How to Use 4-20mA Sensors to Monitor Industrial Applications

Sometimes you need a way other than MODBUS to connect third-party systems to an environmental monitoring unit and the 4-20mA current sensor from HW Group provides an ideal method. Typical applications for 4-20mA sensors including measuring fuel tank levels, gas concentration and connected pressure transducers, oxygen concentration, pH levels and other industrial type system factors.

What are 4-20mA Sensors?

4-20mA sensors are used in industrial applications for transmitting Analog signals over long distances. The current loop varies between 4mA (representing the lowest measurement) and 20mA (representing the highest measurement). These sensors require a power supply and an Analog-to-digital conversion to be interpreted by digital monitoring devices.

The HW Group 4-20mA Current Sensor

The 1-Wire UNI 4-20mA Current Sensor from HW Group is typically used to connect an industrial probe with 4–20mA output 2wire current loop. The sensor has an 8-point calibration table to allow setting of the measured output relative to the industrial application. The sensor is designed for use with ARES, Perseus, Poseidon2 and SD-2×1Wire environment monitors. A WiFi version is also available in the SD-4-20mA Wireless Environmental Monitor

How to Connect the 4-20mA Sensor to an HW Group Device

Using 4-20mA sensors with HW Group environmental monitoring devices involves a few key steps to ensure proper integration and functionality.

Selecting An Appropriate Monitoring Device

There are several monitoring solutions from HW Group that support Analog inputs and are suitable for 4-20mA sensors:

• Perseus and Poseidon2 Models:typically used for environmental monitoring and supports Analog inputs with the addition of a 1-Wire UNI 4-20mA Current Sensor.
• ARES Series: designed for remote monitoring over GSM/LTE; also supports Analog inputs.

Ensure that your monitoring device has the necessary Analog input capability. If not, you might need an additional Analog input module such as the 1-Wire UNI 4-20mA Current Sensor.

Connect the 4-20mA Sensor to Monitoring Device

Materials and items required include:

• 4-20mA sensor
• A compatible environmental monitoring device
• Analog input module (if necessary)
• Power supply for the sensor
• Appropriate wiring and connectors

Then follow these steps to make the connections required:

• Power the Sensor: connect the power supply to the 4-20mA sensor. Ensure the power supply meets the sensor’s specifications.
• Wiring the Current Loop: connect the positive terminal of the power supply to the positive terminal of the 4-20mA sensor. Connect the negative terminal of the sensor to the Analog input module of the HW Group device. Ensure the return loop from the Analog input module is connected back to the negative terminal of the power supply to complete the circuit.
• Analog Input Module: if using an Analog input module like HWg-AI, connect the sensor output to the module input. Then connect the module to the HW Group device using the appropriate ports (e.g. RJ45 or terminal blocks).

Configuring Your Monitoring Device

Once the physical connections are established, configure the monitoring device to interpret the 4-20mA signal correctly. The configuration steps include:

1. Access Device Interface: log in to the web interface of your device using a web browser. Enter the device IP address to access the settings.
2. Navigate to Analog Input Settings: find the section for Analog input configuration. This may vary depending on the device model.
3. Set Input Type: configure the Analog input to accept a 4-20mA signal. This typically involves selecting the input type (current) and setting the appropriate range (4-20mA)

Calibration and Scaling

Input the calibration settings to convert the 4-20mA signal into meaningful data. For example, if the sensor measures temperature from -50°C to 150°C, set the corresponding 4mA value to -50 and the 20mA value to 150. Then, save the configuration settings to apply changes.

Monitor and Analyse Data

With the hardware and software configured, you can now monitor and analyse the data from the 4-20mA sensor through the device interface.

• Real-time Monitoring: view real-time sensor readings on the web interface or using HW Group monitoring software
• Data Logging: configure data logging to record sensor measurements over time
• Alerts and Notifications: set up alerts and notifications based on sensor thresholds to receive warnings via email, SMS, or SNMP traps

Conclusion

Integrating 4-20mA sensors with a compatible environmental monitoring solution can provide a comprehensive way to monitor combinations of systems on industrial sites. By following the steps outlined above, you can effectively connect, configure, and utilize 4-20mA sensors with compatible devices such as the Perseus, Poseidon2 and Ares devices, ensuring accurate data acquisition and monitoring for your specific applications.

For more information see the HW Group monitoring and data logging products available from Server Room Environments or contact our Projects Team.