The following letter was sent to large scale service companies from Doug Musick with the Kansas Department of Agriculture’s Weights and Measures Division on June 15, 2015: (please note that referenced attachments can be obtained by contacting your KGFA staff)
I have been asked to give an interpretation on what scale modifications are allowed beyond what was NTEP’ed and which are not specifically addressed by regulation. This is a very complex issue. The question came about specifically with the addition of concrete sidewalls being added to scales. The safest approach is don’t modify a scale. If you decide modification is the best or only option I encourage you to visit with Loren or I about the proposed modification beforehand and have our approval first. Doing so will avoid most potential conflict.
Most modifications will add increased dead load or force and need evaluated for effects on performance parameters. This is primarily because the additional load was not evaluated as part of the NTEP process. This increased dead load has the potential to exceed various design capacities of the scale such as nominal capacity, section capacity, load cell capacity, bearing surface capacity etc.
Handbook 44, Scales, UR.4.3. allows modifications but requires an engineer and the weights and measures jurisdiction to approve the modification. Attached you will find two spread sheets developed by Henry Oppermann which we will use to evaluate how a modification may affect the performance parameters of the device. When considering the effect on performance parameters for mechanical scales we must consider the increased load on the bearing/pivot surfaces. This is an issue we will want addressed by the engineer.
In lieu of UR.4.3 I have decided to allow an alternative method to be used in some cases such as the cement sidewall example. The alternative is to reduce the nominal capacity of the scale by the amount of additional dead weight added to the scale. For example if a scale has a nominal capacity rating of 120,000 lbs and the increased dead load being added for the modification is 10,000 lbs the scale would then have to be installed and marked with a new nominal capacity of 110,000 lbs or less. We will not allow this simplified method when a modification changes the length or width of a scale. Modifying width and length could introduce lever effects which increase force applied to scale components greater than the amount of dead load added.
Determining added dead load will be an estimate in many cases. We will error on the side of caution and estimate high when we are uncertain of the actual weight added.
No modification will exempt a scale from complying with other specifications, tolerances, and user requirements. For the cement sidewall example we can assume the scale will catch more wind and make accurate measurement increasingly difficult. This needs to be considered and should most likely be discussed with the customer before installation and modification occurs.