Analog input

3-wire sensors

This figure shows the schematic when using power from the Connect Sensor+ to power the sensor.

2-wire (loop-powered) sensors

You can connect the Connect Sensor+ to a 4/20 mA 2-wire sensor, which is also known as a loop-powered sensor.

This figure shows the schematic when using power from the Connect Sensor+ current loop to power a sensor.

Calculating supply voltage for a 2-wire (loop-powered) sensor

The power output from the Connect Sensor+ is configurable. The configured voltage value for the Connect Sensor+ is between the Power and Analog Ground terminals, as shown in the schematic above. The voltage across the terminals of the external sensor device (between Power and Analog Input) fluctuates, depending on the loop current. The fluctuation occurs because the variable loop current through the resistance inside the Connect Sensor+ changes the voltage between the Analog Input and Ground terminals. This is expected behavior for a 4/20 mA 2-wire interface.

When determining the value for the output power, you must calculate the range of voltages to determine whether the voltage setting is sufficient. The voltage across the external sensor device terminals (Power and Analog Input) is always less than the configured voltage.

For example, calculate an estimate of the range of voltage across the external sensor device terminals (Power to Analog Input) when the Analog Output voltage is set to 24 V. The nominal internal resistance of theConnect Sensor+ is 375 ohms, but may vary across current flow and temperature.

• Max: 24 V – (4 mA *375 ohms) ≈ 22.5 V
• Min: 24 V - (20 mA *375 ohms) ≈ 16.5 V