CHAPTER 10 - CURRENT METERS
10. General Procedures and Precautions
Accuracy of measurement can be maintained by observing the following
precautions for Price meters (including the pygmy meter modification of
the Price meter):
- The meter should be spin tested before and after completing measurements
to assure that the meter has no error-causing damage. With the shaft in
a vertical position and the cups protected from air currents, the cups
should be given a quick turn to start them spinning. If the meter is in
proper adjustment and the bearings are free from foreign particles, the
cups should come to rest in not less than 3 minutes. If the length of spin
is only about 12 minutes, but the cup wheel comes to rest gradually, all
flows except those of very low velocities may be measured. If the length
of spin is only about 1 minute but the cup wheel comes to rest gradually,
the meter may still be used to measure velocities above 1 ft/s. If the
length of spin is less than 1 minute, the meter should be reconditioned.
Under laboratory controlled conditions, rotation should continue for about
4 minutes. The manner in which rotation ceases will help indicate the condition
of the meter and should be observed.
- The cross section of the stream should be divided vertically into 20
or more segments. Very small streams and sections with smooth, firm boundaries
are exceptions, and a smaller number of stream cross-section segments would
be sufficient. A single vertical reading is used if the distance between
verticals is less than 1 ft. Horizontal divisions are generally selected
so not more than 10 percent, and preferably not more than 5 percent, of
the discharge will occur between any two adjacent verticals.
- The stopwatch should be checked frequently and kept in good condition.
- For low and irregular velocities, the period of observation should
be lengthened to obtain a more accurate average count.
- The current meter should be withdrawn from the water between velocity
readings to make sure that rotation is not being impeded by debris or any
- The meter should be allowed at least 10 to 20 seconds to attain rotation
speed before counting commences.
- The total operation of the meter at each elevation of a vertical should
consist of at least two consecutive periods of at least 40 seconds. If
significant differences are apparent in each period, more readings should
- Measurements while wading should be done facing the bank, standing
just downstream from the tag line, and at least 18 in to the side of the