Beginner question PLC Q

RoryJ

Member
Join Date
Sep 2010
Location
uk
Posts
5
I have just finished my first PLC lesson and have been asked to design a PLC program to operate a car alarm system. The question is as follows:

Once the car burglar alarm is armed the alarm will sound when the door is opened. It will continue to sound for 5seconds then it will automatically switch off.
A manual reset must be included in the case of an accidental switch on.

I know what components to include within the program i am just unsure as to what order they go in.
Any help would be appreciated along with any other very basic PLC starting material.

Thanks Rory
 
You say you know the components to include -- what are they?

How do you think you should attack this homework problem? We'll help you, but we won't do it for you...
 
i will need inputs (arming switch, a door sensor and manual reset) also will need an internal (timer) and an output (the alarm).
The arming switch should come first followed by the door sensor then I'm lost.
 
Take a look at a different angle.

Programing is about making outputs react to inputs.

Not sure if you have had boolean Algebra but it is how I would attack this problem.
Read below and note that the bold words are your conditions.

IF (Alarm is armed) AND (door switch is on) AND (Manual reset is off) THEN (Alarm horn timer IS on)

IF (Alarm horn timer is timing) THEN (Alarm Horn is on)

IF (Manual Reset is on) OR (Alarm Horn timer is not timing) THEN (Alarm horn is off)

Now all you need to figure out is how to convert the IF, AND, THEN to ladder logic if you are programing in ladder logic.

The point here is breakdown what you want the code to do then worry about the addresses. Sit down with pencil and paaer first, draw out the code using the discrpitons then worry about the actual programing.

The secret to writing goods code is knowing EXACTLY what you want to do. The method I showed you above is what I do every time.
 

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