Hello,
We are using several ‘4-Channel 4-20mA Input USB Wireless endNode’ in a project for an industrial customer. Each of the endnode 4-20mA inputs is connected to a current transducer (2A or 600A) which provides a 4-20mA output signal compatible with the endnode inputs.
Like all current transducers, I believe, the transducers we use do not require calibration.
We use the formula ‘4-20mA Value = ((MSB * 256)+LSB) * 0.0013568521031208’ to convert Endnode signals into 4-20mA values.
For example, for one of the Endnodes we obtain the following values when the current sensors read a current of 0A:
Input 1: 4.013 mA (+0.013 mA, +0.325%)
Input 2: 3.8975 mA (-0.1025 mA, -2.5625%)
Input 3 : 3.885 mA (-0.115 mA, -2.875%)
Input 4 : 3.86725 mA (-0.13275 mA, -3.31875%)
Since, for example, the values read vary by up to -3.3% (-0.13275mA) for input 4, I think we need to implement a calibration function so that the Endnode provides an accurate value of 4mA when the current read by the sensor is 0A.
What do you think would be the best way to do this, given the type of error the Endnode’s inputs can cause?
- Simply add 0.13275mA to all read values ? (see input 4 value)
- Multiply the values read by 103.3% ? (see input 4 value)
Thank you 