Optiquest iRIS 220 Connecting a 2-Wire Loop-Powered 4-20mA Sensor, Required, Signal 4-20mA Sensor

55 - iRIS 220 / iRIS 320, V1.19 User Guide

6.3 Connecting a 2-Wire Loop-Powered 4-20mA Sensor

The iRIS 220 /iRIS 320 also supports the connection of many types of industry standard 4-20mA current loop instruments such as ultrasonic or radar level sensors. A very common configuration used with these devices is known as two-wire or loop-powered mode. This requires only two wires to the sensor and the 4-20mA loop current provides power for the sensor as well as being the proportional Analog sensor signal.

However, theses sensors often require a minimum voltage across them that may not be reliably achieved with a 12V supply, taking into account the voltage drop across the sense resistor. In such cases, a separate 12-24V boosted sensor supply is recommended.

The diagram below shows the recommended connection diagram for such an installation. It assumes the use of AI1 as the desired input channel.

The 250Ω sense resistor generates a 1-5V signal (from the 4-20mA current), which is then measured at the Analog input. The sensor should be configured for the correct channel, scaling and logging regime as described in section 4.3.8. An offset value will be required as part of the configuration, as the 4mA (1V) offset needs to be eliminated.

TOP

AI4
AI3
AI2			250Ω
AI1
			Resistor
AGND
5VOP			-	+
DI2
DI1			24V
DO2
DO1			12V
SDI-12
DGND			-	+
12V+
GND (-)
VIN+		-	+
GND (-)
			External
	Charging source
BOTTOM		12V Battery
	e.g solar panel
		(Required)

iRIS I/O Connector

-

Signal 4-20mA Sensor

+

Isolated 12V – 24V DC- DC Converter