As liquid passes through the flow meter, a bluff (nonstreamline) body generates a coherent series of vortices. At the point of vortex production, the liquid is under shear, and cavitation is possible. The cavitation bubbles interfere with the ultrasonic beam used to sense the vortex production. To prevent this, a minimum amount of back pressure (pressure immediately downstream of the flow meter) is required.
    BP = 2.75 DP + 1.25 PV - 1 BAR
    BP = required back pressure given in gage pressure (pressure
            above atmospheric).
    DP = pressure loss at the maximum flow rate of the system.
    PV = vapor pressure of the liquid being measured.
The minimum back pressure for a 3/4" flow meter measuring water at various temperatures is graphed below.

ACOUSTIC DAMPENING
Acoustic dampening fluids such as glycerin and various glycols are uncommon in semiconductor processing, and therefore are not of significance to this market but may be a consideration in other applications.

ENVIRONMENT
The flow meter has been designed for use in corrosive atmospheres. It is rated IP68 (NEMA-6P) and IP65 (NEMA-X). If measuring 160°C fluid, the maximum ambient temperature is 100°C.

PIPING REQUIREMENTS
This meter needs a straight run of pipe both upstream and down. The minimum distances are usually expressed in pipe diameters (PD) of the nominal meter body size. In the case where the system piping is the same diameter as the meter, there must be 20 PD of straight run upstream and 5 PD downstream. If an upstream elbow is closely coupled to another elbow that is not in the plane formed by the branches of the elbow closest to the meter, then there must be 27 PD upstream straight run. There must be 10 PD downstream between the meter and a valve.  When the system piping is larger than the meter, there must be at least 20 PD upstream of straight run matching the meter diameter, and at least 5 PD downstream matching the system pipe diameter with a total 25 PD overall minimum. If there is a plane change, the overall requirement goes to 30 PD upstream minimum. The downstream requirement is for 2 PD of matching diameter pipe with a 5 PD overall minimum and the usual 10 PD downstream between the meter and a valve. Figure 2 illustrates minimum parameters. Should pipe requirements be less than specified, accuracy may be affected. Pulsating flow will affect accuracy (pressure pulses will not).

MOUNTING THE ELECTRONICS MODULE
The electronics module is intended for mounting on a sub-plate in a non-corrosive protected environment, such as a nitrogen-purged wet bench overhead. The maximum ambient temperature for the module is 70°C. Two mounting holes are provided that will accept up to 4 mm (English #10) screws. The module may be mounted in any orientation, and special ventilation is not required. Do not place the module and its wiring adjacent to sources of electrical noise, such as ultrasonic cleaners or motor contacts. Do not route wiring in the same bundle or conduit as these devices.