Zone Control Data Entry - Lakeshore 340 User Manual

Selecting An AutoTune Control Mode (Continued)
There are three AutoTune modes, each with different system characteristics. For most applications, Auto PI is
recommended.
Auto P. Sets the P parameter value only. I and D are set to 0 no matter what the initial values are. This mode
is recommended for systems that have very long lag times or nonlinearity that prevents stable PI control.
Expect some overshoot or undershoot of the setpoint and stable temperature control below the setpoint value.
Auto PI. Sets values for both P and I parameters. D is set to zero. This mode is recommended for stable
control at a constant temperature. It may take slightly longer to stabilize after setpoint change than Auto PID.
Expect some overshoot or undershoot of the setpoint and stable temperature control at the setpoint value.
Auto PID. Sets values for P, I, and D parameters. D is always set to ¼ the integral time in seconds and
cannot be changed by the operator. This mode is recommended when setpoint changes are frequent but
temperature is allowed to stabilize between changes. Stability at setpoint may be worse than Auto PI in noisy
systems. Expect slightly less overshoot or undershoot than the other modes and control at the setpoint value.
Once AutoTune mode is selected, the Tune annunciator will turn on when AutoTune is active. No AutoTuning
will occur until the setpoint is changed at least 0.5 K. At that time, the Tune annunciator changes to Tuning,
indicating the instrument is gathering data. This process may take from 1 to 17 minutes depending on the
system reaction time. The Tuning annunciator returns to Tune when calculations are complete and new
parameter values are stored. The annunciator will also return to Tune if the algorithm was unable to
complete. Some possible reasons are: setpoint change too small, manual control parameter changed during
tuning, heater not turned on, or control sensor curve not selected.
If the controller is not tuned satisfactorily on the first attempt, make several small (2 degree) setpoint changes
to see if better parameter values are calculated.
To select AutoTune mode, press the AutoTune key. The AUTOTUNE screen appears with the control loop
indicator highlighted in the upper left-hand corner of the screen. Use the s or t key to select Loop 1 or 2.
Press Enter or Next Setting to advance to tuning mode selection. Only one control loop at a time may use
AutoTune. Use the s or t key to select a tuning mode and press Save Screen to store the change. The
default setting is Manual PID.
6.8

ZONE CONTROL DATA ENTRY

The Model 340 allows the user to establish up to 10 custom temperature zones where the controller
automatically uses pre-programmed PID settings and heater range. The user should configure the zones
using 1 as the lowest to 10 as the highest zone in kelvin (K). Make a copy of Figure 6-1 to plan your zones,
then use the manual to record final zone settings.
To program the zones from the front panel, press
the Zone Settings key. Use the s or t key to set
the Loop to 1 or 2. Use the Enter or Next Setting
keys to advance to the first line of the zone
settings. Use the numerical keypad and the Enter
key to enter new zone values. Parameters that
can be specified are Top of the zone (in kelvin),
proportional (P), integral (I), derivative (D), Manual Output (in percent), and Heater Range. Enter these
parameters for each zone. When complete, press the Save Screen key.
Once the zones are programmed, you must place the controller in zone mode. To do this, press the Control
Setup key. Use the Next Setting key to move to the Control Mode entry, then use the s or t key to select
Zones.
Once Zone is turned on, the instrument updates the control settings each time the setpoint is changed to a
new zone. If the settings are changed manually, the controller uses the new setting while it is in the same
zone, then updates to the zone table settings when the setpoint is changed to a value outside that zone.
This feature is most effective when combined with the ramp rate feature. The user can potentially do a ramp
through all 10 zones from 1.4 K to room temperature by only changing the setpoint. The controller
automatically changes the PID and heater range settings as the temperature setpoint passes through the
different zones.
Temperature Control Operation
Lake Shore Model 340 Temperature Controller User's Manual
L o o p : 1 Z O N E S E T T IN G S
T o p P
I
1 10 0 0 .0 0 .0
2 10 0 0 .0 0 .0
3 10 0 0 .0 0 .0
10 0 0 .0
4 0 .0
5 10 0 0 .0 0 .0
M O u t % R a n g e
D
0 0 .0 0 O F F
0 0 .0 0 O F F
0 0 .0 0 O F F
0 0 .0 0 O F F
0 0 .0 0 O F F
6-5