Teledyne ULTRAFLOW 150, Руководство по эксплуатации, Страница: 22 / 162

ULTRAFLOW 150 GAS FLOW AND TEMPERATURE MONITOR
To convert actual flow volume to standard flow volume:




× =
×
Actual
Ref
Ref
Actual
Actual Standard
T
T
P
P
Flow Flow
NOTE: The temperature must be in absolute terms Eg. 459.69 + deg
f
4.2 MONITOR SPECIFIC THEORY
4.2.1 Box Car Integration
At the heart of the Ultraflow 150 is a signal conditioning technique known as
“Boxcar Integration”. Each time a tone burst traverses the stack a 16 millisecond
window of interest within the receive signal is digitized by an A/D converter in
0.5 microsecond intervals. This results in a window of interest composed of
32,768 digital values or “boxcars”. For each tone burst during the integration
period the value of each boxcar is added to the sum of all previous boxcars having
the same location in the window. For example on the fourth tone burst of the
integration period, the value of boxcar #100 will be added to the sum of the three
previous boxcar #100s. This technique greatly enhances the signal to noise ratio.
The true receive signals occur at virtually the same time (boxcar) for each tone
burst in the average period and are always positive thus add up faster than the
background noise which is random in time.
At the end of the integration period the resulting window of 32,768 data bits is
sent through the digital signal processing algorithms and the boxcar integrator
reset for the next integration period. The signal processing algorithms determine
the center of the receive signal and thus the exact transit time across the stack.
4.2.2 Operational Modes of the Transducer Interface Enclosure
4.2.2.1 NORMAL Mode
During the NORMAL mode the transducers of each transducer pair are alternately
transmitting and receiving signal through the medium and performing the gas
stream velocity calculations. The mode code for NORMAL mode is 1. During
NORMAL mode the TIE cycles the transmit pulses to the transducers on a round
robin basis so there are never any two transducers transmitting or receiving at the
same time. If only one path (transducer pair) is being used, the upstream and
downstream transducers will alternate. The TIE processes and reports the data at
the end of each integration period.
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