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RTU/PLC and external sensor compatibility

Lei Reyes

Jul 2, 2014
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Harald Kapp

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The sensor has a 4-20mA output.
The PLU has a 0-20mA input.
Therefore the two should be electrically compatible. The rest is programming/parametreization of the PLU to correctly interpret the sensor's output.
 

Lei Reyes

Jul 2, 2014
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So you mean to say that in that case, it is just a matter of converting the 4-20mA output of the sensor to a range that is the same as 0-20mA input of the PLU ?
 

Harald Kapp

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No, you simply connect the 4-20mA output to the 0-20mA input.
As "0" in a 4-20mA signal is repreasented by 4mA (not 0mA), you need to do offset and gain calibration in the PLU's software. You will need some kind of mapping in the PLU anyway, since you want the PLU to interpret the sensor's output in terms of distance, not mA.
 

Lei Reyes

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Ok got it . So this is the only thing I need to consider (if I intend to use a sensor that will be readable by a certain RTU) ? In short, the sensor must have a 4-20mA or Current output ratio that will match to my PLC's sensor current input ?
 

Harald Kapp

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Yes. The absolute values are irrelevant (although 4-20mA is a very common type of analog interface) as long as the output range of the sensor fits within the input range of the RTU.
 
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