Figure 9: Spring Loading And Sensor Assembly - Honeywell STT25D Operator's Manual

Stt 3000-series stt250 smart temperature transmitter

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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.

Smart Temperature Transmitter STT250 – Operator Manual

SCREWS M4

SPRINGS

FEED-THROUGH

HOLE FOR

SENSOR WIRES

STT250

SENSOR PLATE

ASSEMBLY

CIRCLIPS