A load cell is a transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured. The various types of load cells include hydraulic load cells, pneumatic load cells and strain gauge load cells.
Each strain gauge has a diffrent sensitivity to strain, which is expressed quantitatively as the gauge factor (GF). The gauge factor is defined as the ratio of fractional change in electrical resistance to the fractional change in length (strain).
(The gauge factor for metallic strain gauges is typically around 2.)
We set up a stain gauge load cell and measure that change in resistance and all is good, right? Not so fast. Strain measurements rarely involve quantities larger than a few millistrain (fancy units for strain, but still very small). So lets take an example: suppose you put a strain of 500me. A strain gauge with a gage factor of 2 will have a change in electrical resistance of only
For a 120Ω gauge, this is a change of only 0.12Ω.
0.12Ω is a very small change, and, for most devices, couldn’t actually be detected, let alone detected accurately. So we are going to need another device that can either accurately measure super small changes in resistance (spoiler: they are very expensive) or a device that can take that very small change in resistance and turn it into something that we can measure accurately.
This is where an amplifier, such as the HX711 comes in handy.
A good way of taking small changes in resistance and turning it into something more measurable is using a wheatstone bridge. A wheatstone bridge is a configuration of four resistors with a known voltage applied like this:
where Vin is a known constant voltage, and the resulting Vout is measured. If then Vout is 0, but if there is a change to the value of one of the resistors, Vout will have a resulting change that can be measured and is governed by the following equation using ohms law:
By replacing one of the resistors in a wheatstone bridge with a strain gauge, we can easily measure the change in Vout and use that to assess the force applied.50KG Capacity Strain Gauge Load Cell Load Sensor
Voltage=5 Output Signal=2mv L=130MM W=30MM H=22MMFeature:
- Alloy steel, hermetically welded/sealed by adhesive inside,oil-proof, waterproof and anti-corrosion.Safe and anti-explosive product, can be used in atrocious environment and hazardous areas.
- suitable for crane scale, mechanical conversion scale, hopper scale and other electronic weighing devices.S beam design,tension and/or compression loading possible,easy installation
- Connection mode: red: power supply +, black: power -, green: signal + white: signal –
- Max capacities:50Kg
- Insulation resistance: More than 2000megohm