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1 - Weighing Increments Before discussing capacity ratings, we need to explain the weighing increments used by truck scales. This helps the buyer later understand the legally required scale setup formu- las used to determine a scale’s capacity. It is important to understand weighing increments and scale divisions (sometimes called scale resolution). Many truck scales weigh in increments of 20 kg in OIML locations and 20 lb in NTEP locations. That is be- cause Weights and Measures regulations in most areas specify the number of divisions (units of the scale’s capacity) a scale must use. For truck scales, often this is 3,000 for OIML and 10,000 for NTEP.
2 - Scale Capacity To discuss your capacity needs, you will need to know how many trucks per day you will be weighing, their types and sizes, and the maximum weights. Look at both your current needs and your future needs. The capacity of a vehicle scale can be expressed in multiple ways. • Gross Capacity (or Nominal Capacity) – The total weight that can be evenly distributed over the entire surface of a weighbridge. • Concentrated Load Capacity (CLC) – A declaration of a scale’s ability to handle a load utilizing a limited footprint, intended to represent the load applied by a dual tandem axle.
This is determined using the following formula:
Let’s elaborate on what each of these measures means to the scale buyer.
Scale capacity Number of divisions
= Weighing increment size
Gross Capacity Make sure the gross capacity of your scale exceeds the total weight of the heaviest loaded trucks that you will be weighing. However, be aware of how scale companies discuss gross capacity in sales presentations. Some scale companies will list very large capacities on their scales to appear superior to their competition. However, if you configure your scale for an extra-large capacity, but you do not actually utilize that capacity, weighing regulations still require that the weight increment size also be increased. This is undesirable as it increases the need for the terminal to round weights up or down in larger values.
60,000 kg 3,000
200,000 lb 10,000
= 20 kg in OIML locations
= 20 lb in NTEP locations
Because the number of divisions is set forth by Weights and Measures authorities, the relationship between scale capacity and weighing increment size is fixed. In other words, if the scale’s capacity increases, the weighing increment size also must increase. Why does this matter? With a smaller weighing increment, the scale has a better potential for accuracy because it isn’t rounding the weight value in large intervals. The scale terminal typically can be configured to adjust the maximum capacity, but it must follow the legal formula. Some scale companies will mention that their scales can be configured for small increment sizes, citing this as an advantage. However, keep in mind that this may not be acceptable for your application, based on these formulas.
Some salespeople will discuss gross capacity as a correlation to strength. However, gross capacity is determined by formulas that don’t truly correspond to strength verification.
How is Gross Capacity Determined? Gross capacity is not determined in the way some customers might think. The scale company does not test a scale by loading it until it fails. Gross capacity is typically based on a standard Weights and Measures formula that may take into account the number and capacity of load cells in the scale, the weighing increment size and/or number of divisions, number of scale deck modules and the concentrated load capacity (CLC) rating of the modules. However, gross capacity is not a true measure of the actual strength of a weighbridge. In the real world, trucks don’t distribute their loads evenly over the entire surface of a weighbridge. They concentrate loads on their axles, which is why, in some regions, truck scales may also have a CLC.
Video: Plant Visit Take a video tour of one of METTLER TOLEDO’s vehicle scale manufacturing facilities. www.mt.com/INDplantvisit
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