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2-Dimensional Probes
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FOR MEASURING TOTAL AND STATIC PRESSURES, YAW ANGLE AND TOTAL TEMPERATURE
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Directional probes are used to measure total and static pressure, yaw and pitch angle,
and total temperature. Some United Sensor probes indicate all five
quantities.
United Sensor two-dimensional probes, indicating flow direction
only in a plane perpendicular to the probe axis, have three measuring holes.
The center hole indicates pressure P1, and the two side holes indicate
pressures P2 and P3. Preferably the probe is rotated until P2 = P3; the
flow direction is established as 0° yaw angle and within the probe's limitations
P1 indicates total pressure.
Because the pressure P2 or P3 is highly
sensitive to Mach Number and to small variations in construction, etc., cylindrical
(YA) and cobra (CA or CT) probes are not recommended for indicating
static pressure. To indicate static pressure as well as total pressure and
yaw angle, prism (YC) and wedge (W) probes were developed. These are individually
calibrated. Typical calibrations are shown in Fig. 4. Both
the prism and wedge probes can be supplied with a thermocouple to read total
temperature, designated as YCT and WT, respectively.
A typical installation
with manometers is shown in Fig. 1 for a static pressure indicating probe
such as the YC or W. For a YA or CA probe the choke and static pressure manometer showing P1 - P23 could be omitted. The choke
(USC-8261-3) is not essential, but speeds up the readings considerably. It
provides a high resistance bleed across the differential P2 - P3, tapped at the
center so that the center tap indicates (P2 + P3)/2..
This average
pressure changes only slowly with yaw angle, so P2 and P3 do not need to be exactly
equal when the pressures are observed, and the probe can be effectively
balanced more quickly. As Fig. 2 shows, the probe sensitivity is such that
a yaw angle error of 1° corresponds to a differential P2 - P3 amounting to 5%
of Pt - Ps; and if no choke were used, but static pressure taken to be P2 or P3, the static pressure error would
be 2-1/2% of Pt - Ps. With the use of the choke, the static pressure
error at 1° yaw is negligible (Fig. 3).
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Fig 1. Typical manometer connections for YC or
W probes
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Fig 2. Yaw angle sensitivity of YC and W probes
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Fig 3. Average static pressure (P2+P3)/2 of YC and
W probes versus yaw angle.
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Fig 4. Typical calibration of YC and W probes
versus Mach number and pitch angle
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Standard Specifications
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| YC: |
Three-hole, prism shaped measuring section. Measures total and static
pressure and yaw angle. Insensitive to pitch angle up to 20°. Furnished with
individual calibration curve. Usable up to Mach 0.7. Tip extends 2 diameters
beyond holes. Typical calibration shown in Fig. 4.
Standard diameters
are 1/8", 5/32", 3/16", 1/4", 3/8" |
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| YA: |
Three-hole, cylindrical. For use where only total pressure and
yaw angle are to be measured. Not suitable for static pressure or pitch angles
over 5°. Usable up to Mach 0.7. Tip extends 2 diameters beyond holes.
Standard
diameters are 1/8", 3/16", 1/4", 3/8" |
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| CA: |
Three tubes. For use where only total pressure and yaw angle measurement
are to be measured. Usable up to Mach 0.7. Not suitable for
static pressure or pitch angles over 5°. More accurate for boundary layer traverses
than type YA.
Standard diameters are 1/8", 5/32", 3/16", 1/4", 3/8" |
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| YCT: |
Same as YC, except includes thermocouple inside
the head to measure total temperature.
Standard diameters are 5/32", 3/16",
1/4", 3/8" |
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| CT: |
Three tubes like CA, plus thermocouple to give total temperature, yaw
angle, and total pressure. Same application as type CA.
Standard diameters
are 5/32", 3/16", 1/4", 3/8" |
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| W: |
Three-hole, wedge shaped measuring
section. Measures total and static pressure and yaw angle.
Insensitive to pitch angle up to 30°. Furnished with individual calibration curves. Typical calibration shown
in Fig. 4. Tip extends 1
diameter beyond hole. Usable up to Mach 0.7.
Standard diameters are 3/16", 1/4", 3/8" |
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| WT: |
Same as W, also includes thermocouple inside the head to measure total temperature with separate inlet and
outlet holes.
Standard diameters are 3/16", 1/4", 3/8" |
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Ordering Information
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Typical Example: CT-125-24-F-22-CD-K-Plug
CT: |
Type CT |
125: |
d = 1/8" - Tip diameter. See description of types for sizes in each
type. |
24: |
a = 24" - Overall length - inches |
F: |
m = 1/4" - Reinforcing
tube |
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D |
E |
F |
H |
J |
L |
1/16" |
3/16" |
1/4" |
5/16" |
3/8" |
1/2" |
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22: |
b
= 22" - Length of reinforcing tube |
CD: |
e = 5/32" swaged down to 1/8" |
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A |
C |
D |
E |
F |
1/16" |
1/8" |
5/32" |
3/16" |
1/4" |
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Type of thermocouple wire: |
K: |
Chromel - Alumel
thermocouple |
J: |
Iron - Constantan |
T: |
Copper - Constantan |
E: |
Chromel
- Constantan |
For types CT, WT, YCT only, omit on others. |
Plug: |
Plug termination is standard.
Jacks or leadwire are available. |
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AVAILABLE PROBES
Spherical Probes also Available |
