Digital I/O

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Digital IO card to send a signal for retracting conveyor belt

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I am looking for a PCI Digital I/O card with fast operate time. As I don't know much about electrical stuff, I hope someone in this forum can give an input for the selection. 


We have a machine vision system examining products on conveyor belt. If the system detects a defect, it sends a signal to conveyor belt to retract so that the defect drops. The signal for conveor to retract would be analog 24V. As conveyor belt is moving at 27" per second, the operate time of the card should be around 10-50 microseconds. 


Is there any PCI card with the capacity? If so, could you recommend one?

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Message 1 of 5

I suggest you contact your nearest National Instruments Field Sales Representative.

Or the people who sold you the vision system. Does it have a digital output when a faulty product is detected? A simple solid-state relay might meet your needs, or a PLC.

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Message 2 of 5

Is the vision system running on the PC? That sounds risky to me when you need those pulse rates.  Talk to whoever installed the vision system to get the signal you need.

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Accepted by topic author statcomp

Thanks all for your answers.


I am one of the developers for the machine vision system, and I've found my solution by finding one of isolated digital output cards with PCI bus.

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Okay. I'm sorry if the following is obvious, but as you do not mention this, I will state it here:

Systems of this sort are normally divided into two parts:

A. The inspection system that produces the product good/bad signal.

B. The plant system for dealing with the identified products. Normally this will be implemented in a PLC, and will consist of:

  1. A detector (e.g. photocell) to detect the presence of the product at a known position. Fixed and probably very close to the inspection position (presumably also fixed).
  2. A quadrature encoder to track the exact movement along the conveyor
  3. A delay to wait before the product reaches the kick-off position. If there may be more than one product between the inspection position and the kick-off position, then things get more complicated as you have to track each individual product. Basically you wind up with a FIFO clocked by the encoder. Obviously you no longer need ultrafast hardware, as the delay can be adjusted to accommodate things like signal propagation delays and actuator timing. However they will need to be consistent.
  4. Safety system so that the kick-off cannot operate without all the guards around it, despite whatever you are doing adjusting the vision system.

You might think that a fixed delay, or a delay adjusted by the nominal conveyor speed will meet your needs, but my experience is that it is far better to measure the actual conveyor movement, as this will automatically deal with speed changes, drive roll slippage etc.

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