Mitsubishi Electronics FX1S manual T001 K20 K50

FX Series Programmable Controllers STL Programming 3

•When an STL step transfers control to the next STL step there is a period (one scan) while both steps are active. This can cause problems with dual coils; particularly timers.

If timers are dual coiled care must be taken to ensure that the timer operation is completed during the active STL step.

If the same timer is used in consecutive steps then it is possible that the timer coil is never deactivated and the contacts of the timer will not be reset leading to incorrect timer operation.

The example opposite identifies an unacceptable use of timer T001. When control passes from S30 to S31 T001 is not reset because its coil is still ON in the new step.

S 30

T001

S 31

S 32

K20

T001

T001

K50

T001

Note: As a step towards ensuring the correct operation of the dual timers they should not be used in consecutive STL steps.

Following this simple rule will ensure each timer will be reset correctly before its next operation.

•As already mentioned, during the transfer between steps, the current and the selected steps will be simultaneously active for one program scan. This could be thought of as a hand over or handshaking period.

This means that if a user has two outputs contained in consecutive steps which must NOT be active simultaneously they must be interlocked. A good example of this would be the drive signals to select a motors rotation direction. In the example Y11 and Y10 are shown interlocked with each other.

S30

S 31

Y10

Y11

Y11 Y10

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