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USB-1208LS Wire Encoder only working partially



I have a 2 wire encoder that outputs a 4-20mA. 

Excitation voltage 5V Channel 30 is applied to RED from encoder. Black is connected to a 240ohm resistor. Resistor is connected to GRND (Channel 3). Resistor also connects to Channel 1 for voltage input. 

Channel mode is Single-Ended. 

Voltage seen on Channel 1 is 0.76V. Encoder only increases the voltage up to 0.86V and then it stops. Is this a bad sensor? or is there something wrong with the wiring? 


Encoder is an CWP-S500A. 

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I don't think it's a bad sensor. Typically, 4-20mA current loops need at least 10 volts and more is better. Many use a 24 volts.

A 240 ohm resistor results in a voltage range 0f 0.96 to 4.8 volts leaving little left for the sensor itself. I suspect it will work if you use a 12 volt power supply. Use the differential mode and the input across the resistor. The connection should be as follows: connect (+)12v to (+)input, (-)input to (-)12v. Connect the inputs, (+)input and (-)input, across the resistor. 

Best regards,





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Yes. This worked. I used an independent 16V power source and now I can see the full extent of the wire sensor. Calibration is not an issue for my project since I am importing the data into wit Python script and I can correct values programmatically. 


Thank you for your help!



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