Electrical schematic and sundry questions from a PLC virgin.

ericvfsu

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E
My most immediate concern is how to represent my PLC (inputs, outputs & logic) in my electrical schematic that I need to provide to my customer Yesterday. I have other concerns as you will see below.

I am controlling 2 motors. Each motor has a 3 position selector switch (on, off, auto). I have the electrical schematic down for the motor starters, the "on" portion of the 3 position switch, and the "off" portion of the 3 position switch. Pretty simple stuff.

How do I represent the "auto" portion - which is controlled by a PLC?

The input to the PLC is the system pressure provided by a pressure transmitter (mA). The output is to close the relay that provides the signal to the motor starter. Motor A should start when the system pressure is < 270 psi. Motor B should start when the system pressure is < 260 psi (either because motor A did not start or because more flow is needed to keep the pressure from dropping). Both motors should stop when the pressure is > 300 psi. The designation of Motor A & Motor B is switched each time that Motor A is started so that motor/pump life of the two systems is equal.

A further question is how to represent the pressure transmitter (mA) in the electrical schematic? Also, can you recommend an internet available resource that will have me quickly up and programming the PLC (DL05 PLC from Automation Direct using DirectSoft 32 software)?

I understand the logic (in IF ... Then ... sentences - referring to the I/O addresses) needed to accomplish my task, but don't quite know how to translate that into my software (the manual is useless for the task). I am also completely lost on how to read (and scale) my signals from the pressure transmitters.

Help Please!!??
 
If you sign up it would be easier to anwser your questions.
At this point I don't know where you work. What I have seen in my work in forgein countries is that every country has a couple of way's to set up a set of drawings. Some I like and some I like a little bit less because they are not clear enough.

So for that part specify where you customer is, country or part of the country.

For the programing of the PLC direct PLC I can only tell you to carefully look at the calculation part of your program.
The numbers in the registers are handeld a little bit different then the "common" PLC brands like siemens, mitshubishi.
The main thing is that the numbers are HEX. Keep that in mind when you make equasions and scalings in the program.

Futher more I have a question for you.
It's a discussion that I had with different customers. For my line of work it's what the customer wants.......he gets. But I try to help him by giving him my vision on things. And in the end you wil end up with a nice system.
But back to your project.
The designation of Motor A & Motor B is switched each time that Motor A is started so that motor/pump life of the two systems is equal.

If you look at this way of thinking from a maintance point of view you wouldn't want it.
In this way you will end up with two machines that need service at the same time ! For some plants you want this becaus they go down for a number of day's every so often. At this point you can do maintance at both machines at the same time.

On the other hand when you have smaller plants that don't have a maintance scedule in advance. It can cause problems. Because sooner or later you will have to do maintance on both systems. With the chance that you run without air in the end. That's not something you want. Because "Murphy's law is just around the corner" and that is everywhere the same acrosse the whole globe and back. I found out the hard way !! :D

What a nice option would be is that the customer has a choice wich machine is running first and what machine is running as backup.
A little switch. Machine A master or Machine B master would do the tric.

When you want to make a nice little something extra you can keep track of the running hours for every machine. Installing a maintance light for every machine. Set to light up after X-hours.
After doing maintance you can reset them with a hidden button inside the cabinet.

Hope it helps a little. I have some more nice idea's but then I have to know a little bit more about your aplication.

Jurgen
 
maybe this will help ...

Greetings ericvfsu,

you said:
My most immediate concern is how to represent my PLC (inputs, outputs & logic) in my electrical schematic that I need to provide to my customer Yesterday.

this is QUICK example of one (there are others) fairly common method of taking care of your most pressing problem ...

[attachment]

if you’ll refer to the wiring diagrams provided with your input and output modules, they will probably use something very close to this approach as examples of “how to” wire the field devices ... you can probably just copy the same layout for your diagrams and provide the correct terminal numbers and switch contact schemes as necessary ...

as for all of your other problems ... I’ll personally be tied up all next week but there are many people on this forum more qualified than I am who will be able to help ... but ... you need to provide a LOT more detail to make the project do-able ...

I’d suggest that you post a DETAILED list of the exact hardware you’ll be using ... complete with model numbers ... and show exactly how everything will be plugged together ... that way the guys trying to help will be able to use specific addresses (example: X14) rather than just general terms (example: the auto position of the 3-position switch) ... basic idea: with the exact addresses, they can even help you write the program logic if necessary ... without the addresses all they can offer is usually just general advice ...

final thought: rather that just saying “how do I do this?” try posting what you’ve already done (or plan on doing) ... then let everyone tell you what you need to change to make it right ... remember ... we can’t see the system ... you can ... the more you tell us, the better the final results will be ...

good luck ... and don’t forget to register ...

PS ... the Inputs and Outputs are usually shown in the wiring schematics ... the PLC logic is generally not shown on a wiring schematic ... if you need to diagram that, it's usually done in something like a programming flow chart ... with diamonds for decisions, boxes for actions, etc. ... do you need help with that type of diagram? ...

wiring.jpg
 
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