Wire (2-Wire) Analog Input Devices-Basic Automation

Connecting "loop-powered" 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. The top row is the input signal to the PLC that is the status of the input device.

Below is a typical differential pressure 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, 1VDC (102.3 digital) would equal -0.2 kPa and 5 vdc (511.5 digital) would equal 2 kPa in the PLC logic.