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10 important differences between HART and Foundation Fieldbus

Introduction

Today in this article we will have a look at the 10 important differences between HART and Foundation Fieldbus.

Foundation Fieldbus and HART protocol is managed by the nonprofit organization FieldComm Group.

10 important differences between HART and Foundation Fieldbus

Topology

In the HART system, each field device is connected to the system through its dedicated loop.

While in the case of the foundation Fieldbus, devices are connected to the system in a chicken foot-type configuration.

Typical Network of Foundation Fieldbus

Typical Network of HART

So, when a cable or loop fault occurs in HART, then only that particular device will go offline or malfunction.

While in the case of Foundation Fieldbus, if the cable or loop fault occurs, then more than one device (generally 12-16 devices) will go offline or malfunction.

Cable requirement

For the HART system, each device has its loop, hence more cable is needed. For Foundation Fieldbus devices, typically 12-16 devices are connected through one cable from the Marshalling cabinet to the Field Junction box. Hence less cable is required.

Another important factor is the cost factor. For the HART system, the cost of cable is more as compared to the Foundation Fieldbus system cable cost.

Signal communication method

In the HART system, a 4 mA to 20 mA analog-type signal is used. While in the Foundation Fieldbus system, digital signals are used.

Communication Direction

In HART, only one-way communication is possible. In Foundation Fieldbus, two-way communication is possible.

Time for erection and commissioning

A HART system will take more time and resources compared to the Foundation Fieldbus system for the erection and commissioning of new plants.

Signal type

As discussed in point number 1, the HART system has a dedicated loop for every device.

Hence, there is a single signal on one cable. While in the case of Foundation Fieldbus, the signal used is a kind of multiplexed signal in digital form.

Signal accuracy

As the HART system used an analog signal, the chances of error in the signal decreased.

While in the case of the foundation Fieldbus system, the signal is digital, hence the chances of error are too less. Hence HART signal is less accurate than the Foundation Fieldbus signal.

Interoperability

There is too little interoperability in the case of HART devices. While Foundation Fieldbus devices have a large interoperability

Ease of installing new device

In case of new device installation in the HART system, a spare cable is needed which should be running from the field to the marshaling cabinet.

Because of this, a limited number of new devices can be added to the system due to spare cable availability.

In the case of new device installation in the Foundation Fieldbus system, only a cable is to be laid between the field junction box and the device.

Advanced diagnostics

In HART advanced diagnostics is very limited. In the Foundation Fieldbus system, all device’s advanced diagnostics are available.

Due to this advanced diagnostics feature, device failure can be predicted and action can be taken before the device fails.

Practically which is good HART or Foundation Fieldbus?

Most people prefer HART over Foundation Fieldbus because of the increased reliability of the system.

If the field barrier in Foundation Fieldbus fails, all the devices connected to that field barrier go into a fault state.

Thus, we lose 12-16 devices in one shot. This is the major issue in Foundation Fieldbus. The issue is faced by almost all Instrumentation Engineers and hence HART is preferred.

Also, in critical loops taken for ESD and other essential tripping functions, the HART system is only used. The Foundation Fieldbus system is only used for monitoring parameters and less critical loops.

Resources

Resources

And recently, I also found this interesting free book on Fieldbus by MTL. i hope these resources will help you.


Fieldbus Wiring Guide


And if you are from INDIA I will suggest you below video from the Electrical and Automation YouTube Channel. In this video, you will find how the Foundation Fieldbus network Architecture and its components.


Foundation Field Bus explained in Hindi

EndNote

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