Currency detector

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A currency detector or currency validator is a device that determines whether banknotes or coins are genuine or counterfeit. These devices are used in many automated machines found in retail kiosks, self checkout machines, gaming machines, transportation parking machines, automatic fare collection machines, and vending machines.

The process involves examining the currency that has been inserted, and by using various tests, determining if the currency is counterfeit. Since the parameters are different for each coin or banknote, these detectors must be programmed for each item that they are to accept.

In operation, if the item is accepted it is retained by the machine and placed in a storage container for later collection. If the item is rejected, the machine returns the item. If a coin is rejected, it usually drops into a container for the customer to take back. If a note is rejected, the machine pushes it out and the customer must remove it from the slot in which it was placed.

Coin detectors[edit]

The basic principle for coin detection is to test the physical properties of the coin against known characteristics of acceptable coins. The detector evaluates the coin based on its weight, size, and/or magnetism, and then sends an appropriate electrical signal via its output connection. The next step is generally performed by the banknote-to-coins exchanger.

Today, sophisticated electronic coin acceptors are in use in some places that, in addition to validating weight and size, also scan the deposited coin using optics and match the image to a pre-defined list, or test the coin's "metallic signature" based on its alloy composition.

Normal coins pick up microscopic deposits from human fingers. When a coin acceptor is used long enough, thousands of coins rolling down a ramp will leave enough dirt to be visible. The acceptor requires periodic cleaning to prevent malfunctioning. Coin acceptors are modular, so a dirty acceptor can be replaced with a clean unit, preventing downtime. The old unit is then cleaned and refurbished.

Some new types of coin acceptors are able to recognize the coins through "training", so they will support any new types of coins or tokens when properly introduced.

Testing methods[edit]

Vending and change machines use not one, but several different techniques to check whether a note be genuine. Toggling these settings and the sensitivity of each is programmed via means of dip switches on the internal circuitry.[citation needed]

Optical sensing[edit]

Optical sensing with a small light detector called a photocell or a miniature digital camera is one of the main techniques that vending machines use. Many countries' banknotes are pixelated—that is, they are made out of small dots. The dots are spaced differently and have different sizes, depending on the note. The optical sensors can look for these different patterns to determine what sort of note has been inserted. Some paper money is also fluorescent: it glows when ultraviolet light is shined on it. Some machines shine an ultraviolet light on the note and measure the glow to help determine the note's composition.

GMR sensor proximity detection[edit]

The particles in the ink on many countries' currency have ferromagnetic properties, including some elemental iron.[1] Magnetic composition comprises carbon nanofoam in an amount of from 0.1 to 45 percent by weight of the total composition.[2]

Notes are passed over a permanent magnet array and magnetized along their direction of travel. A magnetic sensor located several inches away with its sensitive axis parallel to the direction of travel can detect the remnant field of the ink particles.

The purpose of the biasing magnet in this case is to achieve a controlled orientation of the magnetic moments of the ink particles, resulting in a maximum and recognizable magnetic signature. Reversing the magnetizing field can actually invert the signature.[3]

Physical attributes[edit]

The thickness and dimensions of a banknote are tested to ensure they are correct. US currency is 2.61 inches wide by 6.14 inches in length and are 0.0042 inches thick, and weigh 1 gram.[4] Currency printed prior to 10 July 1929 had larger physical characteristics.[5] As the notes pass between the rollers, the voltages vary according to their thickness.[6]

Miniature transducers, approximately 3/8" diameter, offer high accuracy linear measurement in a compact space where size constraints prohibit the use of standard LVDTI's. In addition, the low- mass core is ideal for systems with low driving forces or high acceleration and, therefore, will not adversely influence the delicate nature of these applications. Operating ranges are available from ±0.005" to ±1.00", divided into eight intermediate strokes.[6]

Genuine FRNs have a clear polyester thread embedded vertically in the paper. The thread is inscribed with the denomination of the note, and is visible only when held up to light. Each denomination has a unique thread position and will glow a unique color in ultraviolet (UV) light.[7]

Banknote acceptors[edit]

A typical US validator with a green bezel

Also known as validators or acceptors, paper currency detectors scan paper currency using optical and magnetic sensors. Upon validation, the validator will inform the vending machine controller (VMC) or other host device of a credit via a parallel or serial interface. Various interfaces exist for the host device, including a single-line pulse interface, a multi-line parallel interface, a multi-line binary interface, and serial interfaces such as ccTalk, SSP, and MDB. Wrinkled or creased notes can cause these machines to reject them.

An American banknote passing through the device. Note the pistons that grab it when it detects an insert.
Tiny cameras are mounted on the motherboard

There are currently only a handful of companies manufacturing this equipment. Crane Payment Innovations (joining Crane Payment Solutions and MEI), and Japan Cash Machine (JCM) are two of the largest, each maintaining dominance in a particular market segment. Other notable companies producing this type of equipment include Coinco, International Currency Technologies (ICT), Alpha CMS (Cash Management Solutions), Astrosystems, Money Controls, Pyramid Technologies, Validation Technologies International (VTI), Innovative Technology Ltd (ITL), Global Payment Technologies (GPT) and Jofemar. Recent innovations include remote auditing and reporting by these devices as part of an Automated Cash Handling network for amusement, banking, retail, casino and other industries.

See also[edit]


  1. ^ "MONEY IN A BLENDER-A MONEY SMOOTHIE". Steve Spangler Science. 2013. Retrieved 26 May 2014. 
  2. ^ Xerox Corporation (Apr 26, 2006). "Magnetic ink composition, magnetic ink character recognition process, and magnetically readable structures" (EUROPEAN PATENT SPECIFICATION). EP 2 390 292 B1. European Patent Office. 
  3. ^ Caruso, Michael J.; C.H. Smith; T. Bratland; R. Schneider. "A New Perspective on Magnetic Field Sensing" (PDF). Plymouth, MN and Eden Prairie, MN: Honeywell SSEC and Nonvolatile Electronics: 14–15. 
  4. ^ "US Currency FAQs" (FAQ). US Bureau of Engraving and Printing. 14 May 2014. Retrieved 26 May 2014. The approximate weight of a note, regardless of denomination is (1) one gram. 
  5. ^ "Six Kinds of United States Paper Currency". Retrieved 26 May 2014. 
  6. ^ a b "LVDT use in ATM to Sense Dollar Bills" (PDF). LVDT Application (Trans-Tek, Inc.): 1. Retrieved 26 May 2014. 
  7. ^ "Know Your Money" (PDF). US Secret Service. April 2008. Retrieved 26 May 2014.