Truck scales are available in a wide range of sizes. Platform widths from 8 feet up are available while lengths often exceed 100 feet. You should select a platform size that is not only sufficient to weigh the trucks you currently have but large enough to weigh the trucks you may use in the future. Generally, widths of 11 to 12 feet are preferred for trucks used on the highway. Not only are scales of this width easier to ship, but they are approximately the lane width of many of our nation's highways. Scales of greater width are available but are more expensive both in initial cost and in the costs associated with testing. Choose a length that is long enough to weigh the largest truck you anticipate weighing in the future. Remember, adding an extra 5 feet or so to the length seven years from now will be much more expensive than purchasing that extra length initially. Also, keep in mind that the scale must fit within the area you have allocated for the scale remembering to allow for a straight approach and departure from the scale preferably equal in length to the scale platform itself. It's better to be a little large than too small.

What About Weighing Capacity?

Like platform size, weighing capacity should be selected based on your current and anticipated needs. There are two capacities associated with truck scales. The first, nominal capacity, is the total measurable load that can be distributed over the scale platform. Most truck scales have nominal capacities of 200,000 pounds which is more than sufficient to weigh highway trucks. Selection of the nominal capacity is normally not of concern since it is typically great enough to handle all but the most extreme loads.

The second capacity associated with truck scales is concentrated load capacity and is used as a measure of the ability of the scale to measure a load concentrated in a relatively small area. Concentrated load capacity, or CLC, is defined in the National Institute of Standards and Technology Handbook 44 as the maximum load that can be placed in an area four feet in length by the width of the scale platform and is recorded on the scale's identification plate. This area is designed to approximate the area required for the dual tandem axles found on most highway trucks. If you know the spacing and number of axles on your trucks and the CLC of the scale in question, you can easily calculate the maximum load that can be applied to the scale by the truck in question. Refer to Table U.R.3.2.1. in Handbook 44 (Handbook 44 may be ordered directly from the National Conference on Weights and Measures website at www.ncwm.net/pubs.html) By selecting the number of axles and spacing between the two extreme axles you can obtain the ratio of CLC to maximum load or "R" factor. Multiply this "R" factor from the table by the CLC to determine the maximum weight for this configuration of axles.

Using this method, you may calculate the maximum load the scale under consideration is capable of handling for any configuration of axles that will fit on the platform. Remember not to exceed the nominal capacity of the scale. CLC ratings are normally listed in units of tons (2,000 pounds) and vary from 20 tons up to 50 tons depending on the scale model in question. Higher CLC ratings translate to longer life for a given load since the scale structure undergoes less stress each time it is loaded.

What About Options?

There are about as many options available for truck scales as there are cousins at a family reunion. Some valuable options to consider for the scale itself include stainless steel sheathed load cell cable to prevent damage from hungry rodents, digital junction boxes that convert the analog load cell signal to a digital value at the scale then transmit it via fiber optic cables to the weight indicator, guard rails to prevent the truck from driving off a low profile scale, special finishes like galvanizing and other custom features. When it comes to choosing a weight indicator for use with your truck scale, the sky's the limit. Indicators range from simple, weight-only models up to programmable full featured versions with everything in between. Refer to our document on how to select a weight indicator for assistance in making this decision. Other options like remote displays for driver viewing, printers and software for managing your truck fleet and interfacing to your accounting system are readily available. Just contact your Cardinal representative for a recommended instrumentation package for your scale.

What's NTEP and How Does it Relate to My Truck Scale?

Many truck scales are used in commercial transactions where the weight obtained from the scale is used in the determination of the price of the commodity being weighed. In these instances, the scale must be approved for commercial use by your state's weights and measures department. In most cases, this means that it must have an NTEP Certificate of Conformance and be inspected and approved by a state weights and measures inspector. NTEP, which is short for the National Type Evaluation Program, is a program managed by the National Conference on Weights and Measures (NCWM) which is a organization consisting of both public and private members and dedicated to maintaining equity in the marketplace. Scales and scale components are formally evaluated in one of several metrology laboratories under the NTEP program to ensure that the device performs within published tolerances and over the range of environmental characteristics (temperature, voltage, etc.) which have an influence over the measurement process.

You should make certain that the components making up your truck scale system each have their own NTEP Certificate of Conformance. This means that the truck scale should have a NTEP CC as should the load cell(s) used with it and the weight indicator itself. An easy way to independently verify that these components each have a NTEP Certificate of Conformance is to check the NCWM website listing of certificates at http://asphost.isproductions.net/ncwm/certsearch.asp where you may search for certificates by number, manufacturer or type.

What Do I Do After I've Selected My Scale?

You've decided on a scale model and are ready to go, but before you sign on the dotted line, there are a few more things to investigate. First, check with your county and / or city zoning office to make certain that you can place a truck scale at the desired site. Often a building permit along with the necessary fees and drawings is required for installation of a truck scale. This will differ from location to location so it's best to check with your local authorities before you turn that first spade full of dirt.

Keep in mind the following requirements when selecting your scale site:

1. It must have the proper zoning, if required.

2. There must be sufficient room for access to and from the scale. Generally, state requirements mandate that there be a straight and level approach to and from the scale each equal in length to the scale platform or a specific length whichever is less. Your local weights and measures department can advise you of the minimum length and if there are other requirements for the scale foundation design, ramp slope (if a low profile scale is selected) or pit construction. The layout should be such that the truck does not turn onto or off of the scale. It should pull straight on and straight off of the scale platform.

3. The soil bearing capacity must be of sufficient strength to hold the scale and the greatest load to be measured by the scale. Generally, the soil bearing capacity must be a minimum of 3000 to 4000 pounds per square foot although smaller capacities can be used if provisions are made in the foundation design.

4.There must be proper drainage away from the scale foundation to ensure that water does not collect around the scale or in the scale pit. With pit scales this usually means installation of a sump pump with an adequate drain while low profile scales will require a gravity drain and proper ground slope to move the water away from the scale.

5. There should be no overhead power or telephone lines that could interfere with the movement of trucks across the scale.

6. There must be sufficient room for a crane to unload the new scale from the truck when it is delivered to your site.

7. There must be an acceptable site for placement of the weight indicating instrument. Normally the weight indicator is placed within a building of some type within easy view of the scale to allow the scale operator to verify that the truck is properly positioned on the scale before weighing begins. The site should have sufficient power available to power the weight indicator and printer. Power should also be run to the scale pit for pit-mounted truck scales. Refer to your local electrical codes for safety requirements.

8. A means of communication between the driver and scale operator (intercom or radio or similar device) is always a good idea.

9. Guard rails or posts to protect the scale, scale house and adjacent equipment is good insurance against damage from an errant truck.

10. Make certain that the site selected is not in a hazardous or explosive area. If it is, special precautions must be taken in the purchase of the scale to ensure that it is compatible with the environment.

11. Make certain that the effect from other influences to the scale are minimized. This may mean construction of a wind block if the site is in an unusually windy location or in a snow fence to minimize accumulation or drifting of snow over the platform.