Lakeshore 336, Руководство пользователя

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5.3 Zone Settings 75
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5.3 Zone Settings The Model 336 allows you to establish up to ten custom contiguous temperature
zones where the controller will automatically use pre-programmed values for PID,
heater range, manual output, ramp rate, and control input. Zone control can be active
for both control loops at the same time. Configure the zones using 1 as the lowest to
10 as the highest zone. Zone boundaries are always specified in kelvin (K). The bottom
of the first zone is always 0 K; therefore, only the upper limit is required for all subse-
quent zones. Make a copy of FIGURE 5-1 to plan your zones.
To use the programmed zones, the output mode must be set to Zone (refer to section
4.5.1.4.2 to set up Zone mode). In Zone mode, the instrument will update the control
settings each time the setpoint crosses into a new zone. If you change the settings
manually, the controller will use the new setting while it is in the same zone, and will
update to the programmed zone table settings when the setpoint crosses into a
new zone.
The zone settings include a Control Input parameter for each temperature zone. This
allows a different feedback sensor to be used for each temperature zone. For exam-
ple, a diode sensor can be used while cooling down from room temperature to 10 K, at
which point the Control Input could be switched to a Cernox™ sensor for tempera-
tures under 10 K.
To illustrate how the control parameters are updated in Zone mode, consider the
zone settings from the table below. Starting from room temperature (about 300 K),
and setting a setpoint of 2 K (with Setpoint Ramping turned On), the setpoint will
begin ramping at the current setpoint Ramp Rate, then once the setpoint crosses
100 K, the control parameters from Zone 8 will be used. The setpoint ramp will then
continue toward 2 K at a rate of 20 K/min until crossing 50 K, when the control
parameters from Zone 7 are loaded. This pattern will continue until the final setpoint
value of 2 K is reached, or another setpoint is entered. Note that Input B will be used in
all zones greater than 10 K (zones 4 to 8), and Input A will be used in all zones below
10 K (zones 1-3).
Sensor accuracy and placement will affect how smoothly the transition from one feed-
back sensor to another is performed. A large difference between the temperature read-
ings of each sensor at the time of transition could cause a temporary instability in the
temperature control due to the sudden large error introduced into the control equation.
It is highly recommended to use the Setpoint Ramping feature when using the Control
Input zone parameter to change sensor inputs. Otherwise a setpoint change may cause a
control input sensor to be used outside of its usable range, which will cause an overload
condition to shut down the control loop.
Zone
Lower Boundary
(Implied)
Upper
Boundary
P I D
Manual
Output
Range Ramp Rate Control Input
10 n/a 0 K 50 20 0 0.0% Off 0.1 K/Min Default
9 n/a 0 K 50 20 0 0.0% Off 0.1 K/Min Default
8 100.001 K 500 K 200 20 0 0.0% High 30 K/Min Input B
7 50.001 K 100 K 185 25 0 0.0% Med 20 K/Min Input B
6 25.001 K 50 K 150 30 0 0.0% Med 10 K/Min Input B
5 15.001 K 25 K 100 30 0 0.0% Med 5 K/Min Input B
4 10.001 K 15 K 85 35 0 0.0% Med 2 K/Min Input B
3 7.001K 10 K 85 35 0 0.0% Med 0.9 K/Min Input A
2 4.001 K 7 K 70.0 40.0 0 0.0% Low 0.7 K/Min Input A
1 0 K 4 K 50.0 50.0 0 0.0 % Low 0.5 K/Min Input A
TABLE 5-2 Zone settings example