One HMI To Multiple PLC's Best Practice

If I'm buying a machine that will be custom made for me, I will specify the controls to match my spare parts and knowledge on site (or software licenses already purchased) to save money in the long run (in terms of parts and possibly down time).

If I'm buying a machine that is mass made (within reason for industrial equipment), I won't bother specifying how the task is achieved. And although I would have other reasons, the major one is that if someone mass makes anything, they would have put in a lot of time testing and improving the system... a lot of them will even issue bug fixes or product bulletins with fixes or changes to the machine post sale.
If I deviated from their spec, no one is going to put that time in for that one customer in another country and I'm left to my own devises (or paying to get people in) to sort an issue.

Sadly, I've seen this happen in two occasions... one that I'm trying to sort out now and another one with massive (as in millions of dollars of parts and downtime) repercussions because the people in charge of the automation decided that they did not want to have a computer running their control system.
 
Making them identical is the perfect solution for a perfect world. Enjoy it for as long as you can.

Unfortunately it is only a matter of time before they stop being identical :)
 
....Unfortunately it is only a matter of time before they stop being identical :)

I have found they stop being identical after the first one.

Even when working at a machine builder that was making the same models for years everyone was different mechanically and in the controls I had to build for them - no 2 ever went out identical even when a customer ordered 2 together.
 
Allen,

I built a pair of 'sister' machines years ago for an automotive supplier - they were plates on a conveyor that indexed 2" then 3 torque drivers placed screws in to a certain "screw flange to part surface" height.

I built the machines using Crouzet micro-PLC's and they ran fine, even putting out more parts per hour than the customer was asking for and at a better rejection rate than demanded.

BUT - when the customer opened the control panel and saw the 'toys' running them he had major problems. He complained about every aspect of the operation after that and called me back a couple months later, handed me 2 MicroLogic's with 32IO (the machines were running on 10 IO) and demanded I replace the 'toys' and rewrite the program for the ML's. (On the positive side he did pay for the conversion and not demand it be done free)

Maybe if someone made a micro-PLC about the size of a fixed SLC500?


you could go with a Micrologix 1400 or if you prefer using studio 5000 the compactlogix L24ER-QBFC1B. Both would be much cheaper than the controllogix.controllogix would likely be overkill to work a tank.
 
diat,

each tank is going to have the voltages and current monitored from 2 rectifier power supplies, calculating the watt/hours applied to the product for precise replenishment of the chemical, along with monitoring the pressure and flow rate of 2 7-1/2HP pumps controlling them with separate VFD's. And just to put a little pressure on the replenish chemical is a dry powder fed by an auger system that needs a precise amount by weight and the setup from the supplier has no feedback or allowance for voids and clumps in the powder.

Plus, just this week, they added the need for 2 stages on the pumps - after 30 minutes drop the pressure to about half for the rest of the cycle.

And - for the cycle they are not sure yet if it will be by time or by watt/hours, and maybe if it is watt-hours they may want different amounts for the front and the rear cycles.

Then there's next week.....

And IF this chemical does the job it is supposed to do my customer has a customer with a multi-million dollar job waiting. (Maybe I should make these free and charge a licensing fee?)
 
Aabeck, none of the things you mention require a ControlLogix, and none of them will be easier with a ControlLogix vs. A CompactLogix.

I would definitely go with a new 5069 series CompactLogix unless you need thousands of I/O or some other extreme need.
 
Rupej,

The exact PLC has not been spec'd yet - it probably will be a CompactLogix - just being old and set in my ways the entire family is ControlLogix to me.
 

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