Load cells ideas and tips

 Usually you have 3 or more load cells that are placed in each corner of the tank, silo, feeder or whatever "silo/tank" you have to weigh in. Think like this:

1. A tank with 3 load cells often has a mechanically stable position but can sometimes become a little unstable. A tank with 4 load cells can often be more stable but can "jerk" a little. Compare with a three- or four-legged chair.

2. Most load cells that are intended for tank/silo weighing, pallet scales and many other applications have a "standardized" output signal, i.e. they give the same amount of signal for a given load, e.g. 1 ton. This means that several load cells of the same type can be connected in parallel. The scale will read the same regardless of whether it is biased.

3. For many scale plates only one single point type load cell is used. They usually give different signals for a given load and cannot be connected in parallel. The gain is adjusted in the indicator, so that the scale shows correctly. The weighing plate still shows the same weight regardless of where the load ends up on the plate.

4. The load cells are mounted so that any load you want to weigh loads the load cells and nothing else loads or takes the load. Input and output are isolated so that they do not affect the silo/tank. Of course, a tank/silo that is weighed must be mechanically isolated from nearby tanks/silos that are also weighed.

5. Remember that the silo/tank remains on the load cells and that it does not slide sideways or lift in e.g. storm. It is important that there is not too much friction in the construction between the part that weighs and the surroundings.

6. If there are strong vibrations, there is always the option of using rubber dampers for the load cells.

7. Temperature stresses in a load cell construction can occur if there is a long distance between the load cells and the silo/tank is exposed for temperature variations. There are simple means to reduce these lateral forces. You can e.g. give the tank legs the opportunity to slide a little laterally on balls/rolls/slides or to use rubber dampers.

8. Whether to choose load cells made of nickel-plated or stainless steel is determined by the environment. If it is only wet sometimes nickel-plated steel works, if it is aggressive and/or very humid, choose stainless steel. Some stainless load cells are rated so that they can withstand being submerged for a certain period of time, for example.

9. If it is an old silo/tank that you are going to install load cells under, you may lift the silo/tank and mount the load cell and possibly accessories. Be careful not to overload the load cells when setting down a tank. If necessary, blocks can be made and used instead of load cells. Do not weld in the silo/tank when the load cells are installed. Fit an earth braid past the load cell so that it is protected from earth current in case someone accidentally welds.

10. In the case of new workshop-made silos/tanks, you can prepare for load cell assembly with any accessories, but it is usually not possible to assemble the accessories in the workshop.

11. In applications where static electricity can be expected, e.g. in the case of silos that are filled with plastic granules, efforts must be made to reduce the impact as much as possible. For example. to ground filling hoses and sieves and to carefully isolate the scale galvanically during remote transmission of measurement data.

12. Almost all load cells today can be connected in parallel in a junction box. Remember that it is important to have a good connection and that cables are installed so that water cannot flow into the box. Preferably use screw connections that face downwards.

High temperature?

As standard, most load cells can handle approx. -25 to approx. +70 °C. The accuracy is then usually somewhat reduced outside the range of approx. -10 to approx. +40 °C. There are special load cells that can withstand significantly higher temperatures. 

Application in water? 

There are different types of stainless load cells that are rated IP68 and withstand 1 m water column for 100 hours.