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Also known as combination scales, you can see from our multi-head weighers introduction guide that they use a number of different weigh heads to generate precise measurements of products by calculating the weight in each weigh head. Each weigh head has its own precision load cell.
The process begins when product is fed into the top of the multihead weigher, where a dispersal system, normally a vibrating or rotating top cone, distributes the product into a series of linear feed plates. This top cone is normally equipped with a load cell which controls the feed of product to the multihead weigher.
A series of curtains are normally placed around the linear feeders to ensure an even quantity of product is available for distribution to the feed hoppers. The linear feed plates vibrate individually. The amplitude and duration of vibration can be varied to increase or decrease the vibration depending on the characteristics of the product. For sticky products a lot of vibration will be required whereas for free flowing products a minimal amount of vibration will be required to get the product moving.
Each linear feeder will deliver some product into a feed hopper. For example in a 10 head multihead Weigher there will be 10 Linear feeders delivering products to 10 feed hoppers. After each delivery to the feed hoppers the linear feeders will stop vibrating and wait until the feed hoppers have emptied their contents into the weigh hoppers before starting again.
Each weigh hopper is equipped with a highly accurate load cell. This load cell will calculate the weight of product in the weigh hopper. The processor in the multihead Weigher will then calculate the best combination of available weights required to achieve the desired target weight. This is why a Multihead weigher is sometimes referred to as a Combination weigher.
Once the calculation is complete it will open the selected weigh hoppers and discharge the accurately weighed portion into your bagging system or product trays. The feed hopper will then automatically open and fill the empty weigh hopper. The more Weigh heads on your multi-head weighing machine, the faster it can calculate a correct combination, and the more accurately weighed portions of product can be produced in the same time period.
For example;- On a 10 head weigher you set the target weight to 500g, the 10 weigh hoppers have the following weights in them: 120g, 100g, 150g, 125g, 132g, 148g, 200g, 275g, 172g, 178g - There 2 possible combinations to make 500g:- 1. 120g + 100g + 132g +148g or 2. 172g +178g + 150g. The multihead weigher will choose one of these combinations and discharge 500g.
In the above example the multihead weigher has 2 combinations ready and can instantly discharge another 500g weight and, at the same time, refill the empty weigh hoppers. You can see that by adding additional weigh heads the number of combinations is greater and this can increase the speed.
Many optional extras can be added to your multihead weigher to ensure that it works perfectly with different products. The most common of these is known as a timing hopper. A timing hopper collects the product which has been discharged from the weigh hoppers and waits until the packing equipment asks it to open. The multihead weigher will not release any product from the weigh hoppers until the timing hopper has opened and closed again. This helps with speed as it reduces the distance from the multihead weigher to the packing equipment.