I am curious to compare the Profibus-DP flowmeter and profibus-PA flowmeter. They seem all apply even in process plant. What is the application for each type? Please correct me if I am not right. Thanks.

 

Hello Fred;

Over PA, you will have access to more diagnostic information (through external configuration programs, such as PDM or CommuWin) than over DP, but the main process information transferd will be the same; Flow, Totalizer (forward, reverse)..
Endress & Hauser, for example, offer their Promag 53W flowmeter with either DP or PA interfaces (amongst others). We select the interface according to our comm configuration for each plant; whatever is easier for our setup.
PA basically updates more slowly (31,25 kB under FISCO rules), DP can access much higher baud rates. But flow doesn't change quickly enough in our plants to warrant selecting DP over PA as a parameter.

Hope this helps,
Daniel Chartier

 

Just in case you are not aware: PROFIBUS-PA and PROFIBUS-DP are communication protocols, not flow measurement technologies

Flow measurement technologies include: differential pressure, vortex, electromagnetic, coriolis, thermal, variable area, positive displacement, and ultrasonic etc.

Depending on if you are measuring liquid, gas, or steam, and if the fluid is conductive or not, the flow rate, required accuracy, and if you need volume or mass rate etc. you would pick one flow technology the other.

The selection criteria for PA or DP is different. PA can be intrinsically safe if you need that, but DP cannot. PA uses only two wires and provides enough power for some of the above technologies, while DP always needs separate power. DP can be much faster than PA.

In general PA is used for field instruments such as flow meters.

To learn more about PROFIBUS-PA and some interesting alternatives take a look at the yellow book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" buy online: http://www.isa.org/fieldbuses

Jonas

 

Hi, Daniel
Thanks for your experience...