Requirements for Pitless Scales

PURPOSE: This rule covers installation requirements for pitless scales. (1) This rule shall apply to the installation of vehicle, axle-load and livestock scales of pitless full electronic or mechanical and self-contained electronic or mechanical design being installed in one (1) permanent location for more than one hundred eighty (180) days. (A) A pitless scale may be installed in a pit; however, all pit requirements of 2 CSR 90-21.030 must be met. (2) All scales represented as complying with this rule shall meet all of the standards specified and all applicable specifications and performance requirements of the current edition of National Institute of Standards and Technology (NIST) Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. (3) Whenever the provisions of this rule call for the use of reinforced concrete, the concrete shall be of grade and reinforced in the manner consistent with the guidelines established by the American Concrete Institute. (4) A suitable foundation must be provided for the scale to rest on. This foundation should meet the following minimum requirements: (A) Adequate bearing area to match piers to existing soil bearing capabilities stabilized at the desired grade (elevation) to support at least three thousand (3000) pounds per square foot in pier locations; (B) The scale foundations installer shall be responsible for determining whether or not soil characteristics meet the requirements of subsections (4)(A) for a particular design, by employing a penetrometer or plate-bearing test using proper American Society of Testing and Materials (ASTM) guidelines. If soil conditions do not meet those requirements, the installer shall notify the owner; and the owner shall arrange for spread footing design modifications to suit the existing soil conditions; (C) The scale may be installed above the ground; however, the installation should be such that surface water will drain away from the scale area; and (D) Access to critical scale parts must be provided to permit proper inspection, servicing and cleaning. (5) Piers. (A) Piers shall be of reinforced concrete poured to the depth of the local frost line but not less than three feet (3'). (B) All piers must be interlocked by a solid reinforced concrete slab with a minimum thickness of six inches (6"). This slab may be below the top of the piers to promote access and cleanout; or by reinforced concrete sides with a minimum thickness of twelve inches (12") and the same depth as the piers in which case the horizontal area between the piers will be of concrete with a minimum thickness of three inches (3"), not necessarily tied to the piers or in the same plan, to promote cleanliness. (C) Piers must support the combined loads applied by the weight of the scale, the weighbridge, plus the maximum anticipated load on the scale and must distribute these loads evenly over the underlying ground so that any settlement of the structure shall be as little as possible and that settlement shall be uniform throughout the structure. (D) Reinforcing should extend the entire width of the piers and be of a minimum schedule consistent with the American Concrete Guidelines. (E) Anchor bolts for check stands and load cell stands shall be of the embedded type or thunderstuds if installed in accordance with good engineering practice to assure that those working parts of the scale remain securely anchored during normal and reasonable use of the scale. (6) On scales with a mechanical indicating element, the element shall be mounted on a firm foundation which is adequate to prevent deflection or vibration. (7) Approaches to Pit Type Scales. (A) Vehicle Scales. On the entrance and exit ends of a vehicle scale there shall be a straight approach a) the width at least the width of the platform, b) the length at least one-half (1/2) the length of the platform but not required to be more than forty feet (40'), and c) not less than ten feet (10') of any approach adjacent to the platform shall be constructed of concrete or similar durable material to ensure that this portion remains smooth and level and in the same plane as the platform. However, grating of sufficient strength to withstand all loads equal to the concentrated load capacity of the scale may be installed in this portion. Any slope in the remaining portion of the approach shall ensure ease of vehicle access, ease for testing purposes, and drainage away from the scale. (B) Axle-Load Scales. At each end of an axle-load scale there shall be a straight paved approach in the same plane as the platform. The approaches shall be the same width as the platform and of sufficient length to insure the level positioning of vehicles during weight determinations. (C) Livestock Scales. Approaches shall be of reinforced concrete. On at least one (1) entrance there shall be a ten-foot (10') approach at least as wide as the gate with a minimum gate width of four and one-half feet (4 1/2'), accessible for movement of test weights to the scale platform. This approach may be on an incline from the scale platform, but not such that would hamper the movement of test weights onto the scale platform. 1. Livestock scales installed prior to July 1, 1998, shall be exempt from the requirements of subsection (7)(C) of this rule. (D) Railroad Track Scales. Approach rails must be installed in accordance with requirements as outlined in the AAR Scale Handbook. (8) The lever fulcrum stands or load cell stands shall be so designed, constructed and installed that under any practical conditions of loading, the resultant force through the bearings or load cell(s) will fall within the middle third of the length and width of the base. (9) Means shall be provided to restrict motion of the weighbridge or platform, not to exceed one-quarter inch (1/4") in any horizontal direction unless the manufacturer proves this unnecessary for a particular design. (10) Electronic, hydraulic and mechanical indicating elements, where used, shall be installed in a location and in a manner to assure continuous accurate performance under all ambient conditions. (11) Load cells employed in vehicle scales shall meet the following minimum standards. (A) The output characteristics of the load cells shall be such that they will not cause the systems performance to vary beyond allowable tolerances; and (B) Each individual load cell shall be capable of withstanding loads equal to one hundred fifty percent (150%) of its rated capacity without change in span calibration. Each load cell support structure shall be capable of withstanding loads equal to three hundred percent (300%) of the rated capacity of the cell without physical failure of the structure. (12) All cabling between load cells, junction boxes and electronic instrumentation shall be shielded and grounded as recommended by the original scale manufacturer. The ground shall be a copper clad rod which, whenever possible, shall be driven to a depth of the water table. Connection between the ground rod and the common ground points of the system shall be made with heavy copper wire of No. 10 gauge or larger. All cables shall be insulated with materials having good nonhygroscopic qualities and stable capacitance between conductors. All cable connections, as well as the cell itself, shall be properly protected against moisture penetration. Load cell cables physically shall be separated from power cables and never shall be run in the same conduit. (13) The power source for the electronic instrumentation shall be free from harmonics and electrical noise transients. (A) The power source shall be on a separate circuit back to the distribution transformer with no other loads connected, unless it can be demonstrated that the other live loads will not affect the accuracy of the instrumentation. (B) One (1) side of the power source should be at ground potential. (14) Individual requirements of sections (12) and (13) may be waived if the manufacturer or installer demonstrates other means of providing adequate protection against moisture, radio frequency interference (R.F.I.), lightning and power surges. (15) Pitless scales installed prior to April 11, 1985, shall be exempted from the requirements of this rule. (16) Requirements of section 413.175, RSMo must be met prior to the actual installation of devices covered in this rule. Following installation, any device covered in this rule must be calibrated and placed in service by a registered Missouri scale serviceman or officially examined by Missouri Weights and Measures Division before the device can be used in commercial service. (17) If any provision of these rules is declared invalid, the validity of the remainder of these rules shall not be affected. AUTHORITY: section 413.065, RSMo Supp. 1997.* Original rule filed Jan. 15, 1985, effective April 11, 1985. Amended: Filed April 14, 1994, effective Sept. 30, 1994. Amended: Filed Nov. 3, 1997, effective May 30, 1998. *Original authority: 413.065, RSMo 1983, amended 1993, 1994, 1995.