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I am using a US381-0000005-100PA pressure transducer. The datasheet.

The '8' indicates its the 5-20 mA current loop type. The transducer has four wires - red, white, green, and black, but the diagram on page 5 only shows the current loop type to have two wires - red and black.

Why is this, does it not matter with which polarity I connect the white and green (which I infer is where the current loop happens)?

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You do not connect the other two wires. Look at the connector version, it explicitly says NC, or no connect. The same applies to the bare wire version.

In current loop mode, the sensor is connected in series with the power supply and a resistor, and regulates the output. You measure against the resistor. See https://electronics.stackexchange.com/a/372049/17178 for a generic explanation on 4-20 mA current sources.

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  • \$\begingroup\$ So I connect the red to power, and the black to a 240 ohm resistor, with the other lead on the resistor connected to ground? \$\endgroup\$ – A.S. Sep 4 '18 at 23:02
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    \$\begingroup\$ Yes. See the link I added. \$\endgroup\$ – Passerby Sep 4 '18 at 23:04

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