Instruction Manual

IM-106-880, Rev 1.0

January 2007

Section 4

OCX 8800

Using HART Communications

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-1

HART Communicator Signal Connections . . . . . . . . . . . . page 4-1

HART Communicator PC Connections . . . . . . . . . . . . . . . page 4-4

HART Menu Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-5

D/A Trim Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 4-9

OVERVIEW

HART COMMUNICATOR

SIGNAL CONNECTIONS

The HART communicator is a handheld communications interface device. It provides a common communications link to all microprocessor-based instruments that are HART compatible. The handheld communicator contains an 8 x 21 character liquid crystal display (LCD) and 25 keys. A pocket-sized manual, included with the HART communicator, details the specific functions of all the keys.

To interface with the OCX 8800, the HART communicator requires a termination point along the O

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4-20 mA current loop and a minimum load resistance of 250 ohms between the communicator and the power supply.

The HART communicator accomplishes its task using a Frequency Shift

Keying (FSK) technique. With the use of FSK, high-frequency digital communication signals are superimposed on the 4-20 mA oxygen output signal. The communicator does not disturb the 4-20 mA signal since no net energy is added to the loop. HART information is not available on the COe output signal.

The HART communicator may be interfaced with a personal computer (PC), providing special software has been installed. To connect the HART communicator to a PC, an interface adapter is required. Refer to the proper

HART communicator documentation in regard to the PC interface option.

The HART communicator can connect to the OCX 8800 oxygen analog output signal line at any wiring termination in the O

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4-20 mA current loop. There are two methods of connecting the HART communicator to the signal line. For applications in which the signal line has a load resistance of 250 ohms or more, refer to method 1. For applications in which the signal line load resistance is less than 250 ohms, refer to method 2.

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