Of Operation 2

HART FIELD CONTROLLER IMPLEMENTATION
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 (Figure 18). The analog output signal also carries the HART digital signal, which is used for monitoring the process measurement, making setpoint changes, and tuning the controller.



Figure 18: Smart Transmitter with PID
The communication rate of the HART protocol (2–3 updates per second) is generally perceived as too slow to support closed-loop control in the central host. With control in the field, the control function no longer depends on the HART protocol’s communication rate. Instead, the control signal is an analog output that is updated at a rate that is much faster than can typically be processed in a conventional control system. Processing rates vary from 2–20 updates per second, depending on the product. The HART digital communication rate remains sufficient for monitoring the control variable and changing setpoint values.

Industry Applications

Many companies in a wide variety of industries have already realized the advantages of using the HART communication protocol. This section describes some applications in detail and outlines the tangible benefits that result. The applications have been grouped into the following sections:

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  Inventory-management applications
  
• 
  Cost-saving applications
  
• 
  Remote-operation applications
  
• 
  Open-architecture applications
  

Inventory-Management Applications