High Voltage Leak Detection (HVLD) | The World’s First Pinhole Inspector
Nikka Densok is the first company in history to develop an HVLD pinhole inspection machine for sealed packaged foods and pharmaceuticals in the 1960s. Since then, this method has matured and been highly praised as an in-line 100% inspection machine capable of high-speed, high-precision detection of micro-scale holes.
Features for Pharmaceutical Pinhole Inspection
Nikka Densok deploys the High Voltage Leak Detection (HVLD) system to verify and ensure seal integrity across a wide range of pharmaceutical packaging formats. The key advantage of HVLD for production lines is that the inspection method is 100% non-destructive, thereby eliminating any risk of secondary contamination. Leveraging its unique detection principle, the HVLD system can reliably identify micro-defects and pinholes that are often missed by conventional inspection methods. The difficulties of inspecting low-conductivity products with HVLD are a common concern. However, Nikka Densok Limited proudly offers unique technology based on more than half a century of expertise, enabling the inspection of low-conductivity products such as WFI, glucose, amino acids, and more. Furthermore, the inspectability of biological products, including vaccines, has been verified worldwide.
What Containers Can Be Applied To?
The HVLD is capable of inspecting containers made from electrically insulating materials such as glass, rubber, plastic which contains an electrically conductive solution (≥ 1μS/cm).
This versatility allows HVLD to be applied across a wide range of container formats commonly used in the pharmaceutical industry. Examples include:
・Glass vials and ampoules containing liquid formulations
・Plastic bottles and containers for sterile solutions
・Pre-filled syringes with rubber stoppers
・Cartridges used in injectable drug delivery systems
・Flexible containers such as IV bags
・Blow-Fill-Seal (BFS) containers
・Pouches made of plastic film containing liquid-filled units
HVLD Principles
An alternating current (AC) high voltage is generated through a combination of transformers, capacitors, and amplifying boards, and is directed to the area of the container with the highest probability of defects using specially designed electrodes. The frequency of the applied voltage is carefully balanced to optimize detection sensitivity. Depending on the container’s material, wall thickness, as well as the electrical conductivity of the contained liquid, the applied high voltage typically ranges from 12kV to 30kV.
A streamer discharge occurs when a defect, such as a pinhole or crack, causes the electric field to concentrate at that point. The strong field accelerates electrons, which in turn create additional charged particles, forming a temporary conductive path through the defect into the liquid. This sudden increase in current is detected by the HVLD system as evidence of a leak.
Electrical Circuit Principles
A high voltage (V) is applied through inspection electrodes to a specific area of a sealed container made of non-conductive material. If defects—such as a pinhole, crack, or improper seal—are present in the inspection areas of the container, current flows through the compromised area into the solution (R) inside the container. This results in a loss of Z1 resistance, causing a measurable change in current. By detecting this change, the system can identify the presence of defects. The current is then converted into a readable VDC signal within the electronic circuit and displayed on the operation panel.
Current Calculation by Equivalent Circuit
