from the Automation List department...
Smart transmitters
Information resources, documentation. topic
Posted by Paul Yetman on 16 March, 2003 - 6:18 pm
I am currently working on an offshore oil project, the specifications for the job state that the owners prefer "smart" transmitters. I have researched the term for two days now, but I have yet to find a formal definition of "smart". One article referred to HART as the de facto communication standard for "smart" transmitters. Is "Smart" a trademark name? What is the definition of "smart" technoology? De facto implies that HART is not exclusively tied to "Smart", if this is so what are other communication protocols?

Posted by Jonas Berge on 17 March, 2003 - 2:45 am
The term "smart" is a bit confused so it is not clear. It is almost synonymous with HART, but some would argue that many devices not using HART are also "smart".

One definition of "smart" that I have seen some place is that "smart" means you have both 4-20 mA and digital communication, simultaneously. Since this definition mentions "4-20 mA" it rules out the pure digital communication protocols (for "intelligent" devices). The detail "simultaneously" rules out some of the protocols that have 4-20 mA but cannot do 4-20 mA and communication at the same time, e.g. the Honeywell DE protocol.

Lastly, users these days do not like proprietary protocols. You may be able to find something other than HART that also supports 4-20 mA simultaneously, but although this meets the specification, the user may get very unhappy.

Jonas Berge

Posted by wlmostia on 17 March, 2003 - 5:28 pm
I think that the term "smart" came about to describe transmitters that had more capability than a standard analog 4-20ma transmitter(i.e. one you could only adjust range and span on and were based on analog electronics). This generally meant a transmitter that was microprocessor based with communication ability either through HART or a proprietary protocol such as Honeywell DE. Most all standard modern transmitters fall in the
"smart class" and the term generally only has meaning in reference to inexpensive transmitters, legacy systems, and the few applications where
new standard analog transmitters are bought (for example Rosemount's 1151 can be bought in both analog and smart versions).

Bill Mostia
William(Bill) L. Mostia, Jr. P.E.
Worldwide Excellence in Dependable Automation 281-334-3169
These opinions are my own and are offered on the basis of Caveat Emptor.

Posted by Bill Clemons on 17 March, 2003 - 2:52 am
IMO, 'Smart' implies that a digital signal is superimposed over the analog signal so in effect the 'Smart' host is receiving a primary 4-20 mA signal and additional frequency data describing several other variables communicated through the transmitter (alarm state, limit switch position, transmitter health, etc.). Some forms of 'Smart' may include configuration data transfer to populate a transmitter operations database (i.e. Foxboro). The Hart protocol describes basic premise of 'Smart' technology.

Posted by Diana C Bouchard on 17 March, 2003 - 2:04 pm
My impression is, "smart" is about as well defined as "real time", meaning not very. In a general sense, the term refers to a transmitter (or other device) that has some local data processing or communications intelligence, as opposed to just sending/receiving information in a "dumb" fashion.

Diana Bouchard
Pulp and Paper Research Institute of Canada (Paprican)
Pointe Claire, Quebec, Canada

Posted by Anonymous on 18 March, 2003 - 2:54 pm
In the beginning there was a simple transmitter that produced a 4 to 20mAmp signal depending upon the calibration range. This was done by putting the transmitter on a calibration rig and adjusting the output the the input range.
Then a marvelous thing happened, somebody invented the microprocessor that allowed sensor information to be loaded into the transmitter. Suddenly the need to bench calibrate the transmitter disappeared because the scaling was already in the transmitter.
Each major manufacturer then superimposed a digital signal on the 4 to 20mAmp so that created a selling point of remote set-up from the control room. In a spirit of freindliness all manufacturers developed their own communication protocol. Rosemount had HART, Bailey had FSK, Yokogawa had Brain etc. Overtime HART has become the defacto standard. As is the way its not the best but it wasn't the worst either but everybody has access. So low and behold we now have smart transmitters that have a HART communication that allows remote configuration.
The realy nice thing from a users point is that the transmitter turn down is much better, so spares inventories are significantly smaller

Hope this helps

Posted by Mo Khan on 18 March, 2003 - 5:09 pm
Most sensors are inherently subjected to calibration shift. This has precipatated the drive for "smart transmitters". They go all the way from being self checking to to being capable of remote in-line recalibration by a hand held calibrator to being adjusted from a remote control station. I guess that's the only smart thing about those transmitters atleast from a technician's point of view.

Posted by Farid on 10 July, 2004 - 7:45 am
SMART = Signal Modulating Auto ranging Transmiter. Honeywell i suppose was the one to state this termonology. SMART transmitters have not only the built-in microprocessor with this, it can also perform diagnosis and characterisaion. I believe that its not a communication protocal. Smart transmitters can use any protocaol for communication. it may be Digitally Enhanced (DE) , HART or fieldbus.

Posted by Jonas Berge on 13 July, 2004 - 2:21 pm
Hmmm, never heard that definition before... Here is my view:

To me "smart" means that you have a SIMULTANEOUS analogue signal and digital
communication. By this definition HART is "smart" because it has 4-20 mA and
the Bell 202 modulated communication at the same time. However, the
Honeywell DE protocol would not qualify since it is EITHER-OR, i.e. either
4-20 mA or digital communication, but not at the same time. I think that
some of the old Bailey transmitters also had a proprietary protocol also
using some form of FSK making simultaneous digital and analogue signals. DE
and Fieldbus transmitters are "intelligent".

Smart transmitters are not auto-ranging (like multi-meters). You configure a
range for the 4-20 mA signal and it stays there. You can remotely change
this range, but manually.

Take a look at chapter 1 of the book "Fieldbuses for Process Control:
Engineering, Operation, and Maintenance" (buy online in hardcopy or download
immediately in softcopy):

If you can't buy the book now, you can download chapter 1 (overview) for
free in softcopy form. It's free, but you must register an account. If your
email does not support this hyperlink feature correctly, please copy the
entire link and paste it into your Internet browser. Mind the line wrap,
make sure to get the complete path all the way to the 4585: merce/Product

Jonas Berge
Learn fieldbus at your own pace:

Posted by P.Samuthira Pandi on 15 July, 2004 - 11:01 am
SMART FAMILY is the registered trade mark of Rosemount INC.


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