Pepperl+Fuchs introduces Hart Loop Converter

Pepperl+Fuchs's new Hart Loop Converter (HLC) allows users to access the digital information from Hart-enabled field devices and makes it available to the analogue world of process control.

This is claimed to allow access to real-time values and opens 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.

Robert Schosker, product manager, said: 'Until now, digital process data from Hart-enabled field devices could only be accessed in combination with process control systems that were based upon a digital Fieldbus infrastructure.

'All other systems were only able to evaluate their analogue signals, while the digital output remained out of reach.

'Maintaining a safe production process often depends on the right information at the right time.

'The new HLC leverages the full potential of Hart-enabled field devices, acting as a bridge between the digital and analogue world by providing access to vital process data, which until now were simply unavailable,' he added.

The HLC is both a transmitter power supply and a Hart monitor.

It uses the Hart (Highway Addressable Remote Transducer) protocol to communicate with the field device connected to it and transfers its digital values into analogue 4-20mA signals.

Up to three Hart signals can be monitored at the same time and are provided as independent analogue signals.

Hart is the internationally accepted standard for the communication of intelligent field devices via the 4-20mA signal.

Meanwhile, most field devices support Hart and offer this digital protocol next to their standard 4-20mA analogue signals in order to provide the plant operator with vital measuring values or status information.

Currently, a basis of more than 20 million intelligent actors and sensors is installed in the worldwide process industry.

They 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 the form of analogue 4-20mA 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 is intended to open up opportunities for parameter-dependant process control.

Monitoring such information can contribute to improved production process safety or it can 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 with 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 analogue 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 HLC into an alarm device that can detect critical process parameters and helps to keep the continuing production process within safe operating conditions.

Schosker said: 'One major advantage to this is that the alarm is triggered directly by the digital Hart signal and not by a separate analogue signal, which would normally require a separate sensor with associated wiring.

'In the case of the flow meter, such an alarm function could be installed without additional hardware requirements in order to trigger an alarm as soon as the process media exceeds a specified temperature.

'It would even be possible to activate up to four trip values, each of them being connected to an independent relay,' he added.

Instead of converting up to three digital Hart signals into analogue signals, the HLC can also be programmed to provide one signal via three analogue channels.

As a result of this 'signal splitting', it is said to be possible to provide one and the same signal for different systems, such as 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 100ms.

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.

The HLC is an interface component designed to fit into any cabinet with a 35mm 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 connected parallel to an existing power supply without interfering with the safety characteristics.

Within a Hart loop, the device can be configured as a 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 a primary master.

In this case, an additional secondary master can be connected.

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 HLC, Pepperl+Fuchs offers an solution to read essential digital signals and dynamic measuring values that are provided as a standard feature of many Hart-enabled field devices and makes them available under the conditions of conventional analogue process control systems.

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