Falling edge for NC contacts?

[TL140]

So I am doing a project for my PLC networking class. We are using CLICK PLCs by Koyo. I am decently experienced, but my question is more about the control theory.

So I know how to use DFIU, OSR, Rising Edge contacts, etc.., pretty well. But I have never once used a DIFD or falling edge contact. I have always modified my logic to make my contacts be able to trigger an up-pulse, as i have always been taught that it was good practice.

Right now we are just doing a simple GS1 VFD control with the PLC and set-up of a N.O. Start button and a N.C. Stop button. (they are trainers with the equipment already mounted on them) The assignment is basically to let the motor run when the start button is pressed and let go. However, If the start button is pressed while the VFD is in reverse, Only let it run for 5 seconds.

I am one of those over achievers and know I can do this with simple seal-in circuits, but I wanna have a little fun with this thing. I have designed some ladder to basically start the motor with the start button. I can also stop it with the start button, if it is running. I also added safety features including the inavailability to change states of the motor while running.

But there is an unknown factor that I wanted to consult with you guys before I try it out since I have never done this before. It is acceptable to use a falling edge input for a NC contact so that it will pulse when pressed?? I will give you guys a sneek peek at the logic.

Also, with the drive, we are using setup 1 for the wiring.

 

[gclshortt]

I was always told if the program works, then use it.
I have used the trailing edge one shot on several projects.

If you want to get fancy here is some programming of traffic lights. One using traditional timers and bits, and the other using indirect addressing.
http://accautomation.ca/building-a-plc-program-that-you-can-be-proud-of-part-1/

If you like that one, here is a tutorial on building a robust data logging system. It uses a Do-More PLC and Simulator.
http://accautomation.ca/now-you-can-have-robust-data-logging-for-free-part-1/

The above programs use Automation Directs Do-More Software. Free Download at their website.

Regards,
Garry
http://www.accautomation.ca

 

[TL140]

I was always told if the program works, then use it.
I have used the trailing edge one shot on several projects.

If you want to get fancy here is some programming of traffic lights. One using traditional timers and bits, and the other using indirect addressing.
http://accautomation.ca/building-a-plc-program-that-you-can-be-proud-of-part-1/

If you like that one, here is a tutorial on building a robust data logging system. It uses a Do-More PLC and Simulator.
http://accautomation.ca/now-you-can-have-robust-data-logging-for-free-part-1/


The above programs use Automation Directs Do-More Software. Free Download at their website.

Regards,
Garry
http://www.accautomation.ca

Thanks for the advice! I currently have gone through a few certification courses and I had to do a pretty fancy data logger for a temperature of a water tank logged every hour. I had to use indirect addressing on it quite a bit since I was on an omron system (Syswin 3.4) and had no FIFO command.

 

[gclshortt]

My plant currently is running with several Omron PLCs. We collect the data using VB6 and store the information into an Access database. Our Intranet then serves up the Data to the user using ASP.
We also then use the ASP code to send email messages to supervisors, etc.

The sample VB6 code in the previous links use Modbus TCP protocol. I have also the Sysmac Way protocol for the Omron PLCs' and Temperature controllers.

Regards,
Garry
http://www.accautomation.ca

P.S. I use to work at Omron as a Field Application Engineer

 

[Lancie1]

Is it acceptable to use a falling edge input for a NC contact so that it will pulse when pressed??

Yes, it is acceptable. Your method is basically the old well-known flip-flop method (also called the alternator or toggle method). If you want to stick with the Rising Edge and Falling Edge instructions, another way is something like in the attached picture.

 

[TL140]

Yes, it is acceptable. Your method is basically the old well-known flip-flop method (also called the alternator or toggle method). If you want to stick with the Rising Edge and Falling Edge instructions, another way is something like in the attached picture.

That was how I was taught. To map your inputs to a one shot. I like the cleanup