Measuring forces is an important aspect of engineering. We can use a load cell to measure force. The force we are going to measure in this example is the weight of an object. Load cells can be found in your electronic kitchen scales and we are essential going to make a set of scales. The advantage of making a set of scales from scratch is that they are then easy to connect to other devices and/or record the data for other uses etc.
There are a number of different designs of load cell. In this project I am using a 3133 micro load cell as shown in the photo. Each load cell has a rated capacity. The one I’m using has range of 0 to 5 kg. The load cell is a metal bar with strain gauges glued to it. When a load is placed on the bar it deforms very slightly due to the shear force. This deformation is measured by the strain gauges. We will measure the output voltage of the strain gauge as the voltage changes more the more the bar deforms. The change in voltage is very small, however. We will amplify the output using the INA 125P.
The first step is to build a support for the load cell. For the unit I am using the end with the wires should be secured and the load applied to the other end. I quickly made a wooden frame to hold the load cell. I have placed metal fittings around the load cell as I was concerned that the wood would crush under load. I have also made a small wooden platform to carry the objects we want to weigh and secured this to the other end.