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Thermal Dispersion Airow Measurement Technology
Thermal dispersion technology relates the velocity of the air
to the power and rise in temperature of a heated element in a
moving airstream. A precise bead-in glass thermistor probes
the airow rate and air temperature. Multiple sensing points are
used to produce an average velocity for true volumetric airow
(CFM/LPS). Each individual sensor node is calibrated to NIST
traceable airow standards at 16 points, resulting in a accuracy
of 2% of the reading.
Figure 65: Bead-in-Glass Thermistor
Figure 66: Bead-in-Glass Thermistor Probe
Connecting to MicroTech III Controllers
Wiring
1. Connect analog control wires from the MicroTech III
Controller to the outdoor air monitor controller.
a. MicroTech III controller (X1 on the MCB or X11 on the
EXP_D) to the controller's analog output terminal 1.
b. MicroTech III controller (M on the MCB or M on the
EXP_D) to the controller's analog output terminal
COM.
2. Power Wires (24 VAC) to the outdoor air monitor
controller.
a. 24VAC from the unit control panel to the controller
terminals L1 and L2.
Outdoor air monitor controller settings
1. Set Controller SW1 switch to Vdc.
2. Set power switch to ON.
Outdoor air monitor controller conguration/set up
(see Appendix, Figure 87 on page 119 for navigating the
Controller keypad)
1. Set LCD1 U/M to "CFM"
2. Set AR1 (see Table 29)
3. Set OUT1 U/M =CFM
4. Set OUT1 =0–10V
5. Set FSI (see Table 29)
Table 29: Settings by Cabinet Size
Model Unit Size
Area sq.ft.
(AR1)
Full scale output CFM
(FS1)
003–006 Small cabinet 2.25 2,400
007–015 Medium cabinet 4.5 6,000
016–028 Large Cabinet 10.25 11.0
Thermistor material
designed for self-heat
applications is fused
to dumet wire leads
Dumet wire ensures
hermetically sealed
glass encapsulation
Kynar
®
coated wires are
welded to dumet leads
Thermistor aging
process ensures
long term stability
Waterproof potting
compound protects
assembly from the
environment
Zero Power Thermistor
Approaching
Airstream
Self-heated Thermistor
Heat transferred to
the airstream is
proportional to the
airflow rate
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