High Voltage Leak Detection (HVLD) Method

A. Introduction 

Non-destructiveTo detect microleaks in hermetically sealed packages by measuring electrical discharges between the food product and device electrodes.> 20 μm pinhole, > 50 μm micro-channel30 sec/package1 (bench-top off-line), sec/package (on-line)2$50,000

B. Operation 

High-voltage leak detection (HVLD) is one of the emerging technologies for inspecting package defects and tampering. HVLD operates by applying a high voltage potential to electrically conductive products inside non- or semi-conductive package materials. Pinholes are identified when electrical discharges are detected between products and device electrodes. 
The HVLD system with different frequencies has been successfully validated and used for years to test the integrity of glass ampoules and vials in the pharmaceutical industry (1, 2) and recently was introduced into the food industry within the US. It has been demonstrated that this detection system is a powerful tool to detect pinholes in vacuum pouches containing frankfurters. The applicability of this high-voltage technique to various containers of different types and compositions, therefore, is of great interest to the industry.

  • High voltage leak detection unit
  • Safety gloves
  • Sample packages
  • Paper towels
  • Safety glasses
  1. The HVLD system is composed of four unique elements: high voltage power generator, support electrode, inspection electrode, and a detector (Figure 1).
  2. The power generator subjects the outside of a test package to a certain predetermined high voltage (0.1 - 25 kV). 
  3. In typical HVLD systems, a package wall is nearly non-conductive and thus can be regarded as the dielectricum of a condenser.
  4. When high voltage is applied to the support electrode on which a test package is placed, it electrifies product particles inside the package. 
  5. While high voltages are applied, the surface of a test package is scanned with an inspection electrode as shown in Figure 2.
  6. In presence of a leak, electrons are discharged through the hole.
  7. The detector can then measure current and/or voltage discharges through the inspection electrode.
  8. A data acquisition system in connection with an oscilloscope is used to measure voltage or current profiles discharged from a package.

When voltage discharges are measured, V10 (kV) value, a high voltage applied to the supporting electrode when voltage discharge measured from the inspection electrode exceeds the threshold value of 10 volts, can be used as an indication of the detection. When discharge current is monitored, the ability of the HVLD to detect a leak is largely dependant on the gain setting. With the gain control, a minimum current measured at a constant high voltage applied can be adjusted and optimized to within a measurable range to accommodate the most important factors which could influence the detection limit during a leak test.

C. Application 

PACKAGE TYPES AND DEFECTS

 PACKAGE TYPE
DEFECTSFlexible PouchSemi-rigid and Rigid plastic containerPlastic Can (Double-seam Metal End)Paperboard
Abrasion
Corner Dent   
Crushed  
Cut (Fracture)
Delamination 
Double Seam Defects*   
Flexcracks  
Foreign Matter Inclusion  
Gels  
Hotfold   
Label Foldover   
Leaker   
Leaker (Channel) 
Leaker (Corner)   
Leaker (Notch)   
Leaker (Perforation)   
Leaker (Pulltab)   
Leaker (Seal)   
Loose Flap or Ear   
Malformed  
Puncture (Pinhole)
Seal Defects (Blister)   
Seal Defects (Blocked)   
Seal Defects (Burnt)   
Seal Defects (Compressed)   
Seal Defects (Contaminated)  
Seal Defects (Convolution/Embossing)   
Seal Defects (Creep)   
Seal Defects (Crooked)   
Seal Defects (Incomplete)   
Seal Defects (Misaligned/Deformed)   
Seal Defects (Nonbonding/Weak)   
Seal Defects (Plastic Lumps)   
Seal Defects (Seal-width Variation)   
Seal Defects (Stringy)   
Seal Defects (Uneven Impression)   
Seal Defects (Uneven Juncture)   
Seal Defects (Wrinkle)  
Swell (Swollen Package)
Waffling   

Food contents should be in direct contact with packaging material's surface where the inspection electrode is applied.Microchannel leaks can be detected if food contents trapped inside microchannels are exposed to the environment.Contaminated seal defects can be detected if food contents trapped in seal area are exposed to the environment.Delamination can be detected if food contents trapped in seal area are exposed to the environment.

D. Source 

  • Texmac Inc., 3001 Stafford Drive., Charlotte, NC 28366. (704) 394-0314 (http://texmacusa.com/)
  • Nikka Densok., 610 Garrison St Lakewood, CO 08215. (http://www.nikkadensok.com/)
  • Mocon Inc. 7500 Mendelssohn Ave. N. Minneapolis. MN 55428. (http://www.mocon.com/contactusa.php)
  • Jain, B and Song, Y. 2007 Evaluation of a Non-destructive High Voltage Technique for the Detection of Pinholes in Flexible Pouches for Foods. Poster Pres. at IFT, Chicago, IL.
  • Jain, B and Song, Y. 2008 Validation of a Non-Destructive High Voltage Technique for the Detection of Pinhole Defects in Food Pouches Poster Pres. at IFT, New Orleans, LA.
  • Song Y. 2008. High Voltage Leak Detection (HVLD) Technique for Hermetically Sealed Packages. pp 573-575. The Encyclopedia of Packaging Technology, (Third Edition) John Wiley & Sons, Inc., Hoboken, New Jersey.
  • Song Y. 2008. The US Federal Government,s Role to Regulating Container Integrity. pp 330-332. The Encyclopedia of Packaging Technology, (Third Edition) John Wiley & Sons, Inc., Hoboken, New Jersey.1Detection speed per single head unit per manual inspection2Detection speed per single head unit per production line.