FREQUENTLY ASKED QUESTIONS
HOW IT WORKS
Every NJK Precision Sensing Probe is calibrated on a NIST (National Institute of Standards and Technology) certified laboratory testing station and verified for accuracy of flows from the maximum to the minimum flow that can be read with this airflow station.
Inlet air from all inlet apertures is channeled through the inlet chamber and then through the NJK Precision Sensing Probe. Air leaves the Sensing Probe and is drawn into the outlet chamber, where it is brought back into the duct system through the outlet apertures.
A temperature sensor is not currently available. This option is currently under consideration.
TEMPERATURE AND HUMIDITY
Yes! Temperature impacts the density of the air but not the mass. That’s why our airflow measurement utilizes mass airflow technology to measure the true flow of air through the Sensing Probe.
Humidity impacts the density of the air, not the mass. These Sensing Probes can also be used in water flow measurement applications, so they are not damaged by moisture at all. The mass and the viscosity of water is different than that of air. The calibration is made for air so the readings are impacted when they are wet.
The accuracy of these sensors is guaranteed if operated within the range given. Outside of these guidelines, we cannot depend on their accuracy.
The NJK Precision Airflow Measuring Station assembly, Sensing Probe, Transmitter, and Display Module.
If the inner airflow chambers and the outer shell remain intact, the airflow station should still be usable. If the damage is significant enough that the inlet and outlet chambers are exposed to each other (unit housing is broken), the airflow station will not be read correctly.
For the extruded models that can be field assembled, you should be able to assemble the sensor at the point of use and slide the unit into place. For installations where there is a lack of available clearance beside the ductwork, NJK Precision has available extrusion coupling pieces that can be utilized to join smaller sections of the extrusion pieces together to form the longer extrusion sides of our Sensor Flow Frame.
NJK Precision recommends that a sheet metal contractor installs the airflow stations and that they are wired by a licensed electrical contractor. The field-assembled models may be installed by a controls electrician or a mechanical contractor on some job sites.
The NJK Precision system operates by averaging airflow samples around the entire ductwork and measures that averaged flow through one Sensing Probe. Multiple readings across a duct area only represent a snapshot of the air flowing at that one point in the duct. The idea is that if multiple airflow measurements in the duct are averaged, then total airflow can be determined.
The NJK Precision Airflow Measuring Station will remain accurate down to its lowest measurable air velocity, representing the low end of the scale served by NJK Precision. Installations with an extremely small duct feeding into a short transition piece directly ahead of the NJK will not allow the NJK Precision Airflow Measuring Station to read accurately. Also, if the NJK Precision Sensor is mounted on the face of a coil or filter banks in an air handler, the reading can be adversely affected as the coil or filters become clogged with dirt or debris. NJK Precision does not recommend installing the sensor on the face of any coil or filter bank.
In installations where the larger side of the NJK Airflow Measuring Station is greater than 24”, the sensor will have to be verified by a test-and-balance contractor. The correction factor can either be calibrated in the Operators Display or directly in the BAS system. With sensors less than 24″ in size, factory calibration is optional.
The pressure drop is minimal across the airflow station due to the sensor’s small profile and its airfoil design.
The NJK Airflow Measuring Station includes a time-averaging sensor output voltage over longer intervals (15 to 120 seconds) and offers a user-adjustable signal processing function that smooths out rougher airflow signals.
The Flow Frame can be moved out inside of the ductwork when needed. The inherent design of the NJK Precision Sensor Flow Frame allows for a slight negative pressure on the leaving side of the extrusion, which creates a slight draw through the Flow Frame and generally will pull air away from small edge gaps, such as mentioned. Testing has demonstrated that this pulling air away from the edges makes losses or inaccuracies from these gaps insignificant and thus can be ignored. If user decides to fill these gaps, care must be taken not to allow the filling material interfere with the function of the flow frame or its precision formed linear ports.
This is not recommended. The outer edges of both dampers will be sampled only, and the damper area where the minimum and maximum dampers connect has no flow sensing. This will only provide a portion of air being sampled for both sets of dampers.
The NJK Precision Flow Frame has a design that can never fill with water. Both the inlet and outlet apertures are located down in the extrusion so that even the bottom extrusion will never completely fill with water. The NJK Precision Sensor Module should never be mounted on the exterior of the Flow Frame on the bottom side extrusion as that could lead to the Sensor Module and Sensing Probe to fill with water.