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watering system with 2 pumping centres

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Hello

I have been given an assignment  to automate a conveyor line watering system. The system consists of 2 pumping centers. The distance between them is about 20-30 meters. I need to check that, but its about that in lenght. 

1 pumping center consists of 2 electrical motors. One motor is controlled with VFD, the other is just on/off. There are 6 electrical waterpipe valves for spraying the conveyor. They were switched with an power optocoupler.  Also there are 5 water level sensors. In addition, there is 1 flow meter, which analog output is currently connected to VFD, which controls  water pump engine. Other motor is just for mixing the liquid. The pumping centre was connected to siemens PLC system via fieldbus i/o module.

Now the siemens PLC system is gone and I decided to put up a system with Unitronics PLCs, as we studied them in the university. I planned to  use a Vision 230 in one center and in the the other some external i/o module. Flow rate comes to plc, which then controls the VFD via analog output and sends info about  pumping rate to the other centre, so that the pumping rates would be the same. 

The pumping rate will depend on conveyor speed and can also be set by buttons. I chose 230 as it offers buttons, which are beneficial in a factory.

 

My question is about connecting the two center stations. What is the best solution for it, as its a factory with a lot if electromag interferences? 

 

Also, in the old systems motor contactors were switched directly from PLC output module. Is that ok thing to do? Motor contactors in use are Siemens 3RT1015. Why arent flywheel diodes used in parallel with the contactor coil? Or i dont need do use them if I use relay output of the PLC?

 

Im sure I will have a lot of questions coming up, as this is my first project in real life. 

 

Thanks in advance

 

 

 

 

 

 

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I would use CANbus with Unitronics UniCAN protocol.  This is very simple to use and works great.  Use a good quality cable, run the cable away from VFD and power cables and EMI shouldn't be a problem.  Flywheel diodes are not mandatory but are recommended.  It depends on the coil and how often it is switched on and off.  In your case, I would use them on the Siemens 3RT1015.  I don't bother on small relays with infrequent switching.

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But would CAN bus mean that i have to use 2 controllers? Because it seems to me i can use only a special cable  (EX-A2X) to connect a controller to a expansion module, which i would place in the second watering station. 

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The maximum length for the EX-A2X cable is 20m.  I wouldn't be that comfortable running the cable that distance in a noisy environment either.  I recommend using an EX-RC1 and suitable IO module.  Of course this will cost a fair bit more but reliability can be guaranteed.

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Those i/o modules are all connectable with each other? I just choose the the appropriate one with needed i/o's and hook it up? 

I think i will build my system with V130, EXRC1, XL module D16A3-RO16 and AI4-AO2. 

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