Apogee SI-411 Manuale d'uso - Pagina 15

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be found at http://www.nws.noaa.gov/oh/hrl/shef/indexshef.htm. The second value is the units of the parameter.

Additional fields with more information are optional.

The Measurement Parameter Commands work with the Verification Command (aV!), Measurement Commands

(aM!, aM1! ... aM9!, aMC!, aMC1! ... aMC9!), and Concurrent Measurement Commands (aC!, aC1! ... aC9! , aCC!,

aCC1! ... aCC9!).

The format of the Identify Measurement Parameter Command is the address, the capital letter I, the measurement

command, the underscore character ("_"), a three-digit decimal number, and the command terminator ("!"). The

three-digit decimal indicates which number of measurement that the command returns, starting with "001" and

continuing to "002" and so on, up to the number of measurements that the command returns.

The format of the response is comma delimited and terminated with a semicolon. The first value is the address.

The second value is the SHEF code. The third value is the units. Other optional values may appear, such as a

description of the data value. The response is terminated with a Carriage Return (<CR>) and Line Feed (<LF>).

Identify Measurement Parameter Command example:

1,RW,Watts/meter squared,incoming solar radiation;<CR><LF>

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:







where T

is target temperature [K], T

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.

<address>I<command>_<three-digit decimal>!

a,<SHEF Code>,<units>;<CR><LF>

1IC_001!



(1)

is detector temperature [K], S

The Identify Measurement Parameter

Command for sensor address 1, C

command, data value 1.

The response from sensor address 1, SHEF

code RW, units of Watts/meter squared,

and additional information of incoming

solar radiation.

is the millivolt signal from the detector, m is