That's the way to go nowadays IMO. The last brand new Davis Standard extruder I saw, still had individual PID controllers for the barrel zones. The last 2 extruders I modernized, don't have zone controllers any more. All the PID loops are in the PLC. One PID controller was more than the cost of a thermocouple input card which serves 4 zones. Doing the PID in the PLC opens doors for really dialing in the control if the application demands it. Your PID can have modifiers for extruder speed or product type other variables so that it performs proactively rather than reactively.

Our last purchase was a Kuhne and it's like that with a nice touch panel HMI. We've got a few older Wayne units that we gutted and retrofitted with Automation Direct controllers, one controller per zone.

 

It only takes a few hours of lost production to make up for the saving in fuse costs by substituting breakers, and then not having a spare breaker or not having the electrician to change it. Some of those cute little CT current sensors have been tied to PLC inputs for automated machine watching, unfortunately I did not get any details about just how that was done.

Breakers are not a good idea for electric heating elements, even with a light load as the thread starter has mentioned. Today's heater systems use, for the most part, either SCRs or SSRs to power the heating elements. In short semiconductor devices. Less getting into the l2t ratings of the semiconductors used breakers are not a good idea or design practice. There are ultra fast fuses designed especially for heater applications. They are ultra fast blow fuses to prevent damage to the heater element driver source. It's simply good design practice. I am not saying do not use breakers but rather in my opinion I do not see using breakers with heating elements as a good solution. Fuses are lower cost than replacing a SCR control and a box of spare fuses is a good to have.

Back on target with for a single phase 120 VAC element a single fuse on the hot leg is fine. However in a 240 VAC configuration both L1 and L2 should be fused.

Finally my last experience with extruders was circa 1966 when I worked in an injection molding plant.

Ron

 

You already contradicted me and stated your case rather combatively in post #32. I didn't address it because you seemed to be begging for an argument that I wasn't interested in. Now out of nowhere you're bringing it up again. Are you going to keep doing that until I give you what you need to scratch that itch?

If so, here you go:

Is having to replace breakers something that's normal in your experience? Is not having spare breakers (or heaters or controllers or SSRs or anything that is used plant-wide) something that's normal in your experience? How about not having a single person on staff competent to replace a breaker? My experiences of not having the correct fuse on hand is one of the things that led me to suggest breakers. I've watched marginally skilled maintenance technicians blow several fuses in a row before they find the problem, and I've done it myself back before I knew my ass from a hole in the ground.

Bean counter buys a box of ten fuses thinking that should be more than enough, because after all, "every zone would have to blow its fuse for them to run out." Then the night shift extruder operator (Alberto "Executive Decision" Ramirez) who isn't supposed to even know how to open the control cabinet, goes through 8 of them before admitting defeat and leaving it for maintenance to fix in the morning. Then Sparky "Wet Behind The Ears" Tech comes in, checks the heater for shorts, all good, puts the last two fuses in, and turns it on not realizing that there's a 3kW heater plugged into the outlet designated for a 500W heater. He figures out why the last two fuses blew by chipping the molten plastic off the heater to reveal the laser-etched rating. He plugs it back in where it goes, but now there are no more 2.5A fuses to put in. All the 3A and 5A fuses are gone too, from similar incidents or from someone taking the entire box from the spares cabinet and absent mindedly leaving it in some other cabinet somewhere. So, "just to get the line back into production," he puts in the smallest value fuse that he can find which fits: 10A. He informs bean counter who orders 10 more, with the plan to put the correct fuses in when they arrive. That never happens.

1 year later the same operator does the same thing. Different maintenance tech does the same/similar thing. This maintenance tech notices the 3kW heater with "only" 10A fuses installed. "Well, there's your problem!" He says. "Some idiot put 10A fuses in here when a 3kW heater should have 15A fuses." So he puts in the "correct" fuses for the 3kW heater. Everything is great now! All good. Except for some reason the SSR failed shortly thereafter, probably for some unrelated reason.


There are similar devices with switches instead of LEDS. They're a lot more expensive though. You could probably just cut the LED off the others and figure out empirically what kind of rectifier/voltage divider situation would satisfy a PLC input.

I have had to replace 3 GFCI devices that were destroyed by short circuits, which did also trip the breaker. That was the reason for my suggestion. Also, I have had a commercial (40 cubic feet) freezer get switched off and thaw because of leakage in the defrost heater tripped the GFCI breaker. Fortunately the power off was noticed before all the meat thawed and spoiled. The freezer is now on a non-gfci outlet, running happily for many months now. So my experience has not been happy. I did not intend to offend.
And the fuse example does make sense.