event-driven car wash

[rbyrne15 0]

Hi, could anyone help. I am faced with a problem that requires me to write a program for a SLC-500 PLC which will run a car wash. It's a text book problem from Programmable Logic Controllers, Third Edition. Page 352, question 7. I am quite capable of programming up the bullet point no. 5 (*LS4...), but don't know how to work in the IF SELECTED part for the hot wax vale. I thought about subroutines, but didn't think it would work. Help would be appreciated, I'm a college student. Thanks. The question reads: "Using whatever PLC sequencer output instruction you are most familiar with, (in my case the SLC-500), develop a program to implement an automatic car wash process. The process is to be even driven by the vehicle, which activates various limit switches (LS1 through LS6) as it is pulled by a conveyer chain through the car-wash bay. Design the ptogram to operate the car wash in the following manner: *The vehicle is connected to the conveyer chain and pulled inside the car wash bar *LS1 turns the water input valve on *LS2 turns on the soap release valve, which mixes with the water input valve to provide a wash spray *LS3 shuts off the soap and the water input valve remains on, to rinse the vehicle, *LS4 shuts off the water valve and activates the hot wax valve, IF SELECTED *LS5 shuts off the hot wax valve and starts the air-blower motor *LS6 shuts off the air blower. The vehicle exits the car wash" -Richard-

[Chris Elston 79]

They have TEXT BOOK examples that require you to use sequencers? Ack... I never use a sequencer to program an automated machine. It found that it's not very flexible and hard to intergrate conditional inputs into a sequencer design to make it a "safe automation machine". Using regulator outputs, a program could be written fairly simple. Latching a rung and unlatching the next rung on the next sequence or input trigger. Always use "control bits" then map your final controls bits to an output at the end of the file. There are tons of example programs to show this. This would be a good program to look at: http://forums.mrplc.com/index.php?act=Downl...s&CODE=02&id=19 If you HAVE TO do a sequencer...then check out these two examples uploaded by some of our members. http://forums.mrplc.com/index.php?act=Downl...s&CODE=02&id=26 http://forums.mrplc.com/index.php?act=Downl...s&CODE=02&id=25

[Sleepy Wombat 27]

Its a pity that you just could ask BOB... Back Of Book

[rbyrne15 0]

Thanks for the links, I'll have to look at them in greater detail. Yeah I tried looking in the teacher's solution guide for an answer and it said that the solution depended on the PLC used - the book covers PLC-5 and the SLC-500 in its examples. There's also limited coverage of the PLC-2. Thanks again, Richard.