HART is a master-slave communication protocol , which means that during normal operation, each slave
(field device) communication is initiated by a master communication device. Two masters can connect to each HART loop. The primary master is generally a distributed control system (DCS), programmable logic controller (PLC), or a personal computer (PC). The secondary master can be a handheld terminal or another PC. Slave devices include transmitters, actuators, and controllers that respond to commands from the primary or secondary master.in this session we are going to discuss about Basics of Hart Communicator
- The HART Communicator is a menu driven system. Each screen provides a menu of options that can be selected as outlined above, or provides direction for input of data, warnings, messages, or other instructions.
- When the HART Communicator is turned on, one of two menus will appear.
- If the HART Communicator is connected to an operating loop, the communicator will find the device and display the Online Menu (see below).
- If it is not connected to a loop, the communicator will indicate that no device was found. When you press OK (F4), it will display the Main menu.
- The Main Menu provides the following options:
- Offline–saves or retrieves transmitter configuration information.
- Online–connects the communicator to a compatible device
- Frequency Device–The Frequency Device option displays the frequency output and corresponding pressure output of current-to-pressure transmitters.
- Utility–The Utility option provides access to the contrast control for the HART Communicator LCD screen and to the auto poll setting used in multidrop applications.
- Once selecting a main menu option, the HART Communicator provides the information you need to complete the operation.
- The Online Menu can be selected from the main menu as outlined above, or it may appear automatically if the HART Communicator is connected to an active loop and can detect an operating transmitter.
- On-line mode is used for direct evaluation of a particular meter, reconfiguration, changing parameters, maintenance, and other functions.
- The keys of the HART Communicator include action, function, and alphanumeric and shift keys.
- ON/OFF Key Use this key to power the HART Communicator.
- When the communicator is turned on, it searches for a transmitter on the 4–20 mA loop.
- If a device is not found, the communicator displays the message, “No Device Found. Press OK.”
If a HART-compatible device is found, the communicator displays the Online Menu with device ID and tag
- Use these keys to move the cursor up, down, left, or right.
- The right arrow key also selects menu options, and the left arrow key returns to the previous menu.
- Use this key to quickly access important, user-selectable options when connected to a HART-compatible device.
- Pressing the Hot Key turns the HART Communicator on and displays the Hot Key Menu.
See Customizing the Hot Key Menu in the HART Communicator manual for more information
- Use the four software-defined function keys, located below the LCD, to perform software functions. On any given menu, the label appearing above a function key indicates the function of that key for the current menu. As you move among menus, different function key labels appear over the four keys.
- For example, In menus providing access to on-line help, the label may appear above the F1 key. Simply press the key to activate the function.
- In menus providing access to the On-line Menu, the label may appear above the F3 key. Simply press the key to activate the function.
Alphanumeric and Shift Keys
- The alphanumeric keys perform two functions: the fast selection of menu options and data entry.
- Some menus require data entry. Use the alphanumeric and shift keys to enter all alphanumeric information into the HART Communicator. If we press an alphanumeric key alone from within an edit menu, the bold character in the center of the key appears. These large characters include the numbers 0 through 9, the decimal point (.), and the dash symbol (—).
- To enter an alphabetic character, first press the shift key that corresponds to the position of the letter you want on the alphanumeric Then press the alphanumeric key.
- For example, to enter the letter R, first press the right shift key, then the “6” key (see Figure). Do not press these keys simultaneously, but one after the other.
Hart Communicator Connections
- The HART Communicator Model 275 / 375 can interface with a transmitter from the control room, the instrument site, or any wiring termination point in the loop through the rear connection panel as shown in Figure
- To communicate, connect the HART Communicator in parallel with the instrument or load resistor. The connections are non-polarized.
- Avoid contact with leads and terminals.
- The HART Communicator needs a minimum of 250 ohms resistance in the loop to function properly. The HART Communicator does not measure loop current directly.
Benefits outlined in this section include:
Improved plant operations
Instrumentation investment protection
for know more about how to calibrate transmitters with hart communicator click the link belowCalibration procedure of DPT transmitter