Table of Contents
Advertisement
64
APPENDIX F – Glossary
Bandwidth
Beam splitter
Compensation
Count rate
Fundamental wavelength
Hysteresis
Measurement beam (arm)
NTP
Reference beam (arm)
Resolution
RS422/485
Stabilised laser
Switch parity
Tristate
Update rate
The maximum count frequency which may be applied to the controller/
counter input. In a quadrature signal, count rate is 4 × signal
frequency.
An optic which is used to split the two polarisation states of the laser
beam into measurement and reference arms.
The process of applying a defined formula (Edlen) to the
environmental conditions in order to correct errors on the laser
wavelength to improve accuracy.
The rate at which count increments are produced by movement.
count rate =
quadrature resolution
This must be below the update rate, otherwise an overspeed error will
occur.
The wavelength of the helium neon laser tube which can be expressed
at vacuum or defined conditions such as NTP.
A method of reducing noise or oscillation in measurement signals by
using a positional delay of 1 count.
The part of the split laser beam which passes to the moving optic
being measured.
Normal temperature and pressure
(20°C, 1013.25 mbar, 50% RH).
The part of the split laser beam which passes through the fixed
reference path in the detector head.
The distance separation of the encoder output signal, this being the
smallest increment possible.
An electronic line transmission standard using noise immune
differential signals.
A laser tube which is actively controlled to achieve a constant laser
frequency.
A method of detecting errors by checking that the number of switches
in the enabled position is odd.
An open circuit state condition which may be applied to the laser
output signal lines to indicate an error.
The rate at which the digital output quadrature is updated. The
minimum edge-edge time may be calculated by:
t =
update rate
feedrate
1
Advertisement
Table of Contents
