Field of invention
The present invention relates to a system for measurement of pushing current in a coke
oven battery. In particular, the present invention relates to a system for measurement of
pushing current and bilateral communication of data between the pushing car and the
main control station. The system of the present invention is immensely useful for
measuring pushing current which is an indirect indicator of the pushing force required to
push the coke in the ovens.
Background of the invention
A typical coke oven battery comprises a series of coke ovens, e.g. 65 ovens. Each oven
is pushed after its coking period is over, i.e. after the coke in it is ready. A pusher ram,
which is installed at a movable car, called the pusher car, does this pushing. The pushed
coke falls on a car called the quenching car. This pushing current is an indirect indicator
oi' the pushing force required to push the coke. The pushing force assessment in each
pushing is very vital in coke ovens, since it depicts the health of an individual oven. The
coke after optimized heating becomes ideal for pushing since at this .stage there is
minimum coefficient of friction between its layers and with the wall of oven. However,
this is not so for under-coked or over-coked coke. Therefore coking period is always
taken into consideration before analyzing the pushing current signature. Abnormal
coking periods lead to sticker formation in the oven which in turn damages battery life.
Pushing current also has a correlation with the coke end temperature. Therefore, for apt
analysis of each oven, both of these parameters are displayed in adjacent columns for
convenience of the user.
The known art of measuring the pushing current is by tapping the bus bar current, which
accumulates all loads like pushing, charging, trolley movement etc. The bus bar is in the
stationary side, i.e. not in pusher car. The known art of transmitting the pushing current
is through hardwired cable, since the bus bar is in stationary side.
However, since this bus bar current is a superimposition of all currents relating to several
operations, therefore, it cannot be termed strictly as a pushing current. Moreover, since
the cars have a movement range of around 100-meter (for the whole battery), therefore, it
is not possible to have a cabled connection for its transmission. Even in radio
communication, the system is prone to inference leading to malfunctioning and is more
vulnerable to industrial noise.
Objects of the invention
Therefore the object of the present invention is to provide a pushing current measurement
system by help of which the pushing current can be measured at the pushing car itself
Another object of the present invention is to provide a radio communication based
transmission system for pushing current to the main control station that is not vulnerable
to industrial noise and enables reliable communication of data.
Yet another object of the present invention is to provide a system for measurement of
pushing current and communication to main control station which is robust, accurate and
reliable even when working round the clock amidst harsh conditions.
A further object of the present invention is to provide such a system for measurement of
pushing current and communication to main control station which has tall and large
structures with high Electro Magnetic Interference (EMI).
A yet further object of the present invention is to provide for bilateral communication
system between the main control station and pusher car for meeting operational
exigencies.
A yet further object of the present invention is to provide for bilateral communication
system for meeting operational exigencies of battery operation.
Summary of the invention
Accordingly, the present invention provides a system for measurement of pushing current
in a coke oven battery and bilateral communication of data between each pushing car and
the main control station comprising:
data acquisition system located in the pusher cars and operatively connected to the pusher
cai" motor comprising:
means for converting the pushing current from AC to DC and
a slave PLC with an analog input module for receiving and recording said DC
converted pushing current;
radio communication based transmission system for transmitting data corresponding to
the pushing current to the master PLC located in the main control station, the system
comprising a radio modem and a unidirectional antenna mounted on said pusher car for
communication with said master PLC using spread spectrum technology.
Detailed description of the invention
The pushing current measurement system of the present invention measures the pushing
current from the pushing motor located in the pushing car. The Pusher ram comprises a 3-
pliase squirrel cage motor. The pusher car data acquisition system of the present
invention acquires the following process information and communicates them to control
system. The system comprises means for converting the pushing current from AC to DC
v\ Inch is preferably a current transducer. According to a preferred aspect, the system also
comprises a current transformer means for converting the pushing current linearly to C'-5
Amp level. Preferably, the system further comprises infrared sensors to confirm the
pushing operation.
The system for radio communication based transmission system for transmitting data
corresponding to the pushing current to the master PLC located in the main control
station comprises radio modems communicating through spread spectrum technology,
which is based on frequency hopping. Omni directional antennas are mounted on each of
tiic pusher cars and the main control system for radio communication therebetween.
The radio modem is also adapted so as to enable bilateral communication between the
pusher cars and the main control station. In a coke oven battery operation, many exigency
situations arise for example, a door not opening or coke not yet ready etc. For mitigating
these situations, both main control station and the pusher car can communicate these
c\ents bilaterally. Also, the master PLC communicates to the pusher car about the time
and number of the next oven to be pushed etc. All these communications are thorough
the said radio modem.
Description of preferred embodiment
The above and other objects, features, and advantages will become more readily apparent
from the following description, reference being made to the accompanying drawing in
which:
Figure 1 shows the data acquisition system located in the pusher car.
I'igurc 2 shows the components in the main control system
I'igurc 3 shows a flowchart for the array based messaging software
Figure I shows the data acquisition system mounted on the pusher cars and operatively
connected to the 3-phase squirrel cage motor of the pusher car. The main components
arc:
A current transformer: 300 Amp/ 5 Amp (AC Current): This converts the pushing
current linearly to 0-5 Amp Level.
A current transducer: 5 Amp AC/ 4-20 milli Amp DC: This changes the AC
current to DC current and makes it compatible for the analog input module of the
PLC.
A slave PLC with an analog input module: A PLC is there in the movable Pusher
Car itself with an analog input module for recording of this pushing current.
Infrared sensors: A pair of transmitter and receiver for each oven to confirm the
pushing operation.
Since the current transformer is connected to one of the phases of the 3-phase motor,
tlierefore the invention shall work, in best mode, when there are no load imbalances
between the different phases.
The current transducer has to be perfectly linear while converting the AC current to 4-20
mA DC. Therefore, intermittently this linearity is calibrated through simulation.
The scaling of the analog channel in the Pusher PLC should be such that the complete
span of operating current values correspond to 4-20 mA.
The radio communication based transmission system for pushing current to the Main
Control Station i.e. Master Programmable Logic Controller (PLC) located in the
stationary coal tower is shown in figure 2. The communication is effected through an
array based developed software.
The pushing current is recorded in the slave PLC. The system software used here is PLC
ladder logic. The inventor has developed an array-based logic for recording this pushing
current. This array of 600 data points of pushing current is then transmitted to the Master
PLC located in stationery coal tower through a Radio Modem. This communication is
through spread spectrum technology, which is based on frequency hopping. This means
that there is a small band of frequency, whenever there is any problem with a discrete
frequency, the system automatically jumps to another frequency within the band. It
reduces the communication error to a 1 ppm. The radio modem used here has a
frequency range of 2.4 to 2.483 GHz. On the Pusher Car station i.e. Slave PLC side an
Omni Directional Antenna is mounted on the top of the Pusher car, such that it has a line
of sight view with the other Omni Directional Antenna of the Main Control Station.
Tlic software part of the invention is messaging through array based software. The
flowchart of the algorithm is shown in figure 3. The protocol used here is DFl, which is
based on RS232 standards. The pushing current of the pusher motor in the pusher car is
stored in a one-dimensional array of 600 elements. On crossing a threshold current value
of pushing current, it is deemed that pushing operation has started, which is confirmed by
tiic status of any one of the 65 Infrared receivers. This current is logged at a rate of 250
milliseconds in the array. Once the logging is complete, the contents of the array are sent
to the Main Control Station using messaging through the radio modem. The software has
both read and write options from both ends. A 32 bit Cyclic Redundancy Check (CFLC)
runs for error checking in the messaging.
Though the radio communication is based on line of sight, however it was found that
limited multiple reflections do not affect the communication, primary due to the
frequency hopping technique. For best mode of working, the omni-directional antennas
at both ends are installed in sufficiently high and clear spaces.
There is even a provision that the application program of the pusher PLC in the pusher
car can be downloaded from the Main Control Station through the radio modem itself
This means that one does not require going to the pusher car with a Lap Top Computer,
i his mitigates the hardship of the maintenance personnel.
We claim:
1. System for measurement of pushing current in a coke oven battery and bilateral
communication of data between each pushing car and the main control station
comprising:
data acquisition system located in the pusher cars and operatively connected to the
pusher car motor comprising:
means for converting the pushing current from AC to DC and
] a slave PLC with an analog input module for receiving and recording said DC
^N ' converted pushing current;
* f ^
I,
radio communication based transmission system for transmitting data corresponding
' to the pushing current to the master PLC located in the main control station, the
system comprising a radio modem and a unidirectional antenna mounted on said
pusher car for communication with said master PLC using spread spectrum
technology.
2. A system as claimed in claim 1 wherein said means for converting the pushing
current from AC to DC is a current transducer.
3. A system as claimed in claim 2 wherein said current transducer is a 5 Amp AC/ 4-20
milli Amp DC transducer.
4. A system as claimed in claim 1, wherein said data acquisition system optionally
comprises current transformer means for converting the pushing current linearly to 0-
5 Amp level.
5. A system as claimed in claim 4. wherein said current transformer means is a 300
Amp/ 5 Amp (AC Current) transformer.
6. A system as claimed in claim 1, wherein said data acquisition system optionally
comprises infrared sensors to confirm the pushing operation.
7. A system as claimed in claim I, wherein said radio modem is adapted so as to enable
bilateral communication between said pusher cars and the main control station.

The present invention relates to a system for measurement of pushing current in a coke
oven battery. The system also provides for bilateral communication of data between the
pushing car and the main control station. The system comprises data acquisition system
located in the pusher cars and operatively connected to the pusher car motor comprising
means for converting the pushing current from AC to DC and a slave PLC with an analog
input module for receiving and recording said DC converted pushing current and radio
communication based transmission system for transmitting data corresponding to the
pushing current to the master PLC located in the main control station, the system
comprising a radio modem and a unidirectional antenna mounted on said pusher car for
communication with said master PLC using spread spectrum technology.