The present invention relates to ton i mprovrc rcl' ash level
m o n i t o r i n g f o r e 1 e c t r o s t a t i c p r e c i p i t a t o r s .
(Ft* Id of th*
Electrostatic prec ipi t ators are used for collecting dust particles from dust laden gases. For example, in a thermal power plant electrostatic precipitator is used for collecting fly ash from exhaust gas or flue gas from the furnace. This reduces pollution of the atmosphere.
The hoppers at the bottom of electrostatic precipi tator collects the fly ash and the ash is disposed to ash silos periodically by wet or dry ssh handling system.
The ash level measurement, sensors probes are fixed on
the hoppers at a definite level. Power and signal wires are run
to their respective ash level indicators at ground level for
h u m a n i n t e r a c t ion.
Prior art
In the conventional ash level indicator the probe head electronics contains RF admittance type sensing electronics. The analog signal from the sensor is passed on to

analog window compare electronics in ash level indicator at hopper bottom. The set level is to be tuned very precisely by the analog potentiometer in the level indicator. This set point or the analog signal is prone to drift due to temperature variations and lead to unstable operation. Limited length of PTFE cable for signal and a separate cable for power supply has to be run between sensor and level indicator.
In most cases individual level indicators with its sensor probes are required for every point of level measurement. Two cables - one for power and one for signal has to be run from (": a c h 1 e v e 1 i n d i c a t o r t o s e n s o r head.
Object of t»ne Invention
The ash level indicators as of now known in the art of electrostatic precipitators has certain limitations, vis. tuning the analog potentiometers for level setting in ash level indicators mounted near hopper bottom is very critical and unstable in operation. Healthy operation of every indicator can not foe ascertained easily. Limited length of PTFE insulated signal cable and power cable has to be run between sensor and lev e .1 i n d i c a t o r.
Thus it is another object of this invention to propose such a method of ash level monitoring for use in electrostatic precipitators, which ensure reliable digital turning for level
«_> "*"

setting and for stable operation simple single twisted pair wire
carrying signal and power between sensor probe and centralized
ash level monitor. 64 numbers of sensors' healthiness and
effective operation can be monitored by single ash level monitor
at control room and has serial communication with the host
system.
BuMnitry of the Invention
The present invention relates to a method of ash level monitoring for electrostatic precipitators. This ensures reliable digital tuning for level setting and for stable operation. A single twisted pair wire is used for carrying signal and power between sensor probe and centralized ash level monitor. 64 numbers of sensors' healthiness can be monitored by single «sh level monitor- at control room. It also has serial communication with the host system.
This method is that the sensor's variable RF admittance analog signal is converted into variable frequency and the frequency is modulated on its power supply lines. At the monitoring end, the variable frequency is trapped from and processed indigital way for level setting and trouble shooting.
Thus the present invention provides a method of ash level monitoring for electrostatic precipitators' comprising

A. Using an ash level sensor converting the variable
RF admaittance analog signal into variable frequency.
B. Converting variable frequency into current
modulation on the single twisted pair supply power line.
C. Trapping the variable frequency from the power
supply line using OPTO couplers,
D. Actuating reference frequency of each sensor
stored in EEPROM date menory?
E. Digital tuning to set the value for 'Ash high
1 eve 1 ' j
F. Integrating the sensors^
G. Signaling the alarm through Relay output.
The invention will now be explained in further details with reference to the accompanying drawings, wherein -
Fig.l shows the conventional ash level indicatory Fig.2 shows an improved ash level monitor.
With reference to the drawings, in the conventional ash level indicator, the probe head e 1 ectron ics (0.1. ) contains RF admittance type 'sensing electronics. The analog signal from the sensor is passed on to analog window compare electronics (03) in ash level indicator at hopper bottom. The set level is to be tuned very precisely by the analog potentiometer in the level indicator. This set point or the analog signal is prone to drift-due to temperature variations and lead to unstable in operation. Limited length of FIFE cable (02) for signal and a separate cable for power supply has to be run between sensor and level indicator.
In most cases individual level indicators with its sensor probes are required for every point of level measurement. Two cables - one for power and one for signal has to be run from each level indicator to sensor head.
In the probe head electronics, the signal (RF admittance type) from the sensor (04) is converted into variable frequency. This frequency is super imposed in the power supply lines (signal twisted pair wire) feeds the power to the
(•? 1 ectronics (ø5 ) .
The centralized ash level monitor in the ESP control room has a digital scanner with OPTO coupled frequency / pulse trap circuit (06) at its front end. The power supply lines to
every sensor is connected through its pulse trap circuit. The special microcontroller based integrated ash level monitor (07) can handle up to 64 sensors. The frequency output from the sensor of the empty hoppers can be stored as a reference value in the EEPROM of the microcontroller. Once the frequency crosses above the reference plus constant value, then it is declared that the hopper has reached the set point