User's Manual

Automation and Drives - SCE

T I A Training Document Page 32 of 64 Module

Structogram

A structogram shows the rough structure of a program plan. The structogram below shows the

possible structure of a program for a two position controller.

First, a scan is made whether the controller is switched on.

If it is switched off, only the program is executed in which the outputs and flags are reset.

From the program-engineering view, this is done most simply by means of jump instructions.

If the controller is switched on, the setpoint and actual value are entered, and the calculations for

switching hysteresis, differential and the lower operating point are made.

Then, another scan follows: whether the actual value is below the low operating point.

If this is the case, the controller output is switched on, and a jump is made to the end of the program.

If this is not the case, the high operating point is calculated, and a scan is made whether the actual

value is above the high operating point.

Then, again a jump is made to the end of the program.

Controller switched off?

YES NO

Outputs

and

Flags

Display: Switch on SH10

Enter actual value x and

setpoint w

Normalize

Clear Calculation of the switching hysteresis Xs = w/10

or Calculation of half the differential X1 = Xs/2

Reset Calculation of the low operating point Xu = w - X1

Is the actual value less than the low operating point?

YES NO

Pump ON Calculation of the high operating point Xo = w + X1

Actual value X larger than Xo?

YES NO

Pump OFF

Preface Fundamentals Discontinuous Action Controllerr Controller Block (S)FB41 Setting the System Appendix

Issued: 02/2008 Control Engineering with STEP 7