Problem With Air Compressor

[elhagan 0]

Hello friends I have new project Air compressor the company want to upgrade it to work with PLC and HMI The compressor work with micro processor and the micro processor Is damaged the problem in 2 solenoid open the air gate and if the solenoid coil is broken the micro processor stop the machine and make alarm The solenoid coil is normal only 2 wire 24v dc How the micro processor feel the broken coil and if the wire is cut And the owner need in the upgrade this feature How can I make the plc feel the coil if broken or damaged I will use plc s7 200 with out put relay I think the micro processor measure the coil resistance But in the plc ? what we will use ? Sorry about my little English And I am wait to answers me

[benbrad 0]

One way of doing this would be to use a "Reed Switch". A reed switch is an set of switch contacts placed in a small glass bulb/tube with the air vacuumed out. This is a very inexpensive method and, provided everything is soldered and covered in heat shrink tubing, is very reliable. To check for open circuit, turn on the solenoid then wrap the power wire of the solenoid around the reed swich several times. When the switch closes stop winding the wire. Cover it with heat shrink tubing so that the wire does not come off. The reed switch can now be connected to the PLC input. When the solenoid is good, the switch is closed and PLC input is on. When there is an open circuit, the switch is open and PLC input is off. I've attached a cude drawing to give you an idea. Good luck Ben

[gravitar 3]

That's interesting.. the only industrial application I've seen for a reedswitch is to sense the presence of a magnet mounted on the piston in an air cylinder. I imagine wrapping the energized wire around the switch would have the same effect as the permanent magnet. Good stuff!

[benbrad 0]

Something I picked up out of a very old machine supervising a motor. Made before CTs and A to Ds, intrinsically safe, waterproof, the old timers sure had some good ideas. Cut down the number of coils around the reed and it can be used for over-current too.

[KinK 0]

good stuff.

[elhagan 0]

hello all thanks for help but i need another thing like plc detect open circuit i need to feel the the solenoid if the wire is cuting or the plug is down pls help me

[gravitar 3]

Why do you think the reedswitch circuit would not work for you? The coil wrapped around the glass tube goes to your solenoid.. the circuit that you want to monitor the continuity in. the two leads from the switch itself go to a power source and an input on the plc. when you energize the solenoid, you set a timer to start running. If you don't see the switch in a certain SMALL amount of time, you stop running and set an alarm. If the switch makes before the timer times out, you seal the solenoid output with the switch closed condition. (and other conditions determined by the machine) You would also want to verify that the reedswitch OPENS when you remove power from the solenoid. If not, you prevent the compressor from starting back up and set another alarm. That's just something off the top of my head, but unless there's something else we aren't considering, this should work for your compressor

[OkiePC 14]

The reed switch idea is very interesting. Looks like it would work with any PLC just by adding an input that only detects the flow of current. My only experience with reed switches has been pneumatic cylinder feed back (magnetic piston). I found them not to be the most reliable sensors in my applications. I think we really had more problems with wiring getting damaged and shorts causing the delicate switches to fail. On another note, I know you have already selected a PLC, but the A/B controllogix platform has output cards available that can detect an open circuit condition. I believe the part numbers are listed with a D suffix (D for diagnostic). something like 1756-OB16D i think. (They probably have tiny little reed switches on the card LOL) Edited 31 Jan 2006 by OkiePC

[benbrad 0]

Another way that would work is a current transformer and an A/D card measuring the volts returned. Or a differencial pressure switch across the solenoid, or two pressure switches one before one after the solenoid. These methods would also work but the CT method is expensive, and the pressure switch method doesn't check for open circuit just whether or not the solenoid operates. The machines that I have worked on that utilise the reed method have been in service since the sixties without problems. Machines that employ more sophisticated methods in general are less reliably. Magnets triggering reeds at a distance or through a solid medium tend to be less reliable on the whole, but wrapping a coil around a reed puts the reed right in the centre of the electro-magnet field. This makes it very reliable.

[elhagan 0]

thank you very much OkiePC can you give me manuals to this output module

[OkiePC 14]

http://literature.rockwellautomation.com/i...um058_-en-p.pdf Look at page 123 for the dignostic configuration details You can confugre each output point individually to use the load sensing feature and latch the fault if detected. Read up on it carefully, but I think this module will do what you want. If you have never used contollogix, it's great stuff, but the reed switch idea would be much easier IMHO. Good Luck!

[elhagan 0]

dear sir OkiePC thanks for help you are very good man and you are very good in electric i read the manual you think 1756-OA8D module its work with what i need i teel you what i need 1- digital output 2- if the wire cut the module stop the plcs 3- if the output like the solined is damged the module stop the plcs 4- if no load in the output and i force to the output but no load the module stop the plcs this is what i need i see the maunal but i am new in AB but i read and i think this module 1756-OA8D its good i am zero in AB can you help me to make full system plc with AB like i need plcs 1- CPU 24vdc 2- momery card 3- i need 16 input 4- 16 output 5- power supply 6- programing cable 7- programing software thank you for your help man best regard elhagan

[gravitar 3]

OkiePC's a good guy, but we should all give it up for Benbrad.. He brought a real good idea to the table. The reedswitch continuity detection concept is so simple and (seemingly) reliable, I find it hard to believe that there hasn't been a commercially-marketed device based on this principle. Maybe Elhagan and others would feel a little comfortable using it if it had a molded plastic housing and some company's logo on it

[TimWilborne 108]

I haven't really been following this topic but just thought I would through another solution out there as far as detecting open and short circuited inputs and outputs. This method can be done on projects that require simple logic (air compressor is in that category). I have successfully done this with the 100-DNY42 and the Armorblock Maxim I/O blocks made for Devicenet (keep reading, you don't need the Devicenet). This can be done with any AB (other manufactures probably) that supports DeviceLogix. For a little background about why I did this we were building some control panels for machines to be controlled from Devicenet but the network did not exist yet. There was a push to get these machines in but no time to get the network ran. To make a long story short DeviceLogix was meant to be a secondary control method for when the network was offline. But after some experimentation we found that we could control the machines with the DeviceLogix and never run the network. Enough rambling, here are some details and why I suggest this. Cost - The Armorblock I/O is cheap compared to a Controllogix setup and has Input and Output Open and Short Circuit Protection. I know the CompactBlock, 1799, and there nice looking motor starters that I can't remember the part number too all support DeviceLogix and probably more do now. Many other reasons that it is good but go to Abs web site and read under Devicenet DeviceLogix – This uses flow chart programming in RsNetworks do configure the device. You do not actually need the Devicenet network. Put 24Vdc on pins 1 and 5 and leave pins 2 and 4 off and the module will operate. Configure your logic and set it to run. Individual modules can also communicate with each over with Devicelogix without a master controller so if you run out of I/O no big deal. But for an air compressor control one Armorblock should do the trick. I don't know if Rockwell ever intended for this product to operate like this and when I originally asked them about it they said it would not work without a master controller. But it has been over a year and I still haven't got the network ran to 5 of those machine and they are doing fine. To tell you the truth I had forgotten about them until I was reading this post Edit - I like Benbrad's idea too. May be he should put a plastic case around it and put a logo on it and sell it. But come to think of it I had a company come to me and show some small round sensors that clamped around a wire and gave you a contact closure if current was flowing. Hum...I wonder if that is what they were? Edited 31 Jan 2006 by TWControls

[gravitar 3]

Interesting concept.. Using a Devicenet I/O block as a micro PLC! I think its safe to say not many have tried that! I wish I had a price book handy, I wonder what the cost of one of the ArmorBlock modules is compared to a Micrologix of similar I/O count.. How much logic can you program into one of these? It MUST be very little.. like 100 instructions or something. Surely A-B wouldn't be foolish enough to let these blocks compete very well with their PLCs!

[TimWilborne 108]

They are limited in memory but will do simple programs. I'll see if I can look it up today but probably around 100 instructions. I can't remember how much the armor block was but I know the 100-DNR42R which is a 4 in 2 out was cheaper than a Pico controller and you got the network port and the Auto Device Recovery. This statement is only true for devices hooked to the devicenet network. Auto Device Recovery - The Devicelogix code is stored both in the module and the scanner module. If you have a Devicelogix module go bad, when you replace it, the scanner will see it and redownload the program for you. Pretty much a plug and play mini Plc. The Devicelogix code can be enabled even when the Plc is hooked to the network

[OkiePC 14]

I totally agree. That is a very unique, inexpensive idea. I love it and will definitely use it sometime. Thanks BenBrad