Platform scales use a solid platform and levers to measure weight, commonly used for heavy or bulky items. They differ from weighing scales, which use internal mechanisms. Strain gauges and pneumatic pressure cells are used to measure weight, and platform scales can be used for weighing heavy machinery. Trucks and tankers are weighed on large drive-over platforms, while train cars are weighed on calibrated platforms. Vessels are typically not weighed on platform scales.
A platform scale is a device that measures the weight of an object using a solid platform or base along with a series of levers and scales that together calculate the overall mass. These tools are most commonly used to weigh very heavy, bulky, or awkward items. People often hop on these kinds of devices in medical clinics and fitness centers to gauge their weight, for example, and they’re also often used to measure machinery and things like cars and trucks. Smaller models are common in science labs. From a technical point of view this type of device is different from a weighing scale, but the two are often grouped together and as a result a weighing scale is often thought of as one type of weighing scale. A real balance usually works with a series of internal mechanisms and shows the results on a dial or digital display, while a scale almost always works with a series of external moving arms that must be manipulated and moved to counterbalance the weight on the platform and finally the line with the reading which is the final weight. The overall goal of each is the same, though; that is, to accurately and clearly display a particular weight.
Basic functionality
The mechanism behind the balance is based on comparing the object with a set of standard weights on opposite arms of a central fulcrum. A two pan scale, as seen in food aisles, is an example of this type. Similarly, a gym or doctor’s office will often have a platform that weighs a person by moving the weights across a metal bar or arm. The arms in such balance are not as conspicuous as plant balance and are usually of uneven length. This creates a multiplier, which allows you to fit heavier weights into a smaller space.
Resistance and regulation
In a standard scale designed to measure smaller objects, the movement of a pointer across a dial surface is caused by the deflection of a spring or by the bending of the pendulum weight. The core mechanic works similarly in a platforming environment. Strain gauge load cells and pneumatic pressure cells also detect force and therefore can measure weight in these contexts and the devices have the advantage of not having load-bearing moving parts.
Strain gauges typically use the four circuit legs of a Wheatstone bridge, an electrical device, to measure weight in a load cell. Stress is applied to a calibrated metal plate due to the pressure of the object to be weighed on the platform. This strain causes the metal’s resistance to electric flow to change, which causes the Wheatstone bridge to be out of balance. The comparative lengths of the bridge legs are adjusted and the loop flow returns to balance. The adjustment amount is usually the weight of the item.
Pressure scales
Pneumatic pressure cells are also commonly part of large-scale measurement operations. These are devices that measure pressure by force against a liquid or gas. They can be coupled with a strain gauge to change the range of weights that can be measured. These devices can also use electronics such as the Wheatstone bridge to directly measure weight, although in most cases they are not as sensitive.
Weighing heavy machinery
The strain gauge output can be added to allow for more sensors to be used in weighing very heavy loads such as trucks and tankers, and in these cases there is often a pit under the platform where most of the heavy measurements are taken. However, this isn’t really necessary in all circumstances. The small physical package of a strain gauge, coupled with its relative low cost and maintenance, means that the platform scale can be only a few inches or centimeters high and not require a pit depending on the intent and how it is used.
Trucks and tankers are usually weighed on large drive-over platforms near street level, making them fairly easy to physically pass. Train cars are also weighed on specially calibrated platforms to compensate for the cars being coupled together. These scales can typically accommodate loads in excess of 50 tons (45 megagrams). Vessels are usually not weighed by a platform scale but rather by the use of a sling or by measuring water displacement, unless out of water, in which case they are often treated the same as a car or truck, especially if it can be mounted on a trailer or a wheeled platform that can be weighed separately.
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