Wiring Variations; Input Sensor Wiring - Honeywell 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. Optionally, a 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
o
or 4 wire approach.
Dual-input units wired for a 4-wire RTD will automatically disable
o
Input 2.
To minimize common noise problems in the application, a
o
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.
o
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-25-06 (STT850) for details.

Input Sensor Wiring

Connect the input sensors as shown in Figures below:
Figure 9:
Figure 7
*STT750 Hart only
Figure 12:
Figure 12: HART/FF Dual Input Wiring Diagram, mixed sensors
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
o
thermocouple type and the second input is a 3-wire PT100
ohm RTD
The STT850 can have different sensor types on its inputs
o
for split range or averaging applications
Remote C/J and Mixed Sensors Connections
3