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Issue 2,   Nov-98.  Applies to software versions 1.3 & 1.4                           -10-                                                                                         HA026270

A

UTOMATIC 

T

UNING

In PID control, the output from the controller is the sum of three
terms: Proportional, Integral and Derivative.  These three terms
deliver just the right amount of power to hold the temperature at
setpoint without oscillation.  For stable control, the PID values
must be ‘tuned’ to the characteristics of the process being
controlled.  In the 2132 and 2116 this is done automatically using
advanced tuning techniques.
Automatic tuning is performed by switching the output of  the
controller On and Off to induce an oscillation in the measured
temperature.  From the amplitude and period of the oscillation, the
PID values, shown in the table below, are calculated.

Parameter

Display

Meaning or Function

Proportional

band

The bandwidth in 

°

or 

°

 over which the output

power is proportioned between  minimum and
maximum.

Integral time

Determines the time taken by the controller to
remove steady-state error signals.

Derivative

time

Determines how strongly the controller will react
to the rate-of-change of temperature.

Low cutback

 

The number of 

°

or 

°

 below setpoint at which

the controller will cutback the output power to
prevent overshoot on heat up.

High

Cutback

The number of 

°

or 

°

 above setpoint at which

the controller will increase the output power to
prevent undershoot on cool down.

Relative

cool gain

 

Only present if cooling has been configured.
Sets the cooling proportional band by dividing the
Pb value by the 

 

 value.

If the process cannot tolerate 100% heating or cooling during
tuning, the power can be restricted by the heating and cooling
limits in the Output list.  However, the measured value must
oscillate to some degree for the tuner to determine values.
Tuning is normally performed only once during the initial
commissioning of the process.  However, if the process under
control subsequently becomes unstable (because its characteristics
have changed), you can re-tune again at any time.
It is best to tune starting with the process at ambient temperature.
This allows the tuner to calculate more accurately.

Heating and Cooling Output Cycle Times

Before commencing a tuning cycle, set the values of 

!$!%

(heating output cycle time) and  

!$!! (cooling output cycle time)

in the 

 (output) list.

For a logic heating output (switching a SSR), set 

!$!% to & sec.

For a relay output, set 

!$!% to && sec.

For a logic cooling output used to control a solenoid valve, set
!$!! to & sec.

Tuning procedure

1.  Set the setpoint to the value at which you will normally operate

the process.

2.  In the ‘

’ list, select ‘'

’ 

and set it to

 ‘

3.  Press the Page and Scroll buttons together to return to the

HOME display.  The display will flash ‘

'’ to indicate that

tuning is in progress.

4.  The controller will induce an oscillation in the temperature by

turning the heating on and then off.

5.  After two cycles of oscillation the tuning will be completed

and the tuner will switch itself off.

6.  The controller will then calculate the tuning parameters and

resume normal control action.

If you want ‘Proportional only’ or ‘P+D’ or ‘P+I’ control, you
should set the ‘

’ or ‘’ parameters to    before

commencing the tuning cycle.  The tuner will leave them off and
will not calculate a value for them.

Typical automatic tuning cycle

Calculation of the cutback values

When low cutback or high cutback is set to ‘

(’ their values

will be fixed at three times the proportional band, and will not be
altered during automatic tuning.  If set to any other value, they will
be calculated as part of the tuning process.

MANUAL TUNING

If for any reason automatic tuning gives unsatisfactory results, you
can manually tune the controller.
Proceed as follows:
With the process at its normal running temperature:
1.  Set the Integral Time ‘

’and

 Derivative Time ‘

’ to   .

2. Set 

High Cutback 

%)’ and Low Cutback ‘)’, to ‘’

3.  Ignore the fact that the temperature may not settle precisely at

the setpoint

4. Reduce 

the 

proportional band ‘

)’ until the temperature just

starts to oscillate.  If the temperature is already oscillating,
increase the proportional band until it just stops oscillating.
Allow enough time between each adjustment for the
temperature to stabilise. Make a note of the proportional band
value ‘B’ and the period of oscillation ‘T’.

5.  Set the PID parameter values according to the formula below:

Type of control

Proportional

band ‘

Integral time

Derivative time

Proportional only

2xB

OFF

OFF

P + I

2.2xB

0.8xT

OFF

P + I + D

1.7xB

0.5xT

0.12xT

Setting the cutback values

The above procedure sets up the parameters for optimum steady
state control.  If unacceptable levels of overshoot or undershoot
occur during start-up or for large step changes in temperature, then
manually set the cutback parameters 

) and %).

Proceed as follows:
1.  Set the low and high cutback settings to 3 x the proportional

band (that is to say, 

) = %) =  3 x *).

2.  Note the level of overshoot or undershoot that occurs  for large

temperature changes (see the diagrams below).

In example (a) increase 

) by the overshoot value.  In example

(b) reduce 

) by the undershoot value.

  

Example (a)

           Example (b)

When the temperature approaches the setpoint from above, you can
set

%) in a similar manner.

Manual reset

When 

 =     manual reset (' ) appears in the + 

This parameter sets the output power when the error signal is zero.
It can be manually adjusted to remove steady state error - the
function normally performed by the Integral term.

Time

Temperature

Temperature

Time

Undershoot

Overshoot

Time

Temperature

Summary of Contents for 2116

Page 1: ...e latching ears click back into place to maintain the IP65 sealing Output ratings Logic Output 9Vdc 12mA non isolated from sensor input Used for Heating Cooling or Alarm Relay Output 2A 264V ac resistive Used for Heating Cooling or Alarm Contact Closure Input replaces Logic Output Used for Alarm Acknowledge or Timer start reset Wire Sizes The screw terminals accept wire sizes from 0 5 to 1 5 mm 16...

Page 2: ... TO ADJUST THE REQUIRED TEMPERATURE SETPOINT Press and release quickly the or button The setpoint will be displayed for 2 seconds TO VIEW THE DISPLAY UNITS Press and release quickly the or button The display units will be flashed for 0 5 sec If you get lost pressing and together will always return you to the HOME display If at any time no key is pressed within 45 seconds the display will always re...

Page 3: ...ge setpoint limits and access the in built timer Change input and output limits TO ADJUST THE ALARM SETPOINTS TRIP LEVELS Alarm setpoints are found under the list Press twice to choose the list Note The other parameters listed on pages 4 and 5 are accessed and adjusted in exactly the same way as this example Keep pressing to select more list headings eventually returning to the HOME display This i...

Page 4: ...larm type setpoint limits Alarm 3 Setpoint Full Scale Low Full Scale High Deviation Deviation High Deviation Low Alarm Hysteresis to in display units This value is common to all alarms Hysterisis is used to prevent the alarm output chattering by setting a difference between the alarm switch ON and switch OFF points Loop Break Time to minutes Home List Alarm List Autotune List PID 2 List Setpoint L...

Page 5: ...o seconds Cold Junction Temperature measured at rear terminals Read only Millivolt Input measured at the rear terminals Read only Process value Offset to display units Calibration Password to User Calibration Enable Re instates factory calibration Re instates user calibration Low Calibration Point to display units Low Point Calibration Offset to display units High Calibration Point to display unit...

Page 6: ...ill switch to standby mode The MAN beacon will light and will be flashed in the main display The process will cool down The timer will remain indefinitely in this state until reset When Reset will stop flashing The controller will return to reset in standby mode It can be returned to automatic control by setting the parameter in the HOME list to Mode 2 Dwell No Switch Off High alarm 2 has been sel...

Page 7: ...art when is within 1 o C of the target setpoint TO START AND RESET THE TIMER There are two methods Method 1 This is the simplest method to control the timer Press until you reach the list Press until you reach the parameter time remaining TIP Promote to the HOME list for quick access as described in To Hide Revealing and Promote Parameters As soon as a value is entered into timing will commence wi...

Page 8: ...larm Configuration The list configures the three internal soft alarms and causes the appropriate alarm message to be flashed in the HOME display At this stage the alarm is indication only known as a soft alarm To make the alarms operate the relay or logic outputs follow the instructions under Relay and Logic input output Configuration Alarm Type Meaning Alarm 1 The alarm is disabled Full Scale Low...

Page 9: ...ions can be added to the relay or logic output by repeating steps 4 5 and 6 above Two decimal points will appear in those functions that has been added to the output Continued in the next column To Clear Alarms from an Output 1 Press until to reach 2 Press or to select 3 Leave for 2 seconds The display returns to which disconnects all alarms from the relay Passwords Passwords Range Default Full an...

Page 10: ...ons together to return to the HOME display The display will flash to indicate that tuning is in progress 4 The controller will induce an oscillation in the temperature by turning the heating on and then off 5 After two cycles of oscillation the tuning will be completed and the tuner will switch itself off 6 The controller will then calculate the tuning parameters and resume normal control action I...

Page 11: ...n these instructions is subject to change without notice While every effort has been made to ensure the accuracy of the information Eurotherm Controls shall not be held liable for errors contained herein Unpacking and storage The packaging should contain the controller with two panel retaining clips and this instruction leaflet If the packaging or the controller are damaged do not install the prod...

Page 12: ...oming detached from the process thermocouple wiring becoming short circuit the controller failing with its heating output constantly on an external valve or contactor sticking in the heating condition Where damage or injury is possible we recommend fitting a separate over temperature protection unit with an independent temperature sensor which will isolate the heating circuit Please note that the ...

Page 13: ...Issue 2 Nov 98 Applies to software versions 1 3 1 4 13 HA026270 ...

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