Bristol 871A - Page 18

Model 871A User’s Manual USING THE LASER WAVELENGTH METER
Bristol Instruments, Inc. 18
Wavelength Display
The most recent wavelength measurement.
Error Display
The difference between the target wavelength and the Wavelength Display.
Output Display
The current voltage output being delivered through the BNC connector on the
back panel of the 871 instrument.
Data Table
Allows entry of the PID parameters, default output voltage, and voltage offset
values. Click on any field to change the value and type the desired value in using
the keyboard. Click Save Instrument Settings from the Instrument menu to
commit these changes to the PID calculation.
• Set Point – The target wavelength, frequency, or wavenumber for the PID
calculation.
• Offset – An additional voltage offset added to the PID computed voltage.
This is useful for centering the voltage output swing at a value other than
zero.
• Scale – Multiplier for converting the error signal into a voltage, expressed in
volts per nanometer. Even when multiplied by the Scale the output voltage
remains capped by the instrument limits of ± 5 volts or the user defined
maximum and minimum voltages.
• K
p
– Proportional gain constant. The Proportional gain constant is unit-less,
and has the highest contribution to guiding the measured wavelength
towards the desired frequency.
• K
i
– Integral gain constant. The Integral gain constant, expressed in Hz,
accounts for the sum of past errors to minimize the effects of outlying data
peaks or spikes on the output voltage.
• K
d
– Derivative gain constant. The Derivative gain constant, expressed in
seconds, factors in the current rate of change to avoid oscillation about the
desired wavelength.
• Minimum Voltage – The lower limit, expressed in volts, for the output
voltage. This voltage is automatically limited by the instrument to - 5 volts.
• Maximum Voltage – The upper limit, expressed in volts, for the output
voltage. This voltage is automatically limited by the instrument to + 5 volts.
• Default Output – The voltage output when the PID calculation is paused.
The Default Output is expressed in volts, and must be within the instrument
limits of ± 5 volts.