Analog and digital communication

Field Network Q&A

Hi, I am new to instrumentation and need to know the difference between HART and FOUNDATION Fieldbus. I mean, the process range usually converts from HART to 4-20mA, but what about FF communication?

Expert’s answer: Analog and digital communication

Ok, so you want to know more about the difference between HART and FOUNDATION Fieldbus as analog and digital communication.

Welcome to the world of instrumentation! Let’s start with the HART (Highway Addressable Remote Transducer). I’ll explain how the device works. Then we’ll look deeper into HART and FOUNDATION Fieldbus to understand them better.

The HART transmitter converts internally to send process values through the 4-20 mA current. Then the information mechanically converts to analog. Next, the transmitter converts the analog signal to digital. Here, you have a processor that can access and set up the device data as range, calibration, output, and more. Past the processor, the signal will convert from digital back to analog.

How the process value converts to 4-20mA

So the HART allows a digital signal to overlap the 4-20 mA current in the same cable without interference. You can learn more details here.

Digital over analog

If you have a multidrop network, then it’ll use 4 mA to power the field devices. The control signal transmits in frequencies of 1200Hz-2200Hz, allowing up to 15 devices per network.

Multidrop network

It’s rare to see a multidrop HART setup in the field, and you have to configure devices through the HART.

On the other hand, the FOUNDATION Fieldbus (FF), as a digital protocol, only converts the process data from analog to digital once. It doesn’t use analog output, so it can show the process values directly to the control system instead of having to convert. It can also make remote setup possible, a big advantage.

Want to know more about analog and digital communication?

The following links have more about FOUNDATION Fieldbus:

Other resources that might interest you

FOUNDATION Fieldbus architecture
What architecture we can build in a FOUNDATION Fieldbus network?

FOUNDATION Fieldbus troubleshooting!
What to do when you have problems with network stability for a FOUNDATION Fieldbus network?

Can a converter or a gateway connect a HART device in an FF network without data loss from the field devices, or do you have to stay with a HART over PROFIBUS remote IO?

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