I want to make a scale which I will place under a wood stove (downdraft gasifier) to measure the amount of wood that goes into the wood stove. The amount of wood which is being measured will be displayed using a raspberry pi on a local page. After some research I was about to order four S-type load cells. The problem which I encountered was the permanent load placed on top of the load cells. The load cells are designed to measure weight for a short period of time. The load cells under the wood stove will be loaded with permanent weight. Does anyone know which load cells I could use to put permanently under the wood stove without loosing accuracy after long periods of time? Some technical information:
Wood stove itself weighs around 700 kg’s.
The capacity of wood in the stove is between 20 kg and 50 kg.
The desired accuracy is 0.5 ~ 1.0 kg. (0.1%, better accuracy would be great)
The load cells won’t be (extremely) heated. The temperature will vary between 10 and 35 degrees Celsius, but that won’t be a problem I assume.
It is a little project on which I intent to spend a maximum amount of 200 euro’s on. Because it is quite some weight it would be the most steady if I use 4 load cells (each corner one load cell). All idea’s are very welcome, even if the accuracy and/ or price won’t meet the desired conditions.
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Thanks for your reply.
The problem with these load cells is, from what I have found in some product details and articles, that it is not designed to withstand a permanent load. If the load cells are permanently loaded there will be some accuracy loss over time. This is called ‘creep’. After some searching I encountered this article (load cell accuracy.
The most important quote from this article about ‘creep’ is as follows:
“The change in load cell output occurring with time while under constant load ( >90% of the load cell capacity ) and with all environmental conditions and other variables remaining constant.”
For example: a load cell loses accuracy if it is loaded with 90% of its maximum weight. Will it loose accuracy if the load cell is loaded with, for example, 60% of its maximum weight? The measured weight will be less accurate, but its accuracy is at least steady and reduced to a minimum.
My question is if there is a product that won’t loose accuracy over a long period of time with permanent load.
Or, is there an optimal load capacity, from the load cell you’ve recommended or the S-type load cell, of which the accuracy is high and the ‘creep’ is reduced to a minimum? I can’t find this information in the product details of such load cells.
I hope I’ve explained it enough for you to understand the problem, if not, please tell me!
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Hey Stef*, I know this is an old thread, but I’m running in to the same issue. Any chance you’ve found some sort of measurement device that can tolerate a permanent load? I’m looking at a similar project for something much lighter (maybe 50-80 Kg) but haven’t managed to find anything yet… Also, how did your gassifier project turn out?? 
--Subscript.
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--Subscript.