Honeywell SmartLine ST700, User Manual

Page: 21 / 202

Revision 4.0 ST 700 Series HA
RT/DE Option User’s Manual
Page 7
3 Communication Model for ST 700 Standard
Transmitter
3.1 Overview
The ST 700 Standard SmartLine Pressure Transmitter can be configured for operation with
Honeywell’s Digitally Enhanced (DE) communication protocol, HART version 7, and Fieldbus
communication. This manual addresses the processes to configure and calibrate a Transmitter for DE
and HART communication. Refer to the
ST 700 SmartLine FF Transmitter with FOUNDATION
Fieldbus Option Installation & Device Reference Guide , Document # 34-ST-25-48 for Fieldbus
details.
3.2 Digitally Enhanced (DE) Mode Communication
Although it is unnecessary to put a control loop in manual mode before communicating
with a Transmitter operating in DE mode, caution is required if there is potential for error in
identifying the operating mode.
In DE mode, the PV is available for monitoring and control purposes; and the meter body temperature
(secondary variable) is available for monitoring purposes only.
Much of the operation in the Digitally Enhanced (DE) mode is similar to that of analog operation.
The essential characteristics of DE mode operation are shown in
Figure 4 .
Figure 4
– DE Mode Value Scaling
As indicated at the right of Figure 4 , output values of process variables, as well as communications
are transferred to a receiving device digitally. The digital coding is Honeywell proprietary, which
requires the use of DE-capable Honeywell control equipment.
The use of DE mode offers several advantages:

Process Safety : Unlike analog mode, communications devices do not bump the PV value.

Accuracy: requires less maintenance.

Digital communication: Relatively immune to small variations in circuit resistance or supply
voltage.

Facilitates Maintenance Tasks : Honeywell control systems include operating displays that
enable direct communication with transmitters operating in DE mode.