An industrial facility required a cost-effective method to integrate two remote 4-20mA tank level signals into their central Distributed Control System (DCS) without installing expensive new cabling over a 100-meter distance. A wireless system, featuring battery-powered transmitters at the tanks and a multi-channel receiver at the control cabinet, was implemented to replicate the analog signals seamlessly.
- Cable Replacement: Wirelessly transmitted two 4-20mA signals, eliminating the need for complex and costly hard-wired installation.
- Zero-Maintenance Installation: The field-mounted transmitters are powered by batteries with a five-year life, removing the requirement for local power infrastructure.
- System Integrity: The receiver includes alarm relay contacts to alert the DCS of a low battery or loss of wireless signal, ensuring operational reliability.
- Future-Proof Design: A five-channel receiver was used to handle the two required signals, providing spare capacity for future expansion.
An electrical technician at a large industrial facility was tasked with integrating two remote tank level monitoring systems into the main Distributed Control System (DCS). The existing setup consisted of two tanks, each equipped with an ultrasonic level sensor that provided a 4-20mA analog output to a local controller. The challenge was to replicate these two 4-20mA signals at the main DCS cabinet, located approximately 100 meters away. The path between the tank location and the control cabinet contained various structures, making the installation of new, hard-wired signal cabling a complex, disruptive, and costly undertaking. The goal was to find a reliable and efficient solution that could transmit the two analog signals wirelessly and interface seamlessly with the analog input card of the DCS.
The proposed solution was a wireless transmission system comprising two IWmAT series transmitters and a single IWR-5 series receiver. Each IWmAT transmitter was connected in-line with the 4-20mA passive signal output from the existing tank level controller. This configuration acts as a simple and effective cable replacement, requiring no modification to the existing sensor wiring. A key advantage of the IWmAT transmitter for this type of field installation is its self-contained power source; a user-replaceable lithium C cell battery provides up to five years of operation with a 10-second transmission update rate, eliminating the need to run power cables to the tank location. The transmitters, housed in IP68-rated plastic enclosures, are well-suited for industrial environments. With a line-of-sight transmission range of up to 500 meters, the system offered a robust and dependable signal link over the required 100-meter distance, ensuring signal integrity.
At the control cabinet, the IWR-5 five-channel receiver was installed to capture the wireless data from both transmitters. This unit was factory-preset to provide two corresponding 4-20mA outputs, allowing the technician to directly wire the replicated tank level signals into the DCS analog input card for immediate integration. A significant benefit of the IWR-5 receiver is its built-in alarm functionality. A dedicated 5-amp rated changeover relay contact can be configured to activate in the event of signal loss from a transmitter or a low battery condition, providing a critical diagnostic alert to the DCS. This ensures that operators are immediately aware of any potential issues with the monitoring system. The selection of a five-channel receiver also provided the facility with three spare channels, offering a scalable solution for easily integrating additional wireless sensors in the future. The entire system delivered an end-to-end accuracy of better than 0.25% of full scale, providing the precision required for the plant’s process control network.
IWmAT 4-20mA Signal Input to Wireless Transmitter
- Part No: IWmAT
- Input: 4-20mA
- Supply: User replaceable Lithium C Cell battery
- Transmission Frequency: 2.4GHz using ISM bands
- Transmit Power: 18 dBm
- Antenna: Integral 0dBi
- Operating Temperature Range: -20 to +50°C
IWR-5 Five Channel Wireless Transmitter to 4-20mA Output Signal Receiver
- Part No: IWR-5
- Output: User-selectable 1-5V or 4-20 mA
- Power Supply: 12-32V dc
- Transmission Range: Up to 500 m line-of-site range
- Accuracy: <±0.25% FS BFSL end to end
- LED indication of the wireless link
- Installation: DIN rail or wall mounting kits available