Honeywell STT25D, Operator'S Manual

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16 Smart Temperature Transmitter STT250 – Operator Manual
SCREWS M4
SPRINGS
FEED-THROUGH
HOLE FOR
SENSOR WIRES
STT250
SENSOR PLATE
ASSEMBLY
CIRCLIPS
46188463-201
33 mm
Figure 9: Spring Loading and Sensor Assembly
Spring loading is available worldwide with direct head mounting. In North America, the
spring loading is typically included in the sensor/thermowell assembly and is available
with all housings. For non-North American spring loading as shown in Figure 9, simply
include the springs under the 33 mm pitch mounting screws, pass the screws through
the module and sensor mounting plate and snap in the retaining circlip to the screws
to hold the assembly together. Guide the sensor assembly through the housing sensor
entry and screw down the 33 mm screws until the limit is reached as the sensor
presses against the bottom of thermowell.
For wall or 2'' pipe mounting, the temperature sensor can be remote from the STT250
field mount housing or integral to the housing. For remote installations, the sensor
wiring should be run in shielded, twisted pair wiring and connected via one of the
housing wiring entries. For explosionproof/flameproof installations, ensure that the
cable entries are fitted with flameproof adaptors and that the wiring grade complies
with local standards.
Note that for internal spring loading applications including flameproof requirements,
the direct head mount housing should be ordered with the sensor to incorporate the
flame trap. Then connect the sensor wiring to the appropriate input terminals. Ensure
that you have selected the desired failsafe link direction (up/down). Connect the
output 2 wire signal to power connections. Screened, twisted pair wiring is
recommended but not essential. The connection route to the receiving device may be
run in multicore cable without any cross talk concerns for either HART or DE protocol
units. However, ensure that no digital I/O signals co-exist in the same multicore as
HART protocol signals since these signals can cause interference. Galvanic isolation
of input/output circuits enables use with grounded or ungrounded probes. This
enables connection of the output signal to ground (e.g. at safety barriers), without
creating a ground loop.
Screw down the housing cover securely.