INDUSTRIAL CONTROL CIRCUITS 215

INDUSTRIAL CONTROL CIRCUITS 215

INDUSTRIAL CONTROL CIRCUITS 215

industrial control circuits 215

industrial control circuits 215

INDUSTRIAL CONTROL CIRCUITS 215 (2) When the beam UP-push button b1 is pressed , up contactor U is energised through closed contacts B1, b1, A1, D2 and LS1 . Energisation of contactor U will cause operation of loading solenoid valve SV5 and also up solenoid valve SV1 through contacts U5 and U6 and therefore the beam will start moving up. (3) Contactor U gets hold through its contact U1 before the opening of contact B1 as a result of de – energisation of contactor B . Contactor B gets de-energised due to opening of contact LS4 in line 20 when the beam moves in the upward direction . (4) When the beam reaches its upper limit , limit switch LS1 is actuated . Its NC contact opens and de – energises contactor U. De-energisation of contactor U stops movement of the beam in the upward direction due to de – energisation of solenoid valves . (5) Acutation of limit switch LS1 also closes its NO contact in line 5 and thus supply reaches the Forward-push button b2 . (6) When Forward-push button b2 is pressed contactor F gets energised through close contacts LS1, b2, A2, R2, and LS2 in line No . 5 . Energisation of contactor F also helps energistaion of the respective solenoids through its contacts F5 and F6 . The beam moves in the forward direction till limit swtich LS2 is actuated . (7) On actuation of LS2 forward contactor F is de-energised and the beam movement in forward direction stops while supply reaches Down-push button b3 through the closed contact of LS2 in line-8 . (8) The beam can be run in down motion by pressing push button b3 . When the limit switch LS3 is actuated , the beam can be run in reverse direction by pressing its push button b4 . Limit switch LS4, when actuated stops the reverse motion of the beam . This way one cycle of beam movemnt is completed . In practice , the beam is not run in this fashion . It is run mostly in auto operation . The manual push button b1 to b4 are mostly utilized only to reset the beam if it stops inbetween due to power failure . ( b ) Reset mode of operation of walking beam . Reset mode is required to reset the beam since neither the manual nor the auto cycle can be started if the beam positon is such that no limit switch gets actuated . The beam will stop in any intermediate position during its travel cycle if there is power failure . On restoration of power the beam cannot be made to run in manual or auto mode from such intermediate position . For example let us examine the case when the beam has stopped while moving in forward direction due to power failure . In such a case , both the limit switches LS1 and LS2 are in deactuated condition . The beam cannot be run in forward direction as contact of LS1 in line 5 is open and hence supply does not reach upto push button b2 . To make the push button effective the beam should be reversed to actuate LS1 or alternately the beam should be taken to fully forward condition to actuate LS2 so that operating cylcle can be started for downward motion . The beam is reset to actuate LS1 or LS2 with the help of reset-push button b6 . When the beam is to be reset , first the selector switch SW is put on reset mode , This will energise the reset control bus L-R . Now b6 is pressed which energises contactor C. Its contact C5 closes and energises the manual control bus L-M . Also the control contacts C1,C2,C3 and C4 close to bypass the contact B1 and normally open contacts of LS1, LS2 and LS3 . Thus supply reaches at all the push buttons from b1 to b4 . The required push button can now be pressed along with b6 to complete the beam movement in a particular direction . Push button b6 is released when the beam reaches the required limit and the concerned limit switch has actuated . Then the selector switch is returned back to Manual or Auto mode as per requirements .

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