24
Chapter 5. PID locking
5.2.1
PID commands
The
PID
gains can also be set using
PID,KP
and similar commands
as in the example script below.
# define the desired lock point (in THz)
PID,SET,384.22924169
# set the gain to 10 V/GHz
PID,GAIN,10
# define the PID gains
PID,KP,0
PID,KI,1
PID,KD,0
# set the output range to be 0 to 2.5V centred at 1.25V
PID,MIN,0
PID,MAX,2.5
PID,OFFSET,1.25
# activate the PID
PID,ENABLE
Listing 5.1:
Example script to configure the
PID
controller
The front-panel interface includes a multi-colour
LED
which indicates
the status of the lock at a glance.
The indicator is green when the
lock is stable, yellow when the lock is engaged but the error signal
has not converged to zero, and red when the output has saturated
indicating the lock has failed (see also §2.1).
5.3
Integrator windup
Integrator
windup
is
caused
by
saturation
of
an
output
actuator.
Once
the
FZW
output
voltage
reaches
the
maximum
(or
minimum)
value defined by V
max
or V
min
, the integrator will continue to accu-
mulate error (“wind up”), but the actuator is not able to respond to an
increased control voltage. For example, on
MOGL
abs
DLC
controllers,
the piezo control voltage is limited to 0 to 2.5 V range and output
voltages exceeding that range will not have any additional effect.
If
the
actuator
(laser)
finally
returns
to
within
range,
the
“wound
up”
integrator
has
to
reset
from
a
value
far
from
where
it
should
be for the existing actuator value.
That recovery can introduce a
Summary of Contents for FSW4
Page 1: ...Fizeau Wavemeter and Fibre Switcher FZW600 FSM2 FSW4 FSW8 Firmware v0 9 5 mogfzw v1 4 5 ...
Page 36: ...30 Chapter 5 PID locking ...
Page 50: ...44 Appendix A Specifications ...
Page 60: ...54 Appendix C Command language ...
Page 62: ...56 Appendix D Errors and troubleshooting ...
Page 67: ...F Dimensions and PCB 83 120 146 32 9 30V PID TRIG FSW Figure F 1 FZW chassis dimensions 61 ...
Page 68: ...62 Appendix F Dimensions and PCB 146 33 37 120 18 Figure F 2 FSW fibre switch dimensions ...
Page 71: ......