Emerson Exchange 365

Hi Yunus,

The main things to take into consideration when selecting your transmitter are:
What information do you want out of the transmitter, and how frequently do you want that updated?

With many transmitters, 2 wire can provide voltage to the transmitter, together with analog output, and your choice of HART or Foundation Fieldbus (FF) protocol. These data signals allow you to get more than just the single output value from the same device. For example, you might want static pressure, differential pressure, and temperature from Emerson's Rosemount 3051SMV, or you might want mass flow, volume flow, and density from Emerson's Micro Motion 2200S. The problem is that the update rates of HART and FF data signals are much slower than what you might be accustomed to seeing with analog current outputs. Analog is constantly updating to represent current process conditions, unless you apply damping to it, whereas HART and FF can take several seconds in between burst communications, or poll and response. You have to determine if these extra seconds are critical in your process.

4 wire can give you options like Modbus and Profibus, which offer much more information at much faster (higher baud) rates, compared to HART and FF. Two of the four wires power the device. The other two wires communicate the data signal from the transmitter to the DCS.

You should also consider how you want to manage your field instruments. If you want to minimize the need to send engineers to the field to extract transmitter and process information, then you will want more data communicated into the DCS and Device Manager -such as diagnostic information, which can give you insight into why an instrument is having problems, without the need for a field visit. Emerson's AMS Device Manager allows you to manage your instruments from the control room through a single software interface that can capture and report on device alarms and diagnostic information.

Let us know if this is the answer you were looking for. If you are looking for more application-specific advice, I recommend getting in touch with your local Emerson office.

Best regards,
Travis