6
.
TEC Controller and
Temperature
Sensors
As
some models may
h
ave
more
than
one
TEC
controller,
the
temperature
sensor
or
TEC
controller
is
selected
by
a
prefix,
in
this
chapter
written
as
x
.
So,
x
has
to
be
replaced
by
a
digit
(or
letter)
to
select
the
temperature
sensor
or
TEC.
The
first
temperature
sensor
or
TEC
corresponds
to
1
,
the
second
to
2
,
the
third
to
3
and
so
on.
As
the
first
temperature
sensor
or
TEC
is
usually
used
for
a
laser
and
the
second
for
a
crystal,
a
deprecated
option
for
selecting
them
is
the
use
of
the
letters
L
and
C
,
respectively.
6.1 PID Controller Parameters
The
temperature
controller
in
devices
with
TEC
support
has
a
PID
structure
with
the
common
formulas:
G
c
(
s
) =
k
p
1
+
1
T
n
s
+
T
v
s
u
(
t
) =
k
p
e
(
t
) +
1
T
n
Z
e
(
t
)
d
t
+
T
v
d
e
(
t
)
d
t
k
p
– proportional gain –
x
TCCK
T
n
=
T
i
– integral time
–
x
TCCN
T
v
=
T
d
– derivative time
–
x
TCCV
The values of these three variable parameters have to be found. After Ziegler-Nichols
for example you can calculate
k
p
=
1.2 ·
T
L
T
n
=
2 ·
L
T
v
=
0.5 ·
L
Here,
T
is the base time constant and
L
is the delay time, both derivated from a
step response. Note that the so found parameters differ slightly from the theoretical
values. In practice typical value ranges for a TEC circuit are:
23
Содержание Laser Lab Source LDC Series
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