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Pepperl+Fuchs announces HLC HART Loop Converter

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Pepperl+Fuchs announces HLC HART Loop Converter

March 12, 2009 - Pepperl+Fuchs introduces the HART Loop Converter (HLC). The HLC allows users to access the digital information from HART-enabled field devices and make it available to the analog world of process control. This allows access to a wealth of real-time values and opens completely new opportunities to achieve more targeted process control, detect critical situations at an early stage, and add more transparency and safety to the complete production process.

The HLC is both a transmitter power supply and HART monitor. It uses the HART protocol to communicate with the field device connected to it, and transfers its digital values into analog 4-20 mA signals. Up to three HART signals can be monitored at the same time and are provided as independent analog signals.

Highway Addressable Remote Transducer (HART) is the internationally accepted standard for the communication of intelligent field devices via the 4…20 mA signal. Meanwhile, most field devices support HART and offer this digital protocol next to their standard 4...20 mA analog signals in order to provide the plant operator with vital measuring values or status information. Presently, a basis of more than 20 million intelligent actors and sensors is installed in the worldwide process industry. They have field-proven reliability, and are used to control valves and measure vital process data, such as flow, level, temperature, pressure, or pH value.

A typical example of such a device is a multi functional HART flow meter, which is used in combination with many processes in the chemical and petrochemical industries. These devices usually measure three different types of process data: pressure, temperature and differential pressure. Based on these data, they calculate the flow of the respective process media and provide the process control system with this information in form of an analog 4...20 mA signals.

As a result, a multi-functional flow meter will not just provide the calculated flow values, but also directly measured process data such as pressure and temperature. This opens up new opportunities for parameter-dependant process control. Monitoring such information can contribute to improved production process safety, or enable users to keep an eye on specific parameters that can be important to maintaining consistent quality levels.

Additionally, the HLC allows access to additional functions of HART field devices for monitoring and control of production processes without requiring additional wiring and without the need to interfere in any other way into the existing communications infrastructure. In practice this means that the HLC converter contributes to protecting investments into the production control system by allowing access to the HART functionality of existing field devices, while preserving the available analog communications infrastructure.

The HLC is equipped with two or four trip values. These can be programmed to monitor specific error conditions detected by the field device and will react as soon as a specific value falls below or exceeds a pre-defined trip value. This turns the HART Loop Converter into a reliable alarm device that is able to detect critical process parameters, and helps to keep the ongoing production process within safe operating conditions.

Instead of converting up to three digital HART signals into analog signals, the HLC can also be programmed to provide one signal via three analog channels. Due to this so-called “signal splitting,” it is possible to provide one and the same signal for different systems - for example, the process control system, a data recorder or a display for operator interaction.

Depending on the field device that is connected, the HLC can be operated in one of two operating modes. Normally, the device operates in burst mode, which allows considerably faster communication. In this mode, the field device automatically provides an updated value three to four times per second, which the HLC will confirm within 100 milliseconds. In case the field device does not support this mode, the HLC will enter into command-and-answer mode and will request the dynamic values from the field device at the highest possible sampling frequency.

Physically speaking, the HART Loop Converter from Pepperl+Fuchs is an interface component designed to fit into any cabinet with 35 mm DIN mounting rail. It can be integrated into the current loop of the field device in various ways. If active connection is chosen, power supply of the field device will be provided via the HLC. In this case, intrinsically safe connection of the field device without the need for additional isolated barrier or Zener barriers is guaranteed. If passive connection is chosen, the HLC is simply connected parallel to an exiting power supply without interfering with the safety characteristics.

Within a HART loop, the device can be configured as primary or secondary master. In case the process control system does not communicate with field devices via the digital HART protocol, the HLC will be configured as primary master. In this case, an additional secondary master can be connected. As an example, this might be a mobile communications device used to read digital signals or program the converter. In case there is already a master in the form of an asset management system, the HLC can alternatively be used as a secondary master.

The converter features a built-in display and keypad for status indication and programming. Additionally, an external programming device or PC/notebook may be connected via a front side terminal.

With the HART Loop Converter, Pepperl+Fuchs offers an unique solution to read essential digital signals and dynamic measuring values that are provided as a standard feature of many HART enable field devices, and makes them available under the conditions of conventional analog process control systems. This not only provides long-term protection of the system investment, but also leads to increased process safety and plant availability since this solution allows information into the process control system that was previously unavailable, or required considerable hardware and installation efforts.

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