (11, 21, 31,
or H1), vvv is a three character field specifying the sensor version number, and xx...xx is serial number.
Target Temperature Measurement:
SI-400 series infrared radiometers have an SDI-12 output. The following equations and the custom
calibration coefficients described in this section are programmed into the microcontroller. Target
temperature is output directly in digital format.
The detector output from SI series radiometers follows the fundamental physics of the Stefan-Boltzmann
Law, where radiation transfer is proportional to the fourth power of absolute temperature. A modified
form of the Stefan-Boltzmann equation is used to calibrate sensors, and subsequently, calculate target
temperature:
4
4
T
−
T
=
m
T
D
where T
is target temperature [K], T
T
detector, m is slope, and b is intercept. The mV signal from the detector is linearly proportional to the
energy balance between the target and detector, analogous to energy emission being linearly
proportional to the fourth power of temperature in the Stefan-Boltzmann Law.
During the calibration process, m and b are determined at each detector temperature set point (10 C
increments across a -15 C to 45 C range) by plotting measurements of T
and b coefficients are then plotted as function of T
results to produce equations that determine m and b at any T
2
m
=
C
2
⋅
T
+
D
Response
n<cr><lf>
Response
a13Apogee SI-
4mmvvvxx...xx<cr><lf>
⋅
S
+
b
(1)
D
is detector temperature [K], S
D
C
1
⋅
T
+
C
0
(2)
D
Description
Change the address of the
sensor
Description
The sensor serial number and
other identifying values are
returned
is the millivolt signal from the
D
4
T
and second order polynomials are fitted to the
D
:
D
– T
4
versus mV. The derived m
D
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