While both Foundation Fieldbus and HART have their own PROs and CONs, and are equally important protocols used in the Process Automation industry, the applications they are used in makes it differentiate from each other.
FOUNDATION Fieldbus vs HART
HART communication protocol
In multidrop installations, HART communication protocols are rare in the field. While we can have up to 15 devices installed in parallel, with multidrop we don’t have the variation of 4-20mA or the current fixed at 4 mA. We only have the HART information.
We can have two masters in the HART setup, the control system as the first and usually a handheld as the second, and each device will have a non-zero HART address. We’ll sometimes find this rare system when we have more than one device on a WirelessHART adapter.
We’ll also find two standard setups for HART. The first uses a HART card in the programmable logic controller (PLC) or distributed control system (DCS). We need to keep in mind that this doesn’t mean that the HART does the loop process control. It only uses the intelligent device management (IDM) in a plant asset management (PAM) system.
To know more about HART, you can read the Visaya Article on HART Basics
The second setup reads the current value and has a multiplexer among the field devices and the PLC, to catch all the HART data and send it to the system. This is typical because it makes the current loop a robust and straightforward installation.
One last option is setting a HART over other digital protocol; we can have HART over PROFIBUS or HART over EtherNet/IP. This way, we have HART field devices and an input/output in the field sending data to the system digitally. We can save money with this setup because the protocol needs fewer cables than a traditional current loop installation.
FOUNDATION Fieldbus communication protocol
The FOUNDATION Fieldbus (FF) is the most common digital communication protocol in major oil and gas companies around the world. It differs from HART in that it provides digital access to the analog signal, and companies usually use it only for IDM. The FOUNDATION Fieldbus offers many advantages over a traditional installation, giving the same smart device management with digital closed-loop control. The traditional system typically uses the 4-20 mA to do the loop control instead of a HART. With the FOUNDATION Fieldbus, the system uses the protocol for the control and the IDM.
Furthermore, FOUNDATION Fieldbus comes in High-Speed Ethernet (HSE) and H1. In the HSE version, you have ten megabits per second to integrate high-speed controllers, subsystems, servers, and workstations. The H1 link has 31.25 kilobits per second to connect field devices as 2sensors, actuators, and input/output. Unlike 4-20 mA and HART, FOUNDATION Fieldbus allows multiple variables from each device. The H1 also allows many devices to connect to a single wire pair, reducing the cost of installation.
The FOUNDATION Fieldbus HSE is the same protocol that we have in the field, but with its high velocity, we can have field devices in the network as well as controllers, subsystems, data servers, workstations, and more. We can also set up redundant systems and equipment for backups.
Conclusion: FOUNDATION Fieldbus or HART?
If our plant has a new project, we should consider a digital protocol. In that case, FOUNDATION Fieldbus will provide more benefits than a traditional setup. On the other hand, if the company already has 4-20 mA, we can switch all your networks to FOUNDATION Fieldbus or install WirelessHART to have easy and secure remote access. In either case, digital communication like FOUNDATION Fieldbus will probably serve you best.
To know more about FOUNDATION Fieldbus and HART, you can get in touch with our engineers and we will be happy to help.