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.

Manometer

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.