TYPE PS
Senses Static Pressure Only.

MACH NUMBER RANGE

The lower usable limit for Pitot-Static probes depends on the sensitivity of the readout device used with the probe.  A differential pressure of 1" of water, for example is about the minimum that can be measured with 1% accuracy with ordinary slant gauges, so the lower limit is approximately at a Mach Number of 0.06 or velocity of 70 ft/sec for air at standard atmospheric conditions. While there is no minimum Mach Number for the probe itself, there are viscous drag effects that should be considered when using a probe in a low velocity fluid field.  (See Reynolds Number Range).  The upper limit is at about Mach 0.95 for the total pressure reading and 0.70 for the static as shown in Figure 1.  The static reading is accurate to 0.5% to a Mach Number of 0.50 and to 1.5% up to Mach 0.70.  At this point the calibration becomes erratic due to the formation of local shock waves on and around the tip of the probe and the reading can vary as much as 10% with slight changes in flow conditions or proximity to solid boundaries. Above Mach 1.0 both the total and static readings vary considerably from true stream values but they can be corrected theoretically.

Figure 1. Mach Number Range.

Figure 2. Yaw and Pitch Angle Error.

Note that yaw and pitch angle affect the readings exactly the same.  The errors in total and static pressure increase quite rapidly for angles of attack higher than 5°, but they tend to compensate each other so the probe yields velocity and weight flow readings accurate to 2% up to angles of attack of 30°.  This is the chief advantage of the Prandtl design over other types.

The dimensions a, b, and d should satisfy the following:
            d <=  5.0 x a - 2.9 x b