1. Load Cell &DP Cell
2007-CHEM-17

2. Load Cell
A load cell is a transducer that converts a load acting on it into an analog electrical signal. This conversion is achieved by the physical deformation of strain gages which are bonded into the load cell beam and wired into a Wheatstone bridge configuration.
A load cell is a type of transducer and this transducer is used for converting forces into electrical signals. For example, changes in pressure or weight may be converted into signals which can then be used within an electronic circuit.

3. Load Cell Operating Principles
Load cell designs can be distinguished according to the type of output signal generated (pneumatic, hydraulic, electric) or according to the way they detect weight (bending, shear, compression, tension, etc.)

4. Types of Load cell Load cell consist of two basic types
Mechanical Load Cells
Strain Gauge Load Cells

5. Mechanical Load Cell This load cell consist of two major classes
Hydraulic
Pneumatic

6. Hydraulic Load Cell
It is force -balance devices, measuring weight as a change in pressure of the internal filling fluid. In a rolling diaphragm type hydraulic load cell, a load or force acting on a loading head is transferred to a piston that in turn compresses a fluid confined within an elastomeric diaphragm chamber. As force increases, the pressure of the hydraulic fluid increases.
This pressure can be locally displayed or transmitted for remote indication or control.

7. Hydraulic Load Cell

8. Pneumatic Load Cell
Pneumatic load cell also operate on the force-balance principle. These devices use multiple dampener chambers to give higher accuracy than can a hydraulic device.
The advantages of this type of load cell is that they are explosion proof and not sensitive to temperature variations. Additionally, they contain no fluids like hydraulic type that might contaminate the process if the diaphragm destroyed.
Disadvantages of this type is that they are relatively slow speed of response and the need for clean, dry, regulated air or nitrogen.

9. Pneumatic Load cell

10. Strain Gauge Load Cells
This converts the load acting on them into electrical signals. The gauges themselves are bonded onto a beam or structural member that deforms when the weight or force is applied.
When force or weight is applied, the strain changes the electrical resistance of the gauges in proportion to the load.
Other load cells are fading into obscurity, as strain gage load cells continue to increase their accuracy and lower their unit cost.

11. Strain Gauge Load cells
Strain gauge load cell further classified into
different types.
Bending beam load cell
Shear beam load cell
Canister load cell
Ring and pancake load cell
Button and washer load cell

12. Bending Beam Load Cell
Bending beam load cells need particular care when mounting to ensure good load introduction and to prevent damage from side or non axial forces. Fully weld-sealed stainless steel low capacity beams down to 5kg are now available offering excellent solutions to low capacity weighing in hostile environments.

13. Shear Beam Load Cell Single Ended Shear Beam:
Provide the ideal solution for medium capacity weighing.
Their ability to withstand 100% side load without problems makes them particularly suitable for weighing systems with mixers and agitators.
However these units become costly

14. Shear beam Load Cell Double -ended shear beam:
For medium to high capacity applications, the double ended shear beam offers a number of advantages over other designs.

15. Canister load cell
Traditional canister load cells have stood the test of time and provide a compact and cost effective solution for many high capacity weighing systems.
Canister load cells can be fully weld sealed and stainless steel construction is now an industry standard.

16. Selection of Load cells
Basic type and mode of operation.
The Number of load cells.
Capacity.
Accuracy level related to system requirements.
Method of mounting.
Approval requirements (metrological, safety, environmental)
Sealing level and construction material.
Cost.

17. Applications of Load Cell
Tank/ silo
Tank dispensing
Wind tower
Dual tank level controller
Bag filling machine

18. Differential Pressure Cell
It is a device that measures the differential pressure between two inputs.
Example: we have a pressure container where we connect the H-side (high) of the DP-cell, L-side (low) leave in the atmosphere (open air). The DP-cell will tell us the pressure in the pressure container relative to atmosphere pressure. Depending on what class the DP-cell is, it will give you feedback with a current signal. Normal in Europe is 4-20 m A, where 4 is lowest and 20 is highest.

19. Types of DP Cells DP cell has the following types.
Diaphragm capsules DP cell
Pneumatic DP cell
Electronic DP cell

20. Diaphragm Capsules DP Cell
It consist of 2 circular metallic diaphragms
Diaphragm capsule act as sensor
Diaphragms have concentric corrugations to optimize their flexibility and rigidity
Space between backing plate and diaphragms is filled with silicone oil

21. Pneumatic DP cell
In this type of cell capsule is held between two flanges castings which form chambers on either side as high and low pressure sides of dp cells

22. Electronic DP Cell These cells are much the same as pneumatic cells
Convert the deflection of diaphragms into a change in resistance, inductance or capacitance

23. Applications Level measurement Density measurement
interface measurement