REMARKS OF M. A. HUBBARD, SUPERVISOR OF WEIGHTS AND MEASURES, STATE OF VIRGINIA

Our scale-testing unit (see fig. 32) may be said to be a grandson of the vehicle-scale testing unit of the National Bureau of Standards, and it resulted directly from the bad conditions which the Bureau unit uncovered in Virginia. They found some 76 percent of our scales in poor condition.

Our unit was designed by the Engineering Department of the Virginia Polytechnic Institute with what help we could give them. We think it is well designed and adequately strong. It was built at a cost of approximately $4,000. The unit carries 9,000 pounds of test weights and the truck itself weighs approximately 9,000 pounds, making a total weight of about 18,000 pounds. Although our testweight load is not as great as the loads carried in some other States, we believe that our unit is a very pratical one for conidtions in Virginia, because we have in use many scales of such small capacities that we could not use a heavy truck as a strain load.

There are compartments along the sides of our truck, in which baggage and necessary equipment are carried. The controls for the handling of the weights are located directly behind the cab. The floor of the truck is of 2-inch oak covered with heavy rubber belting that prevents shifting of the weights in transit and also protects the weights from wear. The truck is operated by an inspector and a helper.

We put this unit into operation last August, and since that time we have found that 57 percent of the scales which we have tested have been inaccurate and that the numerical mean of the maximum percentage errors developed is about 15 pounds per thousand. Our mean error is higher than it should be because of a few scales which had abnormally large errors. We tested a coal dealer's scale which I think had not been tested before and found that it developed a 4,000-pound error on an 8,000-pound test load!

REMARKS OF JAMES O'KEEFE, SEALER OF WEIGHTS AND MEASURES, CITY OF CHICAGO, ILLINOIS

We have two equipments, built to about the same specifications as those followed in the Indiana units which Mr. Meek has already described. (See fig. 33.) The loaded weight of each equipment is about 20,000 pounds. The cost of these units was approximately $5,000 each.

REMARKS OF R. W. SMITH, SECRETARY OF THE CONFERENCE, RELATIVE TO VEHICLE-SCALE TESTING UNITS OF THE STATES OF OREGON AND WYOMING

Two States, Oregon and Wyoming, have recently acquired vehiclescale testing equipments, but neither of these States is represented at our meeting. So that our record may be complete, I wish to describe these equipments briefly. The information has been supplied in each case by the head of the State weights and measures office.

The Oregon equipment, illustrated in figures 34 and 35, is a combination unit, equipped for the testing of large-capacity scales and for carrying on tests of large-capacity meters and doing other volumetric work. The unit carries four 1,000-pound weights, twelve

FIGURE 34.-Vehicle-scale testing equipment, State of Oregon.

FIGURE 35.-Oregon vehicle-scale testing equipment, showing auxiliary volumetric apparatus.

FIGURE 36.- Vehicle-scale testing equipment, State of Wyoming.

500-pound weights, twelve 50-pound weights, and the necessary complement of small weights. An air compressor is mounted in the forward part of the body for use in case of tire emergencies and also for purposes of cleaning the body of the truck and the working parts of scales which are being tested. The volumetric equipment comprises standards in denominations of 50 gallons, 5 gallons, 1 gallon, and fractional parts of the gallon.

The weights are loaded and unloaded by power; the controls are operated from the ground from a position at the right rear of the truck body. The total weight of the unit is slightly less than 24,000 pounds. The appropriation granted for the procurement of this unit was $6,500, but the completed cost of the equipment was only $5,983.00; the balance of $517.00 was sufficient to permit equipping a light truck for scale testing in areas where the large unit cannot be used.

The equipment of the State of Wyoming is illustrated in figure 36, and is of the conventional type with which you are familiar, the controls for the power operation of the crane being at the forward end of the body on the left side. The unit carries fifteen 1,000-pound weights, one 500-pound weight, and ten 50-pound weights. The total weight of the unit is approximately 27,500 pounds.

WEIGHBEAMS

By M. J. J. HARRISON, Supervisor of Scales and Weighing, Pennsylvania Railroad

It is the purpose of this presentation to describe in simple language a knife-edge weighbeam and its essential characteristics and elements, and to review certain phases of its design and construction which may not be clearly or generally understood, rather than to advance any necessarily new ideas on the subject.

At the beginning, it would seem that we should have a definite understanding of what we are talking about; therefore, let us turn to the January 1, 1939, issue of the National Scale Men's Association glossary, where we find:

Weighbeam, n. In a scale of other than the automatic-indicating or automatic recording types, that element whose angular position denotes the balance condition. In a more restricted sense, the device or assembly upon which, by the manipulation of poises and/or counterpoise weights, the applied load is counterpoised and its weight value indicated. Sometimes also colloquially called Beam.

Now, clearly, the definition just quoted is both fundamental and inclusive. It covers that element of an equal-arm balance from whose end pivots the pans are suspended; it covers the horizontal lever of a trip scale; it covers the steelyard; and it covers that element of a platform, hopper, vehicle, or track scale which is customarily referred to as its weighbeam (or beam). And all of these have one general, common characteristic-in each case the device is said to be "in balance" when the weighbeam either remains at or oscillates about a horizontal position of equilibrium.

With this preamble, let us examine into the essential characteristics of a weighbeam. These are three in number: (1) Truth, (2) stability, and (3) sensitiveness.

For the reason that a discussion of these three points is simpler of presentation when directed especially to the weighbeam of an equal

arm balance, and since nothing is lost thereby-the principles being readily susceptible of extension to other forms of weighbeams-let us consider briefly the equal-arm balance and its characteristics.

The weighbeam in this case (and therefore the entire device) is truthful when three separate conditions are simultaneously satisfied: (1) The moment of the weight of the horizontal weighbeam about the knife-edge of its fulcrum pivot is zero; that is, the center of gravity of the unloaded weighbeam lies in the vertical plane through the fulcrum knife-edge when the plane through the knife-edges of the end pivots is horizontal; (2) the two pans, with their appurtenances, are of equal weight; and (3) the distances L and L' of figure 37 are equal.

L

G

FIGURE 37.

If condition (1) is not met, the unloaded weighbeam will not balance; that is, it will fall or tend to fall to either the right or the left. If condition (2) is not met, the application of the pans and their appurtenances to the end knife-edges of the perfectly balanced, unloaded weighbeam will similarly throw it off balance. (It may be noted here that a deviation from condition (1) may be exactly offset by a deviation from condition (2), and this is one case wherein two wrongs make a right, only, however, if the same pan and appurtenances are always applied to the same end knife-edge.) And if condition (3) is not met, the application of equal loads to the pans of the perfectly balanced assembly will similarly throw it off balance.

Stability, the second essential characteristic, is obtained when the center of gravity of the weigh beam assembly lies below the point or line about which the weighbeam oscillates. Referring again to the NSMA glossary, we find:

Stable Equilibrium, n. A condition of balance in which, when a weighbeam or indicator is displaced from its position of equlilbrium and left free without disturbance, it either returns to its original position or oscillates about it.