FOR MEASURING TOTAL AND STATIC PRESSURES, YAW ANGLE AND TOTAL TEMPERATURE

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 0yaw 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).
 
 
 

Fig 4. Typical calibration of YC and W probes
versus Mach number and pitch angle


Standard Specifications:
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"
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"
 
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"
 
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"


 
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"
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"
 
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"
 




Ordering Information:




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
D
E
F
H
J
L
1/16"
3/16"
1/4"
5/16"
3/8"
1/2"
22:
b = 22" - Length of reinforcing tube
CD:
e = 5/32" swaged down to 1/8"
A
C
D
E
F
1/16"
1/8"
5/32"
3/16"
1/4"

  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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