Loadcells - Scaletec

Singlepoint, shearbeam, bending beam, compression S Type and pancake loadcells are available, please give us a call to discuss your requirements.

Whether its a budget non trade, top of the line 15000e stainless steel with mounting, or compression cell for your weighbridge you are looking for we are likely to have the solution.

A load cell – sometimes referred to as a ‘force’, ‘weigh’ or ‘weight’ cell – is a transducer that converts the load acting on it into a measurable (analogue or digital) output.  The output is proportional to the force or load applied.

The conversion is achieved by the physical deformation of strain gauges, which are bonded onto the load cell structure. The strain gauges are connected into a Wheatstone Bridge circuit with four strain gauges (full bridge), two gauges (half bridge) or one gauge (quarter bridge).  With half and quarter bridges, the bridge is completed using precision monitors.

Additional bondable resistors are configured within the bridge circuit to compensate for the effects of temperature on the zero or no-load signal and the sensitivity (output due to applied load, plus a further resistor to enable the bridge to be nulled at no load).

The completed Wheatstone Bridge requires a stable DC supply to excite the circuit.  This is usually 5Vdc or 10Vdc, but can be any value from 1Vdc up to 18Vdc.

As stress is applied to the bonded strain gauges, a resistive change takes place which unbalances the Wheatstone Bridge.  This provides an output signal that is linearly proportional to the stress value.   The value of this signal, which is also proportional to the excitation voltage, is typically a few millivolts.

These low level millivolts signals are compatible with a vast range of bespoke strain gauge instrumentation.  These instruments include digital displays, analogue and digital amplifiers.  Typical analogue amplifiers will generate a higher level voltage (0-5Vdc, 0-10Vdc) or current (0-20mA, 4-20mA) for onward processing.

Digital amplifiers typically provide an RS232, RS422 or RS485 output using either the common ASCII protocol or one of a host of more specialised, industry-specific protocols that have been developed such as CANbus or Modbus.  Both the analogue and digital instrumentation have been reduced in size (miniaturised) sufficiently to enable the item to be fitted within the body of a load cell or force sensor.

Load cell designs are either distinguished by the type of output signal they generate (pneumatic, hydraulic or electrical) or by the method in which they detect the load or weight (bending, shear, compression, tension, etc).

Load Cell Operating Principle

Strain gauge load cells convert the load acting on them into electrical signals.  The gauges themselves are bonded onto a beam or structural member that deforms when force is applied.  In most cases, four strain gauges are used to obtain maximum sensitivity and temperature compensation.  Two of the gauges are usually in tension, and two in compression, and are wired with compensation adjustments.   When a load is applied, the strain changes the electrical resistance of the gauges in proportion to the load.  Other load cells are becoming less popular as strain gauge versions continue to increase their accuracy whilst reducing unit costs.

The early load cell designs simply use a strain gauge to measure the direct stress, which is introduced into a metal element when it is subjected to a tensile or compressive force.  A bending beam type design uses strain gauges to monitor the stress in the sensing element when subjected to a bending force.  More recently, the measurement of shear stress has been adopted as a more efficient method of load determination, as this method is less dependent on the direction in which the force is applied to the load cell.

Potential applications for load cells includes the weighing of silos, vessels, crane safety monitoring, weighing of tanks, vessels and conveyors, lifting, fatigue testing, R&D testing, quality control, industrial weighing scales, weigh platforms, Weighbridges, Underhook scales, tensile testing machines and dynamometers.  The marine sector also uses waterproof, submersible or sea water load cells.