Teledyne 4220 installation and operation guide Conversion Type, Data POINTS, and Equation

4220 Flow Meter
Section 2	Programming
2.3.2	Step 2, Flow	Step 2, Flow Conversion Type, determines how the flow meter
	Conversion Type	calculates flow rate and total flow. For the 4220 Flow Meter, flow
		rate is calculated by knowing the measured level and (usually)

the characteristics of a structure called a primary measuring device.

A primary measuring device is a structure placed across a flow stream through which the entire stream must flow. These devices are made in a number of styles and sizes, but they all have one thing in common: For any type of primary measuring device there is a known relationship between the level in the flow stream ahead of the device and flow rate through the device. Consequently, after you measure level with the flow meter, it can calculate flow rate and total flow from the measured level, by consulting built-in look-up tables.

Detailed information about many commonly-used primary mea- suring devices is provided in the Isco Open Channel Flow Mea- surement Handbook. This useful book provides formulas, flow rates at various levels, and values for maximum head, as well as much interesting descriptive material, and is available from Teledyne Isco. If your installation uses a nonstandard primary device, you should consult the manufacturer of the device for flow rates at given levels. The flow meter will then calculate a flow conversion for such a device on the basis of the manufacturers' data you enter as data points or an equation. In some instances, a nonstandard primary device could be supplied with a flow equation; you can enter that equation into the flow meter and the flow meter will calculate the flow rate from that equation.

Note however, that it is not always necessary to have a primary measuring device. The 4220 Flow Meters can measure level and calculate flow without having any primary device installed in the flow stream. Sometimes the shape of the flow stream itself forms the primary device.

The Manning formula uses the shape of a pipe or channel and its slope to calculate flow in open (non-pressurized) pipe situa- tions.

The conversion types available are WEIR/FLUME, MANNING,

DATA POINTS, and EQUATION.

You use Weir/Flume flow conversion when your primary mea- suring device is a weir or a flume. A weir is a wall or dam across the flow stream. Water must rise to the point where it flows over the top of the wall. The measured level upstream behind the wall is used to calculate the flow rate. Flumes differ from weirs in that there is no wall or barrier, but instead a restriction, typically a sharp narrowing or change in the slope of the channel that restricts the flow. Again, the measured level of the stream at some point ahead of the restriction is used by the flow meter to calculate flow. In this flow conversion mode, the flow meter uses internal look-up tables for many common primary measuring devices.

2-6