The invention relates to an apparatus for leak detection in general and
specifically to acoustic sensors used for detecting steam tube leaks in
power plants. The present invention relates to sensors with intelligence,
sensors which are capable of independent operation as well as networked
operation.
BACKGROUND OF THE INVENTION:-
High pressure leaks in power plants can cause extensive damage in
boiler components and unexpected downtimes. Tube failures are
considered as one of the major causes for any boiler outage. If the
leakage of steam from the boiler tube could be detected at an early stage
of operation, planned correction measures can be taken up to avoid
serious secondary damages. Historically, detection methods like manual
inspection, detecting increase in makeup water use and temperature
monitoring were used, which can only find leaks of significant size, when
considerable damage would have already been caused. Presently,
acoustic sensors are used to detect leaks in advance to enable corrective
measures to avoid secondary damages in power or process plants. To
cover the entire plant, multiple sensors, usually 12-30, are employed at
strategic locations all over the plant. The acoustic steam leak detection
systems usually consist of sensor modules with the sensing element or
transducer, field amplifier modules which amplify the signal; cable
means to transmit the signal to a remote processing module; the remote
processing module which processes the independent/ multiplexed
signals; a display unit which provides user interface.

Indian Patent 217835, titled "A Sonic Tube Leak Detection Device for
Boilers To Detect Steam Leakage of Boiler Tubes" relates to a sonic tube
leak detecting device (STLD) for boilers to detect steam leakage of boiler
tubes comprising a sonic tube assembly, an acoustic sensor, a pre
amplifier unit and a system panel, said sonic tube assembly comprises a
matching unit, isolating unit and a heat insulating coupling, said
acoustic sensor comprises a coupling, an electronic unit, an insulated
bush, a s.s. bush and a connector, said system panel comprising a
modular system electronics, a monitor, a PC, an audio system, a key
board and a printer, the steam leak noise being converted into electric
signal in the sensor which is amplified in the preamplifier unit, the
current signal and the voltage with frequency information being
processed through the processor module, the out-put signal being
simultaneously fed to a V/I converter, a comparator circuit, an analog
remote display read out and a computer system for storage, mimic
generation, graphical read out, historical and trend reporting. The
present invention is more featured and minimises analog circuitry.
Indian Patent Application 942/Kol/2014, describes a method and
apparatus for automatic configuration and calibration of acoustic
sensors employing acoustic sensors and calibrator with a wireless/ RF
interface. The method has been further enhanced and used in the
present invention to have automatic configuration and calibration.
US Patent 5623421 reveals a device that monitors a pressurized vessel to
detect small leaks, ruptures and hard hits on the vessel wherein
transducers are attached to the vessel and transmit acoustic signals
which are processed to extract frequency spectra to detect leaks,
ruptures or hard hits. In the present invention, the method of detection
is based on acoustic signals transmitted through air/gas medium and
the sonic sensor is mounted away from the boiler water wall steam pipes.

The processing is also handled directly at the sensor than in a central
processor.
US Patents 5101774 and 4960079 disclose an acoustic leak detection
wherein acoustic signals are passed to a sequential multiplex switching
unit and the output of the multiplexer is further processed using Fast
Fourier Transform (FFT) techniques. The present invention differs the
above patents as the processing is handled in the sensor and does not
use multiplexers, further analog circuitry and PC for processing.
OBJECTS OF THE INVENTION;-
It is an object of the invention to have intelligent sensors for leak
detection which require little manual intervention for operation.
A further object of the invention is to utilize digital signal processing
algorithms and machine learning algorithms to detect leaks intelligently.
Yet another object of the invention is to have intelligent sensors which
detect leak independently and can be connected in a network to provide
more utility to the plant.
Another object of the invention is to simplify and reduce the amount of
cabling required in an acoustic leak detection system.
A further object of the invention is to simplify and reduce the amount of
analog circuitry or modules in an acoustic leak detection system.
SUMMARY OF THE INVENTION;-
The present invention describes an intelligent sensor which is capable of
detecting leaks by itself and has automatic calibration, automatic
purging, acoustic spectral analysis, and machine learning to augment
the leak detection functions. The apparatus for leak detection employs a
sensing element connected to an analog-to-digital converter with
programmable gain means for calibration, further interfaced to a
microcontroller which contains the required logic to detect leaks. Also

included is a wireless interface, especially, RFID or Near Field
Communication (NFC) for automatic calibration and powerless cable free
configuration of the sensor. The sensor has an energy harvesting sub-
circuit, specifically RF energy harvesting and a RF interface connection
to the microcontroller. The energy harvesting is used to power up sensors
even when taken off-line and an equipped calibrator can read and
configure a new or replacement sensor. Also present are visual
indication means such as bar graph LEDs, numeric LEDs and status
indication LEDs to provide information to user. A user input means is
provided to troubleshoot and diagnose the sensor manually. The sensors
include a means of actuating a solenoid valve for automatic purging. The
sensors have a Real Time Clock unit to time and log leak, diagnostic and
other events while also scheduling calibration and purge events. The
sensors also include a secondary communication means to provide
network connectivity for enhanced information.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: -
Figure 1 shows a block diagram of the apparatus in accordance to the
invention.
Figure 2 shows a block diagram of the simplified apparatus in
accordance to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE
INVENTION;-
The apparatus set up for leak detection is shown in Figure 1. The sensor,
100, consists of a microcontroller/ processor 101 interfaced to the sensor
element 102, with its associated amplification circuitry 103, Analog to
Digital Converter 104, programmable gain adjustable means 105,
wireless/ RF transceiver circuitry 106, display or indication means 108,

keys or input means 109, Real Time Clock (RTC) means 110, relay 111,
self-check circuitry 112, memory 114 and inter-connecting interface 113.
The sensor can be powered using conventional means as well as energy
harvesting means 107. The RF interface is primarily for interfacing with a
configuration or calibration or troubleshooting device. Being wireless in
nature enables the sensor to be configured or calibrated or troubleshot
without manual intervention to access connection ports, perform
interconnection via cables, etc. The energy harvesting and/ or RF means
enable configuration or calibration or troubleshooting without the sensor
being powered on. The RF interface along with the programmable gain
means enable automatic calibration wherein a calibration device can
communicate the test pattern to the sensor and the sensor can program
the gain to obtain the known levels. The display/ indication are used to
indicate the user, the mode of operation, status, etc. The key(s)/
pushbutton(s) is (are) used to provide input to the sensor to change mode
of operation, view status, self-check, manual purge etc. The RTC is used
for scheduling purging, calibration etc., and time-stamping for events.
The self-check circuitry is used to diagnose the sensor manually or
automatically by providing a known input to the sensing element. The
relay is used for actuating an external solenoid valve or other means to
perform purging automatically whenever required or on schedule or on
demand. An additional relay can be used to provide leak detection status
output. The memory is used to store parameters, log the configuration/
calibration events, etc. The interconnecting interface, wired serial bus
means or wireless means, is used to interconnect sensors with
themselves or as a secondary interface to a hand-held device for
calibration or troubleshooting or to a remote signal concentrator or
master unit for deriving more utility as a plant-wide sensor network or to
connect to a PC for transferring the logs.

Figure 2, illustrates a preferred embodiment of the invention 200, where
the primary differences from figure 1 are: the usage of a NFC dual port
EEPROM with energy harvesting 205, combining the functionality of RF
transceiver, memory and energy harvesting sub-sections in figure 1;
usage of a microphone 202 as the sensor element; a buzzer 212 as the
self-check circuitry element; usage of a CODEC with DSP processing
203, combining the amplifier, programmable gain and ADC sections of
figure 1; addition of a headphone output 204 for diagnostics and usage
of isolated RS485 circuitry 207, for interconnecting interface. One part
which is suitable for 205 is STMicroelectronics M24LRxxE series of dual
port memories. Other equivalents/ combinations may also be employed
to achieve memory, energy harvesting and RF interface. By using Near
Field Communication NFC as the RF interface, the sensor is capable of
being programmed via many mobile phones. The RF transceivers may
involve a password protected/ encrypted means to ensure security
whereby communication is established only if the password is correct.
One part suitable for 203 is the Texas Instruments TLV320AIC3254
audio codec with miniDSP. Other equivalents/ combinations may also be
employed to achieve ADC and digital signal processing.
The microcontroller 101 or 201, can be any processor with enough
interfaces to connect with the above mentioned peripherals. The sensor
has the following modes of operation: Calibration mode wherein the
sensor adjusts its gain settings to achieve the same levels as the test
input; purging mode wherein the relay/ actuation means is energised for
a programmed duration; programming mode wherein the sensor
parameters are updated; self-test or diagnostic mode wherein the self-
check circuitry is energised and self-diagnostics occur and normal
operation mode wherein the sensor detects leaks using digital signal
processing and machine learning. The acoustic spectrum of the sound is
computed by the miniDSP core of the CODEC or by Fast Fourier

Transform (FFT) performed at the microcontroller. The spectrum of a leak
signal is fed to the controller as input parameters or the sensor learns
the spectrum through machine learning. By comparing the input
spectrum with the spectrum of the leak signal, the microcontroller
detects the leak and the output is available over the interconnecting
interface or a relay. The noise level in a particular band or root mean
square RMS noise level can also be used as the condition for leak
detection. If the noise level is greater than a programmed threshold for a
certain period of time, the sensor detects a leak. The controller can also
include boot-loader code to enable firmware update in the field with the
interconnecting interface or firmware update over the air using the RF
interface. The sensor apparatus described above shall be enclosed in an
industrial enclosure.

We claim: -
1. An apparatus for detecting steam tube leaks in power plant
comprising an intelligent sensor (100) having automatic calibration,
powerless cable free configuration, automatic purging, self-diagnostics
features that consists of a microcontroller (101); interfaced to plurality of
elements that communicate with each other, the said elements being;
- a sensing element (102) interfaced to the microcontroller (101) through
an amplifier (103) that is coupled to an ADC converter (104) and a
programmable gain adjustable means (105);
- display means to output information;
- push button(s) to input data, change mode of operation, etc;

- a memory storage medium to store relevant data which may include
calibration, configuration and replacement log;
- radio frequency (RF) interface for cable free configuration, calibration
and trouble shooting ;
- relay/actuating means to control an external solenoid valve for purging;
- real time clock (RTC) to log time event and schedule calibration,
purging etc;
- self check circuitry for manual or automated self-diagnostics;
- an interconnecting interface (113) - a wired bus or wireless means - to
interconnect sensors or as a secondary interface to couple to a hand held
device to transfer data ;
wherein the sensor detects leak by computing a frequency spectrum
generated and comparing to a preset or learned leak spectrum.
2. The apparatus for detecting steam tube leaks as claimed in claim 1,
wherein the sensor element may be a microphone.

ABSTRACT
TITLE:- INTELLIGENT SENSORS FOR LEAK DETECTION
An apparatus for detecting steam tube leaks in power plant comprising
an intelligent sensor (100) having automatic calibration, powerless cable
free configuration, automatic purging, self-diagnostics features that
consists of a microcontroller (101); interfaced to plurality of elements
that communicate with each other, the said elements being;
- a sensing element (102) interfaced to the microcontroller (101) through
an amplifier (103) that is coupled to an ADC converter (104) and a
programmable gain adjustable means (105);
- display means to output information;
- push button(s) to input data, change mode of operation, etc;
- a memory storage medium to store relevant data which may include
calibration, configuration and replacement log;
- radio frequency (RF) interface for cable free configuration, calibration
and trouble shooting ;
- relay/actuating means to control an external solenoid valve for purging;
- real time clock (RTC) to log time event and schedule calibration,
purging etc;
- self check circuitry for manual or automated self-diagnostics;
- an interconnecting interface (113) - a wired bus or wireless means - to
interconnect sensors or as a secondary interface to couple to a hand held
device to transfer data ;
wherein the sensor detects leak by computing a frequency spectrum
generated and comparing to a preset or learned leak spectrum.