Honeywell Transmitter Output-Digital Enhanced Mode - Honeywell MCT404 User Manual

2. Before you begin
2.2. Transmitter/Communication characteristics

Honeywell transmitter output-Digital enhanced mode

Most of the operation of the Honeywell Smart Pressure Transmitter Digital Enhanced (DE) mode is
similar to that of operation in the analog mode. The essential characteristics of operation in DE mode are
shown in Figure 2-3 Honeywell DE Mode Value Scaling
As indicated at the right of Figure 2-3 Honeywell DE Mode Value Scaling, output values of process
variables, as well as digital 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
accuracy is retained with less
maintenance
facilitates maintenance tasks
CAUTION:
Although it in not necessary to put a control loop in manual before communicating with a
transmitter operating in DE mode, caution is required if there is any potential for error in
identifying operating mode.
Honeywell HART Transmitters
Transmitters with HART capability have features that vary among manufacturers and with the
characteristics of specific devices. The FDC application supports the HART Universal, Common
Practice, and Device Specific Commands that are implemented in Honeywell HART transmitters
As the diagram in Figure 2-4 shows, the Honeywell HART Transmitter is virtually identical to non-
HART transmitters, except that the HART version includes a Digital I/O Modulator/Demodulator block
(key number (4) instead of the Honeywell DE communications block.
As indicated in Figure 2-5, the output of the HART includes two primary modes:

Point-to-Point Mode, in which one transmitter is connected via a two-conductor, 4-20 mA current
loop to one receiver.

Multi-Drop Mode, in which several transmitters are connected via a two-conductor network to a
multiplexed receiver device.
In point-to-point mode, the value of the primary PV is represented by a 4-20 mA current loop, almost
identical to that of the Honeywell Transmitter operating in analog mode. In this case however, the
analog signal is modulated by Frequency Shift Keying (FSK) methods, using frequencies and a current
amplitude that do not affect analog sensing at the receiver.
Note that the accuracy of the analog level must be precisely controlled for accurate sensing, but that
HART communications will not "bump" the process variables.
In multi-drop mode, up to 16 transmitters in HART 5 (addresses 0-15) and up to 64 transmitters in
HART6/7 (addresses 0-63) can exist on the two-conductor network, which precludes analog transmission
Revision 3
Unlike in the analog mode, communications devices do not "bump" the
value of the PV.
Digital communications are relatively immune to small variations in
circuit resistance or supply voltage.
Honeywell control systems include operating displays that enable direct
communication with transmitters operating in DE mode.
MC Toolkit (MCT404) User Manual 9