PLC control process instances - — Light control

Figure 5 - 2 for PLC controller wiring diagram, figure 5 - 3 to control ladder diagram. Figure 5 - 4 describes each scan cycle program execution. Button SB2, although there is no use in application, its state is still influence the state of the corresponding number of internal input relay. Figure ( a) , (1) enter the scanning process, after the state of the two buttons scanning, deposited in the image area, because the SB2 is stop button, so, even if there were no press, its input loop is closed, therefore, the X1 '1' ( ON state) , and the other a '0' ( OFF state) 。 (2) execute program process, based on the use of contact number corresponding internal relay status to operation. Because of OFF X0, therefore, the corresponding dynamic contact in the OFF state, operation result is Y0, Y1 in the OFF state, its results in the output image region, namely, Y0, Y1 '0'. (3) the output refresh process, according to the state of the image area you drive output devices, because of the output image area are OFF state, so, the output light cannot form a closed loop, the light not bright. If the input does not change, the internal state of the relay are not changed. Figure ( b) , press button SB1, X0 input loop closure. (1) input scans the input state in its image region, X0, X1 '1'. (2) the execution process, from left to right, from top to bottom, the principle of detailed implementation. The first line, X0 contact closure, but at this point, the Y1 status to '0', therefore, Y1 contact for the off state, Y0 failed to conduction, its status to '0'. The second line, X0 contact closure, so, Y1 status to '1'. (3) the output refresh process, due to the Y1 show conduction state, 2 light. Figure ( c) For SB1 button after the second scan cycle. (1) the input scan, due to the input state unchanged, the input image area remains the same. (2) the execution process, the first line, X0 contact closure, as in a cycle, Y1 is ON state, therefore, Y1 contact also closed, Y0 is also conducting state; The second line, Y1 also conducting state. Y0, Y1 state are all '1'. (3) the output refresh process, two lights. Note: due to the PLC controller scan cycle is short, the phenomenon we see with the naked eye could be both the light and bright. If the button does not change, the internal relay, output equipment status are no change. Figure ( d) After loosening SB1 button for the first scan cycle. (1) input scans the input image region X0 deposit '0', the X1 '1'. (2) the execution process, X0 off contact, Y1 is '1', because of the last cycle, therefore, Y1 contact is closed. (3) the output refresh process, due to the disconnection X0 contacts, Y0 and Y1 in off state.
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