YOKOGAWA DT450G Series, Руководство пользователя, Страница: 10 / 41

<1.Overview>
1-1
IM 11K01C01-01E
1. Overview
This chapter discusses the following topics.
· Product overview
· Specifications
· Model and suffix code
· Dimensions
1.1 Product Overview
Powder is used in many industries including ceramics, cement, chemicals, pharmaceutical and
food. In their processes, powder is collected in order to reduce the loss incurred in the process.
Dust emissions from industrial plants are limited by the air pollution control law, local regulations
or other guidelines. Each industrial facility is required to be maintained so that its dust emissions
do not exceed the allowable level.
Air pollution control systems such as bag filters and electrostatic precipitators are used to
separate particulate or dust from the gas stream before it is exhausted into the atmosphere. To
maintain the dust concentration of the emission gas below the specified level through effective
operation of the control system, it is essential to continuously monitor the dust concentration of
the exhaust gas.
Based on installation and application experiences with the existing DT400G model, the
microprocessor-based DT450G Dust Monitor features improved operationality and reliability.
Features include one-touch automatic range setup in response to process conditions and
automatic drift compensation. Also, the DT450G can measure at a process temperature of up to
250ºC, allowing it to cover a wide range of applications.
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Measuring Principle
When two solid particles come into contact with each other, charge transfer takes place between
them. This charge transfer is known as the principle of triboelectrification or contact electrification
and the DT450G utilizes this principle. More specifically, charge transfer occurs when particles in
a gas stream collide with (or pass nearby) the sensor probe, producing an electric current. The
DT450G amplifies this current to convert it into its output current. The electric current produced
by frictional electricity is subject to the effects of the following factors:
• Amount of the particles' electrostatic charge and a change in the polarity
• Particle size
• Velocity of particles
• Components of particles
The behaviors of these factors vary widely depending on the object of measurement and their
effects are in no way uniform. In the case of fixed-position measurement in a particular plant
however, measurement conditions, such as the components of particles, are almost constant
and therefore the effects are usually marginal. Dust concentration is also constant in the case of
gases emitted from a bag filter, cyclone or electrostatic dust collector.
A current-mode input signal obtained at the detector block is transferred to the converter block,
where the signal is converted to a 4-20 mA DC analog output signal. The converter block outputs
an alarm contact signal at a desired level, in addition to the analog output signal.