2/11/2018 9:44 PM | |
Joined: 9/27/2006 Last visit: 9/22/2024 Posts: 12282 Rating: (2685) |
Hello success; We generally select a signal isolator (or signal conditionner, or signal splitter, depending on the vendor) for this, as placing the AI modules in series with the sensor (for a current signal) could easily exceed the capacity of the transmitter. The reasons for this is explained in the following thread (from another automation forum), along with some suggestions. http://www.plctalk.net/qanda/showthread.php?t=60064 Hope this helps, Daniel Chartier |
2/11/2018 10:14 PM | |
Joined: 8/1/2016 Last visit: 6/3/2024 Posts: 159 Rating: (5) |
Many thanks... one more question... is there any different between 0-20ma and 4-20ma analog sensor.. and is the scaling method different from each other...? i need install a 4-20ma sensor, i am contemplating if the scaling method will be different from the general one i am familiar with 0-20ma.
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2/12/2018 4:39 PM | |
Joined: 7/7/2010 Last visit: 9/23/2024 Posts: 15217 Rating: (2417)
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If you use NORM_X / SCALE_X for 1200/1500 PLCs, you change the NORM_X low value, then everything else is the same for 4-20mA/0-20mA as far as the PLC is concerned. Reason is because you would then use the output of the SCALE_X for your process making your process not really care what type of field device you have. Not a perfect answer, but I tend to think of the difference between the types of current inputs as either loop powered (4-20mA where the 4 mA is used by the device), and externally powered (0-20mA) where it draws no power from the current loop.
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