What is Equalization of "Load Cells"

A typical configuration might consist of a platform with a load cell at each corner, with the four load cells paralleled to give a total weight. If a test weight is placed at each corner, each individual load cell's circuit can be adjusted ("trimmed") accordingly. Then, no matter where the weight is placed on the platform, the four load cells' contributions should add up correctly to the total weight.

There are several variations of this basic idea.

Tornado did a great job answering the how, so I will answer the why. Because of the mechanical attributes of this electro-mechanical device, calibration should be done on a regular bases. (Part of you electrical PM or instrumentation PM program) Dirt, dust, mechanical wear, vibration and other mechanical force requires regular cleaning and calibration for reliable operation.

Now here's the thing. On a four corner device, such as a belt weigher, there is no need to "trim" the load cells, they are simply paralleled together. The mV output is now averaged across all load cells. If there is large disparity of signal between individual load cells then there is a mechanical problem such as corner loading.

It is indeed an electro-mechanical device and if set up correctly checks should be conducted only. In theory a device such as this should only need to be calibrated once in its lifetime and re-zeroed on a regular basis. The Zero does not affect the span.

Tornado suggests that because of "Dirt, dust, mechanical wear, vibration and other mechanical force requires regular cleaning and calibration for reliable operation." Regular cleaning yes and then calibration CHECK. If the span wants to shift by more than say 1% (less if high precision device) then you have problem. Calibrating over the problem will cause huge linearity issues even though the calibration looks good.

Good point philphy , I should have used "calibration CHECK", not just the said "calibrate".

When weighing tanks and vessels, three legs are preferred over four legs. A tripod will always distrubute the weight correctly without having to make adjustments or add shims. This makes for easier commissioning.

Load cells typically are strain gauges, a transducer that converts mechanical form of energy into an electrical form. Since it's nearly impossible to find load cells that are truly identical, equalization is needed before they can be used properly. To facilitate equalization, 4 load cells are put in a bridge configuration, (like a wein bridge or whetstone bridge). Equalization is balancing all 4, having zero reading during a no load condition.

In practice, a minimum of four (4), bridges that were already "equalized" are put into four corners, as Mr. Tornado mentioned in his post. All four sets of bridges are then balanced again or fine tuned for zero reading as well as for its linearity range..

if we have four load cells, is it necessary that each one measures the same weight (a quarter of the total)? why?

No.

This sounds like more and more like Homework.

A load cell system is a transducer that converts mechanical energy into electrical energy. Not only does it give accurate measurements but it also "lessens" the force/pressure exerted by the heavy equipments or materials that is being measured. Each load cell is designed differently to meet certain specifications and customers need--specifically for industrial, mechanical or personal use.

it also "lessens" the force/pressure exerted by the heavy equipments or materials that is being measured.

Balderdash!!! If this were true you could place the weighed object onto a stack of load cells, each one progressively reducing the force until you reduced the level to below zero. You would then have created an anti-gravity machine.

Some types of load cell mounts incorporate floating bearings designed to relieve lateral stresses, but non-reduce pressure or force.