FIELD OF INVENTION
The invention relates to methodology to improve the calibration parameter computation procedure of the bulk material weighing and metering conveyor of the endless belt type provided with a drive mechanism.
BACKGROUND OF THE INVENTION
The coal based power plants are equipped with coal feeder apparatus for measuring and controlling the feed rate of the coal into the furnace. The Coal feeders are equipped with belt to shear the material, modulates the speed of the belt to adjust flow rate of material being drawn from a source, such as a bunker, bin, silo, hopper, or other suitable storage. This fuel feeding rate is critical parameter, based on the amount of fuel fed the propitiate amount of air is to be supplied for ensuring efficient combustion. All the fuel and air input are measured in terms of tons per hour [TPH] metric unit. The coal feeding apparatus, consisting of a conveyor belt mounted on the set of pulleys driven by a driving unit, for instance, a motor. The coal weighing apparatus have a set of load cell transducer to measure the weight acting on the belt. Both the feeding and measuring is controlled and processed respectively by a controlling unit. The feeding rate is controlled by adjusting the speed of the drive whereas the load cell sensor readings are processed for deriving the actual weight based on calibration parameters.

The material may be conveyed over a weight measuring device such as the belt scale fitted with a load sensor. Between the weigh feeder input and output, the weight kilogram value per unit of length, meter, of the material may be measured at every scan it gives kg/m value. At any convenient location on the feeder apparatus the velocity of the belt may be measured or derived which provides meter per second (m/s) value. The instantaneous product of the above two measurements, kg/m x m/s = kg/s, is the actual flow rate which is compared to a demanded flow rate.
The feeder apparatus gets the input, for arriving at the demanded feed rate (kg/s), from the master control system. In case of the coal based power plants, the overall demand for electrical power determines the amount of coal feeding rate. Typically, in a power plant, there would be 8-10 such coal feeding apparatus. The feeding rate demanded per feeder apparatus from the master control system depends on the actual plant generation requirement, calorific value of coal, combustion efficiency of the furnace, number of feeder apparatus in operation and many other parameters.
The difference between the actual flow rate and the demanded flow rate, is computed by the feeder apparatus section so as to increase or decrease the feed rate of the feeder, by controlling the speed of the drive connected with the belt. This demanded feed rate is continuously varying analog signal which is fed into the feeder control system as input demand feed rate. Generally, every measuring equipment needs

accuracy to the class of its requirement. Here, in the case of power plant coal feeding, the weighing accuracy requirement of the feeder is more than 99.5%. The accuracy of the apparatus is ensured by the calibration of the feeder apparatus. During the calibration of the apparatus, two principal parameters are computed and are used for measuring and feeding the material.
The first calibration parameter is the relation between the belt’s linear speed in meter per second and the drive rotational speed in RPM [Rotations per minute]. This is a linear relationship; the belt speed is directly proportional to the RPM of the drive attached. This parameter would indicate the linear speed of the belt per RPM. The belt is not directly coupled to the drive, the belt is fixed on the pulleys, namely head and tail pulley. The head pulley is the pulley to which the drive is coupled with or without a gear set up.
The first calibration parameter, belt speed relationship is calculated by using two external sensors which is used to measure the time taken by the belt to travel a prefixed distance while the drive is rotating at a constant rotational speed. The time taken is measured in terms of seconds, the prefixed distance is in terms of meter, dividing the later by the former, we get meter per second, linear speed of the belt. Since, the motor RPM is constant during the calibration exercise and the linear speed of the belt is directly proportional to the drive RPM, the parameter derived is in the unit of

(m/s) / RPM. This parameter would be used for computing the linear speed of the belt while the RPM is known, during the actual feeding process. The RPM is a direct measurement from the motor shaft. It is imperative to note that the aforesaid parameter is the relation between the belt’s linear speed to that of the motor RPM considering that the belt response to the motor RPM is constant at all RPMs. This invention is to improve the accuracy of the overall feeder apparatus by improving the computation of the above calibration parameter.
The second calibration parameter is the relation between the load cell output to the weight acting on the load cell. This is a linear relationship, the load cell output increases on increasing the load acting on the belt. The second calibration parameter, load cell output to the weight is calculated in two steps. In the first step, the empty belt is rotated for prefixed number of rotations and the load cell signals are accumulated. The average of the load cell value during the first step is stored as dead weight load, also known as, tare weight. In the second step, a known weight is suspended on the load cells on in addition to the belt weight. The belt is now rotated for prefixed number of rotations and the load cell signals are accumulated again, with the known weight addition. The average of the load cell value during the second step is stored as known weight load, also known as, span weight. The difference in the span weight average to the tare weight average is computed and is placed upon the known weight, which gives the loading parameter in terms of kg weight per load cell output.

In Figure 01, the gravimetric feeder apparatus is situated in between the coal bunker and the pulverizer unit. The coal from the bunker [08] enters to the gravimetric feeder [04] inlet via coal chute [02]. The coal chute has two numbers of coal gates one on each end of the chute. The gate located in the upper side of the chute is called coal inlet gate [01]. The gate located in the bottom side of the chute is called coal outlet gate [03]. The gravimetric feeder apparatus [04] along with the drive mechanism [09] is mounted on the feeder floor [05]. The measured and conveyed coal is fed into the downstream equipment via the pulverizer inlet chute [06]. The outlet measured coal [07] enters into the pulverizer [not shown in the figure] for further processing and conveyed to the furnace burners for combustion.
Referring to the figure 02, is the overall scheme of the gravimetric feeder apparatus [04] for feeding bulk solid materials using an endless conveyor belt [15] mounted on minimum of two pulleys rotated in the clock wise direction. The belt shears the material from the material inlet [10], the belt also rotates in clock wise direction conveys the coal through the weighing apparatus [11] measures the weight acting across the known length [17]. The material weighed and conveyed is discharged into the feeder material outlet [13]. The pulley to which the drive is attached to, is denoted as head pulley [14], also the head pulley is located closer to the material outlet end [13] of the feeder apparatus. The pulley which is located at the other end is denoted as tail pulley [16] which is closer to the material inlet.

During the calibration process, a set of external sensors are used for measure the time taken by the belt to cross a predefined probe span length [17]. With the time measured and the known length, the linear speed of the belt corresponding to the calibration motor RPM is determined. When the marked belt is rotating at a constant velocity, set by the motor rotational speed, while each of the mark crosses the left side sensor [19] the electronics associated with the system starts the timer and stops while the same marker crosses the right side sensor [18] while the belt is rotating in clock wise direction. This process is repeated for predefined times and the average of the linear speed is computed. This linear speed and the motor set speed is compared to derive at the belt calibration parameter which is saved and used while feeding material along with other parameter for computing actual feed rate.
The feeding apparatus once calibrated is ready for the actual process of feeding. The apparatus is demanded for specific tons per hour of feed rate and the apparatus speed is adjusted based on the weight sensed by the load cell to cater the demanded feed rate.
Considering uniformly distributed load on the belt, the load on the belt is derived from the instantaneous load cell output multiplied by the second parameter gives, the weight on the load cell:
Instantaneous load cell output x kg per load cell output (calibration parameter) = kg

It is known that the weight is acting on the specified unit length, dividing by the weighing length we derive, linear weight in terms of kg/m. To find the actual feed rate from this stage, it’s required to utilize the first calibration parameter. At any instant of the time, we get the drive speed in terms of RPM, by multiplying the RPM with the first calibration parameter which is in the units of meter per second per RPM, we get the linear speed of the belt at that instance. In the previous steps, the kg/m is computed and here we have the m/s value. Combining these two, we get kg/s value which is the actual feed rate of the apparatus at that instance of above calculations. The actual feed rate at which the feeder apparatus computes the material flow is compared with the demanded feed rate and the error is computed by subtracting the actual and demanded feed rate. The drive speed is adjusted so as to nullify the error.
The significance of the computed calibration parameters are clearly justified as if there is an error in the computed parameter, it would be carried over to the entire process until the apparatus is recalibrated correctly. The invention is the methodology for deriving the most accurate first calibration parameter.
The first calibration parameter computed is to an extent influenced by the RPM at which the calibration is performed. The belt speed is theoretically considered to follow the drive speed proportionally whereas practically it shall not be realized due to the following reasons:

1. A clean belt while calibration would have no foreign substances or material buildup in the non-laden face of the belt which is in contact with the pulley. Whereas while in feeding operation for a while, there would be buildup of material layer, coal dust, beneath the belt surface which would create mismatch in the theoretically computed linear speed and actual linear speed of belt. This phenomenon is due to the fact that an unclean underside of the belt tends to slip from pulley more than a clean belt due to change in the frictional coefficient, thus reducing the anticipated speed of the conveyors and shrinks the weight carrying capacity of the belt.
2. Belt slippage can also be happening when there is improper belt tensioning or because of over loaded conveyor.
3. Smooth pulleys with loose belt after expansion tends to cause slippage.
4. Frozen supporting roller or idlers can also cause the belt slippage while running. This can be overcome by periodic maintenance of the idlers by frequent lubrication, cleaning and alignment.
5. The type construction of belt can also play a role, belt with a polyester warp system, achieves maximum stretch within the first 24-hour that the belt is operating under full load. At this point, the belt will usually stabilize. The user can make final installation tension adjustment and any tracking adjustments if required. The belt doesn’t tend to expand or contract after this period of operation.

On the other hand, if the belt construction employs a nylon or a cotton warp system, you will encounter two to three times as much stretch in that first 24-hour period at time even more than the specified limit. Cotton and nylon will absorb and/or lose moisture and change dimension. This means that they will not stabilize even after the initial 24-hour break-in period, but will continue to stretch and/or contract. Accordingly, belt re-tensioning must be a routine maintenance procedure in these cases. This causes a change in the practically seen linear speed against the theoretically computed linear speed with respect to motor RPM and the first calibration parameter.
At any given instant we know exactly the RPM of the motor whereas the linear speed of the belt is a derived value using the first calibration parameter considering the belt behaves the same way during calibration and throughout the feeding process across the rotational speed of drive. Practically the belt behavior need not be the same throughout the operational period due to the aforesaid external caused. Consider the scenario where the calibration is performed at 900 RPM of the drive with clean belt and in this case the slip of the belt contact with that of the pulley is proportional to 900 RPM and the first calibration parameter computed at the end of calibration is influenced by the slip parameter.
During the actual process of feeding material, consider that the apparatus is operated at an average motor RPM of 450. Since the slippage of the belt is directly

proportional to the motor RPM, the slip would have been reduced by half during the process. Hence, the linear speed of the belt in terms of m/s, computed by multiplying the first calibration parameter and the instantaneous RPM would not match the practically measured actual linear speed at which the process operates. The linear speed of the belt at 450 RPM would be practically greater than the theoretically computed linear speed, whereas lower linear speed will be used for computation by the controller. This would create a mismatch between the actual feed rate at which the process operates and computed feed rate of the system which determines the next speed set point. Hence, the feeding rate accuracy of the system is compromised to an extent of error.
Since, the feeding rate differs between practical and computed values, the air quantity requirement to the furnace is determined using the computed feedrate value rather than the actual. Hence, the error would contribute to incorrect amount of air supply to the furnace, thus reducing the combustion efficiency and in case of power plant furnaces, this further impacts the boiler efficiency. On long run, this mismatch would have contributed to a considerable amount of the material totalizer error, which is the integration of the feed rate with respect to time.
Consider that the slip of the belt is varying at the rate of 0.5% per every 100 RPM change which influences the linear speed of the belt and hence the derived belt

speed related first calibration parameter. Considering calibration RPM of 900 and operational RPM of 450, the slip would create linear speed difference of (900 - 450) x 0.5% per 100 which is 2.25%. This difference of 2.25% would directly influence the amount of material fed to the downstream equipment since the apparatus would be computing the material flow rate based on the computed linear speed while calibrating at 900 RPM.
The percentage difference would be unaccounted for the material totalizer which accumulates the total weight of the material fed through the apparatus. If the demand requirement of the material flow rate is 60 TPH, the actual coal fed during the above illustration would be 60 x (100+2.25)/100 which is 61.35 TPH. The material feeding apparatus would compute the actual material feeding rate as 60 TPH and the accumulator for the material totalizer would be as per the calculated value. Whereas, practically the apparatus feeds 61.35 TPH of coal. Typically, in a boiler there would be 8 to 10 such feeding equipments. Assuming all of them are having same percentage error, the overall input to the downstream equipment, namely coal pulverizer would be deviating from actual requirement. The coal might not be finely grinded by the pulverizer due to the 2.25% increase in feeding rate of coal to the downstream equipment.

Due to improper grinding of the coal, the surface area of the pulverized coal would be lesser than the target area which might lead to incomplete combustion. The furnace efficiency primarily depends on the effective combustion of the fuel, where as in the above illustration, the furnace efficiency would have been deteriorated due to the incorrect input fuel supply. Due to the incorrect fuel input the amount of combustion air supplied is also affected. The air quantity supplied to the furnace combustion is proportional to the amount of fuel fed, while there is an error of 2.25% in the fuel supply computation, the amount of air supplied would be 2.25% lesser than the actual requirement.
All these aforesaid parameters might lead to improper combustion in the furnace and may lead to high levels of unburnt carbon in the ash. Boiler heat rate is primarily worked out using the feed rate feedback from the coal feeding apparatus. The heat rate of the boiler furnace computed using the feeder, calibrated at operator selected speed rather than recommended speed would be resulting in incorrect value.
Due to the variation in the actual and measured flow rate due to inappropriate calibration speed leads to the following drawbacks:
1. Incorrect material supply to the downstream equipment.
2. Improper material totalizer/accumulator readings.
3. Associated problems in pulverizer.

4. Incorrect air supply to the combustion.
5. Reduced combustion efficiency.
Hence, it’s imperative to correctly predict the calibration speed to overcome the above drawbacks.
PRIOR ARTS:
Patent Number: US2974518A - Method and apparatus of calibrating a belt
conveyer scale:
The aforesaid invention relates to a method and apparatus for calibrating a belt conveyer scale and, more particularly, to a method and apparatus for intermittently calibrating a belt conveyer vertical displacement type weighing device. Moreover, such scales usually have a means for integrating and recording such displacement and belt speed measurements. Most conveyer belt scales in commercial use continually provide an instantaneous load reading and an accumulated total weight reading.
Conveyer belt scales may be employed to maintain a specific predetermined bulk density of the material conveyed as in a coke oven installation, for example, where the automatic addition of oil or water at the loading point will raise or lower the bulk density of the coke oven feed passing over the conveyer belt. They may be employed to deliver a predetermined weight of material per unit of time by appropriately regulating the belt speed or the loading of the belt. The totalizing feature of the

integrating and recording meter frequently provides a cost accounting record for an industrial process.
A device for intermittent calibration of a weighing scale for a moving conveyer belt comprising a freely rotatable cylinder positioned above said conveyer belt and having a rotational axis transverse to the longitudinal axis of said conveyer belt, means to support said cylinder above said belt, a weight positioned above said freely rotatable cylinder, suspension means connecting said freely rotatable cylinder and said weight to an overhead support member, means for adjusting said suspension means whereby said freely rotatable cylinder may be brought to bear upon said conveyer belt at a point directly above said weighing scale, means for further adjusting said suspension means whereby said weight may be brought to bear upon said freely rotatable cylinder, means for measuring the rotational rate of said cylinder while in contact with said conveyer belt, integrating means for multiplying said rotational rate by the effective weight bearing upon said conveyer belt, and means for registering the integrated value for comparison with the corresponding registered value of said weighing scale.
Though the above invention discusses about the calibration of belt type feeder scale and deriving at the best accuracy of the weightometer, the feeder apparatus, the prior art don’t discuss about the speed of the belt at which the calibration is to be performed which is the present invention.

Patent Number: US3976150A- Endless conveyor belt load measurement system and method of automatically calibrating same
Apparatus for automatically calibrating an endless conveyor belt load measurement system comprising the combination of:
a) movement measuring means having a digital pulse output for measuring the movement of the conveyor belt,
b) means to determine one complete revolution of the conveyor belt,
c) scale means having a digital pulse output adapted to measure the weight of successive portions of the conveyor belt and the load carried thereby,
d) hoist means for automatically successively applying at least three calibration weights of known values to the scale means while the conveyor belt is empty, the three weights being respectively representative of lower, medium and upper ranges of the scale means, and
e) means connected to receive the digital pulse outputs of the movement measuring means and the scale means, the digital computer means adapted to:

I. calculate the average pulse output of the scale means during one complete revolution of the empty conveyor belt
II. calculate the average pulse outputs of the scale means during one complete revolution of the empty conveyor belt with each of the calibration weights respectively applied to the scale means, and

III. substitute the said calculated average pulse outputs of the scale means into a set of curve fitting equations to calculate a set of linearization coefficients and then to substitute the said calculated linearization coefficients into formula to calculate the load carried by the conveyor belt.
In all the above claims, there is no mentioning of selection of the speed at which the belt is to be rotated during the calibration. The present invention discusses the calibration speed selection procedure for improved accuracy in calibration parameter computation and hence the feeding accuracy of the apparatus.
Patent Number: US4418773 - Conveyor calibration Technique
For a bulk material weighing and metering conveyor of the endless belt type providing a belt speed pulse signal and a tare-adjusted bulk material weight analog signal, the speed signal and the adjusted weight signal being multiplied to provide a product signal that is converted into a periodic pulse signal of constant amplitude whose frequency indicates the feed rate (net weight per unit of time) of the material being metered by the conveyor, a method of tare weight calibration comprising the steps of:
• Counting the periods of the periodic pulse signal for at least one revolution of the empty conveyor belt without tare weight adjustment to the weight signal;
• Removing the weight signal and substituting in its place a preselected tare compensation signal;

• Counting the periods of the periodic pulse signal for at least one revolution of the conveyor belt with the tare compensation signal substituted in place of the weight signal without tare adjustment; and
• Comparing the counts to determine the difference between them, the degree of difference between the counts indicating the accuracy of the tare compensation signal relative to the actual tare weight of the empty conveyor belt and related tare weight elements.
In the claims of the Patent relating to conveyor calibration technique, there is no mentioning of selection of the speed at which the belt is rotate during the calibration. The entire focus is on how the second calibration parameter, the load cell output to weight relationship is generated. The present invention discusses the calibration speed selection procedure for improved accuracy in calibration parameter computation and hence the feeding accuracy of the apparatus.
Patent Number: US9074923B2 2015-07-07 System and methods for belt conveyor weighing based on virtual weigh span
The computational unit is configured to compute a speed of the conveyor belt, the speed of the conveyor belt being based on a rate of change of the incremental belt travel distance sensed, and wherein the computational unit is further configured to compute a flow rate of material, the flow rate of material computed being a function of

the at least one loading metric computed and the speed of the conveyor belt computed. Computing a speed of the conveyor belt, the speed of the conveyor belt being based on a rate of change of the incremental belt travel distance sensed.
In the invention aforesaid, the speed of the belt is measured based on the rate of change of the incremental belt travel distance sensed and the work doesn’t describe about the calibration speed setting. The entire focus of the work is on, how the second calibration parameter, the load cell output to weight relationship is manipulated. Whereas, the present invention focuses on the selection of the appropriate drive speed for computation of the accurate first calibration parameter.
OBJECT OF THE INVENTION
1. It is therefore the object of the present invention toimprove the accuracy of the bulk material weighing and metering conveyor of the endless belt type provided with a drive mechanism.
2. Another object of the invention is to obtain by improvement in the calibration parameter computation method for the feeder apparatus.
3. A further object of the invention is to obtain accurate feeding rate of the material to match the demanded feed rate and to accurately compute the material totalizer of the apparatus.
4. A still further object of the invention is to find out the correct speed for which the operator should use for the calibration of the feeder.

SUMMARY OF THE INVENTION
In present methods, the calibration RPM at which the entire calibration process is performed is operator selected. The operator choses the drive speed at which the calibration is to be performed. The first calibration parameter computed is influenced by the drive RPM. The belt is fixed on the pulleys. The pulley rotates due to direct mechanical coupling of the drive with the pulley, but this is not the case in belt rotation. The belt rotation is completely due to the frictional force of the belt with that of the pulley.
The frictional force is in-turn depends to some extent on the pulley rotational speed. Higher the drive rotational speed, lower the contact time between the belt and pulley, this introduces slip of contact between the pulley and belt. This slip parameter is a function of the drive speed and is directly proportional. Higher the drive speed, higher the slip whereas the slip is reduced while the drive speed is reduced.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is the schematic arrangement of the location of gravimetric feeder
apparatus in the coal handling system.
Figure 2 is the schematic arrangements of the gravimetric feeder apparatus with
parts indicated thereon.

Figure 1 and 2 are for the illustration of the coal feeding apparatus. The methodology described in the invention does not envisage any physical modification in the coal feeding apparatus. All the components in the figure 1 and 2 exists without any modification.
Figure 3 shows the methodology used in the invention for the computation of the
suggested RPM for calibration.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The coal feeder apparatus shall be operated in different modes, namely, Local, calibration and remote. The remote mode is also known as material feeding mode. Only the remote mode of operation feeds materials to the downstream equipment and accuracy of the apparatus is of most importance in this mode. The accuracy of the feeder apparatus is determined by the calibration of the apparatus.
During calibration, two parameters are computed, relation between the load cell sensor output versus weight acting on the load cell and relation between the motor speed and linear speed of belt.
The coal based power plants are equipped with coal feeder apparatus (04) for measuring and controlling the feed rate of the coal into the furnace. The coal feeder

apparatus (04) are equipped with belt (15) to shear the material, modulates the speed of the belt (15) to adjust flow rate of material (10) being drawn from a source, such as a bunker, bin, silo, hopper, or other suitable storage (08). This fuel feeding rate is critical parameter, based on the amount of fuel fed the propitiate amount of air is to be supplied for ensuring efficient combustion. All the fuel and air input are measured in terms of tons per hour [TPH] metric unit. The coal feeding apparatus (04), consisting of a conveyor belt (15) mounted on the set of pulleys (14,16) driven by a driving unit (09), for instance, a motor. The coal weighing apparatus have a set of load cell transducer (11) to measure the weight acting on the belt (15). Both the feeding and measuring is controlled and processed respectively by a controlling unit (not shown) at control room. The feeding rate is controlled by adjusting the speed of the drive whereas the load cell sensor readings are processed for deriving the actual weight based on calibration parameters.
The material may be conveyed over a weight measuring device such as the belt scale fitted with a load sensor(11). Between the weigh feeder input and output, the weight value per unit of length of the material may be measured instantaneously which gives kg/m value. At any convenient location on the feeding apparatus (04) the velocity of the belt may be measured which provides m/s value. The product of the above two measurements, kg/m x m/s = kg/s, is the actual flow rate which is compared to a demanded flow rate.

The feeder apparatus (04) gets the input, for arriving at the feed rate, from the master control system (not shown) in terms of a continuous analog current input. This analog current is generated by the master control system.
The material (10) measuring and feeding apparatus (04) with conveyor belt (15) needs to be calibrated in a period of time. The first calibration parameter which relates conveyor linear speed to the drive’s RPM is computed during calibration. This computed parameter contributes to the accuracy of the feeder apparatus (04) during the material feeding mode. This first parameter is influenced by the speed of the drive at which the calibration is performed.
The drive motor (09) RPM is set by the operator during the calibration and this is an arbitrary value, presently. The operator decides the motor (09) speed based on the experience and assumption, considering that the motor (09) would be operated around the calibration speed range during the weighing and feeding process.
Through this invention, a continuous average of the operating RPM of the feeder apparatus (04), shall be continuously computed during the actual feeding process for every predefined time interval by the master control unit (not shown). This averaged value of the RPM would be used to arrive at the appropriate drive speed at which the calibration has to be performed.

Conveyor belt (15) linear speed to motor drive (09) RPM parameter computed with this method would be of great precision, omitting the deviations with respect to the belt slippages, which improves the accuracy of the coal feeding apparatus (04) system. Though through the invention, the operator shall be intimated with a recommended speed at which the calibration ought to be performed, there is always a choice for the operator to over-ride the recommended speed and perform calibration with any of the operator chosen speed.
The invention aims at improving the accuracy of the calibration parameter computed by performing calibration at specific recommended speed of the drive (09). This recommended speed is computed by the continuous average speed at which the apparatus was operated during the actual feeding mode among the available other modes of operation by the master control unit (not shown). This recommended speed, at which the calibration is suggested, would be the effective averaged speed computed during the complete material feeding mode, omitting the other modes where material is not conveyed. Drive speed during non-material feeding modes such as local operation, maintenance operation or calibration mode are not accounted for the average computations. Implementing this methodology improves the accuracy of the first calibration parameter thereby improves the accuracy of feed rate computation of the system along with aiding with improved combustion efficiency of the fuel in the furnace.

The method of computing the appropriate speed of the motor drive (09) for calibration is described in figure 03 consists of the following steps:
1. The coal feeder apparatus drive shall be operating. If not, Stop RPM calculation.
2. The coal feeder apparatus shall be in material feeding mode. If not, Stop RPM calculation.
3. The preset timer is loaded with a predetermined value and constantly decremented, till timer is elapsed.
4. While the timer is decremented, the instantaneous RPM of the motor is accumulated and averaged till the timer is elapsed for every iteration "n". The average RPM computed at end of every iteration is Xn.
5. While the timer elapsed, the iteration counter "n" is incremented.
6. For every new Xn value, the suggested calibration RPM Yn is calculated using the
following method:

7. Once timer elapses, go to Step number 1.
Typical example of automatic calculation of the suggested calibration RPM by the master control unit is explained below, considering the preset timer period as 15 minutes:
(Assuming that the feeder is operating in the material feeding mode)



Suppose the feeder trips or stops the material feeding operation. The computation for the suggested RPM is halted by the master control unit automatically. The computation for the suggested RPM is continued once the feeder again operates under the material feeding mode. It is to be noted that the material feeding mode only will be considered for the suggested RPM computation. While feeder motor drive (09) is operating in modes other than the material feeding mode, the suggested RPM is not computed or updated.
Thus by the above method of calculating the correct speed of the coal feeding apparatus (04) for the calibration and thereby the drawbacks said in the background of the invention are eliminated.

WE CLAIM
1. A method for deriving the appropriate speed of calibration of the bulk materials
weighing and metering system in a coal feeder apparatus comprising;
computing the average of operating rotations per minute (RPM) of the feeder apparatus (04) continuously during the actual feeding process by repeating the averaging process after every predetermined time interval while the material (10) is being fed through the conveyor belt (15);
computed RPM of the motor driving unit (09) is used as set point RPM during calibration of the feeder apparatus (04) for determining precise calibration parameters;
controlling the feeding rate by adjusting the speed of the driving unit (09) wherein the feeder apparatus (04) is equipped with a load sensor (11) for deriving the actual weight based on calibration parameters, which gives the relationship between the load cell output to the weight acting on it and the relationship between the belt’s linear speed and the driving unit (09) RPM.
2. The method as claimed in claim 1, wherein the coal feeder apparatus (04) is equipped with a load sensor (11) for measuring the weight value per unit length (kilogram/meter value) at every scan between the weight feeder input (08) and output (07), which determines the RPM at which the drive (09) needs to be rotated for attaining the linear speed of the belt (15) at which the demanded feed rate from the master control system is met by the coal feeding apparatus (04).
3. The method as claimed in claim 1, wherein the average of operating RPM of the feeder apparatus (04) is calculated by summing the instantaneous values of the drive motor (09) RPM at every scan and dividing by the number of iterations calculated during the material feeding mode, according to the equation Yn=[Xn+Xm*m]/n,
where ‘n’ is iteration counter number and m = n – 1.

Yn is the auto calculated suggested calibration RPM based on every new ‘Xn’ value obtained after every iteration, where each iteration is determined by the predefined time interval set by the control unit.
4. The method as claimed in claim 1, wherein the computation of suggested RPM is halted as soon as the feeder trips or stops or the controller is in any other mode than material feeding mode and again a fresh computation is restarted.