Introduction; Overview; Hart  Mode Communication - Honeywell SLG 700 User Manual

1.1 Overview

The SLG 700 SmartLine Level Transmitter can be configured for operation with HART

or FOUNDATION Fieldbus communication. This manual addresses the processes to configure a
Transmitter for HART

1.1.1 HART
As indicated in Figure 1, the output of a transmitter configured for HART
primary modes:

Point-to-Point Mode: where one Transmitter is connected via a two-conductor, 4-20
mA current loop to one receiver.

Multi-Drop Mode: where multiple Transmitters are connected through a two-
conductor network to a multiplexed receiver device.
Operating
Range of
Transmitter
(in "implied" EU;
Example:
0-400 in cm
Figure 1 – HART Point-to-Point and Multi-drop Value Scaling
In point-to-point mode, the value of the Primary Variable (PV) is represented by a 4-20mA current
loop, almost identical to that of a Transmitter operating in analog mode. In this case, however, the
analog signal is modulated by Frequency Shift Keying (FSK), using frequencies and current
amplitude that do not affect analog sensing at the receiver. FSK modulation is for sending digital
messages in addition to the analog value. The accuracy of the analog level must be precisely
controlled for accurate sensing. HART communication will not bump process variables.
In multi-drop mode, theoretically up to 16 devices in HART 5 (addresses 0-15) or up to 64 devices
in HART6/7 (addresses 0-63) can exist on the two-conductor network. Practically, the number of
devices in a multi-drop installation is limited due to design constraints. When installing into a multi-
drop network, consider that the SLG700 requires a minimum startup current of 17mA and a
minimum terminal voltage of 11V during startup. After this initial startup period (approximately 0.5
seconds), the loop current will be fixed at 4mA, and the minimum terminal voltage is 14V. The
power source, wiring, intrinsic safety barriers, and other devices in the network must also be
considered.
Revision 5

1 Introduction


communication.
Mode Communication
SLG 700 Series HART Option User's Manual

version 7

protocol includes two
Page 1