Frequently Asked Questions

**Vehicle and Axle-load Scales**

**NIST Instructor Training School**

**September 21 -- 26, 2003**

Question 1. Under what circumstances would a remote display be deemed
necessary?

Answer: Auxiliary indications are necessary when a device is used in
direct sales and the primary indications cannot be accurately read from
some reasonable "customer" and "operator" position (See G-UR. 2.2. and
G-UR. 3.3.). The permissible distance between the equipment and a
reasonable customer and operator position shall be determined in each
case upon the basis of the individual circumstances. Several Weights and
Measures Officials (Officials) have taken the position that scale
installations comply with G-UR.3.3. if the device user permits customers
or their representatives (drivers) to enter the building that houses the
primary indicator and view the weight indicator.

A remote display would also be necessary on unattended self-service
vehicle and axle-load scales (if access to the primary indicator is not
provided) to alert users that the scale is on zero prior to vehicles
going on the load-receiving element and to then show the weight of the
vehicle. See General Code paragraphs G-UR. 2.2. and G-UR.3.3.

Question 2. If the intent of the code is met in regards to installation,
does it have to meet the specific criteria of the code? (Example: After
the required 3 meter (10 ft) of level approach adjacent to the scale
deck, the slope in the remaining portion of the approach is down toward
the scale, not away.) If appropriate drainage is provided and ease of
testing and vehicle access is not affected, can this be accepted as
correct?

Answer: From the description you provide we believe the scale
installation would meet the requirements of UR.2.6. Approaches if
drainage grates or other means of controlling "normal" water flow keeps
the water out of the scale pit or away from the scale. Some
installations have drainage grates at the bulkhead next to the scale or
at some point in the level area of the approach to the scale.

Question 3. If a scale is interfaced with a computer that generates a
customer ticket, does the computer software have to ensure that the
printed representation records exactly as the indicating element of the
scale. (Example: A tare weight value has been entered on the indicating
element and the display shows a net weight value. The operator then
accepts this value in the gross weight window on the computer screen.)
Is this correct or should the software prevent this from happening?

Answer: If we understand the question correctly our tentative answer is
that G-S.5.2.2 Digital Indication and Representation would apply and it
requires all digital values in a system to agree. If the tare mode is
being used on the indicator, then the computer indications and any
recorded representations must be correctly identified and agree with
those displayed on the indicator. Typically, if an indicator displays
only in the gross mode, the scale operator identifies each weight as a
tare or gross via keyboard entry. Some systems, utilizing stored tares,
allow tare weights to be called up when the scale operator enters the
truck number via the keyboard. Regardless, all displayed values must be
identified properly and agree as required under G-S.5.2.2. and
G-S.5.2.4. Values.

Question 4 If a mechanical lever system scale is retrofitted with a new
full electronic load cell system, is this considered a new installation
with all aspects of the installation being reconsidered (retroactive and
Nonretroactive) or do the other aspects get grandfather status?

Answer: This question involves two separate, but related issues.

> The first relates to the NTEP policy that applies to scales with
> Certificates of Conformance (CC). NTEP policy says that if the levers
> of a scale with a CC are replaced with load cells, the instrument is
> no longer traceable to the original CC and must undergo additional
> NTEP testing. The NTETC Weighing Sector has taken the position that
> replacing [any]{.underline} levers of a mechanical weighing element
> with load cells is a modification of the original type that requires
> NTEP evaluation. The Sector has also decided that the placement of a
> load cell in the steelyard rod to change from a mechanical to an
> electronic indicator is an acceptable modification of type that does
> [not]{.underline} require evaluation for an existing CC to apply;
> however, the modification option does need to be listed on the NTEP
> CC.
>
> The second response applies to scales that are [not]{.underline}
> covered under an NTEP CC. For these, the decision regarding the need
> for type approval of a mechanical scale changed over to full
> electronic rests with the individual State weights and measures
> director. When a State adopts the Uniform Regulation for National Type
> Evaluation in NIST Handbook 130, the director generally establishes
> policies for how the requirements for NTEP CCs will be implemented.
> Generally, a State requires that devices installed after a specified
> date must be covered under an NTEP CC. An NTEP CC is not generally
> required for devices already in use; however, the director may
> establish specific policies regarding modifications to devices. For
> example, some States require that, if an electronic indicator on a
> scale is replaced with another electronic indicator, the replacement
> indicator must be covered by an NTEP CC.
>
> A key question that arises in these scenarios is: When are such
> changes simply routine maintenance and replacement of parts, and when
> are the changes, in essence, creating a new device? We believe that it
> is this question that you are asking in the scenario you have posed.
>
> While NTEP policy does not cover scenarios involving non-NTEP devices
> and the decision rests with the State weights and measures to
> determine how the devices will be handled, some States use the NTEP
> policy as a guideline for making an assessment of when a change is
> significant enough to consider a device different from the original
> device. Thus, if NTEP policy were used as a guideline, some States
> would conclude that the original device in your example has been
> significantly modified or rebuilt differently from its original
> design, creating, in essence, a new device. As such, a State might
> decide to treat the device as a new installation, subject to NTEP
> requirements and current Handbook 44 requirements. Remember that each
> scenario has to be carefully evaluated to determine what changes have
> been made in a system and the impact of those changes on the original
> design.

Question 5 Why do some states rule that any old obsolete mechanical
scale that has a load cell conversion is a "one of a kind device" and
exempt from NTEP Pub. 14 policy? Doesn't that defeat the purpose? I've
seen load cells in the steelyard rods on truck and hopper scales and
even the levers pulled out and replaced with electronic or hydraulic
cells. At what point is the device a new scale and subject to NTEP
certification?

Answer: You are correct that there are variations in how States address
modifications to existing equipment with regard to NTEP. The provision
in the Uniform Regulation for National Type Evaluation in NIST Handbook
130 for accepting "one-of-a-kind" devices is often misapplied. Some
States incorrectly apply the "one-of-a-kind" provision to the scenario
described in Question 4 above.

> Handbook 130 states that a "one-of-a-kind" device is a non-NTEP device
> designed to meet unique demands for a specific installation and is a
> device of a specific *design* which is [not commercially available
> elsewhere]{.underline}. Note that the one-of-a-kind designation also
> means that the manufacturer produces only one of that device design.
> Thus, if the manufacturer produced another in that same State or in
> another State, the device is no longer considered one-of-a-kind.
>
> The device created in the example above is *not* a one-of-a-kind
> device since full electronic truck scales are readily available
> commercially.
>
> If the State determines that a device is, in fact, a one-of-a-kind
> device, the State director "may accept the design of a one-of-a-kind
> device without an NTEP evaluation pending inspection and performance
> testing to satisfy that the device complies with Handbook 44 and is
> capable of performing within the Handbook 44 requirements for a
> reasonable period of time under normal conditions of use. Indicators
> and load cells in all "one-of-a-kind" scale installations must also
> have an active NTEP CC as evidence that the system meets the influence
> factor requirements of Handbook 44."
>
> With regard to the question of when a device is considered a "new"
> device, see Question 4 above.

Question 6 We currently use our weight truck to conduct the shift test
and do not own any weight carts. Is there a consensus regarding
equipment use for shift tests of a vehicle scale? Our test truck has a
very short wheelbase and we have rejected scales immediately after they
were adjusted using weight carts. Our rear axles will weigh more than
the typical weight cart. Our thought has always been that a vehicle
scale is designed to weigh trucks and not weight carts. The added weight
will also show deflection in the deck if the metal is getting weak.

Answer: Your state's experience in using a truck to conduct shift tests
probably differs from what others have reported over the years. Scale
service agencies used to use their trucks to do shift-test but that
practice usually involved the use of specially built short wheelbase
weight trucks. Today, most service agencies and Officials have turned to
calibrated weight carts as the preferred test equipment. Weight carts
have been used by Officials for more than 70 years. However,
jurisdictions have to do the best job they can with their equipment and
each state has the authority to define how it does a test.

> Motor trucks cannot be used to conduct section tests under N.1.3.
> Shift Test in the Scales code of NIST Handbook 44 for several reasons.
> These include the fact that vehicles are not "calibrated" mass
> standards and their accuracy cannot be maintained in conformance with
> Section 3. Testing Apparatus under the Fundamental Consideration of
> the handbook (See N.2. Verification (Testing) Standards.) Nor are
> motor trucks suitable for applying the concentrated load within the
> prescribed test pattern because part of the truck is always on another
> section of the scale. While the rear tandems are sitting on one
> section the weight of the front axle is being measured by another
> section of the scale so it would be difficult to apply the agreement
> of indication requirements in T.N.4.4 Shift or Section Tests.
>
> Over the past few years, there has been a large increase in the number
> of states and service agencies using gasoline or electrical powered
> weight carts to test and calibrate vehicle and axle-load scales. One
> main benefit of the weight cart in the testing of these types of
> scales is that their use allows a large amount of known mass to be
> concentrated over a relatively small area of load receiving element.
> As a result, individual load bearing points can be tested and
> calibrated providing improved consistency in weighing regardless of
> where the load is placed on the platform. Additional benefits of the
> carts are ease of use and increased speed in the testing process.
>
> NIST is in the process of finalizing a NIST handbook, Handbook 105-8,
> which includes specifications, tolerances, and design considerations
> for weight carts.

Question 7 How do other states handle the issue of NTEP? Are NTEP
inspections being done on these devices and or the components, i.e. load
cells? Are CC's ever checked or is this something which would not be
done in the field?

Answer: We have not done any formal studies or surveys to assess how the
majority of States implement NTEP; however, from our experience, we
believe the issue of inspecting CC's and verifying NTEP certification
varies widely among the states. If you are in an NTEP jurisdiction, the
CC should be carefully reviewed and compared with the device being
inspected; this is particularly relevant for initial inspections of new
devices. In some cases, inspectors have access to copies of the CCs at
the site or through the Internet. In other cases, inspectors must
contact their main offices and ask office personnel to read information
from the CC. In states with a device registration program,
administrative or office personnel sometimes verify that the device is
traceable to an NTEP CC as new installations are being reported to the
agency for compliance with device registration.

> Field verification and oversight are key elements of an NTEP program.
> Remember that an NTEP CC is not a guarantee that the specific device
> you are inspecting complies with Handbook 44. You should carefully
> examine the device and its features and options to ensure that it is
> consistent with the device evaluated by NTEP, while realizing that
> there are some tests such as temperature testing that cannot
> realistically be conducted in a field environment. An NTEP CC may list
> a number of features, options, and setup parameters that are included
> on the CC based upon the evaluation conducted by NTEP. It is essential
> that you verify the device you are inspecting has been set up and
> installed consistent with the parameters covered by the CC.

Another aspect of this question has to do with the issue of ensuring
that "production meets type." That is, are devices being produced
consistent with the device evaluated by NTEP? The NCWM is presently
developing a formal program to ensure that production devices are
consistent with devices evaluated by NTEP.

Question 8 Do other jurisdictions conduct scale pit inspections? Should
they be conducted or avoided? We have recently looked into the issue of
confined spaces and OSHA regulations and found there are some issues
there. Is a scale pit and or understructure inspection ever necessary?

Answer: Yes, regulatory officials are still conducting scale pit
inspections. There has been a recent increase in the awareness of safety
regulations as they relate to scale pit inspections. There are many good
reasons why the scale pit should be included as part of the official
inspection process. Some of the more important reasons are as follows:

-   Determine proper scale maintenance.

-   Determine possible causes of large weighing errors observed in an
    official test.

-   Locate required marking information -- load-receiving element or
    load cells.

-   Inspect for fraudulent manipulation of the weighing elements, etc.

> Pit/weighing element inspections should be conducted only when all
> potential hazards have been identified, adequate protective equipment
> has been obtained, and all necessary safety training completed.
> Regulatory officials conducting pit inspections should also inquire
> and adhere to all OSHA regulations and company safety policies in
> effect at the scale site location.

Question 9 Why are the tolerance values two times the values specified
in T.N. 3.1 and T.N.3.2 for wheel load weighers and portable axle load
weighers of Class IIII as specified in T.N.3.3?

Answer: Wheel load weighers and portable axle load weighers are Class
IIII devices used in highway weight enforcement. The provision you
referenced was included in the handbook as part of the new scales code
in 1986. At that time, the tolerances listed in Table 6 were too
restrictive for the wheel load weighers and axle load scales of the
time. The expanded tolerances for wheel load weighers and portable axle
load weighers were implemented to ensure that the new scales code would
not prohibit the continued use of these devices for highway weight
enforcement.

> The practical needs of the law enforcement community to use weighing
> devices under less than ideal (for commercial devices) conditions and
> the desire to effectively enforce the highway weight laws have led to
> acceptance of larger tolerances for highway weight enforcement
> purposes. The tolerances for these devices are larger in recognition
> of the conditions under which the devices are used, the purpose of the
> application, and the fact that no jurisdiction has the resources to
> place a full size Class III L scale and weigh station on every
> highway.
>
> As we will discuss in the vehicle and axle-load scales course, the
> theory of tolerances is to achieve a level of accuracy that does not
> cause economic harm to either the buyer or the seller while remaining
> at a level that enables the device manufacturer to produce the device
> at a reasonable cost. In this case, the tolerances must be small
> enough to ensure proper enforcement of highway weight enforcement
> laws, yet not so small that the effects of the environment in which
> the devices are used make it unrealistic to manufacture devices to
> meet the requirements.

Question 10 Why does U.R.3.3 (Single Draft-Vehicle Weighing) not apply
to highway law enforcement scales?

Answer: NIST Handbook 44 specifically exempts these applications from
the requirement because the primary goal of highway weight law
enforcement is to control axle weights in order to protect highway
surfaces and bridges from damage. While gross weight is a factor it is
the individual axle loads that must be controlled as a truck can be
legally within the gross weight load limit and still have axle weights
that can seriously damage roads. As stated above, portability and cost
are the also factors as no jurisdiction has the resources to place a
full size Class IIIL scale and weigh station on every highway.

> In addition to the higher tolerances applicable to these scales,
> enforcement personnel, prior to the issuance of over weight citations,
> typically grant special allowances and most state laws provide for
> those allowances. We also understand that many law enforcement
> agencies will offer a trucker the opportunity to drive the truck to a
> permanently installed vehicle scale to have the weights confirmed
> prior to issuing a citation.
>
> The accuracy of weights obtained from split-draft weighing has been
> argued for many years. It is accepted that split-draft weighing has
> the potential to result in weighing errors that exceed the scale
> tolerances applicable to vehicle scales used for commercial
> transactions. The maintenance tolerance for vehicle scales used
> commercially is effectively 0.2 percent of the applied test load. Due
> to the potential errors, split-draft weighing is not permitted for
> commercial applications. However, the practical needs of the law
> enforcement community and the desire to effectively enforce the
> highway weight laws have led to acceptance of split-draft weighing for
> this purpose.
>
> The accuracy of weights obtained by split-draft weighing depends upon
> many factors, including the accuracy of the scale, the shifting of the
> load on the truck as the truck goes onto the scale, the extent to
> which the scales are level when being used, the setting of the truck
> brakes during the weighing process, the care used in the weighing
> process, and the truck suspension system. The limited amount of
> testing to date indicates that, although there is significant
> potential for weighing errors in split-draft weighing, the actual
> errors tend to be distributed in a manner where most are
> \"relatively\" small, but occasionally rather significant weighing
> errors occur. Studies of the magnitude of weighing errors from
> split-draft weighing has been limited, but they have convinced the
> weights and measures community that split-draft weighing is not
> sufficiently accurate for commercial purposes. When this issue was
> last reviewed by the NCWM, split-draft weighing was considered
> sufficiently accurate for law enforcement purposes when all factors
> were considered. The appropriateness of split-draft weighing for law
> enforcement and its associated accuracy are still often questioned.

Question 11 Does UR.2.6.2 (Axle-Load Scales Approaches) also apply to
portable axle-load weighers?

Answer: No. UR. 2.6.2. does not apply to portable axle-load scales; the
handbook defines an axle load scale as a one that is "permanently
installed in a fixed location." However, note that UR. 3.4.2 Level
Condition requires vehicles weighed on portable axle load scales to be
"in a reasonably level position at the time of such determination."

Question 12 Why are wheel load weighers and portable axle load weighers
exempt from the shift test under N.1.3.8?

Answer: Wheel load weighers and portable axle load weighers are
typically excluded from shift test requirements because there is a
physical limitation of the size of the load receiving element. This
limitation in size prevents an adequate test load from being loaded onto
each shift test position.

Question 13 What is the definition of a "reasonably level position" as
described in paragraph U.R.3.4.2. in NIST Handbook 44?

Answer: The application of this paragraph requires you to use your
knowledge of good weighing practices, and the condition must be
determined on a case-by-case basis. The note included in Paragraph
S.2.4. requires portable wheel-load weighers and portable axle-load
scales to be accurate when placed out of level up to and including 5
percent (approximately 3 degrees) so this offsets some of the concern
over the exact level of the weighing site. Remember that most highways
are designed to drain water so a perfectly level location may not be
readily available for the weight enforcement officer to use. However, if
the scale is placed on a solid - "reasonably" level surface it should
provide a good weighing result.

Question 14 Should I reject a scale on a strain load test if the range
in the vehicle's weight alone (not the error between empty and loaded)
is more than the applicable tolerance, and there are no other failing
errors in the remainder of the test?

Answer: We don't understand the use of the term "range." Under what
circumstances is a range in the vehicle's weight being observed? When
conducting a strain load test, the tolerance is applied only to the
known weight of the load.

Question 15 When a test load or vehicle is removed from a scale, if any
value remains (whether positive or negative) and that amount slowly
returns to zero, is this scale failing the zero load test? In other
words, is there a time allowance for the scale to return to zero after a
load is removed? Some scale technicians say that it is the
characteristic of a particular make of instrument to be slow returning
to zero, is this true?

Answer: Handbook 44 does not specify a time limit for the return to
zero. It is true that some scales will return to zero more slowly than
others. For example, digital indicators update their indications at
varying rates that, in many instruments, can be changed to suit the
installation. Assuming the question pertains to a scale with a digital
indicator, a possible remedy may be simply for a service technician to
increase the update frequency of the indicator, which may speed the
return to zero. The slow return to zero is permissible providing that
under routine normal use, the scale is returning to zero each time a
load is removed and before the next vehicle is weighed. See also
paragraph UR. 4.1. Balance Condition, which requires the user to
maintain the scale in a zero balance condition with no load on the
scale.

Question 16 Is there a need to perform a strain load test on in-line
multiple platform scales such as the CAT scales?

Answer: Each scale should be tested to at least the used capacity. If
insufficient known test weights are available for this purpose, it may
be necessary to use substitution and/or strain load test methods.

Question 17 Should two vehicle scales that are installed at the same
business location (an inbound and outbound for instance) agree to within
applicable tolerance of each other? For example, if 80 lb is the maximum
permissible error and one scale indicated + 80 lb and the other
indicated -- 80 lb, could both scales be rejected because of the
deviation in the two?

Answer: No. Tolerances are applied separately to each individual scale.
However, if you suspect they are being intentionally adjusted to take
advantage of the tolerances consider applying G-UR.4.1. Maintenance of
Equipment.

Question 18 For scales with an Automatic Zero Setting Mechanism (AZSM),
should the AZSM be turned off prior to conducting an official test if it
can be easily done?

Answer: It is not necessary to turn off AZSM to conduct a routine test,
but it can be turned off at the discretion of the inspector. However, if
the scale is normally used with the AZSM on it should be tested with the
AZSM activated. It is acceptable to test with the AZSM in either the
"on" or "off" position. Effective January 1, 2001, NIST Handbook 44,
Scales Code, Paragraph S.2.1.3.1. (Added 1999) requires Class III L
devices equipped with AZSM to be designed with a sealable means to allow
AZSM to be disabled during the inspection and test of the device.

Question 19 Are side-to-side tests necessary and if so, how frequently
should they be performed?

Answer: An off-center (side-to-side) shift test should be conducted on
all vehicle and axle-load scales. Adhere to the prescribed test patterns
and maximum loads specified in N.1.3.4. (Shift Test) when conducting
this test.

Question 20 Besides looking for binding between pit wall and deck,
cracks in decks, foreign objects and dirt buildups underneath the deck,
what other inspections should be done routinely?

Answer: In addition to verifying compliance with other Handbook
requirements such as device specifications and suitability, the
inspection phase of an examination is concerned with the physical
characteristics and condition of a device and how it is installed,
maintained, and used. We will also cover this aspect of inspection in
class.

Question 21 If a mechanical scale's levers appear to be out of plumb or
anything else appearing to be not level to the naked eye, are there
grounds (specifications in Handbook 44) to condemn the scale or have it
re-installed?

Answer: To operate properly, the lever systems of mechanical scales must
be installed so they are plumb, square, and level. Since these elements
are typically specified by instrument manufacturers, G-UR.2.1.
Installation would apply. You should confirm the problem using a
suitable level (there are leveling lugs on most levers) and take
appropriate action based on the results.