Control System Questions

I have been reading old posts on the site for a while now but just joined today as I have some questions about my first project.

This will be a new plastics recovrey system we are adding to an existing system. The existing system has a Micrologix 1400 PLC with no free Io so the idea was to ad a small CompactLogix PLC to this new system and message between them as we need to make sure the recovery system is running before we turn on the roots blower to deliver material.

I had though about using one of the new L30 series CompactLogix PLC's and a Panelview plus 600 as this is a dual box station and we may add a Prosoft module and weigh scales for each box station later.

We will have a total of 7 motors in the system but only 2 on the dual box station. We plan to use across the line starting as 20 HP is the largest motor.

I have not designed my E stop system yet but was considering using the Guard master 440 series form AB as it has anew Ethernet adapter out that you can read status into the PLC and I can display it on the Panel View.

I had planned to provide an e stop button on the dual box station itself and on the front of the control panel located about 50 feet away.

I don't know if I need safety rated contactors or any safety speed detection for the dual box station or not and wanted to get some input on it.

I stand at 6-2 and from the floor reaching up into the down tube I still can't reach the blades of the rotary airlock. I have been informed that operators will sometimes try to clear a material jam with a broom handle while the system and air lock is running but if they are caught will be terminated as it's considered a safety violation.

I consider that you would have to be trying to get injured on purpose to get injured on the equipment as it's so simplistic so would the estop going to a safety relay and the output of the safety relay going to the PLC be good enough for this application?

I have included a link below that has a photo of the equipment in question.

I know these are beginner questions but this is my first project since I graduated last year with my engineering degree. I am finding there are many thing out here in the field that we did not cover in college.

Thanks for your input and consideration. Michael Craddock



https://www.dropbox.com/sc/67shz3t5wpx3bwz/iC5lZq8pgc

https://www.dropbox.com/sc/67shz3t5wpx3bwz/iC5lZq8pgc

Output of the safety relay should go to circuits that should be turned off in the event of an E-Stop. Sending it to the PLC would generally only be as a courtesy so the PLC would know and reset some logic. We label power devices downstream of the safety relay as hazardous, and are cut off from power so they cannot do any harm during E-Stop.

danatomega said:

Output of the safety relay should go to circuits that should be turned off in the event of an E-Stop. Sending it to the PLC would generally only be as a courtesy so the PLC would know and reset some logic. We label power devices downstream of the safety relay as hazardous, and are cut off from power so they cannot do any harm during E-Stop.

Click to expand...

My question is more of do these loads need to be on the estop circuit and controlled from the safety relay considering the equipment itself?

I generally place any device that can move and that the operator can get to on the E-Stop circuit which include safety rated (force guided contacts) relays.
I don't know of a situation where the operator tries to get hurt (short of physically removing guards or defeating safety circuits) where the company would not be held liable. Better safe than sorry.

I cannot consider the equipment itself as I do not know enough about it to judge.

Can anyone take a look at the equipment picture and help me understand if the motor controls need to be part of the safety relay and estop circuit and if I need safety break contacts for the motors?

E-Stop must kill all power. The rule is no stored energy. That means dropping the compressed air supply for valves too if you have that.
The only thing with power after E-Stop is the 24 volt circuit powering the E-Stop. That means one large contactor immediately after the main breaker.
The control transformer is powered after the main breaker, and before the main contactor.

Estop really must kill motors but do the motor contactors need to be the safety rated red type? Does there need to be 2 as the examples I have seen have 2 safety contactors above a motor and 2 above a drive.

I know there are different categories but from the machine picture it would be difficult to get hurt by one of the motors load as one is 15 feet in the air with no access and a hard guard around the chain. You could put a broom handle in the air lock blades from the discharge chute but you could not reach it with you hand without really trying and being around 7.5 to 8 feet tall.

The other motor load is just a vacuum pump direct drive.

Just trying not to spend money on safety rated contactors if I don't need to.

mcraddock1210 said:

Estop really must kill motors but do the motor contactors need to be the safety rated red type?

Click to expand...

No. Standard Estop circuits. The logic you use is to prevent bypassing by operators. Main breaker must be turned off before enclosure can be opened.
Main EMO contactor is inside the protected enclosure.

I've used the red relays for a press and a 2 hand operator. Those are designed so the operator can't bypass one button and operate one-handed.

You don't have to go crazy spending money. OSHA inspectors use common sense. How do we prevent injuries? The broom handle thing is an issue that might require a red relay. The threat of termination is not enough.

Add a light beam or light curtain. The light curtain will drop a red relay. The red relay will drop the control power to the blower contactor.
With at least one brand of light curtain, the red relay (safety circuit) is built in. Direct drive of your contactor control circuit.

Ok so we have a compact logix safety plc from a project that got canceled so I am going to use that and the point I/O safty modules also. Do I need the red contactors above the standard motor starters? Using the 100C motor starters and will 1 be enough or do you need 2?

The plain contactor and overload will be 120 Volts but the red safety contactors are 24 DC. Is this ok?

mcraddock1210 said:

Ok so we have a compact logix safety plc from a project that got canceled so I am going to use that and the point I/O safty modules also. Do I need the red contactors above the standard motor starters? Using the 100C motor starters and will 1 be enough or do you need 2?

The plain contactor and overload will be 120 Volts but the red safety contactors are 24 DC. Is this ok?

Click to expand...

Yes.

Try to design your entire machine for 24VDC. Much safer and easier to work on. If this is a small system and you don't have long wire runs where you need to worry about voltage drop, all of your contactors and interposing relays should be 24VDC. Size your power supplies accordingly - it's not hard.

Many contactors already have built-in surge supression. If not, it can be added. Check Automation Direct for contactors, relays and surge suppressors that go with them.

As far as whether or not the contactors need to be red - for machines that do not have inherent dangers to life and limb, I have seen it done with two "normal" contactors in series to kill power to motors and outputs. The safety circuit - EStops, light curtains, door switches, safety relay - need to be "red."

The contactors that are driven by the safety relay, well, we do not normally do red contactors on small machines that are are simple electropneumatic assembly or testing machines, where the biggest cylinder is maybe a 1in diameter with a 4-6 inch stroke. Machines with components that can injure or kill somebody, then a real hazard analysis should be done and "red" components should most likely be used. YMMV - if there is any doubt, spend the money.

But anyway, my main point was that you should try very hard to use 24VDC for all of the machine IO and control circuits. That is another safety concern, and one that comes up every time the machine needs to be worked on.

I am still not convinced this system needs an Estop circuit at all. Are we sure it does? Maybe just for the airlock motor but from the pic with notes you can see that even at 6-2 and standing inside the cone with my are stretched out I have a good 10 inches before I could touch the blades and I would have to really be trying.

Will someone take a look at the notes picture where I have measurements and se if safety system is really needed? WE have a couple more of these by a different OEM and they have no safety system just start /stop for the motors.



Here are some finished pics of the equipment with notes.

https://www.dropbox.com/s/t7424bif98w84c2/Notes.jpg

Side View

https://www.dropbox.com/s/vvg0lw0k3i6s362/photo 1.JPG

Bump

What about using estop going to guardmaster safety relay and have it remove power from the PLC output card that drives the 4 motor contactors?

I have seen this done in the past but what category would that be?

Would that be ok for the equipment based on my pictures in the links?

Anyone?