capable of withstanding a saturated condition without permanently affecting
calibration or sustaining damage. Sensing elements shall be bulk polymer
or thin film polymer. Sensing elements shall have an accuracy of plus or
minus 2 percent of full scale within the range of 20 to 80 percent relative
humidity. Provide a two-wire, loop-powered transmitter located at the
sensing elements to convert the sensing elements output to a linear 4 to 20
mA dc output corresponding to required humidity measurement. Output error
shall not exceed 0.1 percent of calibrated measurement. Transmitter shall
include offset and span adjustments. Transmitter shall have ability to be
calibrated electronically by using a one-point, in-situ method which allows
for error correction with a single potentiometer.
2.6.4
Dew Point Instruments
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NOTE: Provide 2 degrees C 3 degree F dew point
allowable deviation for normal control, as in
commissary refrigerated display case, anti-sweat
heater controls; provide a 0.55 degree C one degree F
deviation for critical occupied space, as in
computer rooms.
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Provide analog salt-phase transition or dual chilled, mirror type sensor.
Sensor shall have an allowable deviation of plus or minus [0.55] [2]
degrees C [one] [3] degrees F dew point over the range of minus 12 to plus
27 degrees C 10 to 80 degrees F dew point.
2.6.5
Airflow Sensors
Provide airflow sensors.
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NOTE: Use only where necessary. Airflow sensors
are high maintenance items.
**************************************************************************
2.6.5.1
Electronic 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 RTD or thermistor type, with linearizing
means. 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 and
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 0.64 to 12.70 m/s 125 to 2500 fpm scaled to air
volume. Use stations if required velocity measurement is below
2.50 meters per second 500 feet per minute.
b.
Transmitters shall produce a linear, temperature compensated 4 to
20 mA dc output corresponding to required velocity pressure
measurement. Transmitters shall be a two-wire, loop-powered
device. Output error of transmitters shall not exceed 0.5 percent
SECTION 15901N
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