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LOAD CALIBRATION PROCEDURE FOR WEIGH FEEDER

Example for Weigh feeder Capacity : 100 TPH Speed : 0.182 m/s Load cell : 50 Kg EXC : 11.81 Volt Tare mV : 2.4 mV Span mV : 11.4 mV (keeping the test weight on the knife edge for calibration) Test weight : 16.4 Kg. mV for Lever ratio : 5.38 mV (Keeping the test weight on the center of the center measuring idler ) Step by step of calibration calculation: TPH : Kg/m x m/s x 3.6 Kg /m : TPH / (M/s.x3.6) : 152.672 Kg (100 / (0.182*3.6) “GM” (Kg @ Measuring Zone 0.35m) : Kg/m x 0.35 : 53.435 Kg (152.672 x 0.35) “FM” (Load on Load cell) : GM / Lever ratio : 20.552 Kg (53.435 / 2.6)…. 100% Lever Ratio: As per the design the Lever ratio is 2,5, but due to the mechanical clearness the Lever ratio is possible to vary, so calculate the exact lever ratio and proceed to “FM”. It means how much Kg applied on one side and how much Kg is getting on the another side, This ratio is called as lever ratio. In Weigh feeder “GM” is applied weight & getting weight is “FM”. By the calculation of exact “FM” (Based on the cross calculation of load cell mV), the exact Lever ratio is calculated. Lever ratio point: Remove the skirt board and keep the test weight in line with the Center of the center measuring idler.

“FM”: Load on the load cell

“GM”: Load on the load cell

“Kg/m”: Load on the load cell

Test weight “ GP” Calibration point “e” distance

Test weight “ GP” Lever Ratio point

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50 Kg = 23.62 mV (11.81 x2) Net mV : (Lever ratio mV – Tare mV) : (5.38 mV – 2.4 mV) : 2,98 mV As per mV cross calculation getting Kg : 6.308 Kg …. (( 50/23.62) x 2.98) Applied weight is 16.4 Kg but getting 6.308 Kg. Therefore Lever Ratio : 16.4 / 6.308 : 2.6 (use this value for FM calculation) Calibration Percentage: It is derived based on the comparison of “FM” with Test weight simulation. It is obtained by two methods, Method 1: The calibration percentage is calculated based on the “e” distance w.r.t to Test weight. Formula: “e”distance for 100 % Calibration percentage: (FM x 200) / Test weight. Note:

1. In this method, the error is possible in the calibration due to following reason: 1.1 Mechanical clearness error. 1.2 Operation error while setting “e” distance.

2. The accuracy of the weigh feeder is got disturbed due to this above error. 3. To over come this error, cross check the calibration percentage w.r.t load cell mV.

Method 2: It is derived based on the comparison of net weight on the load cell (by cross calculation weight w.r.t to mV) with “FM” Note:

1. In this method the all the errors are possible to over come. Method: 1

“e” distance : (FM x 200) / Test weight. : ( 20.552 x 200) / 16.4 : 250.6 mm Keep the16,4 Kg test weight on the knife edge at 250.6mm “e” distance of for 100 % calibration. Note:

1. After keep the test weight at “e” distance, note down the span mv, Once again ensure the calibration percentage by the method-2

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Method: 2 Note down the span mV, after keeping the test weight with the same “e” distance.

The span mV: 10.8 mV. EXC : 11.81 V Load cell Sensitivity : (2mV/V) 50 Kg = 23.62 mV (11.81 x2) As per test weight mV : Span mV – Tare mV (11.4 – 2.4) 9 mV = 19.051 kg ((50 / 23.62) x 8.4) …….( By using test weight simulation) 100 % weight is : 20.552 K …….. (Fm) 19.051 Kg is : 92.69 % Calibration … (Before cross check test) Calibration counts : 1853 d …….( 2000 d = 100 % ) Therefore as per the cross check the calibration percentage is not a 100% it is 92.69% . The error in the calculation is around 8%. There is no needed for drop test if the calibration has been done by method: 2. Note:

1. The site readings entered as a “RED” colour. 2. The calculated values are marked as a under line. 3. Enter your site readings in “RED” colour area and calculate the value and proceed

the calibration.

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Speed Calibration

1. Measure the total belt length, operate the weigh feeder inching by inch and put a measurement mark on the belt and find out the total belt length.

2. Run the weigh feeder at calibration speed (33Hz / 1000RPM). 3. Measure the time for 5 revolution, & average the revolution time, at the same time

note down the “Ta” indication in the TUC display. 4. Calculate the M/s. 5. Enter the displayed “Ta” & M/s in measuring parameter.

Example: Belt length : 7 Meter Time for 5 Rev : 146 Sec Average time : 146 / 5 = 29.2 Sec Speed : Meter /sec = 7/29,2 = 0.24 m/s. (At the time Ta is 557 Hz). Enter this Ta ”557” in nominal tacho frequency & 0.24 in Belt speed in the measuring parameter. Cross check:

1. Run the weigh feeder at 20Hz, calculate the Practical m/s and compare with the TUC displayed M/s.

2. The same way ensure 4 to 5 point of drive frequency and conformed the indicated M/s. is in line with the displayed M/s.

Note: Once the cross checking is perfect, “TF” correction is not advisable for error correction.