Purpose of set-retentive coils?

[gravitar 3]

Help me out with this, guys.. I'm familiar with the concept of set/reset coils. It's the same as latch/unlatch in an A-B PLC, it seems. But this whole "M" coil thing.. give me an example that I can grasp of what this would be used for! Especially SM/RM coils.. What is the benefit of adding retentiveness to a set output? This program I'm dealing with is full of SM/SR's.

[Steve Bailey 118]

The -( S )- and -( R )- pair are not retentive when you stop/restart the PLC, either by cycling power or by switching out of run. The -(SM)- and -(RM)- pair are retentive upon restart. When the PLC stops, all outputs get turned off. Retentive means if the coil is ON when the PLC stops, then when the PLC restarts, the coil will take the ON state unless there is something in ladder logic that says otherwise. Other PLC brands manage this by defining certain PLC addresses as retientive upon restart or by making you declare a variable to be retentive or non-retentive. One of Versa Pro software's major flaws, in my opinion, was that it made you declare a variable as retentive or non-retentive, but it defaulted to retentive. Proficy Machine Edition software returns to the way that Logicmaster used to handle it, by making the instruction retentive or non-retentive, rather than the variable. You should also be aware that a standard coil (as opposed to a Latch) can also be retentive. Use the -(M)- coil instruction instead of the -( )- coil. Edited 6 Aug 2008 by Steve Bailey

[morgandeo 0]

hi, Sorry friend because i am new in this forum, but if i have any solution from anywhere definately i will give you the solution.