DeviceNet

[LSV 0]

Hi, I have Micrologix1500 with scanner 1769-sdn and flex i/o with adapter 1794-adn. DeviceNet was set up at 125kbits/sec. Flex i/o not far from the PLC (about 3-5m). I am trying to figure out what is the minimum time input at flex i/o can change its state so that it can be detected by PLC. Lets say input changes from off to on and again to off. So what is the minimum time input should be ON so the PLC can read it through the network? I guess it might be 1/125k=0.000008sec? Or it's to simple. If somebody has an idea, please help me. Thanks.

[Wordman 0]

The bottleneck isn't going to be the baud rate, but the scan time of the scanner, and the rate at which the PLC reads the scanner image table. Keep in mind that using the I/O mapping is faster than using the M image file. Because copying from/to the M file will add to your PLC's scan time. COS will yeild higher performance than polled I/O. But I don't really think if you are just using one FLEX module that this is a concern. Maybe you could find more information in the SDN's manual

[LSV 0]

Thanks for the respond. So SDN scan time depends on number of i/o bytes I have in the network + PLC reading rate, and +, I guess, interscan delay. I couldn't find in manual how to monitor scan time to have an idea how long my input should stay ON. Thanks.

[Wordman 0]

Curious: what's the application? why are you concerned about how long you keep an input on?

[Gerry 13]

You should be looking at the specs for the input module that you're using. Pay attention to the input filter time constant.

[Guest Guest]

The aplication is a BX making machine that spins at certain high speed, and when the BX is broken, we have to detect it. I found on allen-bradley web site a spreadsheet that helps to approximate the overall network wire time for a DeviceNet. http://domino.automation.rockwell.com/appl...E1?OpenDocument Think I can use it for reference.

[LSV 0]

Sorry, Guest it was me. Forgot to log in.