Data on the AQ Sensor
The Purpose of the sensor is to
control the amount of fresh air introduced by a ventilation plant and
therefore, reduce energy consumption. This is achieved by measuring
the level of contaminant gases found in the controlled space and providing
a singal to the ventilating plant to control the damper positions, thereby,
saving on the energy consumed by heating or cooling fresh air during
periods of little or no occupancy.
The transmitter circuitry, which utilizes surface mount techonology is supported by a rigid circuit board. In the room sensor it is fixed to a surface pattern base plate suitable for wall amounting. A ventilated cover provides physical protection to the components while allowing sufficient air flow for detection purposes. The circuit board in the duct mount sensor is protected by a polycarbonate housing with a removable cover. A theaded conduit entry is provided for electrical connection. The sensing element is positioned at the tip of the duct tube and it protected by a sintered filter. This filter serves to control the effects on high air velocity and to prevent the build up of dust on the element.
The sensing element is a specially developed sintered semiconductor which when heated to a predetemined temperature causes the gases to oxidize on the surface coating of tin dioxide (SNO2). This causes a change in conductivity and the resultant resistance is then fed into the amplifier and output to the terminals as a 0-10 volt signal proportional to contamination. The amplifier in corporates a rate or rise circuit to filter out short term disturbances and provide a stable output (the damped output).
The room sensor should be mounted
at a height of 5 feet from the floor of the area to be controlled away
from doors, opening windows, supply grill, or other know disturbances.
The sensor is calibrated at manufacture to be suitable for use under
avearge room conditions. In the event that recalibration on site is
required an initial burn in time of 7 days should be allowed before
making final adjustments. Per commissioning is possible after apporximately
The adjustment controls the start point of the operating band and allows
the sensor to be trimmed for background contamination for say restaurant
use or in urban areas. This adjustment should be carried out at the
beginning of the occupied period when conditions are likely to be at
the correct level for minimum fresh air. It is recommended that the
system be set such that voltages below 2 volts are disregarded and 2
volts in minimum point at which fresh air will be introduced into the
plant. It is also recommended to have the introduction of more fresh
air that voltages above 5 volts.
This adjustment controls the maximum output voltage and allows the sensor to be used with various input requirement (0-5 volts) for example or to limit the influence of the sensor when directly connected to 0 - 10 volt equipment, damper motors for example. This adjustment should be carried out during periods of maximum load.