Panametrics DewPro MMY30, Руководство пользователя, Страница: 16 / 43

Chapter 2. Installation Guidelines
8 DewPro
®
MMY30 User’s Manual
2.2 Method I - Orifice at Outlet
Figure 5 below illustrates installation of the DewPro MMY30 at the outlet orifice.
Figure 5: DewPro MMY30 Installation at Outlet Orifice
2.2.1 Pressure Dewpoint
Air dryers producing general instrument air are typically specified with a pressure dewpoint rating. The majority of
dryers operate in a dewpoint range between –40°C and –75°C (–40°F and –100°F). A pressure of 7-8 bar (100 psig) is
very common.
2.2.2 Air Flow
The DewPro MMY30 is designed to measure the pressure dewpoint. By restricting the flow at the outlet of the integral
bypass with an orifice, the sensor monitors the dewpoint at process pressure. The flow rate of the bleed-off air to the
atmosphere at 7-8 bar (100 psig), is approximately 70 cc/min (28 L/h / 1.0 SCFH). For smaller dryers with flow rates of
3m
3
/min (100 ft
3
/min) the air loss is only 0.002% of the air production and is negligible. Despite the very low flow rate
through the bypass, the air sample in the DewPro MMY30 bypass chamber is refreshed every second due to the small
hold-up volume design of the chamber. As a result, the sensor responds to changes in moisture content
instantaneously. Due to the low flow rate, the flow velocity is also very low at <0.01 m/sec (34 m/h).This low flow
velocity prevents the inlet filter from clogging since there is not enough kinetic energy to push dust particles into the
filter.