Model 871A User’s Manual MAKING MEASUREMENTS
Bristol Instruments, Inc. 34
High Speed Data Acquisition
This section describes the semantics and formatting of the measurement data along with
the back panel pinout of the RS-422 port. The instrument ships with a RS-422 to USB
converter cable for transferring data to a computer, though any computer interface which
can read an RS-422 signal can be used.
Measurement results from the 871 Laser Wavelength Meter can be retrieved through the
standard SCPI messages over Ethernet or USB. The RS-422 output port must be used to
achieve the highest measurement rates and most reliable timing. Every wavelength
measurement computed by the 871 system, either internally or externally triggered, will be
sent out the RS-422 port. The Application Software flash drive included with the 871
system contains several coding examples to demonstrate the proper method of reading
the data from the RS-422 port at the maximum continuous measurement rate. If only a
finite number of measurements are desired, then the internal data buffer can be used (see
following section).
Communication Protocol
The communication protocol for the RS-422 port is as follows.
Data Semantics
Each measurement consists of a wavelength, a relative power, a status word, and a scan
index, in that order. The description of each field is as follows.
• Wavelength – The wavelength is given in nanometers. It is expressed as a
double-precision (64-bit) floating-point number.
• Power – The power is given as the relative intensity on the detector. It is
expressed as a single-precision (32-bit) floating-point number.
• Status – The status word is a 32-bit-wide bitfield. The hexadecimal value for
each status word are listed in Appendix E.
• Scan Index – The scan index is a 32-bit, unsigned integer whose value
increases by one with each measurement. The first scan index emitted by the
instrument is 0, and the measurement after scan index 2^32 = 4294967296
will have scan index 0 again.
To Next Page
Loading...
