Hello,
I have a project where I need to know the weight that we put on a tray ( 1m x 80 cm) with a maximum of 250kg.
I don't know what kind of sensor I need and how many I need.
For the output I want to connect the sensor(s) with an Arduino so I don't know If I can use all kinds of sensors or just few.
Load cells are a set of strain-guages on a milled block, normally you directly connect the sensor
to a instrumentation amp designed for the purpose like the HX711.
Transmitting the load to the cell mechanically needs some decisions - load cells only want uniaxial
force, no torques. You can use the mechanical setup(*) to remove any torque component, or have a
sensor at each corner and sum them (needs more sensors, but mechanically much simpler).
(*) such as a set of linear bearings
Thnaks for the information !
I wanted to know more about the Load cells. How can I know the area that a load cells is able to measure ?
I mean how can I know if the sensor is sufficient for a tray of 1m x 80cm ?
My main issue is : if I put an object at the coner of the tray how the sensor (that is in the middle of the tray) can know the weight ?
I don't know If I was clear and thank you for your time.
Alex321fr:
My main issue is : if I put an object at the coner of the tray how the sensor (that is in the middle of the tray) can know the weight ?
It can't. As MarkT said, if you want to measure load on a surface when the load is uneven, i.e. can be placed anywhere on the surface, then you need a load cell at each corner NOT just one in the middle.
Steve
Alex321fr:
My main issue is : if I put an object at the coner of the tray how the sensor (that is in the middle of the tray) can know the weight ?
Support the tray on linear bearings as I suggested, so that any torque component goes through the bearings
and the net weight always acts downwards, torque-free.
There are other mechanisms that achieve the same effect - look at how balances are constructed,
most balances have to solve this problem. Even mechanical bathroom scales do this.
how can I know if the sensor is sufficient for a tray of 1m x 80cm?
Read the specs.
Some single load cells are capable of supporting a "tray" and are designed to accommodate eccentric loads.
They are usually called "platform" or "single point" load cells.
For example, in Omega's LCAE series, their 35 kg cell's maximum platform size is 300 mm x 300 mm.
https://www.omega.com/en-us/sensors-and-sensing-equipment/load-and-force/load-cells/lcae/p/LCAE-35KG
It may be difficult to find a cell capable of 1000 mm x 800mm.
I wrote a whole blog post on using Arduino with load cells. It uses a 1kg load cell, but there are many out there that can handle human weighing, so I imagine 250kg shouldn't be a problem for a set of four that you can buy online that act like a scale. You'd just have to build your own platform that can handle the weight. Here's an image of the load cell:
You can follow the tutorial to get you started:
Arduino Weighing Scale with Load Cell and HX711
Just a few comments on the text.
(Arduino 0-5V)
Don't know why you have put that there,
I don't see what a digital sensor has to do with 0-5volt (analogue).
The HX711 can be powered anywhere from 2.7V - 5.5V.
YES for the chip, but NO for the breakout boards.
Absolute minimum for HX711 boards is 4.6volt, for the E+ voltage regulator (~4.35volt) to do it's job.
A <4.6volt (3.3volt) supply means an unstable excitation voltage, and unstable results.
There are HX711 boards with split analogue/digital supply for 3.3volt processors (Sparkfun),
but the analogue part of the board still needs ~5volt.
Leo..
This is how the cantilever type load cell is to be mounted with the frame. The tray is placed on the cantilever end of the load cell in such a way so that center of mass of the tray approximately coincides with the center of gravity of the load cell. The load is to be placed on the center of the tray and then apread away evenly -- not putting on a corner purposely; man and machine have to be co-operative with each other!!
GolamMostafa:
The load is to be placed on the center of the tray and then apread away evenly -- not putting on a corner purposely.
This is not true for all load cells. Some are made to be loaded anywhere on the tray. See post #5.
DaveEvans:
This is not true for all load cells. Some are made to be loaded anywhere on the tray. See post #5.
I have noted down. Thanks.
