QUESTION

The errors are then combined in a square root of the sum of the squares as depicted in the ASTM standard.  Giving you a total %error for tonnage.  Here is a sample rough calculation:

C = Ö(D² +A²)             Where:                      C = combined error (percent)

                                                                      D = percent density test error

                                                                      A = percent volumetric survey error

Several factors are considered in the volumetric survey error calculation:

1.     Aircraft flight height above the ground surface.

2.     Focal length of the camera.

3.     Stereo compilation instruments used to read and collect the digital data.

4.     National Map accuracy standards.

5.     Contour interval.  (Compiled in 1 ft. intervals.)

A series of variables based on the above factors results in a vertical accuracy of approximately 0.50 feet.  The percent volumetric survey error is then calculated using the equation:

                     A = (±0.50 feet/ average pile thickness) x 100%

The average pile thickness for the Main Pile was calculated to be 51.28 feet.  Using these numbers, the percent volumetric survey error is:

                        A_Inactive  = (±0.50 feet/ 51.28 feet) x 100% = ± 0.98%

The percent density test error is calculated using the estimated error at the 98% confidence interval and the corresponding average wet density using the following equation:

                        D = (estimated error at 98% confidence interval / average wet density) x 100%

The average wet density (linear regression method) for the Main Pile was 67.6 pcf with an estimated error at the 98% confidence interval of 0.7 pcf.  Using these values, the percent density test error is:

                                D_Inactive      = (±0.7 pcf / 67.6 pcf) x 100% = ±1.04%

With D and A calculated, the combined error (percent) in tonnage for each method is:

                                C_Inactive      = Ö[(±1.04%)² + (±0.98%)²] = ±1.43%

With the combined error calculated for the tested pile, the following error statements can be made in regards to tonnage (wet weight basis) reported:

                  Pile                          386,470.0 tons ± 5,526.5 tons

As you can see, these are based on statistics and this is used as an example only.  The calculations are found in the ASTM standards. Therefore, the higher the piles and lower the density standard deviation (which can be accomplished with exceedingly increasing number of tests or consistent pile construction) the lower the overall PHYSICAL INVENTORY measurement error. 

QUESTION

ANSWER

If a truck scale spills more than the equivalent of 3 divisions on the weigh platform the truck scale operator is supposed to either clean off the material or do a manual auto zero.  If the truck spills less than 3 divisions the ASTM will zero the truck scale.  The truck scale operator must be aware that the sum of the truck scale tare weight and net weight must not exceed the gross capacity of the truck scale thus the truck scale operator must clean off the truck scale prior to this condition.

My company produces a product and ships it by conveyor  to our customer.  We have a belt-conveyor scale as a basis of payment.  It doesn't meet HB44 and we can't material test it at this point.  My boss said they have an agreement with their customer to use this scale  for payment.  I maintain this scale and I'm sure the customer is getting more than it shows.  There are other people involved that receive benefits from this scale.  I'm sure they are not aware of HB44 and its requirements.  What is the NW&SA response to this question?

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