controller supports direct connection of RTDs. When RTDs are connected
directly to the controller, keep lead resistance error to 0.25 degree F or
less. Total error for a RTD circuit shall not exceed 0.5 degree F, which
includes sensor error, lead resistance error or 4 to 20 mA or 0 to 10 VDC
transmitter error, and A/D conversion resolution error.
2.2.1.3
Temperature Sensor Details
a.
Room Type: Conceal element behind protective cover matched to the
room interior. Room temperature sensors connected directly to
application specific controllers shall have integral pushbutton,
system override digital input button, and a setpoint adjustment
lever. Provide a connection to allow interrogation of the digital
controller.
b.
Duct Averaging Type: Continuous averaging RTDs for ductwork
applications shall be one foot in length for each 4 square feet of
ductwork cross-sectional area with a minimum length of 6 feet.
Probe type duct sensors of one foot length minimum are acceptable
in ducts 12 feet square and less.
c.
Immersion Type: Three inches total immersion for use with sensor
wells, unless otherwise indicated.
d.
Sensor Wells: Stainless steel [brass] material. Provide
heat-sensitive transfer agent between exterior sensor surface and
interior well surface.
e.
Outside Air Type: Provide element on the buildings north side
with sunshade to minimize solar effects. Mount element at least 3
inches from building outside wall. Sunshade shall not inhibit the
flow of ambient air across the sensing element. Shade shall
protect sensing element from snow, ice, and rain.
**************************************************************************
NOTE: In most cases transmitters are not needed for
temperature. An RTD sensor without transmitter is
accurate for most applications and may be calibrated
within controller software.
**************************************************************************
2.2.2
Transmitters
Transmitters shall have 4 to 20 mA or 0 to 10 VDC output linearly scaled to
the temperature, pressure, humidity, or flow range sensed. Transmitter
shall be matched to the sensor, factory calibrated, and sealed. Total
error shall not exceed 0.1 percent at any point across the measured span.
Supply voltage shall be 24 volts AC or DC. Transmitters shall have
non-interactive offset and span adjustments. For temperature sensing,
transmitter stability shall not exceed 0.05 degrees C a year.
2.2.2.1
Spans and Ranges
Transmitter spans or ranges shall meet the following:
a.
Temperature:
(1) 50 degrees F span: Room, chilled water, cooling coil
discharge air, return air sensors
SECTION 15910N
Page 36
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