Custody transfer is defined as the way to measure the commercial exchange of a commodity. When a business purchases a commodity, there is a pre-established method to verify the amount of product purchased. Gasoline, chemicals and even milk is all traded this way. It is common to use a weigh scale for custody transfer. The truck is weighed when it is full and when it is empty. The difference, of course, is the amount of product you purchased. Variances in the measured weight and the actual contents supplied is referred to as shrinkage. You will be surprised how much shrinkage there actually is.
Dairies are some of the worst offenders when it comes to shrinkage. When a truck pulls up to deliver raw milk it is weighed (the driver stays in the truck) and the driver proceeds to the off loading bay. At this point, the driver connects the tanker to the supply hose and proceeds to unload the truck. During this time, the driver will clean all the dirt, mud and possible snow (raw milk is received on farms) off of the truck. Once unloaded, the driver will then use onboard chemicals to clean the inside of the tanker. When this is all done, the driver heads back to the scale and gets out to collect his paperwork. In this instanced the dairy didn’t just pay for milk, they paid for the weight of the driver, mud, snow, and cleaning chemicals. That can produce a significant amount of shrinkage.
Frankly, there is a better way to account for the raw milk that is received by a dairy, or any other commodity received by a plant. Rather than measuring the weight of a product, obtaining a true mass measurement should be considered. Coriolis mass flow meters are extremely accurate and can be used specifically for this. In the example above a dairy truck would proceed directly to the off-loading bay to unload the truck. The mass flow meter would be inline with the piping and measure the actual amount of milk received. All of the mud, snow, cleaning chemicals and driver would not be included, thereby eliminating any potential shrinkage due to measurement error. What is extremely cool is you no longer have to maintain your weigh scale. This is quite expensive to have someone come out and verify it annually, and repair it when it breaks. This money used for this will pay for a mass flow meter installation.
For general application consideration, the Coriolis flow meter should be able to measure air entrained in the system, as there will be some at the beginning and ending of the transfer. The meter should be mounted vertically to mitigate entrained air. It is also important to realize the meter will need to be verified by a state’s Office of Weights and Measures. Most meter manufacturers are familiar with this process.
The same strategy can be applied for many commodities. If a weigh scale is being used, considering eliminating it. Shrinkage is costing you money. This is a great way to shrink the shrinkage.
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