I have to use more than 40 servo motors and 20+ load cells using PLC. But the problem is that I have to use many I/o modules ( that is costly and hectic). Can I reduce the no of I/o modules by any means or can you suggest something like decentralized control system? Please help me.

image of the tube which I am designing

In, this picture you can find a tube that I am making. This tube would give me the exact amount of material that I want. It includes 2 servo, 2 stoppers and 1 load cell for measuring the weight. For eg, I want 10 gm sugar. I program the plc in such a way that Stopper 1 that is attached to Servo 1 rotate 90 degrees to uncover the hole, then the sugar falls on the load cell which tells me the weight. When it measures 10 gm on the load cell. Servo 1 comes to its original position with stopper 1 thus stopping the flow of the sugar. Then stopper 2 opens with the help of servo 2 and sugar falls out of the tube. The problem is that servo is using 2 outputs of PLC. Imagine I have to use 40 such tubes. To accomplish this I have to use many i/0 modules both for load cell and servos. This would increase complexity, cost and reduce the overall capacity of plc to do other tasks very greatly. Also, I want individual load cells and individual servos connected to each tube. Can you suggest me how to reduce the no of i/o modules or you can also suggest a simpler method to measure the weight of a material that is less complex and solves my problem.

  • 1
    \$\begingroup\$ How can we tell? We don't know how many need to run simultaneously, we don't know your PLC make and type, we don't know your servo make and type or what kind of encoders it uses, we have no idea of your application, speed, response times and complexity. Please read your question out loud from the point of view of someone not familiar with your application then edit it to fix. \$\endgroup\$
    – Transistor
    Jul 15, 2020 at 13:20
  • \$\begingroup\$ what do you mean by hectic? \$\endgroup\$
    – jsotola
    Jul 15, 2020 at 14:36
  • \$\begingroup\$ Please see my whole problem that i have updated. \$\endgroup\$ Jul 15, 2020 at 15:17
  • \$\begingroup\$ If you haven't selected the servos yet. consider some smart servos, or smart drivers. My personal favorites are ims mdrive motors made by schiender electric. each motor has Volatage supply input, 8 i/o and a RS485 serial port, and they support multi-drop configurations, so you could control as many of them as needed from one RS485 port on your PLC \$\endgroup\$
    – Whistler
    Jul 15, 2020 at 15:59
  • \$\begingroup\$ Hi Karan, Welcome to Electrical Engineering Stack Exchange! Please understand that only a focused question will elicit pertinent responses. A brief insight into the equipment, as a whole, would be of help. Is the question related to the control of 20 identical machines (packaging for example) or a 20-station machine or line? \$\endgroup\$
    – vu2nan
    Jul 25, 2020 at 17:50

1 Answer 1


Well, you could use a load cell multiplexer like this one: -

enter image description here

It uses an SPI bus to communicate with the host so, if your PLC can provide this, one multiplexer can get you 6 bridge input channels. These units can also be used with single-ended inputs to take the servo potentiometer signal (if you need that level of control).

You can probably find an SPI card like the above suitable for driving several servo motors too.

There is also the Microchip MCP3424EV demo board that can provide 4 channels and costs £16: -

enter image description here

Or build one yourself.

  • \$\begingroup\$ I have updated the question . The question cover my whole problem .So please go through it . \$\endgroup\$ Jul 15, 2020 at 15:16
  • \$\begingroup\$ @KaranSrivastava it doesn't affect my answer as far as I can tell. \$\endgroup\$
    – Andy aka
    Jul 15, 2020 at 15:23
  • \$\begingroup\$ Can you please tell me in a simple language about the method you are telling .i know about multiplexers but i have never heard about Microchip MCP3424EV so i am having problem understanding what you are saying . \$\endgroup\$ Jul 15, 2020 at 15:47
  • \$\begingroup\$ It can combine and digitize 4 differential analogue inputs that can be read using an SPI serial bus. \$\endgroup\$
    – Andy aka
    Jul 15, 2020 at 17:01
  • \$\begingroup\$ @KaranSrivastava are we done with this question and answer now? If so then please formally accept the answer so that people visiting can see it works for you or, raise a new comment if you need clarification or, if you have found a different way of doing this that fits within the constraints of your question, please leave that as an answer. This is a question and answer driven site and it's good to complete the final part of the process. \$\endgroup\$
    – Andy aka
    Aug 2, 2020 at 17:42

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