The Price SP300 sensor utilizes aerodynamic principles to optimize the velocity pressure signal amplification. Strategic location of the total and static pressure ports provides the necessary amplification
without the need to increase the sensor profile. An increased sensor profile can result in added noise levels and higher minimum static pressure requirements, both of which are undesirable. The Price SP300
sensor has been designed with minimum cross-section and an aerodynamic profile which has negligible pressure drop or noise contribution.
The Price SP300 has superior tensile strength compared to other flow sensors on the market. Price does not recommend lifting terminals by the air flow sensor, however, it is often a common practice in the
field. With this in mind the Price SP300 has been designed with molded reinforcement to prevent accidental handling damage. To ensure reliability, the SP300 was subjected to numerous tensile strength tests.
These tests prove that the SP300 successfully withstands loads beyond 115lbs., significantly exceeding the weight of typical Single Duct Terminal Units.
All plastic components are Fire Resistant and meet UL 94-VO.
Control tubing is protected by grommets at the duct wall, and is securely fastened to the sensor.
The rugged construction features of the SP300 sensor ensure a trouble free installation and reliable operation.
Optional removable SP300 Sensor is available and suggested for hospital grade jobs where sensor needs to be removed and periodically cleaned due to build up of lint.
The Price SP300 Velocity Pressure Sensor represents the next generation of air flow measurement devices, significantly advancing VAV sensing
technology. Developed by Price Engineering, the SP300 addresses many of the sensor issues that are critical to today’s modern HVAC designs:
Traditional Velocity Pressure Sensors function best under ideal inlet conditions. Most devices require at least four inlet diameters of straight duct before the air
terminal connection – a condition that may not exist for a jobsite installation. Space constraints, other mechanical system components, and structural elements, are factors that can influence air
terminal inlet conditions.
When poor inlet conditions exist, the profile of the air moving through the terminal and across the sensor becomes distorted, resulting in non-uniform velocity distribution, and inaccurate air flow
measurements. Under these conditions, the flow sensor must provide a true averaged velocity pressure signal for proper control.
The Price SP300 overcomes the effects of variable inlet velocities by averaging and amplifying pressure signals.
Optimal Center Averaging
To compensate for variations in pressure within the inlet, the Price SP300 averages the high and low Velocity Pressures that are found on opposing sides of the duct. These measurements are collected
and averaged in a chamber located at the center of the sensor. The signal is then sent to the air flow controller.
Multiple ports for sensing both Total (tp) and Static (sp) Pressures are designed and located to maximize accuracy. Extensive research and lab testing was conducted under various air flow conditions to
determine the proper location of the multiple sensing ports. Twelve total pressure ports are located on the upstream side of the sensor legs. Four static pressure ports are located on the downstream
side of the averaging chamber. The multiple sensing ports not only provide a good indication of velocity across the duct but prevent loss of signal due to blockage by dust or dirt.
While equal area velocity pressure traverses are recommended for uniform flow conditions, substantial errors occur with non-uniform flow created by a 90° elbow, for example. The total and static
pressure port locations for each size of the Price SP300 sensor have been determined by extensive lab tests and experimentation. The end result is flow measurement accuracy within 5% with a 90° sheet
metal elbow connected directly to the terminal unit inlet.
Elbows, transitions and duct takeoffs, within three duct diameters of the terminal unit inlet should be avoided due to sound and pressure drop considerations. However, when job conditions do necessitate less
than ideal inlet conditions, the Price SP300 will maintain flow accuracy.
Optimal Signal Amplification
Amplifying the Velocity Pressure signal that is sent to the controller will enhance accuracy, especially under low air flow conditions. It is important to note, however, that too much amplification,
and the methods used to achieve it, can be detrimental to sensor performance. In fact, sensors that provide excess amplification may require the use of controllers with higher velocity pressure ranges,
thereby reducing low end resolution. The amplification of the SP300 sensor has been designed to provide velocity pressure signals which fall within the standard 0-1.0 in. range of most flow controllers and
transducers. By matching the sensor output to the controller input range, optimum flow accuracy is obtained.
Generally, VAV controllers require a minimum differential pressure signal of .03 in. w.g. to maintain reasonable control accuracy. The Price SP300 will provide a .03 in. w.g. signal for flows as low as 400
fpm at the inlet. Most sensors require more air flow and a higher differential pressure, and many will not function properly below 700 fpm.
Precise control at minimum settings is critical in maintaining the air change rates called for by ASHRAE and good IAQ design practices. Accurate control at minimum flow can also reduce the requirement for
reheat and increase room comfort conditions by prevention of overcooling.