Hydraulic vs. Pneumatic vs. Electronic Load Cells: Which is Best for Hazardous Areas?

Safety First: Understanding Weighing in Classified Areas

In environments where flammable gases, vapors, mists, or combustible dust are present (known as Hazardous Areas or Classified Locations, such as those defined by ATEX/IECEx or NEC/CEC), weighing equipment must not become a source of ignition. When selecting a load cell for these zones—common in oil and gas, chemical processing, and certain food industries—the intrinsic design of the sensor is critical. We compare the three main types of load cells to determine the best fit for safety and operational integrity.

1. Electronic (Strain Gauge) Load Cells

Electronic load cells, which rely on the resistance change of a strain gauge circuit, are the most common type globally. Their use in hazardous areas requires specific and often costly protection methods.

• Operating Principle: Converts force into a proportional electrical signal (millivolts).
• Hazardous Area Solution: Electronic cells are inherently an ignition risk due to the electrical energy in the circuit. They must be protected by one of two methods:
  • Intrinsic Safety (IS): This is the most common and safest method. It limits the electrical and thermal energy to a level so low that it is incapable of causing ignition even under fault conditions. This requires certified safety barriers to be installed in the safe area.
  • Explosion Proof (Ex d): The cell and indicator are housed in an enclosure strong enough to contain any internal explosion, preventing flames from reaching the external atmosphere. This method is often heavier and more costly.
• Best for: Applications requiring high accuracy, complex data processing, and communication with modern indicators and PLCs (when protected by IS barriers).

2. Hydraulic (Hydrostatic) Load Cells

Hydraulic load cells are completely mechanical and are therefore inherently safe in any explosive atmosphere, making them a popular choice for extreme hazardous applications.

• Operating Principle: The load applied to the cell compresses a piston, which applies pressure to a sealed, incompressible fluid (usually oil). The pressure is transmitted via a tube to a remote pressure gauge or transmitter.
• Hazardous Area Solution: Inherently Safe. Since they contain no electrical components, wiring, or ignition sources at the point of measurement, they require no special certification or barriers (such as IS) for use in Zones 0/1/2 or Division 1/2.
• Drawbacks: They are typically less accurate than high-end electronic cells and are sensitive to temperature changes, which can cause fluid expansion and pressure drift. The remote gauge is often difficult to integrate into modern digital control systems.
• Best for: Extreme environments where maximum safety is paramount, such as continuous monitoring of silos or reactors in Zone 0, and where high precision is secondary to reliability and safety.

3. Pneumatic Load Cells

Pneumatic cells utilize air pressure and are very rare in modern industrial weighing but are sometimes used in specific legacy applications.

• Operating Principle: The applied load is measured by the change in air pressure required to balance the force.
• Hazardous Area Solution: Similar to hydraulic cells, they are Inherently Safe as they only utilize mechanical and air pressure, posing no electrical ignition risk.
• Drawbacks: These cells require a constant, clean, and stable compressed air source, making them complex and expensive to maintain. They are highly sensitive to temperature fluctuations and pressure losses, making them generally unsuitable for high-accuracy commercial applications.
• Best for: Highly specialized applications in corrosive environments where the cost of maintaining electronic cells is prohibitive, or where a suitable air supply is readily available.

Comparative Summary for Hazardous Areas

For most modern industrial applications in classified locations, the choice is between the high precision of a protected electronic cell and the inherent safety of a hydraulic cell.

Conclusion: Selecting the Right Safety Strategy

For most new installations requiring high commercial accuracy and full digital integration, the Electronic Load Cell protected by Intrinsic Safety (IS) barriers is the industry standard. This offers the best balance of safety (via limited energy) and performance.

However, for the most challenging, high-volume applications where the simplicity of zero-ignition risk is the priority, the Hydraulic Load Cell remains the unmatched choice due to its inherent mechanical safety and robustness.