The question is not clear. What quantity do you want to measure? Is it weight or volume? Why indirect measurement?

We want to measure the weight.
We are going for indirect measurement because we don't want to expose electronics on the product.

Are you filling something in the SS container or you want to weigh container itself?

We have filling in the ss container.

Why not just weight it normally with a scale? You're going to get garbage because you've got no way to accurately calibrate.

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We are trying to build a smart lunch box which can measure the amount of food in the ss container.

Weight by pressure measurement is OK for liquids with direct contact. I am not sure how flexible is your ABS base to exactly convey the pressure and then how the system takes care of density changes in the fill. Better to go with load cells. Again the problem of how exactly the ABS base can convey the actual loads. If you explain the full process then you may get ideas.

What level of accuracy? Is this for school?

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IRstuff,
The accuracy is +/- 40gms.
The range of measurement is 60gms to 1200gms
THIS IS NOT FOR "SCHOOL"

I suggest https://www.youtube.com/watch?v=iywsJB-T-mU

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Quark,
we planned going with the load cells but they are too bulky for our application
ABS virgin grade is 2.5mm thick.
Density changes are taken care by defining the range 60gms to 1200gms.

IRstuff,
the application in the video uses load cells,and load cells are too bulky for our application so is the reason we chose flexible pressure sensors

is there any way to measure calories also?

Sure, you burn stuff

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IRstuff,
Burning is not suitable for our application.
Can you suggest any cost effective device or method which can measure calories for the application

You can find approaches on the web; it's a pretty standard high school physics experiment.

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i made a mistake in my previous post.
burning is not suitable for our application.

OK, let me hit this straight. Your requirements are unique and the methods you are considering are neither standard nor specific ones. They are beyond that. So far, the replies you got are with standard courtesy this forum maintains.

Without understanding your exact process and what you want to accomplish, the help you get will be minimal. For example, why do you want to check weight in the container? Why you want to weigh the container with in enclosure and why can't it be done outside? What is the relevance of temperature measurement and calorific values (or calories) etc. May be there is other way of controlling your process or may be not.

Quark,
we are trying to implement a lunchbox which would measure the weight of the content in food container to calculate the calories in the food.
to calculate calories in the food, we need the calories of the food present in the box and also the amount of food in the box. So, we can give the total amount of calories in the food contained in the box.

The only way, short of burning, is to have the user enter the food items into the app that you probably will have for reading the weight. Or, weigh the individual food items during prep.

I'm having difficulty believing that this is for work, when you have no detailed requirements and no detailed concept and are asking strangers on the internet for help.

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So, you want to manufacture lunch boxes with calorie content showing up once filled, for lazy, rich and health conscious guys. Good luck to you. I saw some super inventions by one of my previous companies, for commercial purposes, so I don't want to disappoint you.

As IRStuff already mentioned, the only way to check food strength is using a calorie meter and this is no more being practised as database usage is more handy now a days. Personalized and portable calorie meters are not a possibility, presently.

The option for pressure sensor is incorrect as solids don't exert uniform pressure as liquids do. If the solids are granular then cohesion forces between solid particles tend to reduce pressure at the bottom of container. Sometimes, at certain conditions, increased height of solids won't even impact the pressure at the bottom.

I think the OP is weighing the entire container, contents and all, and doing a simple tare weight, either store in memory, or measured prior to placing contents in the container.

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How will pressure be transmitted from the more rigid steel container to the abs shell and pressure sensor?

Why not a spring and a cheap capacitive, or IR reflective, or inductive displacement sensor? Better yet, why not graduations on the side of the cylinder to indicate filled volume (too low-tech?)

Measurement of calories is impossible without either burning in a bomb calorimeter (as suggested by IRstuff, but note that this method has issues with non-digestible materials) or by prior knowledge of the foodstuff calorie content per unit weight.

The OP stated they wanted to measure "weight" not volume.

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Hi,
Thank you for the suggestions
Burning food is not suitable for our application. So, there is no point in measuring the weight of the contents in the container when there is not scope of measuring calories without burning .
Can you suggest some methods to measure volume.

Why do you need volume and not weight? One without the other makes no sense, particularly since volume is even hard to measure, in a practical sense. The classic volumetric measurement is Archimedes' Principle, which can't be readily done with foodstuffs. Alternately, you could use a camera with structured light and with a laser distance measurement.

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A simple way is to mark the internals as btrueblood suggested and then providing circumferential slide rule to check the calorie content by food item. This won't be appealing to premium segment, however. Why can't you go with a mobile phone type camera in the lid (the plastic one) and connect this to an existing database? Simpler version can be a mobile app.

If you want to measure weight, then use a load cell as use din digital scales. The tare function, as mentioned, would subtract the weight of the empty steel container so that weight of the contents in steel container is measured.

Walt