Wiring Variations; Note: After Wiring, Torque The Screws To Around 4 To 5(Lb-In). Maximum Should Not Exceed 1.1 Nm (10 Lb-In). Don't Pull The Wires After Connecting To The Screw Terminals; Input Sensor Wiring - Honeywell SmartLine STT850 Quick Start Manual

Figure 8: Transmitter 9-Screw Terminal Board and Grounding Screw
As shown in Figure 8, each Transmitter has an internal terminal to connect it to earth
ground. Connect sensor shield to the internal ground screw. The ground terminal can be
added to the outside of the Electronics Housing. Grounding the Transmitter for proper
operation is required, as doing so tends to minimize the possible effects of noise on the
output signal and affords protection against lightning and static discharge. An optional
lightning terminal block can be installed in place of the non-lightning terminal block for
Transmitters that will be installed in areas that are highly susceptible to lightning strikes. As
noted above, the Loop Power wiring shield should only be connected to earth ground at
the power supply end.
Wiring must comply with local codes, regulations and ordinances. Grounding
may be required to meet various approval body certification, for example CE
conformity. Refer to Appendix A of this document for details.
Note: Terminal #3 is for loop test and is not applicable for Fieldbus option.
Terminal #4 is for Digital Output and is not applicable for Fieldbus option.
Foundation Fieldbus not applicable to STT750
For HART and DE the Transmitter is designed to operate in a two-wire power/current loop
with loop resistance and power supply voltage within the operating range; see
With an optional remote meter, the voltage drop for this must be added to the basic power
supply voltage requirements to determine the required Transmitter voltage and maximum
loop resistance. Additional consideration is required when selecting intrinsic safety barriers
to ensure that they will supply at least minimum Transmitter voltage, including the required
250 ohms of resistance (typically within the barriers) needed for digital communications.
Figure 10: DE Dual Input Wiring Diagram
•
Resistance temperature detector (RTD) measurements use the 3 or 4 wire
approach.
•
Dual-input units wired for a 4-wire RTD will automatically disable Input 2.
•
DE dual input device needs to be power cycled whenever sensor input wiring
changed
•
Supports dual thermocouple or RTD inputs for differential temperature
measurement
•
Supports dual thermocouple sensor inputs for redundant sensor operation.
•
To operate DE dual input device, it is required to connect both sensor inputs
•
To minimize common noise problems in the application, a strap/jumper
should be wired between terminals 6 and 8.
For differential T/C operation on DE Models, a second strap/jumper should be wired
between terminals 6 and 7. Do not install this strap for Non-DE models. The output for
differential operation is calculated as T/C 1 - T/C 2.
Figure 10: DE Dual Input Wiring Diagram
Thermocouple and RTD Connections (not applicable to single input sensor)
DE not applicable to STT750 transmitter

Wiring Variations

The above procedures are used to connect power to a Transmitter. For loop wiring and
external wiring, detailed drawings are provided for Transmitter installation in
non-intrinsically safe areas and for intrinsically safe loops in hazardous area locations.
This procedure shows the steps for connecting power to the transmitter.
Wiring must comply with local codes, regulations and ordinances. Grounding
may be required to meet various approval body certification, for example CE
conformity. Refer to the SmartLine Transmitter User's Manual 34-TT-25-03
(STT850) or 34-TT-25-13 (STT750) for details.
Note: After wiring, torque the screws to around 4 to 5(lb-in). Maximum should not
exceed 1.1 Nm (10 lb-in). Don't pull the wires after connecting to the screw terminals.

Input Sensor Wiring

Connect the input sensors as shown in Figures below:
Sensor Grounding:
1. For ungrounded Thermocouple, mV, RTD or ohm inputs connect the input
wiring shield(s) to the Internal Ground Connection shown in
2. For grounded Thermocouple inputs, ground the sensor wiring shield at the
sensor.
Ensure the sensor wiring and signal wiring shield is electrically isolated from the
transmitter housing and other grounded fixtures
Figure 9:
*
Only HART available for STT750 transmitter
Figure 7
Note: Dual Input is not available on the STT750.
Figure 12:
STT850/750 Quick Start Guide
HART*/DE/FF Single Input Wiring Diagram.
Figure 9: HART*/DE/FF Single Input Wiring Diagram
RTD Thermocouple, mV and Ohm Connections
Figure 11: HART/FF – Dual Input Wiring Diagram
RTD Thermocouple, mV and Ohm Connections
HART/FF Dual Input Wiring Diagram
•
For External C/J compensation, the first input is a thermocouple
type, and the second input is a 3-wire PT100 ohm RTD
•
The STT850 can have different sensor types on its inputs for split
range or averaging applications
Figure 12: HART/FF Dual Input Wiring Diagram, mixed sensors
Remote C/J and Mixed Sensors Connections
Figure 8.
3