A centrifugal pump located in the receiving tank is started, which circulates flow to the head of the flow calibration unit.  Once a steady rate of flow has been established, head measurements are taken in the converging section of the flume and a flow rate in GPM and MGD is recorded on the DE flow calibration form (see chart and form below.)


Depth and velocity measurements (using the Marsh-McBirney Model 2000 Flow-Mate portable velocity meter) are taken at the sub A/V sensor insertion point.  This point is located 86” below the outlet of the flume.  Head and velocity measurements are then recorded on the flow calibration form and flow rates in both GPM and MGD are calculated and recorded. 


At this point the sub A/V flow sensor to be calibrated is zeroed and installed on an 8” mounting band.  The sensor is then placed in the calibration flow line where head and velocity readings, along with flow rate output values, are recorded in the DE flow calibration form.  Output values for depth, which are not within an acceptable range established by the flow meter manufacturer and DE, will be adjusted (calibrated) to the appropriated depth.  Since poor velocity readings cannot be adjusted (for most sub A/V sensors) sensors reading outside those considered acceptable by the manufacturer are discarded and replaced with a new unit.  The sensors are then left in the calibration chamber for no less than three minutes of continuous readings to check for sensor drift.  If the sensors maintain an acceptable level and velocity output they are then removed or checked at an alternate depth, established by raising the level in the calibration flow line.  Upon removal, the sensor is placed on the appropriate size band prior to field installation.