background with the probe pointed to maximize the leak indication). The leakage rate can then be
approximated by the following:
Leakage Rate (std cm3/s) = Detection Distance (feet)/2.
For example, assume the maximum detection distance is 1 foot.
Leakage Rate = 1/2 = 0.5 std cm3/s.
Testing For Internal Leaks with Contact Probe.
a. Perform step a. through e. in paragraph 5.6.3 to verify proper operation of the equipment. Use the
standard probe for these steps. If the equipment is not operating properly, it must be replaced or
repaired by the PMEL.
b. Connect the contact probe to the instrument. Place the tip of the probe firmly against the test assembly
on a surface close to the suspected location of internal leaks. The tip of the probe should be pressed
normal to the surface (see Figure 5-82). Move the probe from spot to spot over the test assembly and
note increases in the meter reading and noise from the earphones or speaker. Noise indications not
observed at similar locations in an assembly known not to be leaking indicate internal leaks in the test
assembly. By moving the probe to where the maximum noise and meter reading is obtained, the
location of the leak can be estimated.
Figure 5-82. Correct and Incorrect Application of Leak Testing Contact Probe.