envea STACK 710, Руководство пользователя

Страница: 53 / 68

STACK 710 6 Theory of Operation and Application
ENVEA UK Ltd
(PC-000878-MA Issue 7, December 2021)
53
6.5 Requirements for Environmental Legislation
The STACK 710 meets or exceeds the requirements of U.S. 40CFR 0 AppB PS1
and ASTM Standard Practice D 21 .
6.5.1 General Description
The STACK 710 measures opacity by shining a light beam through flue gases. An
internal microprocessor calculates opacity, dust density and other parameters.
The instrument comprises the following parts:
 The Transceiver- contains all the optical and electro-optic components
 the Retro-reflector- contains a glass reflector and an air purge system.
The air purge system can take several forms depending upon individual site
requirements. Single and dual electric blowers are available, as are compressed-
air driven devices. The continuous purge air supply is essential to prevent dust
and corrosive gases from affecting the optical system. Automatic fail-safe shutters
can also be fitted for temporary protection in the event of a purge air failure.
The entire system is designed for continuous operation in all weather conditions,
with minimal maintenance.
Figure 20: STACK 710- overview.
6.5.2 Principle of Operation
The main light source uses three green LEDs in a special configuration (patent
pending) to ensure homogeneity over the entire transmitted light beam.
The
light source is modulated at a frequency of 1 kHz to reduce electrical noise and
eliminate errors due to ambient light. A second light source, the (patented) “Flood
LED” is used to reduce the effect of temperature drift in the detectors to an almost
immeasurable low level.
Electronic modulation eliminates the need for a mechanical chopper, and so the
only moving parts are the motors used in the calibration system. These motors
have a very low duty cycle and are very reliable.