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1.5 SAMPLE TIME

• In deadbeat type controllers we do not typically see mentions of the sample period, but in most practical systems we see a mention of the sample time ‘T’.

• We can use the system transfer function to calculate the acceptable range of controller time. In all cases the lower sample period is 0, but for practical reasons we may want to make this larger.

• A shorter sample time requires a faster computer, and steals cycle time from other processes.

• The general procedure is,

1. Find the characteristic equation of the overall system transfer function.

2. Determine the roots (symbolically) of the equation.

3. Select values of ‘T’ that ensure that all of the roots have a value of 1 or more.

4. Select a sample time that is less than the longest time.

• Consider the example below,

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