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5-15
Programming Commands
Measurement Instructions
Measurement Instructions
Use the measurement instructions documented in this section to perform
measurements and return the desired results to the computer. Four basic
measurement instructions are used: CONFigure, FETCh, READ, and MEA-
Sure. Because the command trees for each of these four basic measurement
instructions are identical, only the MEASure tree is documented.
To perform a measurement, append to the measurement instruction a POWer
or LENGth function. The POWer functions select power, frequency, wave-
length, or wave number measurements. Use the LENGth functions to config-
ure the instrument to measure coherence length. The instrument measures
the coherence length in the time domain by rectifying and low-pass filtering
the interferogram. The resulting waveform is then curve fit into a decaying
exponential. Refer to “Measuring Coherence Length” on page 3-12.
When the :SCALar command is used, data for a single measurement value is
returned. When the :ARRay command is used, multiple data values are
returned.
The
MEASure
measurement instruction always acquires new measurement
data. In order to obtain both wavelength and power values from the same mea-
surement data, use two FETCh commands. This is shown in the following pro-
gram fragment:
OUTPUT 720;”:INIT:CONT OFF;”
OUTPUT 720;”:CONF:ARR:POW MAX”
OUTPUT 720;”:INIT:IMM”
OUTPUT 720;”:FETC:ARR:POW?”
ENTER 720:powers$
OUTPUT 720;”:FETC:ARR:POW:WAV?”
ENTER 720:wavelengths$
In the example above, the data in the power and wavelength arrays are
returned in the same order so that powers can be matched to wavelengths.
You can
also
send a
MEASure
command followed by a FETCh command.