SMART Type - HART Compatible Instruments

Hart is a analog communication protocol.

Smart is a digital communication protocol that overlays the analog.

Microprocessor‐based smart instrumentation enables control algorithms to be calculated in the field devices, close to the process. Some HART transmitters and actuators support control functionality in the device, which eliminates the need for a separate controller and reduces hardware, installation, and start‐up costs. Accurate, closed‐loop control becomes possible in areas where it was not economically feasible before. While the control algorithm uses the analog signal, HART communication provides the means to monitor the loop and change control set point and parameters.

A HART field controller takes advantage of the HART Protocol's simultaneous analog and digital signaling by converting the transmitter's traditional analog measurement output into a control output. The analog signal from the smart transmitter (controller) is used to manipulate the field device. The analog output signal also carries the HART digital signal, which is used for monitoring the process measurement, making set point changes, and tuning the controller.

Hart Communication Foundation (now Field Comm Group) Lots of good information.

Hope this gets you started with Hart. Just about any sensor from pressure transmitters to temp sensors to control of equipment used in most any industrial environment can be programmed, read, controlled with Hart.

Charles

That will work for one type of smart protocol there is also profibus and foundation fieldbus as well. Both of which have differernt levels of what is phrased as intelligence. This will range from health of the transmitter, calibration date, status drift in calibration to other varibles measured from the process such as pressures and temperatures to calculations within the transmitter to provide control to the process locally based on an operator setpoint. The key is understanding the requirments needed versus those that are preferred. Each will have an increasing cost... ie the more information = more dollars in the cost of the device. Also the wiring methods that support each type also changes and cannot be intermixed... Hart is typically a single 2 wire 4-20 FSK signal, where Fieldbus and Profibus is a multidrop wiring method supporting multiple devices over a pair of wires that is more of a communications protocol than that of a 4-20 wiring method... Both Profibus and Fieldbus Foundation have standards that can be downloaded from thier sites...

Hope this helps muddy up the water... ;-)

Hello ral412, I have worked with fieldbus a little, building control boxes. They had an internal data logger with proprietary connectors that chained multiple test instruments in a daisy chain. then the control boxes were linked to gather to a computer. The computer then controlled/read the test instruments.

With Smart controllers/transmitters you could also daisy chain "I think" up to twelve transmitters on one cable run. Then this meant the transmitters were set to 4ma output analog. Then we has an external power supply that fed the transmitters. The computer was set up for USB/Serial to Hart communications and read or talk to each unit on It's daisy chain. Which allowed our engineers and techs to run a single line from data logger/computer instead of cables to each transmitter back to data loggers. In addition with the digital signals there was less problems with interference. You could query a single transmitter or the whole string. It all was in how you setup your software.

Last with the smart/hart setup it was flexible and backwards compatible with our older units. This let us change over as we replaced the older analog only units.

Charles

Hi,

I am going to give you a simplified answer for both of your questions.

"dumb instruments" do not have memory.

"Smart Type" instruments have memory where you can store or save "settings" for example ranges,dampening,etc.

To store this "settings" in the instruments memory you will have to communicate with the instrument using that particular instrument's "language".

Most of the instruments I work with use HART "language" therefore they are HART Compatible.

Honeywell instruments don't use Hart protocol or "language" so they are not Hart compatible.

I hope this helps ...Thank you

There are articles on these topics in Wikipedia.