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Old March 6th, 2018, 08:25 AM   #1
toddp65
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Question regarding Ethernet/IP vs Analog I/O

This may be a simple question.
I understand the concept and application of analog modules (i.e. Compactlogix) for transducers, and outputs for VFD speed reference and such but my question is regarding the use of Ethernet/IP for the analog. For example we have a couple Ethernet based SICK encoders that do not report to a HSC module--there isn't one on the rack and Drives are speed referenced thru Ethernet as well....does this indicate the analog and signals are traveling thru the Ethernet and these modules are not necessary as the code is being handled in the controller without the dedicated module interface of a HSC or Analog input/output modules?
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Old March 6th, 2018, 09:40 AM   #2
jraef
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Yes and no. The actual analog SIGNALS are not being transmitted in the Ethernet media. The analog values are being converted to digital values, and those digital values are what is transmitted within a packet of data from device to device. Since whatever needs that information was going to convert analog to digital internally anyway, it ends up the same and in fact can acutually avoid errors in transmission of the analog values over long distances. In your example if the SICK encoder has an Ethernet I/P output port, that means is had the transducer (HSC) built-in that is doing the converting to a digital value right at the encoder and making it available to the Ethernet I/P network.
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Old March 6th, 2018, 09:57 AM   #3
toddp65
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Ok--so there's no actual analog travelling thru the Ethernet because, well, it's not capable of doing so, therefore the PLC is receiving digital data. So am I correct in assuming that control of a VFD, i.e. a Powerflex 525, the speed reference can be transmitted without an analog ouputt card and an analog output from the drive (amperage) does not need an analog input card-- so basically a controller without those modules is capable of performing these tasks?

thanks
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Old March 6th, 2018, 10:14 AM   #4
cardosocea
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Quote:
Originally Posted by toddp65 View Post
Ok--so there's no actual analog travelling thru the Ethernet because, well, it's not capable of doing so, therefore the PLC is receiving digital data. So am I correct in assuming that control of a VFD, i.e. a Powerflex 525, the speed reference can be transmitted without an analog ouputt card and an analog output from the drive (amperage) does not need an analog input card-- so basically a controller without those modules is capable of performing these tasks?

thanks
Yes. Generally you can control every parameter of a drive... so not only the speed reference but the mode (speed versus torque control) and torque, current limits, etc...

You usually can also retrieve a lot of information from the drive such as faults and fault codes that can make it simpler for maintenacne to troubleshoot the system.
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Old March 6th, 2018, 10:22 AM   #5
toddp65
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Thanks--I was aware of that as I've added a 525 to a project before--I was just hazy about the interaction between an ethenet/ip device such as a drive or encoder or anything else analog (I've seen summing boards for scales) and the need or lack of a need for dedciated analog cards.


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