System/Product

Atlas

Model/Module

All

Subject TypePC Software

Subject Version

1.0Author

SVDate17/04/2008
Technical Note – Altering PID Values in Atlas Software

1 Changing the PID for specific steps
1. In the atlas software, go the recipe window.
Drag and drop an action onto
the recipe to open up the step
properties window.
If the step is already present,
double click it to open the step
properties window.
The step properties that use aPID control loop will have a PID
user editable tab.

2. Click on the PID tab to access thesevalues. The values contain in these boxes
are the default PID values. If you changethese values, you change the control
properties FOR THAT STEP ONLY. Anyother steps in the recipe will have theirown default values and may need to bechanged as well to suit the recipes needs.

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2 Changing the default PID for an Action.
Changing the default PID for an action will mean the chosen PIDs will be
automatically selected when an action is used in a recipe file.

1. 1. Firstly, click on the admin tab and then click on the manage actions toaccess all available actions.
2.

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3. The action wizard should start up when you click the select the edit option. Do
NOT change any of the values on the first window. Click next to move onto
the next screen.

4. In this screen, you can enter proportional, integral and derivative values thatwill become the default every time an action is used in the recipe window.
Make note of the originalvalues before you makeany changes. Thechanges made here will
have a direct influence inthe way the hardware
involved in this action willbehave. Make note of any
subsequent changes thatare made. That way,should a set ofparameters fail to deliver
the correct behaviour, theprevious values caninputted carry on tuning.

Once finished, click next and next again to finish the wizard and save the values.

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3 Basic Tuning Tips
If you type the words ‘PID tuning’ into an Internet search engine, you will find aplethora of website with advise and software on how to obtain the perfect proportion,
integral and derivative values for your given control loop. Here is a very basic
method for tuning a system from first principals. In the example given below,
temperature control is the loop.
Proportional Value
Start with no proportional, integral or derivative values at all and enter a value for P.
Write a very simple recipe which involves going to and maintaining a temperature e.g
10 - 20°C above room temperature.
Start by choosing a P value (e.g. 2) and see what effect that has on the profile. If P is
too low, increase it and try the same step again. Do the reverse if the P value is toohigh and there is a massive overshoot.
Once you’ve got the correct level of overshoot, deduct 10% from you P value andmove onto tuning the integral value.
P value too
highP value right for further
investigation

Parameter (E.g. °C, rpm)

Target/Set point

P value too low

Time

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Integral Value
With your P value in place from the previous section, start increasing the I value tosee what effect it has on the temperature profile. Increase or decrease the I value
until the profile reaches the target /set point in the quickest time possible, with theminimum of overshoot and the minimum of oscillation. In most cases, oscillation will
be negligible and no further tuning would be necessary.

Correct I

Not enough I
Target/Set point

Parameter (E.g. °C, rpm)

Too much ITime
Derivative
If the degree of oscillation is not suitable for your needs, start applying small
quantities of D value. The D value should be used with caution as small changes canlead to very large effects to your control loop.

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