Bristol 871A - Measurements and Data Handling; Measurement Procedures

Model 871A User’s Manual MAKING MEASUREMENTS
Bristol Instruments, Inc. 31
5 MAKING MEASUREMENTS
System Calibration
The 871 system calibrates itself with an internal reference laser, and interrupts the
wavelength and power measurements for approximately 2 seconds. Calibration is initiated
manually using the Calibrate menu item in the NuView software, automatically at user-
defined temperature or time intervals, or using the corresponding SCPI command.
NOTE: The 871 system will calibrate periodically during the initial instrument warm-up
time, even if the Calibration Method is set to Manual.
Setting Measurement Rate
The measurement rate of the 871 system is controlled with the Frame Rate setting on the
NuView software. When set in Internal Trigger mode, the number of measurements per
second will correspond to the Frame Rate. When set in External Trigger mode, the Frame
Rate will define the measurement time initiated by the input trigger. The measurement
time includes the exposure time and read-out time. The equation below shows the relation
between the Frame Rate and exposure time for the 871A-NIR system. The read out time
is a fixed 0.575 milliseconds.
𝐸𝑥𝑝
(
𝑚𝑠
)
=
1
[
𝐹𝑟𝑎𝑚𝑒 𝑅𝑎𝑡𝑒 (𝐻𝑧)
]
−
[
𝑅𝑒𝑎𝑑 𝑂𝑢𝑡 𝑇𝑖𝑚𝑒 (𝑚𝑠)
]
For the 871A-VIS system, the exposure time is simply one over the Frame Rate.
Setting the Auto Exposure
Tunable or swept lasers can result in rapid changes to the measured signal intensity. The
Auto Exposure feature of the 871 system allows the instrument to compensate for
changes in signal intensity that would result in low signal or saturation conditions for the
instrument. When enabled, the Auto Exposure function increases or decreases the
exposure time of the detector as necessary to keep the signal intensity within the dynamic
range of the 871 system.
The Auto Exposure algorithm will not change the instrument Frame Rate. The maximum
exposure achievable is limited by the instrument set Frame Rate. To assure a valid
measurement across the full laser scan, the 871 Frame Rate should be set to measure the
laser at the lowest output intensity.