7VORTEK Doc.# VT5 OM 050499, Rel. 2.1
Chapter 1 Operation
1.4 Transmitter Operation
The enclosure located on the external end of each duct probe bar is the probe
electronics housing. It contains the electronics which sense the vortices gener-
ated by the VorTek probes. At the bottom of the enclosure is the electronic con-
nector required to connect each duct probe to the transmitter. A ten foot long
connecting cable is provided for each duct probe for this purpose.
The VorTek transmitter is capable of accepting inputs from as many as four probe
bars from one measuring station, each with a maximum of four VorTek sensors
each. Up to six sensors may be located on a single probe support bar but the
total number of sensors can not exceed 16.
In the simplest sense, the transmitter electronics can be considered a pulse
frequency-to-analog converter. The transmitter receives electronic pulses from
each of the VorTek sensors. As every pulse represents the same increment of
velocity, the pulses need only be summed together and integrated over time to
determine velocity. Additional circuitry converts the total pulses per second into
analog, 4-20mA signal which is proportional to either CFM or FPM.
The VorTek transmitter consists of a minimum of two circuit boards: the Amplifier
board and the mother board. The amplifier board performs the required signal
conditioning on up to eight VorTek sensor inputs. Either one or two amplifier
boards are provided depending on the number of probe bars used at the station.
The mother board accepts the conditioned pulses from the amplifier board(s),
sums them, integrates them, and converts them into a 4-20mA output signal. The
mother board also provides the power supply, calibration adjustments, internal
calibration standard, and circuitry to drive the optional digital display.
A “PROGRAM MODULE” is installed on the mother board and programs the unit
for the correct number of sensors required for the specific configuration. This
module “plugs-in” and can be changed easily for an alternate configuration if
required.
Because airflow is inherently turbulent, it tends to produce fluctuating electronic
output signals if not damped when high turbulence is present. Also, some com-
mercial direct digital temperature control systems update control outputs only on
changing input signals. The rapid input changes caused by airflow turbulence
can cause these types of systems to effectively overload and crash. To allow the
user to select the damping to meet his application, the transmitter includes a
switch-selectable damping constant of either 2 or 4 seconds.
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