time diagram

Do you think that to write a good ladder program do we need to
draw time diagram of all inputs and outputs ( happen in a cycle )
?
Thanks in advance

It's not essential, but it's very good design practice, and is very heavily used in electronics design. A well-written timing diagram will help you with most aspects of writing good quality code.
(a) Plan the code, taking into consideration rate requirements, cycle times etc.
(a) Write the code (use the timing diagram as the spec)
(b) Commission the code (check operation against spec)
(c) Document the way the system works for yourself and others
(d) Help identify ways to speed up the machine or system

I would go for a timing diagram only for certain sub-task, if it is

1. Complex
2. Acts too fast
3. Which is difficult to achieve within the existing PLC Scan time.

Regards
_______

Any type of design method can help and a timing diagram is definitely one. Others you can use are sequential function charts (which are not mainly a means of programming, but of designing), Nassi-Schneidermann diagrams, flowcharts dynamic state diagrams and some others I might not even have heard of. You do have to start by dividing the program up to manageable part. The worst you can do is typing in the program without any preparation at all.

Kind regards,

It all depends on the desired end result. If the program is to be time based, like a drum timer then a timing diagram would be a good choice to start with. However if it's not a pure timing application, then a flow chart or truth table might be a better choice.

I supply a blank timing diagram to our mechanical designer that he fills out so that he can double check his design intent and the customer can sign off on it. It includes cylinder sizes for any fluid power devices so I can determine hydraulic pump and valve sizes and air prep requirements. We then include a copy of the diagram in the mechanical, electrical, and fluid power drawing sets. Its normal practice in the automotive special machinery business and for many of our customers, a requirement. I find it handy because I don't have to pester the mechanical folks about how the machine is supposed to work and it gives all of the expected cycle times of each element so I can easily set up my timers for over-cycle time measurements.

Your ideas are experiences to me
To me , I think that when you dont use time diagram , you can easily repair your instructions better than have to concern with time diagram , it just for the clever and short solution but hard to modify for adaptting to another change when needed .

Hi Smiles

Here's another spin on the topic. In the life sciences industries such as Pharmaceuticals, Medical Devices, Complementary Medicines etc, there is such an activity called "validation". We have to validate all our system / equipment, process etc. One of the most critisied aspects of automated system / equipment is PLC programming or should I say code design. Because usually there ain't none. This gives validation engineers a headache because most PLC systems are designed for specific customer needs and this means bespoke / customised code. This means full on validation.



So my point is going to be that PLC programmers should begin the design of their systems with standard system analysis & process design tools / charts / diagrams / flowcharts /pseudo code. What ever it takes to develop good PLC code that can be easily (financially & technically) maintained. This gives guys like me something to compare against the ladder logic so I can say hey (white box testing) this code is well written there are proper safety aspects it is fail safe and I reckon it will work, now lets black box test it.



But if you are just programming for fun so that you can open the door on the dog kennel then go for your life and hack the **** out of it.



Regards

PaulS

It just depends.
I have written one PLC program that was exactly 7 rungs long.
For that I needed no timing diagram.

I see timing diagrams as more of a help when you get into motion controllers and things of this nature.

PaulS said:

So my point is going to be that PLC programmers should begin the design of their systems with standard system analysis & process design tools / charts / diagrams / flowcharts /pseudo code. What ever it takes to develop good PLC code that can be easily (financially & technically) maintained. This gives guys like me something to compare against the ladder logic so I can say hey (white box testing) this code is well written there are proper safety aspects it is fail safe and I reckon it will work, now lets black box test it.

Click to expand...

The way things have been going lately (wrt safety and accountability) I believe that it wont be too long before a lot more industries will be doing the same. The days of "just do it" are most defintely numbered.