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timberleek

i like the samba, but need more IO, how? (plc newby)

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Hello,

I'm new to the forum and to the world of PLC controllers. I've been in electronics for over 10 years (first hobby, then study and now work).
A lot of hardware design and also software, but mainly C, java and vhdl. So i know my way around electronics, but not this kind of stuff. I hope you can help me with this.

I want to automate a machine with a PLC. As tI won't be around the machine all the time i don't want to make custom, impossible to replace hardware for it.

It's not completely sure yet, but at this time i have these needs for IO:

  • 16 relay outputs
  • 11 digital inputs
  • 1 analog output (0-10v) 
  • maybe an analog input, but that's not certain

    I probably also have to read 3 loadcells, but i don't know yet what kind of unit (bare or with controller outputting a normal analog value).

I'd like to use a nice touchscreen interface on the machine. Therefore i initially landed on the Samba system. But i now found out it doesn't support extra IO. Only via an expensive external controller option.

Another option i found was the vision systems, but text based hmi's already hit the 500 dollar mark and i haven't even looked at the touchscreen versions. Therefore i slightly suspect it's an extremely overkill system.  As for functionality i think i can make the sacrifice for a text based hmi with the buttons around it (like the v120). The functionality the moreimportant

A third option i found was to use cheaper modbus IO module on a samba system.

What do you guys think in terms of hardware? I'm a total noob on this type of systems.  And as a part time worker, part time student, there is a concern for budget.

As for the software, i'm driving a motor and a number of valves. The program wil largely consist of a number of states which will drive the motor and valves for certain times. On the hmi panel, some of the states are initiated and some of the timer values can be adjusted.

Hope you guys can point me in the right direction.  For the past days i've been searching across countless manufacturers and systems to no avail.

Thanks in advance

timberleek

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Adding Modbus I/O to a Samba will quickly push the system price above a Vision.  The Samba is not intended to be expanded.

I, too, know my way around electronics.  The Nuts and Volts magazine I subscribe to has proven time and time again the ingenuity of what can be done with a basic microcontroller, some external function-specific ICs, and some well designed circuitry to connect a 5 volt brain to a 24 or 120 volt world. 

PLCs have gotten ALOT cheaper since I started in the biz, but they are not in the same leaque as a controller like an Arduino or Raspberry Pi.  You're paying for a canned system where someone else has figured out the interface circuity, professional finished appearance housings, and ease of programming.  So many programmers I know do not value their own time.  You are wise in not wanting to make a system you'll be married to.  

If your experience is with microcontrollers you're going to experience sticker shock with PLC hardware.  But you can have a finished PLC control system in a couple of days, once you've learned ladder logic.

Unitronics is by far the best bang for the buck in PLC land.  I can't say I've programmed them all, but as a system integrator I've programmed many.  Your own research has proven this.

Figure on spending about $1,000 on hardware for a capable V350 system as you describe, which includes a three channel load cell interface module.  You can shave a few hundred dollars off with a monochrome V130.  The color touchscreen does look a lot better, though.

Joe T.

 

   

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