Technical Data on the AQ Sensor
The Most Advanced VOC Sensors In The World

 



IMPORTANT!!!
THESE SENSORS ARE NOT DESIGNED OR INTENDED FOR USE IN SAFETY SYSTEMS WHERE PERSONAL INJURY MAY RESULT.

 

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Application

     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 principal feature of the "AQ" sensor is that the mixed gas level is monitored and not any one specific gas. The sensor, therefore, does not distinguish between contamination from say tobacco smoke or cooking smells and people, thereby providing the air correction necessary for comfort as well as health.


 

Construction

     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.


 

Function

     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).


 

Mounting

     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 duct sensor should be mounted in the return air duct of the area or areas to be controlled in a convenient location for maintenance and commissioning. Althrough the sensor incorporates a filter, locations such as kitchen hoods should be avoided when oil and grease will foul the filter and prevent correct operation, even trough the filter is washable.


 

Adjustment

     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 30 minutes.
Using the calibration and span potentiometers the sensor may be set to the required state as follows:

Calibration

     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.

Span

     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.

 

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