Wire (3-Wire) Analog Input Devices – Basic

Connecting standard 3-wire analog input devices is usually straight-forward. They connect directly to the dual level terminal blocks in the control panel. The bottom row contains the positive DC reference wire connection on the left, and the negative DC reference wire connection on the right. The top row is the input signal to the PLC that is the status of the input device.

Below is a typical pressure regulator sensor field device wiring diagram.  There are a wide variety of field sensors available on the market.  Wiring is usually/can be polarity sensitive.  Refer to the manufacturer’s installation instructions for specific wiring diagrams per your application.  Use twisted-shielded cabling whenever possible, grounding only one end of the shield to earth ground.

*Note – Inputs 0 – 3 can be used for analog inputs. Be sure to scale the analog input correctly in the programming according to the linear scale as shown above to the right.  In this case, 0VDC (0 digital) would equal 0 PSI and 10 vdc (1023 digital) would equal 130.5 PSI in the PLC logic.