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wal

How to notice a rapture in the analog input card?

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Hi, I work with FX2N-4AD card. Minimal signal corresponds to 4mA input. When I disconnect input the configured register shows zero. How can PLC distinguish the minimum signal from a rapture (0 mA input)? regards, Wal

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As I recall there is a status bit for that. Does Buffer #29 bit 10 do it for you?

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Thank You Jeremy for the answer. I monitored the buffer memory #29 while disrupting an analog input. The value remained zero. Probably, it does need some extra dedicated settings to work correctly.

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I think maybe that bit only comes on if the input is outside the whole analog input range of +/- 20mA. You could maybe configure the input for the whole range instead of 4-20, then you'd see when the input drops to zero. Downside is that you'd lose some resolution. I think the newer version of that card (FX3U-4AD) has more options available.

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As JRoss suggested, select the full value scale from -/+20mA. Once the digital signal drops below minimum(find out digital value corresponding to 4mA), consider cable to be broken.

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Hi, thank You for the answers. Don't think that the range is wrong configured. When the signal=zero, the corresponding input current =4mA, as expected. Did somebody try to distinguish a rapture with FX2N-4AD?

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Yes, the range you have selected will give you 0-1000 for input signal 4-20mA. But that won't give you the "rapture" information you're looking for. If you change to +/-20mA, you will get 0-1000 for input signal 0-20mA. With that setup, at 4mA you'll get 200. If your value drops close to zero, you'll know you lost your signal. The trade-off is you'll lose a little resolution, with only 800 data points over your range instead of 1000.
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Thank You Jeremy, this is a good idea. I will try it.

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