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About Click's new high speed input

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  • About Click's new high speed input

    Trying to understand how to use the new high speed input frequency mode. Does this basically just do the math and store the result in a table location?


  • #2
    Under 'Setup' go to 'High Speed Input'. Choose a mode, the input(s) being used and the destination register.
    thePLCguy

    Bernie

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    • #3
      I am looking for more info on how it works, like refresh rate or compares.

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      • #4
        Originally posted by bilt2spd View Post
        Trying to understand how to use the new high speed input frequency mode. Does this basically just do the math and store the result in a table location?
        if connected properly, the result of the input goes to the destination you specified in setup

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        • #5
          Originally posted by bilt2spd View Post
          I am looking for more info on how it works, like refresh rate or compares.
          Being as it is "high speed" I'd guess it is likely done in hardware and "refresh rate" might not really apply as far as counting goes. The compares I don't know about, but I really, really doubt it is done as a normal scan operation, even if it is done in software I'd think it is interrupt driven and again "refresh rate" may not really be applicable.

          Since there is very little (i.e none) really low level system information publically available on the CLICK ( first, the target audience would generally not need, understand, or want it, second, pretty much nobody provides that kind of information anymore) If you realty want to know about timing I'd suggest buying a 'scope and experimenting.

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          • #6
            The frequency mode of a high speed input determines the frequency of switching for that input. If itís a motor encoder, you can figure out the rpm.

            A high speed input can change state multiple times during the scan time of the program. The state of the input will be updated accordingly. However, the triggering should only happen once during the scan time.

            compare this with a regular input which-in the hardware might change state in the middle of the current scan, but will not reflect the change of state until the next scan updates the input image table into the software. Now a regular input has a latency of 2ms which is comparable to program scan; if an input changes faster than 2ms, the hardware wonít keep up.

            this is the theory. Practically, the hardware is ready and this is why click software has been updated to handle high speed.
            these inputs are usually tied to high speed counters in order to provide triggering for signals like encoder pulses which are inherently high speed.

            there is a problem with high speed: it challenges the programming paradigm of a plc, which says:
            1. Make an image of the inputs
            2. Use the image in the program
            3. Produce an image of the outputs
            4. Reflect the output image in the hardware
            5. Restart the program scan at step 1

            if an input switches fast, then the switching can be serviced once per scantime.

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