NuAire LabGard NU-560-400, Operation & Maintenance Manual

Page: 69 / 103

OM0295
Rev 2 September 2020 Page 69 of 103
7.11 Digital Airflow Sensor Description & Replacement
7.11.1 Downflow Velocity Sensor
The airflow sensor function utilizes two thermistors that provide a constant current source. One thermistor is a
reference that uses a very low current source. The other thermistor is the airflow measurer that uses a very high
current source. As airflow passes over the thermistors, the airflow removes heat from the thermister measuring
airflow. The loss of heat from the thermistor causes the voltage from the thermistor to increase. This increase
subtracted from the reference thermistor output voltage is what directly relates to airflow velocity. A repeatable
curve can be generated (voltage vs. airflow velocity).
The thermistors used are glass bead and coated and can be cleaned by gently using a cotton swab and alcohol.
Formaldehyde gas, Hydrogen Peroxide and Chlorine Dioxide has no effect on the airflow sensors; however, the
formaldehyde/Ammonium bicarbonate residue that remains after decontamination should be removed from the
airflow sensor thermistors.
Disconnect electrical power from the cabinet before
attempting any maintenance action.
The airflow sensor is removed by turning the locking ring counterclockwise and gently pulling the sensor away
from the connector. To reattach the airflow sensor, turn sensor in keyed connector until key matches, push in and
turn the locking ring clockwise until ring locks. Proceed to calibrate sensor menu.
7.11.2 Exhaust Pressure Sensor
The exhaust pressure sensor is a digital differential velocity pressure flow grid. The exhaust pressure sensor board
is located within the right side of the control center.
The exhaust pressure sensor function utilizes a differential pressure transducer and electronic temperature sensor
to measure exhaust volume. A flow grid mounted in the exhaust airflow stream provides a velocity and static
pressure to the differential pressure transducer. An equation using the pressure drop across the flow grid along
with the temperature reading provides a volumetric flow reading. The volumetric flow reading is then calculated
by the duct area to provide the displayed exhaust volume.
The flow grid located in the exhaust airstream is made from PVC and is not affected by Formaldehyde, Hydrogen
Peroxide or Chlorine Dioxide.
Disconnect electrical power from the cabinet before
attempting any maintenance action.
The exhaust pressure sensor board is removed by unfastening (2) 6/32 nuts and removing the connectors and
tubing then gently pulling up the board until free. To reattach, reverse the above procedure. The exhaust sensor
also has an onboard LED indicator that indicates a properly operating sensor. The LED DS1 blinks in slow 1 second
intervals during normal operation. It will blink faster or full on when a sensor error occurs at which time the
sensor board needs to be replaced. Proceed to calibrate sensor menu.
CAUTION
!
CAUTION
!