booths. Only velocity ranges from 0 to 300 fpm
are applicable to this device.
The diffuser probe (fig. 13-7) is used for
measuring air output at duct supply diffusers. It
can also be used with some meters on return air
diffusers. The meter reading and the K factor
established by the diffuser manufacturer can be
used to determine air volume outputs.
Figure 13-7.Diffuser probe.
The static pressure probe (fig. 13-8) is used for
measuring drops across blowers or fans in duct
systems. The probe is carefully placed over an
opening in the wall of a duct so as to form a
positive seal. The hole should not be less than one-
quarter inch in diameter.
RANGE SELECTORS. These are devices
(fig. 13-9) that permit a rapid change of measuring
ranges without the need for shifting to separate
jets for each range. They are provided with
connections that accept the various probes. These
probes can also be connected to the meter. With the
exception of the low flow probe, measurements
may require a range selector.
A manometer is an instrument that indicates
air pressure by employing the principle of
Figure 13-8.Static pressure probe.
Figure 13-9.Range selector.