I wouldn't try.

Are you making a commission on the deal?

The guy runs a molding shop. How do you know he needs plc?

First, you want us to tell you how to download free manuals for forklifts, and now, you want us to sell your "friend" a technology he may not need???

WHO ARE YOU?

Never mind. I went back and looked at you. I know who you are.

Here, you need this flowchart to help you solve problems with your customers:

lol, just don't get caught in the loop....

Wow.

You asked a customer to convert their working machine to your product and you're stumped for a reason why they should do this. I hope that you're not in the sales department for your sake.

Unless you can prove to him that changing to a PLC will provide benefits AND will result in increased productivity that will pay for the upgrade (in a sensible amount of time) then there is no reason for him to change (short of a catastrophic failure of his existing relay logic system that would be more expensive to fix than replace with a new PLC system).

As always, it comes down to a simple case of economics and convenience. New technology is nice, but if it cannot be justified then it's back to the old saying "if it aint broke don't fix it".

Don't try doing it in writing....

--Editor Crankshaft

A PLC (Programmable Logic Controller) does employ relay logic!

I'm with pretty much everyone else here. If it works, don't fix it!

Actually, I thought the Engineer's Motto was "Fix it until it breaks".

If it works, and spare parts are available DO NOT FIX IT!

A system -a tiny bit larger - the New York subway system still runs on relay logic. Modern upgrade is now underway, haltingly. It will have to be done, sometimes. But, buying something new with new quirks can get lethal quickly in a citywide system.

Relays are and will be available in a foreseeable future. No problem there. The main concern with them are heat, dirt and contact wear.

The most I can recommend is a very clean air blown into the relay enclosure. All it takes a pancake fan and an absolute filter used to keep hospital operating rooms clean. The cartridges are freely available. I used them in my data centers.

Other than that, DO NOT FIX IT.

You want to keep your customer, buddy? Do not force it.

On a more positive note, here are a smattering of reasons for change.

1. The system is breaking down frequently and he wants something that will increase his up-time (benefit = productivity increase).
2. His machines are requiring frequent changes in logic and settings or "recipes" for different end products, but the set-up time to accomplish that with relay logic is costing him money or preventing him from adapting to his customer demands(benefits = productivity increase, flexible manufacturing to meet changing market conditions).
3. He wishes to implement some energy saving strategies by utilizing VFDs in his moulding machines (assuming injection moulding here) and relay logic does not lend itself well to VFD implementation (benefit = reduced operating expenses, more profit).
4. He wants to be able to properly document and archive machine operating programs and data so that he can quickly replace a controller when something bad happens, i.e. fire or flood, or apply Predictive Maintenance principles to his operation to avoid unscheduled down time (benefit = increased continuity, lower operating losses, more profit)

Get the drift here? There must be TANGIBLE MONITARY BENEFITS to the end user. If none of those is important to him, he has a point.