Converting a force into electrical signal for measuring weight is called Load cell. Load cell is a transducer, used to convert a force into electrical signal. The conversion of force into electrical signal is indirect and occurred in two steps. By a mechanical system, a force is creating through outer portion of load cell and strain gauge start deforms of force. In the second step, strain gauge converting the force into electrical signal by changing resistance of the wire. Four strain gauges are using like Wheatstone bridge configuration in a load cell. At the end of load cell, a controller is using for calculate and showing the result for the user. For quick and exact measurement, load cells are using commonly. Load cells are relatively more efficient, affordable and have a longer life span than the other weight sensor.
How a Strain Gauge load cell works
When the resistance of the electrical conductor changes when its length changes due to stress, this fact is used as the principle of operation of Strain gauge load cell. For the construction of strain gauge, Cu Ni alloy is commonly used as the resistance change of the foil is vertically proportional to the applied strain. By using appropriate measuring circuit, the change in resistance of strain gauge can be utilized to measure strain accurately. Normally, a load cell is a package of four strain gauge in a Wheatstone bridge configuration. As a output of load cell, it gives few milivolts as a electrical signal. This electrical signal amplified by a circuit before sending it to measurement system. Depending on the application, output can be in Digital or Analog (0 – 5v).
How a Capacitive Load Cell Works
The principle of a capacitive load cells is based on the capacitance changes of a capacitor as the load presses the two plates of a capacitor closer together. Capacitive load cells construction is simpler than a resistive load cell. For measuring proximity, humidity, tilt, force, torque, fluid quality, acceleration and many other physical parameters, capacitive techniques can be used. It is a very versatile parameter that offers tremendous sensitivities in a small package. The capacitive technology is more rugged than strain gauge designs and can therefore be used in a wider variety of engineering applications.
How a Hydraulic Load Cell works
By changing in pressure of the internal filling fluid a hydraulic load cell measuring weight. This load cells are force – balance device. A load or force acting on a loading head, this load transferred to a piston that compresses a filling fluid, which surrounded by an elastomeric diaphragm chamber. So, when the force increases, the pressure of the hydraulic fluid increases. This pressure can be locally indicated or transmitted for remote indication or control. This sensor has no electric components and immune to transient voltages so it is ideal for use in hazardous areas. The disadvantages of Hydraulic load cells are it is expensive and very complex.
How a Pneumatic load cell works
Pneumatic load cells operate on the force-balance principle. These devices use multiple dampener chambers to provide higher accuracy than can a hydraulic device. Pneumatic load cells are often used to measure relatively small weights in industries where cleanliness and safety are of prime concern.
Advantages of Load cell
• Rugged and compact construction
• No moving parts
• Can be used for static and dynamic loading
• Highly Accurate
• Wide range of measurement
• Can be used for static and dynamic loading
Disadvantages of Load cell
• Mounting is difficult
• Calibration is a tedious procedure
