## KIEL PROBES

#### GENERAL INFORMATION

**Aerodynamic Properties** Kiel probes are used to measure total pressure in fluid stream where the direction
of flow is unknown or varies with operating conditions. Their correction
factor is 0 when used within the ranges outlined below.

**Mach Number Range**
True total pressure is indicated up to a Mach Number of 1.0. There is
a slight drop in yaw in sensing range above Mach Number 0.3m. This decreases
averages about 4% for all types at a Mach Number of 1.0.

**Reynolds Number Range**
Insensitive to Reynolds Number except at extremely low velocities for Pitot-Static
probes. For air this limiting velocity is about 4 ft/sec for the
smallest size Kiel probes listed.

**Time Constant**
This depends on the complete installation, probe, pressure lines, and manometer.
With 1/8" connecting hose up to 20 ft. long and a liquid manometer
of 1/4" ID, the Type B probe will reach equilibrium reading in approximately 15
seconds. Using this time "t" as a standard the other time constants for
average stem lengths will be:

Type |
Constant |

A |
2.4t |

C,D,H |
.04t |

E,F |
.02t |

**Turbulence Errors**
Negligible, especially since the probe is yaw insensitive. Very High
turbulence may cut down the yaw and pitch insensitive ranges however.

**Boundary Effects** Boundary effects are small as in all total pressure probes. However, in steep
total pressure gradients as near solid boundaries or in "trough" behind guide
vanes a shift in the effective center of the probe occurs, so the total pressure
measured corresponds to the streamline 0.5d away from the geometrical center
of the head in the direction of the higher total pressure as
shown in Fig. 3 below.

**Yaw and Pitch Angle Range**
The outstanding advantage of Kiel probes compared with other total pressure
probes is complete insensitivity to direction of flow within certain limits.
Their yaw and pitch characteristics are generally the same although stem interference
on some designs will change one from the other. Fig. 1 shows
these flow angles and Fig. 2 is a typical calibration curve of a Type A probe.
It can be seen that the correction factor equals 0 up to the limits of the
yaw range and then drops very sharply. The range is arbitrarily defined
as the point where the error equals 1% of velocity pressure. Symbols used
in these figures are:

Pt: Total Pressure | Ps: Static Pressure |

Ptp: Indicated Total Pressure |

The yaw and pitch range for all types listed above at a Mach Number of .25 are:

Type |
Yaw Range |
Pitch Range |

A |
±52° |
+47° - 40° |

B |
±48° |
±45° |

C |
±54° |
±49° |

D |
±54° |
±49 |

E |
±63° |
±58° |

F |
±67° |
±61° |

G |
±31° |
±35° |

H |
±35° |
±38° |

**Installation** These probes are usually installed through holes large enough to pass the head
as listed on the Kiel Specification pages. See each individual type for
the minimum size.

**Special construction including other material, designs to customer's specifications,
special take-offs, and mounting adapters quoted as requested.**