FIELD OF THE INVENTION
This invention generally relates to an Ash level indicator switch for hoppers of an
electrostatic precipitator, which is a dust collection equipment widely used in
thermal plants, cement plants, steel plants, and sugar plants. In particular, this
invention relates to an RF admittance based sensor for monitoring the level of
ash in a hopper of an electrostatic precipitator, to an enhanced micro-controller
based Ash Level indicator switch for on-line monitoring of ash level in the hopper
of an electrostatic precipitator.
BACKGROUND OF THE INVENTION
Electrostatic precipitators are pollution control equipments widely used in large
plants for example, thermal power plants, cement plants, steel plants and glass
plants.
The electrostatic precipitators are configured with number of fields, which have
collecting and emitting electrodes. A high electric field is generated between the
electrodes to charge the dust particles and collect the charged particles on the
collecting electrodes. The collected dust layer is removed from the collecting
electrode by a rapping mechanism using electrical rapping motors.
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The dust collected in the hopper and emptied at a regular interval of time for
continuous and safe operation of the electrostatic precipitator. For monitoring of
ash level in the hopper, Ash level indicator switches are used. Indication of the
ash level in the ~opper is used as trigger for evacuating the hoppers.
In the prior art, the RF admittance method is used at the Ash Level sensor probe
whose output is compared with a calibrated signal level using analog
comparators. Electromechanical relay sWitching is used for Level Indication.
Analog tuning is used for calibration.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an enhanced micro-controller
based Ash Level Indicator switch for on-line monitoring of ash level in the hopper
of an electrostatic precipitator.
Another object of the invention is to propose an enhanced micro-controller based
Ash Level Indicator switch for on-line monitoring of ash level in the hopper of an
electrostatic precipitator in which the microcontroller has at least one probe and
sensor electronics mounted on the hopper wall.
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A still another object of the invention is to propose an enhanced micro-controller
based Ash level Indicator switch for on;.line monitoring of ash level in the hopper
of an electrostatic precipitator, in which at least one sensor processing unit is
enabled to monitor and indicate the states of four probes simultaneously.
Yet another object of the invention is to propose an enhanced micro-controller
based Ash Level Indicator switch for on-line monitoring of ash level in the hopper
of an electrostatic precipitator which is provided with a remote display unit for
communicating with a multiple sensor processing units with a standard protocol
for monitoring and calibration of the operating parameters from a remote
location.
SUMMARY OF THE INVENTION
Accordingly, there is provided an enhanced micro-controller based Ash Level
Indicator switch for on-line monitoring of ash level in the hopper of an
electrostatic precipitator which is based on embedded hardware. It consists of a
probe with sensor electronics mounted on the hopper wall, the sensor processing
unit which feeds the RF signal to a maximum of four probes and based on a level
feedback signal detect whether the hopper is filled with ash to the probe level, a
display unit which communicates to multiple sensor processing units with a
standard protocol for the purpose of monitoring and calibration of the operating
parameters from a remote location.
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BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 : Block diagram of Ash Level indicator Switch and the associated
monitoring system according to the invention.
Figure 2 : Schematic diagram of the mounting arrangement of the sensor and its
connection to the sensor processing unit.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
On mounting the level indicator switch, at least one mechanical Probe (1) forms
one of the plates of the capacitor, and the hopper (6) wall forms the other. An
insulator with a low dielectric constant is used to isolate the conductive probe
above the housing, which is connected to the hopper wall. The sensor electronics
(2) which is mounted at the end of the Probe (1) is connected via cable.
An RF signal is applied to the conductive probe (1). The RF signal results in a
minute current flow from the probe (1) to the hopper (6) wall through the ash in
the hopper (6) acting as a dielectric.
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When the hopper (6) is empty the dielectric material between the hopper (6)
wall and the probe (1) is air which results in a certain amount of current flow.
When the level of ash in the hopper builds up to the probe (1), the dielectric
constant of ash being higher than that of air, there is an increase in capacitance
and a minute increase in current flow. This change of capacitance is converted
into the change in output voltage level by the sensor electronics (2).
This change of voltage level is detected by the micro-controller of the sensor
processing unit (3) and is indicated as a change in the state of the level switch.
One sensor processing unit (3) has build in channels to monitor up to four sensor
probes (5).
It also monitors the sensor (5) healthiness continuously. When there is a
permanent damage in the probe (1) the sensed voltage level will be above the
expected range due to an increase in the RF admittance. If electrical connection
to the sensor (5) is broken the sensed voltage will drop close to zero level. Both
these fault conditions are identified and indicated by the sensor processing unit
(3).
Remote display unit (4) communicates over RS-485 bus with multiple sensor
processing units (3). It indicates the status of the associated ash level switches
on the LCD. It has a provision for calibrating the RF admittance level of all
sensors (5) during the routing maintenance. The calibrated values are stored in
the flash memory of the sensor processing units (3).

WE CLAIM :
1. A system for monitoring of Ash level in ESP hopper which is based on
embedded hardware and which consists of multiple probes with sensor
electronics that are mounted on the ESP hoppers, the multiple sensor
processing units feeding RF signal to the four probes, and a display unit
communicates sensor processing units with a standard protocol, wherein
the change in RF admittance between the probe and the hopper wall is
converted to a change in the output voltage level by the sensor
electronics and wherein based on the feedback signal level from the
sensor electronics, the sensor processing unit detects whether the hopper
is filled with ash to the probe level.
2. The system for monitoring of Ash level in ESP hopper as claimed in claim
1, wherein the sensor processing unit is enabled to identify and indicate
fault condition to the sensor such as permanent mechanical damage to
the probe or break in the electrical connection to the sensor.
3. A system for monitoring of Ash level in ESP hopper as claimed in claim 1,
wherein the display unit monitors the states of multiple ash level switches
and has a provision for digital calibration of the operating parameters
from a remote location.