Title of Invention

AN AUTOMATED DEAD WEIGHT FORCE MEASUREMENT MACHINE USEFUL FOR CALIBRATING LOAD CELLS

Abstract The present invention provides a low cost, accurate, dead weight force measurement machine useful for calibrating load cells of 5 to 10 KN. The system uses a single central pin for stacking the weights and a hydraulic system for loading and unloading of these weights. This results in achieving an almost vibration less system giving stabilization of the machine in the fastest possible time. The calibration of the force transducer can be carried out both in tension and compression following any one of the internationally accepted calibration procedure to the highest possible accuracy requirements as per the standards.
Full Text The present invention relates to an automated deadweight force measurement machine useful for calibrating load cells.
More particularly the dead weight force machine is capable of providing calibration of load cells in compression and tension modes.
The ever-increasing requirements for improved accuracy in measuring tensile forces as well as machines of all kinds used in strength testing, make it necessary for the national metrological laboratories to pay special attention to improve upon the accuracy and standardization of force measurement. Accurate measurement of forces has become increasingly important in designing safe buildings, evaluating the strength of materials, controlling production process, thrust measurement of jet engines, rocket aircraft gas turbine engines, in load cell weigh bridges, weighing of aircraft and for comparing large weights. Some areas that can not be ignored include field of automobiles, and in the medical research for the measurement of forces in bone joints of human body, though the precision required may vary from a few percent to a few parts per million.
The primary method to realize / generate forces from a few Newton to a few mega Newton has traditionally been done by direct application of the dead weights which is generally regarded as first principle instrument. Primary standard in force measurement are machines whose uncertainty can be verified through physical principles directly to the fundamental base units of mass, length and time. The vertical force exerted by a stationary dead weight on its support in air is given by F = (g-4g) m (1 - lPm)
where F is the force in Newton (N), 'm' is the mass in kilogram (kg), 'g' is the local gravity measured near the bottom of the machine, 2Jg is the variation of the g along the height of the machine are the densities of air and of the material of the masses, respectively..
It is evident from the above equation that the over all uncertainty in the force applied by the dead weight machine incorporates the uncertainties associated with the determination of the mass m of the dead weight, the acceleration due to gravity g , the mass and air densities as $a and #m , respectively.
It has been observed that by dead weight or by lever multiplication system, we may achieve forces upto a magnitude say 1 or 2 mega Newton but in actual practice we have requirement of forces to be measured of higher order say 15 or 20 mega Newton. Practical realization of such a higher magnitude of forces is only possible with hydraulic machines. To get a low uncertainty in the measured forces, the machines are built on the hydraulic amplification of dead weights. A small force in the form of dead weight is placed on the small diameter piston - cylinder assembly. This small assembly is connected through a hydraulic line to a large diameter piston -cylinder assembly. The force generated in hydraulic force machine is the force generated by the larger diameter piston which is equal to the force on the smaller diameter piston multiplied by the ratio of the effective area of the piston - cylinder assembly. In other words, the force (F) generated by the large diameter piston -cylinder assembly is given by.where F is the force in Newton (N), 'm' is the mass in kilogram (kg), 'g' is the local gravity measured near the bottom of the machine are the densities of air and of the material of the masses, respectively. A and a are the effective area of the larger and smaller diameter piston - cylinder assemblies in order. Friction will cause an error because the friction transfers force from the piston directly to the cylinder instead of to the fluid . The friction can be minimized by sufficient clearance and by long guiding surfaces to prevent binding. To minimise the frictional forces the cylinder is rotated.
Though, these methods are in use to realize static forces depending upon the range and the accuracy required but the most commonly used method to get the highest possible accuracy is only the dead weight machine. A dead weight force-generating machine provides a convenient means of selection and application of known static forces, in the form of dead weights directly on the force-measuring device being calibrated.
The dead weight force machine manufactured and marketed by M/s Moorehouse, USA, M/s Carl Schenck, Germany, M/s GTM, Germany, and M/s Power House MNC, Korea and by National Physical Laboratory ( NPL) ( a constituent laboratory under the Council of Scientific and Industrial Research New Delhi, India) uses a motorized platen to accommodate the force transducers of different shape and sizes. All these machines are prone to jerk, vibration due to the motorized motion of the platen. All these force machines, use electromechanical system to load and unload the desired dead weights, are susceptible to vibration, oscillation and hence need extra time for stabilization. Moreover it is inconvenient to have different loading regime as per the
requirement of the different international standards like ASTM E-74-2000.ISO 376-2000,184169-1988 for calibration of the force transducers used for calibrating the material testing machines.
The dead weight force machine manufactured and marketed by M/s Moorehouse, USA, uses the pneumatically controlled system to load and unload the desired dead weights used has some limitations as the pneumatic system is used to control the lever which is in turn used to load and unload the dead weights and therefore are prone to jerk and hence sufficient time is needed for the stabilization before the observations can be recorded. In this dead weight force machine , the weights are stacked together with the help of either a two or three mechanical lever arrangement which are actuated by pneumatically controlled switches to load and unload the desired dead weights. In a similar machine manufactured by M/s Carl Schenck Germany, all the weights are interconnected with the help of three centrally connected metallic rods . The dead weights are stationary on the mechanical levers which are actuated electrically to load and unload the desired weights. These system have their own limitations as the force transducer can not be calibrated in equal steps without returning to zero in case of the former machine made by M/S Moorehouse USA and one has to apply an additional pressure equivalent to the applied force while taking the hysteresis in case of the latter machine made by M/s Carl Schenck Germany as the machine is incapable to unload the dead weights in the same sequence as of the loading without removing first the loaded weight. In general, the dead weights are stacked together either by using the three couplings or by using a special type of conical coupling (GTM, Germany) around the
circumference which are more prone to give rise to non axial load due to the misalignment of the couplings besides the higher magnitude of oscillations and vibrations and hence larger uncertainty in the applied force.
Since the dead weight machines are bulky and expensive, their use in general is restricted to low capacity. Moreover these can not be designed and fabricated for ultra high capacity due to the limitations of matching of natural frequency with the frequency of the weights. An alternative to dead weight force machine, dead weight cum lever multiplication machines is being used to realize the forces in the higher ranges. These machines use levers to multiply a small dead weight to generate a high magnitude of force. Dead weight components in these machines may be of five to ten percent of the capacity of the machine, i.e. lever transmission ratio of 10 or 20 may be used. When a single lever is used for the required transmission ratio, the dimensions of the lever have to be kept very large for giving adequate rigidity so that deflection is kept to a minimum. Later on the single lever multiplication has been replaced by the compound lever mechanism where the individual member has a smaller length with adequate rigidity. Now there are machines of capacity as high as 2.5 MN with total uncertainty as low as 4 parts in 10,000. Reference may be made to a recent strain gauge controlled leaf spring joints described by A.Sawlan, H.Gassmann and W.Kuhn in Proceedings IMEKO "Force, Torque, Mass Measurement , September 2001. Instead of the conventional knife-edges system, leaf springs are used in lever multiplication machine to lower down the uncertainty in the force measured both in compression and tension. These machines besides their relatively higher uncertainty in the forces measured due to the larger uncertainty in accounting the frictional forces
at the knife edges, and the effective length of the lever arm used can not be used for
purposes where the uncertainty in the application of the force required is lower than
that of 1 part in 10,000.
The main object of the present invention is to provide an automated dead weight
force measurement machine useful for calibrating load cells which obviates the
drawbacks as mentioned above.
Another object of the present invention is to provide a dead weight force machine
capable of being used either in an auto mode or in manual mode.
Yet another object of the present invention is to provide a force measuring machine
which circumvents the problems of vibrations, oscillations in loading and unloading of
dead weights.
Still another object of the present invention is to provide facility of time scheduling
sequence in automatic operation of the system.
A further objective of the present invention is to provide a single point linking
mechanism for stacking dead weights for quicker stabilization .
A still further objective of the present invention is to provide a force machine capable
of giving very low uncertainty in generation and measurement of forces.
A low cost accurate dead weight force measurement machine capable of calibrating
load cells of 5 & 10 KN capacity has been developed. The system uses a single
central pin for stacking the weights and a hydraulic system for loading and unloading
of these weights. This results in achieving an almost vibration less system giving
stablisation of the machine in the fastest possible time The calibration of the load
cells can be carried out both in tension and compression following any one of the
internationally accepted calibration procedure to the highest possible accuracy requirement as per the standard.
In the drawings accompanying this specification Fig 1 shows the dead weight force machine of the present invention.
In Fig 1: (1) is a top end plate. (2) is a bottom end plate. (3) and (4) are interconnected rods connecting the end plates (1) and (2) making a rigid frame. (5) is a compression platen. (6) is a tension platen. (7) is the top plate and (10) is the bottom plate of tension platen (6). (8) are the rods connecting the plate (7) to the plate (1). (9) and (11) are the holes in plates (7) and (10) to fix a test load cell (12). (13) is top plate connected by rods (17) to a bottom plate (16) making the loading hanger. (18) are the plurality of holes allowing the rods to pass through compression platen (5). (15) is a test load cell .(20) is a coupling through the hole (19). (21) is the stack of weights (22). (23) is the central pin. (24) is a force transducer. (25) is a hydraulic jack . (26) is the hydraulic system. (27) is the flange connecting the hydraulic jack to the bottom plate (2)..
Fig 2 shows the scheme of the coupling of the dead weights, (a) shows weights coupled in loaded position and (b) shows weights coupled in unloaded position Fig 3 shows the flow chart of automatic operation of the machine. (28) is the micro controller and (29) is a Personal computer. (30) is a digital indicator and (26) is the hydraulic system.
Fig 4.shows the calibration of the load cell with the load cell kept rotated by different angles on its axis. Set of points (a) is for the as kept load cell, (b) is for the load cell
rotated by 120 degree, [c] is for the load cell rotated by 240 degree and [d] is the set of points for rotation of the load cell by 360 degree or back to its original position. Figure 5 shows the set of data variation of force generated by the dead weight machine and as measured by standard transducer; [a] set of points show the variation when the standard load cells is in as kept position and [b] shows the set of points as measured when the load cell is shifted by 0.5 mm off axis.
Accordingly, the present invention provides an automated dead weight force measurement machine useful for calibrating load cells which comprises: a rigid main frame having a top end plate ( 1 ) and a bottom end plate( 2 ) circumferentially connected by plurality of interconnected rigid rods ( 3 ) and (4) passing through circumferential holes in a compression platen ( 5 ), the top end plate (1) further holds by means of plurality of rods ( 8 ) a top plate ( 7 ) of a tension platen ( 6 ) consisting of the top plate (7) provided with a central hole ( 9 ) and a bottom plate ( 10 ) also being provided with a central hole (11) capable of holding a test load cell (12) for calibration under tension, the said bottom plate (10) of the said tension platen (6) being fixed to a top plate (13 ) of a loading hanger by means of plurality of rigid rods (14 ) in such a manner as to hold a test load cell ( 15 ) for calibration under compression mode between the said top plate (13) and the said compression platen (5), the said loading hanger having a bottom plate ( 16 ) placed below the compression platen (5) and fixed to the top plate (13) by plurality of rigid rods (17 ) passing through holes (18 ) in the compression platen (5), the said bottom plate (16) of the loading hanger being provided with a central hole (19) capable of accepting a coupling (20) attached to a stack (21) of a plurality of weights (22), characterized in that each of the said weights ( 22 ) being interconnected to weights by means of a
central tapered pin (23) passing through a tapered central hole provided in the said weights (22), the lowermost weight of the said stack (21) resting on top of a conventional force transducer (24) connected at the bottom through a central hole provided in the bottom end plate (2) to a hydraulic jack (25) of a conventional hydraulic system (26) through a linear actuator, the said hydraulic jack (25) being connected to said bottom end plate (2) of rigid frame by means of flange (27), the electrical output of the said force transducer (24) and electrical output of said test load cell (12), (15) being connected to a conventional digital meter (30), the output of the said meter (30) being input to a conventional micro controller system (28 ) capable of controlling the loading and unloading of weights by mechanical actuation of hydraulic system (26) , the said micro controller (28) , digital meter (30) being further connected to a PC (29).
In an embodiment of the present invention, the magnitude of applied force may be in
the range of 1 KN to 10 KM.
In another embodiment of the present invention, the force may be measured in a
range of 1 KNto 10KN.
In yet another embodiment of the present invention, the uncertainty in force
measurement may not be more than 0.005% both in compression and tension
modes.
In still another embodiment of the present invention, the vertical axes of the tie rods
may be at the vertices of an equilateral triangle.

In a further the embodiment of the present invention the distribution of the mass to the upper and lower part is such that the center of gravity of the loading frame may be situated below the load cell (12),(15).
In still further embodiment of the present invention the weights may be stacked uniaxially.
In a further embodiment of the present invention the gap between any two weights may be between 3.5mm to 9.5 mm.
In yet further embodiment of the present invention the taper of the central hole of said weights (22) may be of an angle in a range between 30° -50°. In another embodiment of the present invention the central tapered pin of each of the weights may have a taper angle in a range between 30° -50° . The dead weight force machine generally consists of loading hanger to support the dead weights, dead weights which can be applied through loading hanger to generate the desired forces, loading platen to support the force transducer and a rigid main frame to support all these components. The hydraulic system, equipped with directional solenoid and hydraulic flow control valves, is used for the smooth motion of the linear actuator of the hydraulic jack, that loads and unloads the dead weights. Two-column system is considered not so sturdy against twisting and four-column system is conjectured to be difficult to get an accurate plane.
The three-column system of the present invention allows operator to take observations from three different directions when the force transducer is rotated along its axis during calibration as per the requirement of standard calibration procedures.
The main frame of the machine consists of heavy plates ( 1 ),( 2 ) and ( 5 ) joined together by heavy duty tie rods ( 3 ) ( 4 ), as shown schematically in Figure. 1, so as not to affect the measurement results by buckling load and deflection. The vertical axes of tie rods lie at the vertex of an equilateral triangle. Such positioning of tie rods minimizes unsupported area of the plate ( 5 ) also called the compression platen, thereby ensuring the stiffness in the structure. Three leveling screws are provided in the bottom plate for leveling of the machine. Upper part of the frame can accommodate test load cell (15) of 100- 300 mm in compression and 100- 500 mm in tension ( 12 ). Loading pads , on which the load cell is made to rest, are hardened to HRC 50-65 and grounded to an average surface roughness of 0.2-0.4 micron Concentric circles are made on the loading pad to ease the centering of the load cell. The height from the ground floor to the upper most supporting plate (1) is approximately .between 5 meters and the top of the weight stack (21 ) is approx. 2.5 meters high, from the ground floor, where the value of 'g' is practically measured. Load is applied to the load cell (15 ) through the load-carrying hanger(14), preferably triangular in shape. The distribution of the mass to the upper and the lower part is such that the center of gravity of the loading frame is situated below the load cell (12),(15). The load cell supports the upper plate (13 ) of the hanger whereas the lower end (16 ) of the hanger is directly connected to the weight stack.( 21 ).
The weights are linked in series to increase or decrease the calibration forces sequentially.
However, in the present case a tapered central pin (23) is used to hold a weight with another weight to minimize the error due to uniaxial. The taper angle is in a
range of 30° - 50° Each weight is connected to the other through such a central pin. Guiding taper between pin (23) and weight body (22 ) helps in achieving better alignment as shown in Figure2 (a) and (b). The top weight is connected to the loading frame (14), to apply the load to the load cell.
The hanger is always the first to be applied and the last to be removed from the load cell under calibration. Each weight is designed to the same thickness and the spacing of 3.5 and 9.5 mm between the two weights is maintained within a close tolerances of ± 0.5 mm to allow the loading and unloading of the weights within specified time interval in a range of 30 sees to 300 sees.. All the weights at start up, rest on the weight table attached to the rod end of linear actuator which is flange mounted to the bottom plate ( 2 ) of the system frame. If this is not true , a command is sent to micro-controller to lift the linear actuator till all the weights are supported. On gradual lowering of actuator, the loading hanger picks up predetermined dead weights sequentially thus loading the load cell. The weights applied to the force gauge is the sum of the weight selected plus the weight of the loading hanger. A reproducible conventional force gauge ( 24 ) called the Feed Back Load Cell-( FBLC) of 10 KN full scale with long term stability is mounted co-axially on the rod, at the top end of linear actuator.
The machine is fully automated through a menu driven solenoid valve and the hydraulic flow control valve using a FBLC as its feedback sensor. The FBLC is calibrated directly against the reference force machine to ensure the reliability of its output signal, which in turn is used to trigger the loading and unloading of desired weights. The hydraulic system maintains the proportional ram of the linear actuator
in fixed position and is connected to PC ( 29 ) Comport II via RS232 interface. Therefore loading sequence can be programmed and controlled independently as per the sequencing of operational parameters shown in Figure 3. Custom designed hard ware and software( HW/SW) sub systems were used to automate the force machine. A micro-controller based interface with PC makes the operation of the machine, interactive with the menu driven window based display system.
The machine S/W is capable of handling the calibration of force gauges as per any one of the standard procedure ASTM E-74-2000, ISO 376 -2000 or IS 4169-1988, automatically upon receipt of commands from PC.
The machine operation both in auto or manual mode is selectable on restart up window from the computer. In its auto mode operation, prior to starting the calibration, the operator has option to select the force steps, the dwell time at each step to register the observation, whether the force series are to be taken in both direction for hysteresis, or only in one direction. The number of pre- loading either to a full capacity or 10 % overloading can also be pre-selected before stating the calibration. Then the machine HW/SW control system executes the calibration by clicking preload and subsequently a click on " get reading". The weight stack is applied sequentially against the center of force gauge, upon receipt of command sent from PC holds for a time for stabilization and fulfilling the requirement of the standard and takes the reading from the digital indicator before it moves on to the next calibrating force. The same process is repeated as per the command set in the beginning of the calibration process. The full load can be applied or removed within a predetermined
time with negligible oscillations and vibrations ensuring better stability and
repeatability.
Auto mode is controlled through a window base software and the push button station
is used to apply the desired force when the machine is operated in manual mode. In
manual operation the application of the load can be done in two ways: Firstly .through
a window base interactive display system as is done in auto mode except that it will
stay at a desired load and will wait for the next command which is usually, given after
recording the out put of the force gauge manually. In the second case the solenoid
controlled directional valve and hydraulic flow control valves can be operated
independently without PC through a push button station to apply / remove the
required dead weights. With this method of force control, it is possible to apply and
hold constant a precise desired force for sufficient long time whereas in case of the
auto mode the flow is so adjusted to have reduced vibration and low stabilization time
for the applied force before the reading is registered automatically within 30 sec, once
the load is applied or removed.
Special precaution is taken in the software to provide alarm as and when the weights
not in use come in contact with the dead weight applied to the loading hanger during
calibration.
A software developed by us is made for further computation and calibration report
printing. It then proceeds for the analysis of the observed data, polynomial fit in case
of the continuously force measuring instrument, estimation of the uncertainty,
classification as per the standard requirement and finally preparing the calibration
report.
The minimum force of 0.5 KN, which is the nominal load of the calibrated loading hanger, is always included as the first applied force. The weight stack consists of 1-21 weights which are made up of SS 304.
In the calibration of force transducers, five-force cycles were carried out. In one cycle the force was increased in steps of 10% within the range of 40-100% range of the transducer and then decreased in similar steps from 100% to 40% before bringing it to zero force. After waiting for three minutes on returning to zero, the same force cycle was repeated at the same position of the load cell. One cycle of the observations following the same force sequence, was taken after rotating the transducer through 120°. After rotating load cell again through 120° from its previous position fourth cycle was carried out and then the transducer was brought back to its initial position to take the fifth force cycle. In one force cycle 11 observations were taken, leading to a total of 55 observations per calibration. The load cell of 5 KN full-scale is used from its 40%-100% range and as such a total number of 65 observations recorded following the same procedure. The mean of the five series of readings was calculated As at this stage we are interested in relative error and not in the absolute values and as a result all the values are in indicative units only. The rotational error in all the five force cycles with respect to the first cycle in ascending as well as in descending force series is shown in Figure. 4 of the drawings. It is evident that the maximum rotational error of 27 ppm and the hysteresis is within 18 ppm over 50% to 100% range of the machine. Similar scatter in the calibration data of 5 KN full-scale transducer, when it is calibrated under identical conditions is observed and is also shown in Figure 4.
Further, as it may happen in special cases during practice, the force transducers when placed in the machine is off centered, which will give an error in the observed results. Two independent calibrations one with the transducers is at exactly at the center and in the second it is + 0.5 mm off centered are carried out under similar conditions over whole of the force range. A closeness between these two independent calibrations as shown in Fig. 4 of the same force transducer generates the confidence about the performance of the machine even when a the transducer under calibration was slightly off centered.
The novelty of the present invention lies in the independence of force measurement on the positioning accuracy of a calibrating load cell both with regard to angle and the off centered conditions. A further novelty lies in the negligible vibration and oscillation of the weights during loading and unloading. Another novelty lies in the uncertainty of 0.005% in force generation, calibration both in compression and tension.
These novelties are realized due to the unique constructional features of the present invention particularly to an inventive step of providing tapered central pin to each of the weights having corresponding tapered central hole and eliminating the motorized motion of the compression/tension platen. In addition rigidity of the frame has been made possible by providing tie rods in such a manner such that the vertical axes lie at the vertices of an equilateral triangle.
Following examples are given by way of illustration only and should not be construed to limit the scope of the invention.
Example-1
A well-characterized strain gauge force gauge of 5KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than + 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling rate of 50Hz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to its vertical axis. The gauge was kept in its position and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 2KN to 5KN. The relative deviation of measured force from the standard value is between (-)lxlO"5 and 7x10"6
Example-2
A well-characterized strain gauge force gauge of 5KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than + 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling

rate of SOHz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to its vertical axis. The gauge was kept at a position of 120° and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 2KN to 5KN. The relative deviation of measured force from the standard value is between (-Jl^xlO"6 and =0
Example-3
A well-characterized strain gauge force gauge of 5KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than + 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling rate of SOHz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to

its vertical axis. The gauge was kept at 240° in its position and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 2KN to 5KN. The relative deviation of measured force from the standard value is between (-HxlO"6 and 7x10"6
Example-4
A well-characterized strain gauge force gauge of 5KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than + 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling rate of 50Hz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to its vertical axis. The gauge was kept at an off center position by 0.05 mm and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 2KN to 5KN.
The relative deviation of measured force from the standard value is between (-J6X10-6
Example-5
A well-characterized strain gauge force gauge of 10KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than + 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling rate of 50Hz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to its vertical axis. The gauge was kept in its position and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 4KN to 10KN. The relative deviation of measured force from the standard value is between =0 and 7x10"6
Example-6
A well-characterized strain gauge force gauge of 10KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than + 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling

rate of 50Hz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to its vertical axis. The gauge was kept at a position of 120° and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 4KN to 10KN. The relative deviation of measured force from the standard value is between
Example-7
A well-characterized strain gauge force gauge of 10KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than + 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling rate of 50Hz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to

its vertical axis. The gauge was kept at 240° in its position and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 4KN to 10KN. The relative deviation of measured force from the standard value is between (-)3xlO-6 and 2x10"6
Example-8
A well-characterized strain gauge force gauge of 10KN full scale, having an uncertainty of + 0.02% in the measured forces and repeatability better than ± 0.002% was used . This is traceable to the national reference force standard by its direct comparison. A high - resolution indicator (Model DK-38, HBM, Germany) was used throughout these studies having resolution and stability of 5 ppm with a data sampling rate of 50Hz and transmitted to a PC through GPIB interface. The force is transmitted through a ball and compression pad of hardness 58HRC and a soft flat spacer. No visible, indentation mark on the pad was found when checked after each force cycle. The machine interaction due to misalignment of the applied force on a force gauge can significantly affect the accuracy of measured values, it is therefore desirable to observe the response of the force gauge at several symmetrical positions relative to its vertical axis. The gauge was kept at an off center position by 0.05 mm and the loading test was repeated twice in each direction by increasing and decreasing the force in equal steps covering the range from 40% to 100% of the force gauge, i.e 4KN to 10KN. The relative deviation of measured force from the standard value is between (-)I.8xlO-6 and 1x10-6
Main advantages of the present invention are:
1. The device can be used for calibration as it can generate, measure and
calibrate force with an accuracy of 0.005 % over the force range of 1KN to10
kN. Both in compression and tension modes.
2. The device is reliable, easy to use and economical which will find its use in
many industries for up gradation and quality control of their product.

3. The device uses the hydraulic loading and unloading of the dead weights
which has an edge over the electromechanical system as the vibration and
oscillation are minimized and hence needs very low stabilization time.
4. The machine is capable to carry out the calibration of the force transducers as
per all the international standards used for the calibration of the force
transducers used for the verification of the tensile testing machines.

We claim:
1. An automated dead weight force measurement machine useful for calibrating load cells
which comprises: a rigid main frame having a top end plate ( 1 ) and a bottom end
plate( 2 ) circumferentially connected by plurality of interconnected rigid rods ( 3 ) and
(4) passing through circumferential holes in a compression platen ( 5 ), the top end
plate (1) further holds by means of plurality of rods ( 8 ) a top plate ( 7 ) of a tension
platen ( 6 ) consisting of the top plate (7) provided with a central hole ( 9 ) and a
bottom plate ( 10 ) also being provided with a central hole (11) capable of holding a
test load cell (12) for calibration under tension, the said bottom plate (10) of the said
tension platen (6) being fixed to a top plate (13 ) of a loading hanger by means of
plurality of rigid rods (14 ) in such a manner as to hold a test load cell ( 15 ) for
calibration under compression mode between the said top plate (13) and the said
compression platen (5), the said loading hanger having a bottom plate ( 16 ) placed
below the compression platen (5) and fixed to the top plate (13) by plurality of rigid
rods (17 ) passing through holes (18 ) in the compression platen (5), the said bottom
plate (16) of the loading hanger being provided with a central hole (19) capable of
accepting a coupling (20) attached to a stack (21) of a plurality of weights (22),
characterized in that each of the said weights ( 22 ) being interconnected to weights
by means of a central tapered pin (23) passing through a tapered central hole provided
in the said weights (22), the lowermost weight of the said stack (21) resting on top of a
conventional force transducer (24) connected at the bottom through a central hole
provided in the bottom end plate (2) to a hydraulic jack (25) of a conventional hydraulic
system (26) through a linear actuator, the said hydraulic jack (25) being connected to
said bottom end plate (2) of rigid frame by means of flange (27), the electrical output
of the said force transducer (24) and electrical output of said

test load cell (12), (15) being connected to a conventional digital meter (30), the output of the said meter (30) being input to a conventional micro controller system (28 ) capable of controlling the loading and unloading of weights by mechanical actuation of hydraulic system (26) , the said micro controller (28) , digital meter (30) being further connected to a PC (29).
2. An automated dead weight force measurement machine as claimed in claim 1, wherein the magnitude of applied force is in the range of lKNto 10KN.
3. An automated dead weight force measurement machine as claimed in claims 1-2, wherein the force is measured in a range of lKNto 10KN.
4. An automated dead weight force machine as claimed in claims 1-3, wherein the uncertainty in force measurement is not more than 0.005% both in compression and tension modes.
5. An automated dead weight force measurement machine as claimed in claims 1-4, wherein the vertical axes of the rigid rods (3, 4) are at the vertices of an equilateral triangle.
6. An automated dead weight force measurement machine as claimed in claims 1-5, wherein the distribution of the mass to the upper and lower part is such that the center of gravity of the loading frame is situated below the load cell (12), (15).
7. An automated dead weight force measurement machine as claimed in claims 1-6, wherein the weights are stacked uniaxially.
8. An automated dead weight force measurement machine as claimed in claims 1-7, wherein the gap between any two weights is between 3.5mm to 9.5 mm.

9. An automated dead weight force measurement machine as claimed in claims 1-8, wherein the taper of the central hole of said weights (22) is of an angle in a range between 30 to 50 degrees.
10. An automated dead weight force measurement machine as claimed in claims 1-9, wherein the central tapered pin of each of the weights has a taper angle in a range between 30 to 50 degrees.
11. An automated dead weight force measurement machine useful for calibrating load cells substantially as herein described with reference to the examples and drawings accompanying this specification.

Documents:

405-DEL-2002-Abstract-(02-07-2008).pdf

405-del-2002-abstract.pdf

405-DEL-2002-Claims-(02-07-2008).pdf

405-del-2002-claims-(14-07-2008).pdf

405-del-2002-claims.pdf

405-DEL-2002-Correspondence-Others-(02-07-2008).pdf

405-del-2002-correspondence-others.pdf

405-del-2002-correspondence-po.pdf

405-del-2002-description (complete)-02-07-2008.pdf

405-del-2002-description (complete)-14-07-2008.pdf

405-del-2002-description (complete).pdf

405-del-2002-drawings.pdf

405-DEL-2002-Form-1-(02-07-2008).pdf

405-del-2002-form-1.pdf

405-del-2002-form-18.pdf

405-del-2002-form-2.pdf

405-DEL-2002-Form-3-(02-07-2008).pdf

405-del-2002-form-3.pdf


Patent Number 221789
Indian Patent Application Number 405/DEL/2002
PG Journal Number 31/2008
Publication Date 01-Aug-2008
Grant Date 04-Jul-2008
Date of Filing 28-Mar-2002
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 KAMLESH KUMAR JAIN NATIONAL PHYSICAL LABORATORY DR K S KRISHNAN MARG NEW DELHI-110 060.
2 HARI NANDAN PRASAD PODDAR NATIONAL PHYSICAL LABORATORY DR K S KRISHNAN MARG NEW DELHI-110 060.
3 RAGHUNANDAN PRASAD SINGHAL NATIONAL PHYSICAL LABORATORY DR K S KRISHNAN MARG NEW DELHI-110 060.
4 MIHIR KUMAR CHAUDHAURI NATIONAL PHYSICAL LABORATORY DR K S KRISHNAN MARG NEW DELHI-110 060.
PCT International Classification Number G01G 19/52
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA