Vortek VT-5000 Airflow Measuring Device

Sample Specification

Airflow Measuring Device with transmitter output for use with either Tek-Air or ATC controllers, suited to larger ducts (over 3 sq. ft.).

Rev. 1, 1/24/01

X.X SUPPLY AND EXHAUST AIRFLOW MEASURING DEVICES

A. Airflow measuring devices of the Vortex Shedding type, capable of continuously monitoring the airflow volume of the duct served and electronically transmitting a signal linear to the airflow volume, shall be provided where indicated. Airflow measuring devices shall be of the insertion type, or built into airflow control valves, as required, with the capability of measuring velocity over the full range of 400 to 7000 FPM. Devices shall consist of multiple velocity sensors, supported on insertion probe bars.

B. Individual airflow sensors shall be of rugged construction, and shall not require special handling during installation. Sensors shall be mounted on support bars, as required to achieve an equal area traverse. Standard Materials shall be aluminum bars with aluminum and ABS sensors. Support bars over one foot in length shall be supported on both ends. Where utilized in corrosive air streams, sensors and support bars shall be manufactured of corrosion resistant CPVC and ABS. All mounting hardware required shall be furnished by the Laboratory Airflow Control System Manufacturer.

C. Individual velocity sensors shall not be effected by dust, temperature, pressure, or humidity. The sensors shall be passive in nature, with no active parts within the air stream. The output from individual sensors shall be linear with respect to airflow velocity and shall be capable of sensing airflow in one direction only. The velocity sensors shall not require calibration.

D. Multiple sensors shall be utilized in all ducts with areas over .3 square feet in accordance with the following recommendations:

AREA RECTANGULAR CIRCULAR

less than .3 1 1

.3 to .8 2 2

.8 to 3.0 4 4*

3.0 to 5.0 6 4 or 8*

5.0 to 8.0 8 8*

8.0 to 15.0 12 8*

15.0 to 32 16 12**

Note *: Two support bars in a cross pattern

Note **: Three support bars in a cross pattern

Where sensors are installed at the inlet of Pneumavalve airflow control valves, fewer sensors are allowable due to improvement of airflow profile by vanes in Pneumavalve.

E. Velocity measurements from individual sensors shall be summed in the associated airflow transmitter. The transmitter shall be connected to the probes via factory-assembled cables, provided by the Airflow Controls manufacturer.

F. The measurement shall be input and conditioned digitally to eliminate Analog-to-Digital conversion input error. The transmitter shall provide a scaleable output over the full range of control of the unit, via on-board adjustments. The output signal of the transmitter shall be industry standard electronic signals, selectable on-board via jumpers or switches, for 4-20ma, 1-5vdc or 2-10vdc. Power requirement for the transmitter shall be 24VAC or DC.

G. Measurement system accuracy shall be plus or minus 2% of volumetric airflow rate. Turndown capability shall be at least 10:1.

F. Velocity sensing methods other than those specified shall be acceptable, provided the basic requirements for linear electronic output, turndown, accuracy, materials of construction, and output signal are met. If differential pressure devices are used, dual differential pressure transmitters, the span of the lower transmitter being one tenth the span of the higher, with an accuracy not less than +/- 0.5%, shall be utilized to provide the required turndown. Orifice type devices shall have a Beta ratio of 0.7 or less, and shall be installed in accordance with ASME guidelines for up and downstream conditions.

G. Pitot devices constructed of aluminum are not acceptable in the fume hood exhaust air; 304 stainless steel shall be used.

H. The airflow sensors shall be easily removed from the duct for inspection. If this is not possible, then access doors must be installed in the duct upstream and downstream of the airflow sensor.

I. Use of valve or damper position for calculation of airflow volume is not acceptable. Direct airflow measurements must be taken.

J. Sensing methods employing thermal devices in the airstream shall not be acceptable.

END