Highland Controls

That all depends on how you have it set up. What model is this? For the most part, the drive will put out max current in a locked current situation, but will only do that for a short time. Do you have the proper group 99 parameters in there? Did you do an ID run?

A typical lead-lag system will allow someone to select the lead pump manually, or automatically rotate all pumps through the lead. For example, in Auto lead, pump 1 might be the lead pump for 1 day, then pump 2 is the lead pump for 1 day, etc. The lead pump is the one that is always running. The lag pump(s) is the one that will start up if the lead pump can't keep up. The way i have done it in the past is watch for the lead pump to be at max speed for a short amount of time. If it is there for more than a couple of seconds, then start up the lag pump. You then trigger the drop out of the lag pump by watching lead speed. If is drops below a certain value, then it is OK to drop out the lag pump(after a time delay). Depending on your process, you could have more than one lag pump. I always make the lag pump the next one after the lead pump.

I have used them for a couple of simple projects. The PLC programming is clunky, although some "old-timers" don't mind it. Simple programming, but it is difficult to do anything more than the basics. Can be done, just not easily.

The ABB AC500 PLC lineup is pretty solid, but unless you are used to CoDeSys, you will have a steep learning curve. The AC500 offers a wide range of processors and options, so you only buy what you need. Your supplier should be able to work with you on the cost of ControlBuilderPlus. Even if you have to pay list, it is a one-time deal. All updates are free after that, no maintenance contract. The drawback is that tech support for the AC500 is a little light at this point, but getting better. Be sure your local supplier has a thorough understanding of it. I am fully behind the product and am using it in more applications. I had heard of issues in the past with not being able to get product, no tech support, etc. I know ABB has made a commitment to support this product in the States, and now has a product in stock, and are adding tech support personnel. Again, if your local supplier can't help you, then I would be hesitant to make that switch.

I love SFC. I don't use it for everything, but where it makes sense. It is a different mindset, but once you get it, you will want to use it more.