Flowmeter for fluid flow through weirs and parshall flumes

摘要

A float with an iron rod movable within a double coil AC coupling network measuring backed up liquid level as the measure of open channel, ditch or stream liquid flow through a weir or parshall flume. The AC output of the liquid measuring double coil is rectified and converted to a direct current signal passed to a voltage-to-frequency converter having a frequency output sensed and processed by a microprocessor. In a memory of the microprocessor there is a flow rate for each frequency that is calculated according to the number of gallons that will flow in a unit time. Thus, it is not necessary to linearize the coil and the same kind of coil can be used for any flow, with only a memory table in the microprocessor memory being changed for linear correction. This flow rate may be added for totalizing and/or put out to a digital-to-analog converter for recording and, if desired, controlling. Variation in AC line voltage is compensated for through periodic sampling, through a relay activated by the microprocessor circuit, rectification and voltage- to-frequency conversion to produce a frequency representing a given line voltage. As the line voltage goes up or down, the microprocessor makes corrective changes to the fluid level sensed signal.