Lakeshore 336 - Page 86

74 cHAPTER 5: Advanced Operation
Model 336 Temperature Controller
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AutotuneQInput (A, B, C, D)Q(Autotune P, Autotune PI, Autotune PID)
Stage Description Purpose for Stage Reason for Failure Possible Solution
0 Testing initial conditions Determine if Autotuning can be initiated
Curve not assigned to Input, heater not
on, or temperature not within
5 K of setpoint
Ensure curve is assigned to
input, heater is on, and
temperature is within
5 K of setpoint
1 Waiting for temperature to settle
Ensures that temperature is not still
settling toward the setpoint, or drifting
away from the setpoint
Temperature was moving too much to
properly Autotune
Allow the temperature to
settle more before initiating
Autotune
2 Testing for temperature stability
Ensures that there is no temperature
oscillation, or excessive noise in the
temperature reading
May indicate that the initial P value is too
high
Use a smaller initial P value
3
Observing system response to
setpoint change
Control parameters are changed based
on observation
System response is too slow, or the heater
is too underpowered for the system to
Autotune
If not already using High
range, increase initial
heater range
4
Waiting for temperature to settle
after returning setpoint to
original value
Provides a baseline for
subsequent stages
System response is too slow to Autotune,
or the new control parameters are caus-
ing instability in the control
Use a smaller initial P value
5 Testing for temperature stability
Ensures that there is no temperature
oscillation or excessive noise in the
temperature reading after control
parameter adjustment
System response is too slow to Autotune,
or the new control parameters are
causing instability in the control
Use a smaller initial P value
6
Observing system response to
setpoint change using new control
parameters
Control parameters are changed again
based on observation. This is the final
stage of P only Autotuning
System response is too slow to Autotune,
or the heater is too underpowered for the
system to Autotune
If not already using High
range, increase initial
heater range
7
Waiting for temperature to settle
after returning setpoint to original
value
Provides a baseline for subsequent stages
System response is too slow to Autotune,
or the new control parameters are caus-
ing instability in the control
Use a smaller initial P value
8 Testing for temperature stability
Ensures that there is no temperature
oscillation, or excessive noise in the tem-
perature reading after control parameter
adjustment
System response is too slow to Autotune,
or the new control parameters are caus-
ing instability in the control
Use a smaller initial P value
9
First of 2 stages of observing
system response to setpoint
change using new control
parameters
Compiles data for characterizing
the system
Will not fail in this stage Not applicable
10
Second of 2 stages of observing
system response to setpoint
change using new
control parameters
Control parameters are changed again
based on observation. This is the final
stage of PI and PID Autotuning
System response is too slow, or the heater
is too underpowered for the system to
Autotune
If not already using High
range, increase initial
heater range
TABLE 5-1 Autotune stages