AUTO-CALIBRATION
OF A SEEDER USING TANK SCALES WITH AUTOMATIC RATE ALARM
FIELD OF THE INVENTION
This invention relates generally to a material distribution apparatus and method which auto-calibrates the feed rate of material being distributed over an area, and, more particularly, relates to a seed planter for planting seeds over a planting area. The apparatus also provides an automatic rate alarm to the user when the feed rate is outside a desired range. The apparatus and method have been developed to allow for more accurate metering of material to ensure accurate coverage and to minimize wastage of material.
BACKGROUND OF THE INVENTION
Accurately applying a material such as seed or fertilizer to an area is an important aspect of farming. The material to be applied may be expensive and distribution area is often very large so mistakes in the rate of application can be expensive.
Prior art systems for distributing material have been developed that allow an operator to vary the rate of application, however, there are no "on the fly" systems for automatically calibrating the apparatus while in use.
US Patent No. 7,765,944 discloses a system and method that employs a loadcell connected to a seed container to determine the change in weight of product over a measured area to determine the actual seeding rate. This allows the operator to determine if he needs to adjust the actual seeding rate to the target seeding rate, but there is no mechanism for automatically adjusting the actual rate to the target rate during use.
US Patent No. 8,695,396 discloses a method of calibrating a distribution apparatus operation in which the apparatus captures the number of revs of the product meter and
- 2 -determines the change in quantity of product in the tank over an area. Using this change in quantity of product and the number of revs permits a meter flow quantity per revolution of the meter to be calculated so that the meter can be set to a desired calibration setting based on the calculated meter flow quantity per revolution of the meter, but there is no automatic calibration of the apparatus.
In view of the above discussion, there is a need for an improved distribution apparatus and method for delivering material to a distribution area that permits auto-calibration of the feed rate of material to permit more accurate metering, and an automatic rate alarm if the feed rate is outside a desired range.
In the following detailed description, a specific application of the apparatus and method in the form of a seed planter and planting method is discussed in detail by way of example. It will be understood that the auto-calibrating material distribution apparatus and method described herein finds application beyond the agricultural field and may be employed in any environment where it is desired to accurately distribute material over an area.
SUMMARY OF THE INVENTION
Accordingly, there is described a distribution apparatus for delivering material to a distribution area comprising:
a frame supported for movement over the distribution area;
at least one tank for containing the material to be delivered to the distribution area;
a load sensor to monitor the weight of the at least one tank and the material loaded therein;
- 3 -a distribution system to receive the material from the at least one tank and distribute the material in a distribution operation, the distribution system including a metering system to control the rate of material flow according to a target rate;
a control unit for receiving data from the load sensor with respect to the weight of the at least one tank and the material loaded therein during the distribution operation, the control unit recording data reported by the load sensor, processing the data and comparing a load sensor derived change in weight (AWL) with a theoretical change in weight (AWT) based on a calibration factor for the metering system to determine if the metering system is operating at the target rate, and assigning a revised calibration factor for the metering system if the target rate is outside a predetermined set point.
There is also described a distribution apparatus for delivering material to a distribution area comprising:
a frame supported for movement over the distribution area;
at least one tank for containing the material to be delivered to the distribution area;
at least one load sensor to monitor the weight of the at least one tank and the material loaded therein;
a distribution system to receive the material from the at least one tank and distribute the material in a distribution operation, the distribution system including a metering system to control the rate of material flow according to a target rate;
a control unit for receiving data from the load sensor with respect to a change in weight of the at least one tank and the material loaded therein during the distribution operation, the control unit processing the data and comparing a load sensor derived change in weight (AWL) with a theoretical change in weight (AWT) based on the target rate of the metering
- 4 -system to determine if the metering system is operating at the target rate, and assigning a revised calibration factor for the metering system if the target rate is outside a predetermined set point.
Optionally, a rate alarm may be activated if the calculated metering rate is outside a predetermined metering rate error.
In a further aspect, there is described a method of distributing material over a distribution area with a distribution apparatus including a frame supported for movement over the distribution area, at least one tank for containing the material to be delivered to the distribution area, at least one load sensor to measure the weight of the at least one tank and the material loaded therein, a distribution system to distribute the material in a distribution operation, the distribution system including a metering system to control the rate of material flow, and a control unit, the method comprising:
setting the metering system to a target rate;
distributing the material over the distribution area by operating the distribution apparatus and the distribution system over the distribution area;
monitoring the change in weight of the at least one tank and the material loaded therein by receiving data from the load sensor at the control unit during the distributing step;
processing the load sensor data to determine a load sensor derived change in weight (AWL);
calculating a theoretical change in weight (AWT) based on a calibration factor for the metering system;
- 5 -comparing the load sensor derived change in weight with the theoretical change in weight;
determining if the metering system is operating at the target rate; and setting the metering system to a revised calibration factor if the target rate is outside a predetermined set point.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present invention are illustrated, merely by way of example, in the accompanying drawings in which:
Figure 1 is a side elevation view of a distribution apparatus according to an embodiment of the present invention;
Figure 2 is a cross sectional side elevation view of the tank with material showing an exemplary arrangement for monitoring the weight of the combination;
Figure 3 is a detail schematic view of the distribution apparatus of Figure 1 showing sensors and their communication with the control unit of the apparatus;
Figure 4 is a graph showing the manner in which the measured data is conditioned in the control unit according to embodiments of the apparatus and method;
Figure 5a is a graph showing the manner in which the weight of the tank with material is measured and processed for a "low accuracy" calculation according to embodiments of the apparatus and method
- 6 -Figure 5b is a graph showing the manner in which the weight of the tank with material is measured and processed for a "high accuracy" calculation according to embodiments of the apparatus and method Figure Sc is a graph showing the derived weight error over time; and Figure 6 is a schematic view of an embodiment of a loadcell calibration apparatus for use with the apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1, there is shown a distribution apparatus for delivering material to a distribution area in the form of a seed planter 10, commonly referred to as an air seeder.
Planter 10 includes a main frame 16 supported for movement over the distribution area.
Attached to the frame is at least one tank 12 for containing the material to be delivered to the distribution area. In Figure 1, there are shown two tanks 12 and 14 and other tank arrangements are possible. The tanks may be any suitable container for storing the material to be distributed. They may be hoppers, bins, boxes or other containers for retaining the material. Frame 16 and tanks 12 and 14 are supported for rolling movement over the surface of a distribution area by one or more wheels 18. In practice, frame 16 is releasably attached to a towing vehicle (not shown) by hitch 20 so that the planter 10 can be towed over the distribution area. A ground-engaging implement 24 for actually delivering the material below the surface of the distribution area includes a secondary frame 26 supported by ground wheels 28 and connected to the rear of the main frame 16 by a secondary hitch 30.
Alternatively, the ground-engaging implement may be positioned in front of the air seeder or the air seeder and the ground engaging implement may be formed on a common frame.
Material from the tanks is delivered to the distribution area by a distribution system designed to receive the material from the tanks and distribute the material in a distribution operation to ground-engaging implement 24. In the illustrated embodiment, the distribution
- 7 -system comprises an air distribution system 34 which includes a fan 36 connected to a material delivery conduit 38. Fan 36 directs air through the conduit 38 and a material metering system 40 is located at the lower end of each tank 12 and 14.
Metering system 40 controls the rate of material flow from the tanks according to a target rate into the material delivery conduit 38. The particular type of metering system is not important to the apparatus, however, commonly, the meter will be a volumetric meter such as an auger or fluted roller. The delivery conduit 38 consists of one or more individual conduits beneath each metering system with a product passage directing product into each conduit. Each conduit carries material in the air stream to a primary distribution manifold 50 which serves to divide the flow of material into a number of secondary distribution lines 58. Each secondary distribution line 58 delivers material to a secondary distribution manifold 51 which serves to divide the flow of material into a number of tertiary distribution lines 52.
Each tertiary distribution line 52 delivers material to a furrow formed by one of a plurality of openers 60 attached to the secondary frame 26 at transversely spaced locations.
Optionally, a trailing firming or closing wheel 62 associated with each opener 60 firms the soil over the material deposited in the furrow. Applicant's co-pending US
patent application no. 15/710,633 filed Sept. 20, 2017 discloses an exemplary air seeder of the type generally discussed above, particularly with respect to ground engaging implement 24.
The air seeder described and illustrated in Figure 1 is an example of a Class A
distribution system. An alternative embodiment using a Class B distribution system could also be used where the metering system feeds material into a plurality of primary conduits beneath each meter, where each primary conduit then carries the product to a secondary distribution manifold. An example of such a Class B distribution system is disclosed in US
Patent No. 6,213,698 to Landphair et al. Alternatively, a Class C distribution system could also be used, where there is a plurality of meters attached to each tank that feed material into corresponding individual conduits that carry the product directly to each furrow separately.
An example of such a Class C distribution system is disclosed in US Patent Application Publication No. US2018/0098485 to Beaujot et al.
- 8 -While an air seeder is described and illustrated in Figure 1, embodiments of the present apparatus and method may also be used to distribute other materials such as fertilizer. In addition, as well as distributing materials comprising granular particulates, such as seeds or fertilizer, it will be understood that the system and method described are also capable of handling liquid material.
In order to control the operation of planter 10, a load sensor to monitor the weight of the tanks and the material loaded therein is employed. A control unit 80 (see Figure 3) receives data from the load sensor to continuously measure the weight of the tanks and the material loaded therein. During a distribution operation, the control unit receives data from the load sensor thereby recording the change in weight of the tanks and the material loaded therein as material is dispensed therefrom and delivered to the distribution area. The control unit dynamically processes the collected data over two dispensing periods and compares the load sensor derived change in weight (AWL) over the period with a theoretical change in weight (AWT) over the same period. The theoretical change in weight may be calculated based on the target rate of the metering system 40 in units of weight/unit area and the distribution area covered. This allows the control unit 80 to determine if the metering system is operating at the target rate. In a feedback loop, the control unit may automatically assign a revised calibration factor to the metering unit 40, if the target rate is outside a predetermined set range, or prompt the user if they would like to update the factor.
The control unit 80, based on load sensor derived data, may also compare the difference between AWL and AWT, and generate an error signal or alarm if an error greater than a set range is determined by an algorithm. An exemplary algorithm may be based on a load sensor capacity rating, a rate, an amount of total material product metered, and load sensor accuracy.
Preferably, the control unit 80 includes an input means to allow an operator to enter control parameters and a display for displaying information to the operator.
In the event that a new calibration factor for the metering system is assigned, the display may prompt the
- 9 -operator to accept the revised calibration factor. The display may also allow an operator to be notified by the control unit if there are repeated and/or large differences between the load sensor derived change in weight over time and the theoretical change in weight based on the metering system target rate to alert the operator to an operating condition that the control unit cannot control via the feedback loop. Such operating conditions may include metering problems that arise due to, for example, tank pressurization issues, mechanical issues with the metering system, and partial or full blockage of the distribution material.
Referring to Figure 2, there is shown a preferred arrangement for using a load sensor to measure the combined weight of the tank 12 and product 13. The load sensor comprises at least one loadcell 102 positioned between tank 12 and the frame 16 and configured to detect the combined weight of the tank and the material therein. In practice, two or more loadcells would be positioned to provide a more accurate reading of the weight. Depending on the structure and configuration of the tank 12, it may be preferable to mount the tank to a sub-frame 16a and fit loadcells 102 between the sub-frame and main frame 16.
Turning to Figure 3, there is shown a detailed schematic view of the system of Figure 1 showing various sensors that may be used in the collection of data.
It is advantageous to include at least one accelerometer 70 for the entire apparatus or, preferably, an accelerometer with each loadcell 102 to measure acceleration to reduce the magnitude of the dynamic error in measuring the tank weight. This arrangement permits the weight of the tanks to be measured despite the entire distribution apparatus moving as it is towed over the surface of the distribution area. Similarly, it is preferable to include an inclination sensor 72, such as a gyroscope or inclinometer, to measure the angle or inclination of the tanks as a group, or each tank individually, to the horizontal to take into account tipping or rolling of the tanks and material during a distribution operation for use in calculating the static weight value. Data from the various sensors is transmitted to control unit 80 where data analysis occurs. In the case where multiple loadcells 102 are associated with a tank 12, preferably, a junction box 75 sums data from the associated loadcells 102 to communicate the raw loadcell data to the control unit 80. The inclinometer 72 and accelerometers 70 are used to
- 10 -condition the raw loadcell data in preparation for averaging the data in order to estimate the weights under dynamic conditions.
Figure 4 is a graph illustrating how the raw loadcell data is conditioned.
Line 180 shows the raw weight data measured by the loadcells over time. Line 180 is non-linear as the collected weight data is affected by hill angle and the dynamic noise created by the motion of the apparatus over the ground. Hill angles result in the loadcells measuring too low a weight and dynamic noise results in additional large weight variations.
Line 200 shows the weight data partially corrected to remove the error created by hill angles using the inclinometer data and to reduce some of the dynamic noise using the accelerometer(s) data.
The control unit 80 then averages this partially corrected weight data to determine the dynamic average loadcell derived weight as represented by line 202.
In general, there are two primary types of calculations processed at the control unit for embodiments of the present apparatus and method; firstly, a short term relatively "low accuracy" calculation, and, secondly, a long term relatively "high accuracy"
calculation. It is the "low accuracy" calculation that permits quick alerts to large metering rate errors to be generated, whereas the "high accuracy" calculation permits the described apparatus and method to perform its automatic calibration function. Generally, the short term relatively "low accuracy" calculation will be comparing the change in weight over a period of less than fifteen minutes and providing accuracies of approximately 5% error or larger. The long term relatively "high accuracy" calculation will be comparing the change in weight over a period of greater than fifteen minutes and providing accuracies of approximately 5% error or smaller. These periods and accuracies are only generalities and it will be appreciated that they will vary depending on various factors which influence the calculation including, but not limited to, the weight of product metered out, dynamic noise, the system's capability to average out that noise, loadcell accuracy, and the loadcell capacity.
Referring to Figure 5a, a graph of tank weight over time, a detailed description of the "low accuracy calculation will be described. Line 200 represents the conditioned dynamic
- 11 -weight data collected over time by the control unit 80 as a distribution operation is performed and line 202 represents the dynamic average loadcell derived weight.
A first averaged weight Wavg 1 is calculated by averaging the "pool" of conditioned dynamic weights measured over a period between time ti and time t2 with the average weight having occurred at the mid-point tml between ti and t2. A second averaged weight Wavg2 is calculated in the same manner over a period between time t2 and t3 at midpoint tm2. The difference between Wavg I and Wavg2 is then used to determine the loadcell derived weight change of the product AWL over the period between the time midpoints tml and tm2. This loadcell derived change in weight AWL is compared to the theoretical change in weight AWT
based on the target rate of the metering system over the same period to determine if the metering system is operating at the target rate.
For the "low accuracy" calculation the period between tml and tm2 is relatively short. It is proposed this period will be between approximately two and fifteen minutes in length. The "pool" of conditioned dynamic weight in this "low accuracy"
calculation is much smaller than the "pool" of conditioned dynamic weight in the "high accuracy"
calculation, so any rate errors create a larger effect on the pool allowing for quicker alarms to metering rate errors but of lower accuracy. Also, for the "low accuracy"
calculation the length of time between the first averaged weight and the second averaged weight will remain constant and continuously update in a rolling fashion, that is, the first averaged weight calculation will roll forward at the same speed as the second averaged weight calculation. For example, a future calculation may be determining the difference between Wavg2 and Wavg3 to determine the loadcell derived weight change of the product AWL
over the period between the time midpoints tm2 and tm3. It is contemplated that there may be value in having multiple rolling rate alarms, each with a different rolling average time.
Each time span will have a different rate error % range, For example, a calculation with a short time span will have a lower accuracy, and, thus, will only be capable of determining larger metering rate errors, whereas a calculation with a long time span will have a higher accuracy and will be capable of determining smaller metering rate errors.
- 12 -Referring to Figure 5b, a graph of tank weight over time, a detailed description of the "high accuracy" calculation will be described. Line 200 represents the conditioned dynamic weight data collected over time by the control unit 80 as a distribution operation is performed and line 202 represents the dynamic average loadcell derived weight.
A first averaged weight Wavgl is calculated by averaging the "pool" of conditioned dynamic weights measured over a period between time ti and time t2 with the average weight having occurred at the mid-point tml between ti and t2. A second averaged weight Wavg3 is calculated in the same manner over a period between time t2 and t3 at midpoint tm3. The difference between Wavgl and Wavg3 is then used to determine the loadcell derived weight change of the product AWL over the period between the time midpoints tm I and tm3. This loadcell derived change in weight AWL is compared to the theoretical change in weight AWT
based on the target rate of the metering system over the same period to determine if the metering system is operating at the target rate.
For the "high accuracy" calculation, the period between tml and tm3 is relatively long. It is proposed this period will be approximately greater than fifteen minutes in length.
The greater the length of time between tm I and tm3 the larger the "pool" of conditioned dynamic weight and the greater the accuracy of the calculation. For the "high accuracy"
calculation, this length of time between the first weight and the second weight will continue to increase along with the "pool" of data also increasing with the result that the accuracy of the calculation will also increase. This increasing accuracy is shown in Figure 5c, a graph illustrating loadcell derived weight error E versus time t. Line 206 represents the loadcell derived weight error E and, as time increases, this error decreases exponentially. For example, referring again to Figure 5b, the second calculation for the "high accuracy"
calculation may now involve determining the difference between Wavg2 and Wavg6 to determine the loadcell derived weight change of the product AWL over the period between the time tm2 and tm6. The period for this second calculation between tm2 and tm6 is greater than the first calculation between tml and tm3, therefore, the accuracy of this second calculation will be greater than the first calculation. The rate error magnitude required to trigger an automatic rate alarm may start at a high value and decrease over time, essentially
- 13 -following the maximum potential accuracy of the calculation as illustrated by line 206 in Figure 5c. There may also be a user adjustable factor in the system to account for sensitivity preferences between users.
The "high accuracy" calculation may also continuously update in a rolling fashion similar to the "low accuracy" calculation, but with a much larger period between the first and second weight. For example, the control unit 80 may only be able to buffer and process a limited amount of data, and, once this capacity is reached, the first weight calculation may roll forward at the same speed as the second weight calculation. It is contemplated that the period between the first averaged weight and second averaged weight for the "high accuracy" calculation may be one hundred and fifty minutes, but this period could be smaller or larger depending on the control unit and desired accuracy.
In both the "low accuracy" and "high accuracy" calculations described above, the first weight of the product is determined by averaging the dynamic conditioned loadcell weights over a period during the distribution operation. Alternatively, and preferably, the first initial weight could be determined by using the static weight measured while the unit is stationary, thus eliminating the time required to average the dynamic conditioned weights.
For example, referring again to Figure 5b, in the "high accuracy" calculation, preferably, a first weight W1 may be determined while the tank is stationary, for example, soon after filling the tank. A second averaged weight Wavgl is calculated by averaging the "pool" of conditioned dynamic weights measured over a period between time ti and time t2 with the average weight having occurred at the mid-point tm 1 between ti and t2. The difference between W1 and Wavgl is then used to determine the loadcell derived weight change of the product AWL over the period between time t1 and tml, which is quicker than the first method described using the difference between Wavg 1 and Wavg3 over the period between time tml and tm3.
In both the "low accuracy" and "high accuracy" calculations described above, the dynamic conditioned loadcell weights are averaged over a period, however, it is obvious to
- 14 -one skilled in the art that instead of averaging over a period, the dynamic conditioned loadcell weights could be averaged over a first area seeded to obtain the first averaged weight, and, then, the same calculation could be performed for a second seeded area to obtain the second averaged weight. Alternatively, the system could calculate the area or time required to dispense a derived loadcell weight, and compare this to the theoretical area or time based on the target rate and area covered or time elapsed.
In addition, it is contemplated that the described distribution apparatus will automatically perform stationary weight measurements of the tanks and material and associated calculations each time the apparatus comes to rest for longer than a pre-determined period to confirm the running average dynamic calculations.
Referring to Figure 5a, refilling of the tank occurs as shown at 204.
Any time material is added to or subtracted from the tank (for example, filling or emptying a tank) without accumulated acres (or metering system revs), the weight of such material is not added to or subtracted from, respectively, the loadcell derived change in weight AWL
over the previous operating period or area. No averaging of weight data will occur when product is being added or removed from the tank without the accumulation of acres or meter revs. For both the "low accuracy" and "high accuracy" rate alarms, it is preferable that the initial weight and all the data points that will be used for the next averaging calculation are offset (either + or -) by the change in weight of the product (for example, when filling or emptying a tank) to eliminate the time required for the alarm to activate.
Alternatively, the system may also be reset such that a new initial first weight is determined either by this new static weight or calculated by averaging the weight over a period. Any time the metering system calibration factor is changed, the running average comparison between AWL
maintained by the control unit is preferably reset and the comparison starts over.
In a preferred arrangement, the metering system 40 comprises a meter such as an auger or roller for feeding material from the tanks. In operation, a rotatable element of the meter is rotated with each revolution of the element dispensing a defined weight of material
- 15 -from the tanks based on a calibration factor of the meter measured in the weight of material dispensed per revolution of the meter, for example, pounds/revolution. After leaving the meter, the material is deposited in conduit 38 to be delivered by air to ground engaging implement 24 as explained above. When the apparatus is engaged in a distribution operation, the control unit 80 continuously calculates a calibration factor (pounds/revolution) for the meter in accordance with the process described above. If the calibration factor moves outside a set range, the operator is prompted to accept the new calibration factor or the operator may be warned to stop, as there may be a mechanical issue causing repeated or large rate differences from the targeted rate.
In the case of the material to be distributed being a liquid, the metering system may include a liquid pump or an orifice/gate mechanism to deliver a controlled amount of liquid per cycle of the pump or per operation of the mechanism. For example, in one embodiment, the liquid pump may be a fixed displacement pump, and the speed of the pump is adjusted to change the rate of liquid delivery. In an alternative arrangement using a constant speed pump, the rate may be adjusted through the use of a regulator valve associated with the pump which acts to return unused flow back to tank. In such a configuration, the calibration factor adjusted to control liquid flow is based on the position of the regulator flow. In a still further arrangement, a flow meter or a pressure gauge is associated with the liquid pump, and the calibration factor of the metering system is based on the flow meter and pressure gauge reading.
Other metering system arrangements may also be used with the apparatus. In an alternative arrangement, the metering system may comprise multiple meters such as augers or rollers associated with each one of a plurality of tanks for feeding material from a particular tank. These multiple meters can be driven from a common shaft so they all turn at the same rate. They may also be individually driven with their own respective prime mover, such as an electric motor or hydraulic motor. In operation, each meter is rotated with each revolution dispensing a defined weight of material from the tank based on a calibration factor of the meter measured in the weight of material per revolution of a rotating element of
- 16 -the meter for example, pounds/revolution. After leaving the meter, the material is deposited in a conduit to be delivered by air to a ground engaging implement as explained above.
When the apparatus is engaged in a distribution operation, the control unit 80 continuously calculates a calibration factor (pounds/revolution) for the meter assembly in accordance with the process described above. If the calibration factor moves outside a set point, the operator is prompted to accept the new calibration factor, or the operator may be warned to stop as there may be a mechanical issue causing repeated or large rate differences from the targeted rate. As there may be more than one metering system feeding material from multiple tanks any change in the calibration factor will be applied appropriately to each metering system.
In a still further arrangement, the metering system may be separated from the tanks, and located in another preferred location such as the drill. In this embodiment, the metering system(s) may be fed with material from the tanks by the method of induction as described in US Patent No. 7,021,224 to Mayerle et al. Alternatively, instead of induction, the metering system(s) may be fed with material from the tanks by another mechanical meter such as an auger or roller distribution system. When the apparatus is engaged in a distribution operation, the control unit 80 continuously calculates a calibration factor (pounds/revolution) for the meter assembly in accordance with the process described above.
Since the described embodiments of the distribution apparatus rely on load sensors accurately measuring the weight of the tanks and the material therein, it is expected that a calibration system for efficiently and reliably calibrating the load sensors may be incorporated into the apparatus.
For example, in an arrangement where the load sensor comprises at least one loadcell positioned between a tank and the frame, the calibration system may comprise means for applying an external force to each tank in the form of one or more telescoping cylinders to load the tank to a known load value. Figure 6 provides a schematic view of such a calibration arrangement positioned between tank 12 and frame 16. One or more telescoping calibration cylinder(s) 90 applies an external, independently measured force via links 96
- 17 -between frame 16 and cylinder 90 and links 98 between the cylinder and tank 12 to load the tank to a known load value. Calibration cylinder(s) 90 may be hydraulic, pneumatic, or electric actuators. The load value applied by each calibration cylinder may be measured with a gauge indicating cylinder pressure (not shown) or with a calibration loadcell or cells 92 positioned in series with each cylinder. Preferably, each tank may be loaded by its associated calibration cylinders to one or more load values to calibrate at more than one point. For example, a lower load value, an intermediate load value, and an upper, near full scale load value may be used. At each selected loading point, the loadcells associated with the tank are read to determine if the loadcells are accurately recording the applied load based on the gauge or loadcell associated with the calibration cylinders.
The above calibration approach offers significant savings in time and effort compared to current methods which tend to rely on an operator weighing a truck full of product on existing scales, filling a tank of a distribution apparatus from the truck, and then weighing the truck again. The reduction in weight of the truck represents the weight of material delivered to the tank for checking against the increased weight of the tank as measured by the installed weight measuring system of the tank.
In addition, an automatic warning may also be provided to the operator if the control unit 80 detects that there may be an error with one or more of the tank loadcells. For example, the control unit 80 stores the weight of each tank when the tank is empty, and, therefore, can compare this known weight with the weight that should be detected by each loadcell when the tanks are empty. When a tank is empty or near empty based on the theoretical weight calculation, if the control unit 80 detects a weight on a loadcell that is a predetermined amount higher or lower than its expected weight, an alarm will automatically be provided to the operator to calibrate the loadcell. Alternatively, every time the user resets a tanks weight to zero, the control unit 80 can check how much weight is being zeroed out compared to the known empty tank weight and provide an alarm, if it is beyond allowable limits.
- 18 -Although the present invention has been described in some detail by way of example for purposes of clarity and understanding, it will be apparent that certain changes and modifications may be practised within the scope of the appended claims.