Many types of gases are stored under pressure in liquefied form. This allows large quantities of the gas to be stored and used in industrial processes. Generally, these gasses are contained in cylinders, dewars or tanks. As the gas is required, and released from the tank, a small amount of the liquid will boil off into gas. A valve will allow this gas to be piped into the required area. The remaining contents will stay in liquid form until further gas is required.
Chlorine is one of the more common materials that are required. But a wide variety of other types of liquids and gases are also stored in this fashion.
Of course, it is very important to know the quantity of the gas in the tank. The flow rate of the gas can be calculated by measuring the change of weight during a fixed period of time. The weight is also used to determine when the tank is running out of gas and must be replaced and refilled.
Cylinder scales are the most appropriate type of industrial scale for this purpose. They are designed to accept different types of gas cylinders. The most standard type of cylinder will easily fit on a small platform with dimensions of approximately 9 x 9. The capacity of this electronic scale is 300 lb. But the larger tanks require a much larger platform. Two of the larger standard sizes are 3 x 4 and 4 x 4. These may have a capacity of 3000 lb and 5000 lb respectively.
There are a number of aspects of the design of large cylinder scales that will impact their accuracy, suitability to the task, and ease of use. Accuracy is primarily associated to the type and number of load cells used in the scale. Load cells are the electromechanical devices that convert a weight into an electrical signal. The least accurate scales employ just one load cell. While this is the least expensive way of producing a large cylinder scale, it relies on mechanical bearings to bring the entire weight resting on the scale platform to that load cell. As the mechanical bearings wear and corrode over time, the scale will become less accurate. It is also extremely important to position the gas tank accurately on the platform. A variety of different types of rollers and edges are used for this purpose. But it is impossible for this position to be accurately maintained all of the time. A somewhat better, but similar design employs two load cells. This ameliorates some of the positioning requirements along the long axis of the tank.
The best accuracy and highest quality large cylinder scales, such as those produced by Arlyn Scales, employ one load cell in each corner of the scale platform, for a total of four load cells. This type of scale is completely electronic, without any of the pivots or bearings required otherwise. The gas cylinders and tanks may be placed anywhere on the platform without affecting the accuracy of the weight reading. As an added advantage, a four load cell industrial scale will also be more rugged than other types, as there are no moving parts that can damaged.
The type of material used for the load cell is also quite important. Many cells are manufactured from aluminum, or from steel that is plated with nickel. Although these will work well at first, they are more prone to long term deterioration from the types of environments that these types of cylinder scales will experience. Corrosive liquids or fumes, as well as moisture or water vapor will eventually produce layers of corrosion on the load cell. Arlyn Scales uses only a special alloy of heat treated stainless steel for their entire line of industrial scales. Besides exhibiting excellent resistance to corrosion, they also provide a higher modulus of elasticity. This gives them excellent characteristics in avoiding the type of damage that may occur when tanks are removed from, or placed onto the scale platform.
The material of the scale platform is also of interest. Some scales are manufactured from steel, which are then coated with various types of paint to protect them from corrosion. Some provide special plastic platforms. But the remaining metal structural components are still subject to corrosion. The highest quality scales utilize full stainless steel construction.
Many cylinder scales are used in environments where there is a wide variety of other types of electronic equipment, including wireless communication devices. These can easily interfere with the very low level electronic signals produced within the electronic scales. To avoid these problems, Arlyn Scales shields the large cylinder scales from both electromagnetic and radio frequency interference.