INTRODUCTION

 

HART (Highway Addressable Remote Transducer) protocol uses the Bell 202 Frequency Shift Keying (FSK) standard to superimpose digital communication signals on the 4-20 mA loop current shown as below figure. HART communicates at 1200 bps without interrupting and interference with the 4-20mA signal and allows a host application (master) to send/receive digital information from a smart field device.  

 

 
 

The 4-20mA signal communicates the primary measured value - the fastest and most reliable industry standard. The digital signal can be used for additional device information including device status, diagnostics, additional measured or calculated values, etc. Therefore, the HART communication including analog and digital information provides a low-cost and very robust complete field communication solution that is easy to use and configure.

 

HART is a master/slave protocol which provides for up to two masters (primary and secondary) and the secondary master such as handheld can be used to monitor/control the informatoin of HART bus. HART can be used in various modes such as point-to-point or multi-drop for communicating information to/from smart field instruments and central control or monitoring systems.

 

HART has two modes of operation: "multi-drop HART mode" where only digital communicaitons is available, and "peer-to-peer HART mode" where both analog and digital signal transmissions are supported simultaneously.

 

 

All of our HART convertors and gateways have a great level of compatibility to HART standards. Both multi-drop and peer-to-peer HART modes are supported. It is very easy to configure a system and test the communications using our software tools provided free with the convertor and gateway modules. Drivers for the models with USB port are also provided and they have full plug and play support.

 

 
In industrial harsh enverionments, communication over the data lines is disturbed by the noise and ripple signals being induced on these lines. Main cause of these noisy signals is the unwanted electromagnetic fileds in the environment and RS485, RS422 and CAN standards overcome this problem by using differential voltage lines for data signals. However, another cause for these noisy signals are the faulty currents flowing through the data cables due to the different grounding potentials at the two end-points of the data line. This unwanted system is called a "Ground Loop". sometimes this faulty current becomes so high that it is enough to damage the equipment at the two ends of the data line. Escessive surge currents flowing through the data  lines during lightning strikes are good examples for these situations. The only way to prevent such damages is to galvanically isolate the equipment attached to the data line. Since same scenairo is also possible for the power lines of these equipment, isolating the power lines also is the best solution.
 

DC / DC convertors are utilized at the power input and optocouplers are used for the signal lines in order to implement an isolation barrier inside a convertor or repeater. Max voltage difference between the input and output of an isolation barrier that the barrier could withstand without a damage, defines the level of that isolation barrier. Convertors and repeaters we are offering all have an isolation barrier of 3000 Vdc or 3750 Vrms AC. Although our standard models have 2-way isolation, there are also special models available with 3-way isolation.