Mace HVFlo XCi, Руководство по эксплуатации продукта

Страница: 158 / 255

NOTE: As a general rule, the velocity range should be set to double the average
velocity of the stream.
Integration period
The integration period is the time period in which samples of the velocity spectrum are taken before an
average velocity reading is calculated. The minimum integration time is 4 sec and the maximum integration
time is 180 seconds and may be reduced automatically by the measurement interval and the maximum
measurement count depending upon the instrument configuration.
The integration time may be varied for several reasons:
l
Under field conditions where the flow is fluctuating dramatically, increasing the integration time will
help to get a more accurate average velocity reading, because more samples are available to
calculate the average .
l
Under field conditions where the flow has a low number of acoustically reflective particles, increasing
the integration time will help to get a more accurate average velocity reading, because more reflective
targets will be sampled to calculate the average.
NOTE: The power consumption of the system is affected by the integration time. The
longer the unit is on and physically sampling, the shorter the battery life without
charging. The XCi device internal battery has a 7.2 Ah capacity. During an
integration period each Doppler sensor will draw approximately 80 mA.
Maximum measurement count
Under certain flow or no flow conditions signal noise may disrupt the calculation of a true average velocity
reading. As described the peak threshold feature is designed to overcome this problem. However, unwanted
velocity readings may be derived from other sources such as aquatic life, which may give strong signal
strengths.
Within all MACE Doppler ultrasonic instruments one of two flow states can occur. The stream can either be
moving or stationary. For example, a sensor submerged in a river diversion pipe that is used to pump
irrigation water may be full at times when no water is being pumped. Under these conditions, it is common for
fish and aquatic invertebrates to inhabit the pipeline. Unfortunately, to a Doppler ultrasonic velocity sensor, a
fish swimming at 500 mm/s is computed as a full pipe of water moving at 500 mm/s. This type of erroneous
flow reading will result in an increase in the totalised flow. Conversely, in a slow moving stream or one that
contains few acoustically reflective particles, a velocity reading may be missed if there is insufficient data to
analyse. Under this circumstance, the totaliser will not be incremented.
MACE XCi User Manual - 158 -