of calibrated measurement.
Transmitters shall have offset and
span adjustments.
2.6.5.2
Pitot Tube Airflow Measurement Stations and Transmitters
a.
Stations shall contain an array of velocity sensing elements and
straightening vanes inside a flanged sheet metal casing. Velocity
sensing elements shall be multiple pitot tube type with averaging
manifolds. Sensing elements shall be distributed across the duct
cross section in the quantity and pattern set forth for
measurements and instruments in accordance with ASHRAE Hdbk-IP or
SMACNA HVACTAB, for traversing of ducted airflows. Resistance to
airflow through the airflow measurement station shall not exceed
20 Pa 0.08 inch water gage at airflow of 10 m/s 2000 fpm. Station
construction shall be suitable for operation at airflows of up to
25.40 m/s 5000 fpm over a temperature range of 4 to 49 degrees C
40 to 120 degrees F, and accuracy shall be plus or minus 3 percent
over a range of 2.5 to 12.7 m/s 500 to 2500 fpm scaled to air
volume. Do not use stations if required velocity measurement is
below 2.50 meters per second 500 feet per minute.
b.
Transmitters shall produce a linear 4 to 20 mA dc output
corresponding to the required velocity pressure measurement. Each
transmitter shall have a low-range differential pressure sensing
element and a square root extractor. The transmitter shall be a
two-wire, loop powered device. Sensing element accuracy shall be
plus or minus 1 percent of full scale, and overall transmitter
accuracy shall be plus or minus 0.25 percent of the calibrated
measurement. Each transmitter shall have offset and span
adjustments.
2.6.6
Pressure Sensors
**************************************************************************
NOTE: Indicate spare pressure taps where in-piping
calibration is required.
**************************************************************************
Provide electronic pressure sensor and transmitter. Sensor shall be a
pressure transmitter with an integral sensing element. Sensor over
pressure rating shall be 172 kPa (gage) 25 psig above its normal operating
range. Sensing element accuracy shall be plus or minus one percent of full
scale. Transmitter accuracy shall be plus or minus 0.1 percent of the
calibrated measurement. Transmitter shall be a two-wire, loop-powered
device. Transmitter shall produce a linear 4 to 20 mA dc output
corresponding to required pressure measurement. Transmitter shall have
offset and span adjustments.
2.7
THERMOWELLS
Provide brass or Series 300 stainless steel thermowells with threaded brass
plug and chain, 50 mm 2 inch lagging neck and extension type well, and
inside diameter and insertion length as required for the application.
Provide thermowells for immersion sensors with conducting material inside
the well.
2.8
THERMOSTATS
Provide thermostats.
SECTION 15901N
Page 26
Previous Page
