The essentials of HART communication and the IIoT

In a process plant operating with 4–20 mA/HART instrumentation, unexpected situations can quickly escalate if diagnostic capabilities are overlooked. This example story summarizes a typical maintenance situation:

Imagine a day of heavy rainfall. The maintenance team anticipates routine operations with minimal intervention. However, multiple issues arise simultaneously, requiring immediate attention. The team is suddenly faced with a critical level measurement problem.

An operator reports that a level transmitter is providing fluctuating readings, and the process is running without reliable level information. The transmitter is located at a remote point in the plant, far from the workshop, and accessing it requires navigating through adverse weather conditions.

Upon reaching the device, the technician discovers that local configuration is unavailable. To diagnose the issue, a field configurator is required - but its battery is depleted. This delay forces the technician to return, recharge the tool, and revisit the instrument. During this time, the process continues without accurate level measurement, and operators are unaware that the level has risen too high.

Ultimately, the point level switch activates, shutting down the process and halting production. While the safety system functions as intended, the incident highlights a significant vulnerability: the lack of immediate diagnostic access prolongs troubleshooting and contributes to unnecessary downtime - an examplary story.

Does the example above sound familiar? Situations like this can often be resolved quickly by accessing device data directly from the field. Even when field devices rely on 4–20 mA analog signals, most are equipped with the HART Communication Protocol - yet in this case, it was not utilized.

HART is not a new technology, as most of us know. Despite the fact that millions of HART-enabled devices are installed across industries worldwide, its fundamentals are still not fully understood by everyone.

HART stands for Highway Addressable Remote Transducer, and the protocol was introduced in the mid-1980s. It became an open standard in 1986, after initially being proprietary.

HART is a hybrid protocol that superimposes a digital signal on the traditional 4–20 mA analog signal—a standard that has been in use for decades and remains prevalent in many plants today.

From a technical perspective, HART uses the Bell 202 standard and employs Frequency Shift Keying (FSK) at 1200 bps. Two frequencies represent binary values: 1200 Hz for “1” and 2200 Hz for “0.” This approach enables communication between master and slave devices without interrupting the analog signal.

HART-enabled field devices provide a comparable level of diagnostic and operational data to fully digital devices. The key distinction lies in how this data is accessed. Digital devices continuously communicate their information, regardless of whether it is actively used. In contrast, many HART devices remain in the field with valuable data locked inside.

All devices using the HART Communication Protocol support Intelligent Device Management (IDM), similar to what is available with PROFIBUS, FOUNDATION Fieldbus, and other digital technologies. While HART offers a multi-drop mode for reading data from multiple devices, this method is slow and therefore not widely adopted. Fortunately, there are alternative solutions to extract this critical information without relying on multi-drop configurations.

So, what is the real difference between HART and fully digital fieldbus devices? In terms of the type and quality of information - such as device health and diagnostics - there is virtually no difference. However, the standard installation of HART devices typically means that the control system only receives the 4–20 mA analog signal, unlike digital networks where all device data is continuously available.

The good news is that modern solutions, both wired and wireless, now enable efficient access to HART data and transform it into actionable insights - such as through an IIoT ecosystem like Endress+Hauser's Netilion.

Situations like the level transmitter example mentioned earlier can often be avoided by leveraging modern connectivity options. There are practical ways to retrieve IDM data from HART-enabled field devices without major investments or extensive plant modifications.

1. WirelessHART Integration: Wireless is one of the most straightforward methods for collecting device data. By adding a WirelessHART adapter to existing field devices, data can be transmitted to a WirelessHART gateway. This gateway - such as the Fieldgate SWG70 from Endress+Hauser - can then be connected to an edge device, enabling seamless integration with IIoT cloud platforms. Wireless solutions are already widely adopted across industries and have proven effective in numerous applications.

2. HART Gateways for Wired Integration For plants that prefer wired solutions, HART gateways offer a reliable way to extract data from the 4–20 mA loop and connect it to IIoT platforms such as Netilion. While this approach may involve a slightly higher initial investment compared to wireless, the return on investment is typically realized within a few months. An example is the Fieldgate SFG250, an Ethernet-based HART gateway that provides a simple and efficient method to access device data and integrate it into cloud systems. HART over Ethernet is one of the most effective ways to unlock valuable information without adding complexity to daily operations.

As demonstrated in the previous examples, IIoT is not as distant or complex as it might seem. The benefits of IIoT services are clear - implementing them in your plant can deliver significant operational advantages.

For instance, IIoT can provide a comprehensive overview of your installed base. Did you know that approximately 30% of assets in many plants are already obsolete? With IIoT services, you can easily register devices manually or automatically via an edge device, creating a digital twin.

Once connected, digital services like Netilion Analytics offer transparent insights through intuitive dashboards and graphs. These analytics reveal critical information, such as device availability and lifecycle status, reducing complexity and streamlining maintenance efforts.

Another powerful application of IIoT combined with the HART Communication Protocol is device health monitoring. Digital services like Netilion Health provide diagnostic information for both Endress+Hauser and third-party devices.

Whether using wired or WirelessHART connectivity, your gateway can link to an edge device, which securely communicates with the cloud. This enables access to device health information from anywhere.

The system displays device statuses based on NAMUR NE 107 standards. When a diagnostic alert or failure occurs, you can drill down into detailed information to identify the root cause and corrective actions. Historical data is also available, showing when and how often events occurred—giving you a clear picture of asset performance over time.

Had such a health monitoring system been in place during the level measurement incident described earlier, the issue could have been detected early, saving time, preventing unscheduled downtime, and reducing costs.

In short: IIoT makes plant management simpler, smarter, and more efficient.