Teledyne ULTRAFLOW 150, Operation Manual, Page: 23 / 162

SECTION 4.0, Theory of operation
4.2.2.2 ZERO Calibration
The mode code for ZERO mode is 4. During the ZERO mode the TIE processes
the signals in a slightly different manner. When both a ZERO and SPAN
calibration have been completed, a comprehensive full system evaluation check
has been done. During ZERO, only the upstream transducer transmits and it
transmits at twice the normal rate. The downstream transducer is receiveing only.
The TIE‘s electronics process each pair of signals as though they were typical
upstream and downstream signals. Since all ZERO mode receive signals go
through the gas stream in the same direction, the time required to traverse the gas
stream should be essentially the same. With no difference in the transit times, the
flow should indicate zero velocity. Small fluctuations in the upstream transmit
and downstream receive properties will indicate non-zero flow readings.
4.2.2.3 SPAN HIGH Calibration Mode (Upscale Calibration)
The mode code for SPAN HIGH mode is 2. During SPAN HIGH only the
downstream transducer transmits and it transmits at twice the normal rate. The
upstream transducer is receiving only. The TIE’s electronics process each pair of
signals as though they were upstream and downstream signals. This would be
expected to produce another zero flow indication. However, in the "SPAN
HIGH" mode every other received tone burst is delayed by a predetermined
amount. This means that the TIE sees a difference in the time required for the
upstream and downstream tone bursts to traverse the gas stream. Small
fluctuations in the downstream transmit and upstream receive properties or
electronics shifts will show changes in the expected flow readings.
4.2.2.4 SPAN LOW Calibration Mode
The mode code for SPAN LOW mode is 3. During SPAN LOW mode the TIE
controls the transducers and processes the signals in the same way as in the SPAN
HIGH mode except that the calculated delay for every other receive signal is
shorter. This gives a shorter transit time difference, thus a lower expected flow
volume.
4.2.2.5 Acquire Modes
There are four Acquire Modes, NORMAL Acquire = 5 , SPAN HIGH Acquire =6 ,
SPAN LOW Acquire = 7 , and ZERO Acquire = 8 . Acquire modes are invoked
during transitions from one mode to another. When the TIE changes modes, the
acquire for the requested mode will be indicated until the number of integration
periods needed for a good average has been reached. For example if the number
of integration periods per normal average is set to 4 and a mode change to ZERO
mode initiated, the TIE will indicate ZERO Acquire mode for 4 integration
periods before switching to ZERO mode for the balance of the calibration periods.
NOTE: The number of periods for a calibration average must be equal to or
larger than the number for a normal average.
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