Liquid gases are used across a broad range of industries. Liquid carbon dioxide is used for the carbonation of beverages, pneumatic systems, filling fire extinguishers, welding, production of plastics and rubbers, and pharmaceutical processing. Liquid nitrogen is used in cryogenics. The semiconductor industry uses many different liquid gases in the production of silicon wafers including nitrogen, argon, silicon tetrafluoride, silicon tetrachloride, silane, disilane, and dichlorosilane, to name just a few. Gases are stored in their liquid form in high pressure cylinders which allows a large amount of gas to be stored at once. For both safety and general production considerations, it is extremely important to be able to monitor the level of liquid remaining in a tank. When filling a gas cylinder, monitoring the liquid level can prevent the danger of overfilling. During production, monitoring the rate of gas use is important to ensure that all products are being made properly. Damage caused to products due to excessive or interrupted gas flow can cost a company tens of thousands of dollars. In addition, it is very useful to know how much gas is remaining in each cylinder so that the supply does not run out at an inconvenient time. There are two ways of measuring the amount of gas remaining in a cylinder. Gas pressure can be measured by using a pressure transducer. Pressure transducers are useless when using liquid gas. As long as there is liquid in the gas container, the pressure in the container will remain the same as gas is released from the cylinder and more gas evaporates from the liquid form. Only once all of the liquid has been depleted will the pressure quickly decline, giving little warning to the operator that the cylinder has to be replaced. A much more useful method of measuring liquid levels in cylinders is by using an electronic cylinder scale, like one manufactured by Arlyn Scales. When a cylinder with liquid gas in it is placed on one of these industrial scales and the known weight of the cylinder is subtracted from the given weight, the total amount of gas in the cylinder can be determined. The remaining liquid level in the cylinder can be constantly monitored. A Setpoint Controller allows alerts to be programmed into the cylinder scale at several liquid levels to warn operators when a tank is nearing empty and has to be refilled or replaced. These electronic scales also allow for other methods of monitoring the liquid level. An analog 4 to 20 ma output signal is commonly used to communicate with other processing equipment. Today, it is becoming more and more common to find a digital RS-232 signal, or a USB interface used with cylinder scales. These electronic signals can be used to open and close valves. In addition, the digital scale can be connected via Ethernet to a local access network, allowing monitoring of the cylinder liquid level from any computer on the network and even opening up the possibility of viewing liquid level data from the internet. Due to the weight of cylinders, it is important for a cylinder scale to have a low profile to allow for easy loading and unloading of the cylinders. Some scale manufacturers, such as Arlyn Scales, produce high quality cylinder scales that are just over 1 inch in height. They do this by creating a pocket within the body of the scale to fit a load sensor. Due to the weight of gas cylinders and the method of loading them onto and off of industrial scales, electronic cylinder scales are subject to extreme shock loads. It is extremely important that the load cells used in these scales are built to survive this shock. Many manufacturers use aluminum load sensors which can easily be damaged by twisting forces. Arlyn Scales cylinder scales contain a much more rugged load cell made from a special stainless steel alloy. These digital scales are manufactured to have a capacity appropriate to that of a full tank of gas, which usually weights around 250 pounds. In addition to being resistant to shock, this special alloy is also much more resistant to corrosion from chemicals, as compared to others using plated steel, allowing these precision scales to last longer and remain accurate throughout their lifetimes.
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