Sigma Metalytics
Also: Sigma device, Sigma tester, Conductivity tester
Sigma Metalytics refers to a product line of portable testing devices that use electromagnetic induction to measure the resistivity of precious metals and thereby reliably expose counterfeits.
Sigma Metalytics is a US brand that manufactures handheld devices for the non-destructive authenticity testing of precious-metal coins and bars. The devices work on the principle of electromagnetic induction: a coil generates a high-frequency alternating field that penetrates the metal being tested and measures its electrical conductivity and permeability. The result is compared with stored reference values for gold, silver, platinum and palladium.
Operating principle and product variants
The measuring principle is based on the penetration depth of the electromagnetic field (skin effect): depending on the set frequency, the field reaches to different depths in the material. This makes it possible to detect clad objects as well, in which a layer of genuine metal conceals an inferior core – for instance the dangerous tungsten counterfeit, in which tungsten cores are coated with gold.
Sigma Metalytics offers two main variants:
| Model | Target group | Feature |
|---|---|---|
| Precious Metal Verifier (PMV) | Dealers, private investors | Compact, several probes for different coin thicknesses |
| Professional Series | Commercial testers | Extended frequency range, higher measurement accuracy |
The probes are matched to common coin diameters and thicknesses (e.g. 1 oz coins such as the Krugerrand or Maple Leaf). An incorrectly chosen probe can lead to false readings.
Strengths and limitations
Advantages over simpler methods:
- Non-destructive, no chemicals (unlike the acid test)
- Measurement in seconds without dismantling a coin capsule
- Detects tungsten cores that may slip through the magnet test and density measurement
Limitations:
- Coins must be tested unpackaged or in thin capsules
- Very thick precious-metal coatings can prevent the EM field from reaching deep enough into the core – a counterfeit approach with a particularly heavy gold shell can distort the result
- No substitute for X-ray fluorescence analysis (XRF) for a complete material analysis
- The device must be calibrated regularly
For a complete check, a combination of the Sigma test, weight and dimension control (use our coin weight checker and coin size checker) and, if needed, a professional XRF is recommended.
In brief
Sigma Metalytics devices are the method of choice when it comes to exposing tungsten-core counterfeits and platings quickly and without chemicals. For the final authenticity assurance of large positions, combining several test methods remains the gold standard.