Setting up Motor Over speed protection in Compactlogix 5000

Hi,

I am needing to create a program that will read the analog +/-10Vdc input from a 1769-IF4I and compare it to a lower fixed value. Once the analog input is more than or equal to that fixed value then a digital output 1769-OB32T will de-energise a relay.

I am using the Full compactlogix 5000 v19.

Please help me


Kind regards,
Adrian

I would be ever so grateful if someone can send me an example program to get me started that would be great.

Tomorrow I will be on the crane with the laptop to make this program. I know how to configure the hardware, I just dont know how to program it to get it to compare the analog input to a fixed value and then once the analog input is more than or equal to the fixed value it will de-energise a digital output.
It sounds really simple and a really small program. I just havnt programmed with analog inputs before only digital I/O.

Have you configured your card in "IO Configuration"?
In other words, have you selected the appropriate Input range and Data format?

If you have, then just use an LES(Less Than) instruction in series with the output you want to de-energize:

|  +--------------+                 O:0.0/1

|--| LES          |-------------------( )

|  |Source A:     |

|  |Source B:     |

|  +--------------+

Source A should contain the address of the Input word containing the analog data.Place the appropriate fixed value in Source B according to your data format.

I added the analog module 1769 IF4I and configured it for +/- 10vdc, filter set at 50hz and have selected engineering units which is +/- 10500.

So do I make a alias tag for the analog input first, if so do I set the alias as a int or dint or real?

Then do I add the new alias tag into source A and then I can just type any number like 5000 in source B in the LES?

Kind regards,
Adrian

You could make an Alias for the analog input channel, or you could use the Module-defined value directly.

Aliases always take on the data type of the base tag, so the datatype will be automatically determined for you if you choose to use an Alias.

If this were my system, I would use a delay timer and a latch as well as a 'GEQ' instruction.

An illustration of the basic syntax of the GEQ instruction is below.

Cranes are, in general, not something you want to mess unless you are certain of your skills with the application and the toolset. If you are doing overspeed prevention or any sort of 'safety' application, get some help with it.

Thank you sosososo much guys!!! I am so glad I found this forum!

Yes I will be needing some form of latching system to keep the relay de-energised and the only way the system can be reset is by an electrician.

I have read somewhere on this forum using latching in a PLC can not always be 100% safe to use?

I should really put this program in the safety side of the PLC since it is a safety rated PLC but I havnt used one before and i Dont know if it will effect the current joystick control program which is not using safety side of the PLC at all?

I cant find anywhere to tell me how the safety side of the PLC works


Kind regards,
Adrian

I am a electrical engineering cadet and capital have thrown me in the deep end and said re design the joystick system for the stockbridge. The electrical for the stockbridge is made in 1965 by toshiba. using ward lenard, amplidynes and mag-amps LOL. we needed to limit the hoisting and closing line joystick control axis quadrands and also give spring return joysticks and overspeed on the hoising and closing motors because we have had faults where if we loose feedback or a motor feild the motors go full speed on there own which is not good if they what to do a rope change LOL . So I have programmed and commissioned the joystick limits and it works firt go and the drivers love it (no more slack rope) now that the tacho's have been wired up to the PLC I have to write a program for the overspeed if the motor goes faster then the highest speed selected then it hits an E-stop. and only an sparky can reset it.
I have never done anything like this before (PLC's,crain control design), and so far everything is going well (touch wood). which is amazing because now one in the company knows how this thing works and i had to do everything on my own. I just found this site which is so good.

Oh my.

I wrote a long and angry post about this and deleted it. So I'm going to try to be gentle.

Cranes are dangerous. Dangerous machinery demands respect.

Attempting to modify the control system without understanding the basic controller principles or applicable machine safety standards is reckless.

I realize you're young and inexperienced, and you've been given a challenge you're eager to solve. I was like that, too.

But it sounds to me like you are unaware of the significant hazards to your career and the life and limb of those around you, and are approaching them with a young man's innate belief in his good luck and indestructibility.

I am a control systems expert, and know both ordinary CompactLogix and the GuardLogix subsystems very well. I even have a professional license in my discipline. And I don't work on cranes: it's outside my scope of experience.

Which is why I can't give you any advice, in public or in private, other than to stop, try to evaluate and understand the hazards of the system you are working on, and proceed with extreme caution.

I am the only one that understands how this crain works. I've been through the aus standards.I also have a principal elec engineer that specializes in crains and will be the competent person to sign off on it all. We have done a risk assessment. The crane isn't safe unless we do the upgrade in question.

Thank you guys soso much for the direction. It helped me to quickly write the program so we could commission today also .
The overspeed system works. If it does overspeed it will open the motor ACB's and the control circuit. Which will kill the motors direct connection to the drives and power the control system.