RTD transmitter shall be selected to match the resistance range of the RTD.
Transmitter shall be a two-wire, loop-powered device. Transmitter shall
produce a linear 4 to 20 mA dc output corresponding to required temperature
measurement. Output error shall not exceed 0.1 percent of the calibrated
measurement. Transmitter shall include offset and span adjustments.
2.6.2.4
Pneumatic Temperature Transmitter
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NOTE: Use smallest span sufficient to cover
operating range. This provides smallest allowable
deviation, improving control accuracy.
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Transmitting sensing elements shall be bi-metal, averaging element and
capillary, rod and tube, or bulb and capillary. Transmitters shall operate
within the range of 4 to 116 degrees C 40 to 240 degrees F. Provide the
following spans and allowable deviations for applications listed.
a.
Room sensors, minus 4 degrees C 25 degrees F, plus or minus 0.28
degrees C 0.5 degrees F
b.
Room, chilled water, dew point, return air sensors, 10 degrees C
50 degrees F, plus or minus 0.42 degree C 0.75 degree F
c.
Outside air, hot water, coil discharge sensors, 38 degrees C 100
degrees F, plus or minus 0.56 degree C 1.0 degree F
d.
High temperature hot water, chilled hot water system sensors, 93
degrees C 200 degrees F, plus or minus 1.11 degrees C 2.0 degrees F.
2.6.3
Relative Humidity Instruments
2.6.3.1
Relative Humidity Sensor
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NOTE:
1. Measuring dew point temperature and relative
humidity with accuracy and repeatability using
"commercial" controls is difficult. It is
recommended that the designer plan the control
system to eliminate the need to control dew point
temperature or relative humidity including
eliminating enthalpy control. Dry bulb temperatures
should be used to control outside, return, and
exhaust air dampers in economizer applications.
Only use humidity control when the space has
specific humidity requirements.
2. Indicate a fan powered type aspirating cabinet,
an electronic relative humidity sensing element, a
transmitter for outside air relative humidity
sensing applications, and a power source for the
cabinet.
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Provide relative humidity sensor.
Use nonsaturating sensing elements
SECTION 15901N
Page 24
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