adccommunitymod (AutomationDirect) asked a question.
Created Date: February 09,2014
Created By: AZRoger
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I'm installing RTD sensors in three freezers. The cable run is about 50 feet. The least cost solution takes each sensor to an input on an F204rtd module. The F204rtd automatically (with the right jumpers set) scales the values on their way to V-memory. A more expensive and complicated solution is to use temperature transmitters like TTD-20-N40160-H and use a 4 input 4-20ma current analog module. This will require some additional scaling in the ladder logic to get the 4-20ma back into the actual temperature. Not a big deal but more fussing. There's only a little discussion on the forum about noise problems with the RTD module. And all of it is pretty old. I'm inclined to skip the transmitter and go right to an RTD. Did things get quiet because everyone went the current loop route? Any advice appreciated. Thanks. Roger
Created Date: February 09,2014
Created by: AZRoger
I'm installing RTD sensors in three freezers. The cable run is about 50 feet.
The least cost solution takes each sensor to an input on an F204rtd module. The F204rtd automatically (with the right jumpers set) scales the values on their way to V-memory.
A more expensive and complicated solution is to use temperature transmitters like TTD-20-N40160-H and use a 4 input 4-20ma current analog module. This will require some additional scaling in the ladder logic to get the 4-20ma back into the actual temperature. Not a big deal but more fussing.
There's only a little discussion on the forum about noise problems with the RTD module. And all of it is pretty old. I'm inclined to skip the transmitter and go right to an RTD. Did things get quiet because everyone went the current loop route?
Any advice appreciated. Thanks.
Roger
Created Date: February 10,2014
Created by: scott.lawrence
The answer to any good question is: It Depends
I laughed at how ridiculously true that statement is :D
Created Date: February 11,2014
Created by: AZRoger
The answer to any good question is: It Depends.
I use 4-20 mA signal conditioners if:
the distance is long from sensor to PLC 50 feet of shielded cable
there are lots of motors or other loads in the vicinity that create a lot of EMI/RFI the only motors are in the freezer compressors
all my other signals are 4-20 and there is only one RTD I have 3 RTDs and no 4-20s
I need to be able to share the signal with multiple devices - say a PLC, and a digital indicator This is very interesting. I hadn't considered running the 4-20 loop through more than one receiver. But I plan to run indicators from the PLC.
Considering my situation, I'll go with the RTDs all the way. The shielded cable for the RTDs should be more than good enough for current loop if I need to switch later to solve noise issues. Thanks for the advice. :)
Roger
Created Date: February 10,2014
Created by: Tom Jenkins
It depends
The answer to any good question is: It Depends.
I use 4-20 mA signal conditioners if:
the distance is long from sensor to PLC
there are lots of motors or other loads in the vicinity that create a lot of EMI/RFI
all my other signals are 4-20 and there is only one RTD
I need to be able to share the signal with miltiple devices - say a PLC, and a digital indicator