A

I am going through the programs and will take some time to understand the total program.

As far as PID algorithm goes, well, there are several ways in which PID is implemented:

*PI*

In the first method Gain, integral time (repeats per minute) is used.

Here the gain value is multiplied by the error. And the Integral time is also multiplied by the error. Typical use that i have seen is in MOD-30 controllers from taylor (now ABB i believe).

The second method is the proportional band and integral factor (minutes per repeat).

Here the error is divided by the proportional band and error integral is divided by integral factor. Such implementation I believe is in Foxboro 761.

*BIAS*

Bias in mathematical terms is the addition to the pid equation.

*Dead time.*

Dead time factor gives the time which is required to see the effect of the gain action. or in some cases PI action. here gain action is first taken and then after the dead time, the I action is to start or the PI action starts and then the D action starts after some time.

*D*

the D factor acts either on process or on error.

i have found that the use of D on process helpful in many cases and on error in some cases.

In the first case the d element value is dependent on the rate of change of the process variable.

In the second case the D element value is dependent on the rate of change of error.

feedforward and dyanamic compensation are some other factors but those are not present in many PID implementations and can be skipped in the

first release unless the algorithm is already present.

hope this helps.

Anand

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