Honeywell STT700 STT700, User Manual

Page: 34 / 64

Revision A STT700 temperature transmitter
User’s Manual
Page 26
5. Operation
5.1. Overview
The Operations section describes the internal operation of the STT700 transmitter and the operations
of the Smart Field Communicator and the HART communicator with the STT700. If an EU Meter is
installed, see the Engineering Unit Meter User Guide 34-ST-25-18 for additional information on
operations.
This transmitter is powered via the 2-wire, 4-20 mA signal connected to the + and - terminals on the
output side of the module.
5.2. Configuration Tools
5.2.1. Smart Field Communicator (SFC) for DE Models
As previously indicated, the SFC communicates by connecting across the 4-20 mA wiring. DE
communication is by 16 mA pulses which disturb the 4-20 mA output signal. When in analog mode,
ensure that receiving instruments are not on automatic control. The SFC does not feed 16 mA pulses
into the loop but instead merely uses the power on the 4-20 mA wires and switches it through a field
effect transistor output switch. The SFC always acts as a master and the transmitter as a slave. When
the transmitter is operating in the digital DE mode, there is no wake-up pulse required and the SFC
communication does not disturb the PV signal. Consequently, there is no need to put the loop on
manual control when operating in the DE mode.
Supported Commands:

Read/write ID (e.g. TID 250)

Select a sensor type (e.g. Pt100)

Enable/disable sensor break detection

Set damping time (e.g. 0 second)

Set LRV and URV

Read URL (upper range limit), LRL (lower range limit) and span

Read process value and cold junction value in engineering units

Read output in % of span

Read software version

Read fail-safe direction configured by link

Set/reset user calibration to specific sensor

Set 0 and 100% output calibration

Force output current

Read/write scratch pad

Select broadcast type 4 or 6 bytes (Digital DE only). 6 bytes broadcasts PV and transmitter
database while 4 bytes broadcasts PV only

Enable/disable write protect

Enable/disable latching. Latching means the alarm needs acknowledgment. Press "STATUS"
key to acknowledge the alarm. If latching is disabled, the transmitter will leave the alarm
mode as soon as the alarm cause disappears.