foundation fieldbus confusion

[here2learnm]

from what I read foundation fieldbus is digital, but I often see people representing the signals as AI (FF) and AO (FF), is this correct? (A=Analogue)

Are the following statements correct?
FF devices have analogue input and analogue output function blocks only inside the device (for example a pressure transmitter).

When a signal is transmitted from a FF device to DCS, the signal will be converted to digital before transmitting.

Finally, On the I/O list I have a level transmitter transmitting signal to DCS, so the I/O signal type should be AI (FF) or just FF or DI (FF)?

Thanks

 

[djs]

Foundation Fieldbus is a communications protocol, similar to say TCP/IP. So what is transmitted over the bus is a string of ones and zeros. How those ones and zeros are interpreted at each end is depends on the configuration of the field device and also of the DCS. BTW the configuration has to match at both ends. Foundation Fieldbus uses the concept of signal blocks for configuring the data received and sent over the bus. Therefore if you want to send an analog signal, you would use an analog block at each end.

 

[here2learnm]

Thank you.

does this mean Foundation Fieldbus can transmit 4-20mA signal if analog blocks are used?

i thought FF replaced 4-20mA?

 

[KiwiMace]

No, Analog Input or Outputs in FF (or by any other digital protocol) means that the data point represents a linear signal, continuously variable over the given range. Digital I/O is a state that is changing between on/off. You still call it an 'analog' input even though the data is communicated digitally.

 

[djs]

In the digital or field bus realm an analog signal usually (but not always) means a floating point number in IEEE format (32 bits). So no 4-20ma signal.