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Airflow reading in Xenta 102-AX fluctuates or is zero

Issue

Airflow reading from Xenta 102-AX is jumping around and will not stabilize or is 0.

Environment

  • Vista
  • Xenta 102-AX Plug-in
  • LonMaker, NL-220

Cause

For a variety reasons parameters may get changed in a Xenta 102-AX adversely affecting the controller's performance.

Resolution

Ensure that all of the parameters that affect the airflow reading are set properly. In some cases it may be best to restore the default parameters.

Parameters that should be checked may be found through the Xenta 102-AX plug-in or through Vista but are grouped below how they are found in the plug-in starting with Unit Parameters:

Unit Parameters

Duct Area

Ensure that the duct area is set properly for the box size. If a formula was used to determine the duct area from duct diameter verify that it yielded the correct result.

For square or rectangular ducts use the following formula:

For round ducts use the following formula:

Pickup Factor

The pickup factor is sometimes known as the K factor and is determined by examining the airflow curve diagram provided by the box manufacturer. It can often times be found on the box itself or in the manufacturer's literature. If the manufacturer's specs cannot be obtained use the default pickup factor, which is 2951.6.

Box Constant

The box constant is a product of the pickup factor and the duct area. It is sometimes available from the box manufacturer. If the manufacturer's data cannot be obtained use the default value, which is 1588.5.

Note that the box constant will be changed from default if a CBC, or, calibrate box constant is performed.

Airflow Parameters

Velocity Pressure Gain

The default settings here are 10 / 10 and are changed when a calibration is performed. If these numbers factor out to be very far from one you may want to reset them to their defaults and investigate if something went wrong with the calibration. For example these values may read 2957 / 3054 but since that factors out to 0.968 which is only about 3% off from one. However, if these numbers were 2957 / 6043 this would be a clear indicator that there was something wrong.

Velocity Pressure Offset

The default value here should be zero and considering that sensor is nominally set up for a 0-1" scale numbers greater than +0.1 or less than -0.1 should be cause to investigate further for mistakes during the calibration process.

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