Unwanted Shadow Coin
A coin acceptor normally has one or more parameters it measures to determine if a deposited coin is to be accepted. Due to slight variations in coins and in how the coin physically passes through the acceptor, it reads a distribution of values about a central value. Coins with parameter readings falling between an upper and lower limit about a central acceptance value, the acceptance window, will be accepted.  (See Figure 1)

Sometimes a second Unwanted Shadow Coin can have its parameters overlapping the distribution of the Valid Coin and fit within the acceptance window of the Valid Coin. Examples of this include a.) a 0.984 70/30 brass token and a 0.984 85/15 brass token,  b.) a $1 alloy 752 casino token and a lead slug, and c.) a Brazilian 25 Centavo coin and a "smashed to larger diameter" 10 Centavo coin.  The typical solution to this problem is to tighten the acceptance limits. While in some cases this may help, in the example shown in Figure 2, there becomes a serious trade-off between eliminating the Unwanted Shadow Coin and reducing the rate of acceptance for the Valid Coin, neither of which is desirable.

In order to simultaneously eliminate the Unwanted Shadow Coin and maintain a high rate of acceptance for the Valid coin, provision has been made to teach IDX Xeptors the properties of the Unwanted Shadow Coin. Having done so,  when the Xeptor finds that a deposited coin falls in the acceptance window of both the Valid Coin and the Unwanted Shadow Coin, it will further look more closely at the individual errors from three separate measurement types, each with their own probability distributions, and use them jointly to determine which of the two coins the three properties most closely match. This method has been proven quite successful for achieving excellent discrimination in these tough situations.

How To Use The Unwanted Shadow Coin Feature
To teach the Xeptor the Unwanted Shadow Coin, go through the LEARN procedure as usual (turn rotary switch SW2 to a Coin Memory #, push the button, drop 6 sample coins). For V4.0 firmware, an unwanted coin may be programmed into and Coin Memory, but for the X-10, x-50 and MA800 Xeptors with V3.0 firmware the Unwanted Shadow Coin must be programmed into Coin Memory #1. In either case and you must press the button 13 times when initiating the LEARN cycle because the firmware uses this marker to identify it as the Unwanted Shadow Coin.

Tip #1
For best long term performance with the Xeptor's built in automatic self adjustment for component drift, we recommend that you only use Coin Memory #2 when learning the Valid Coin, although this is not strictly required for basic operation. If you have slight variation in your tokens from having made multiple purchases (or if the currency coin has some variation over the years), and if the Unwanted Shadow coin is particularly closer to one batch of these coins, then it is best to program Coin Memory #2 with the batch closest to the Unwanted Shadow Coin, and program samples from another batch into Coin Memory #3, #4, #5, or #6.

Tip #2 
Starting with firmware version V3.0p, the diameter also plays a role in the test for an Unwanted Shadow Coin. For defending against stamped currency or tokens from another country or institution, this is helpful if there is a slight (less than .015") difference in diameter. However, if you are defending against crude slugs with a variety of diameter sizes, you should make sure that you train the Xeptor with slugs that are similar in diameter to your good coin because if the diameter of the learned Unwanted Shadow Coin is more than about .015" different from the good coin, it will likely not help with slugs that are very nearly identical in diameter to the good coin as they may be different enough from the learned Unwanted Shadow Coin that they will not qualify as an Unwanted Shadow Coin. Slugs that are different enough in diameter from your good coin will be rejected anyway, and thus are not the threat coin to be learned as the Unwanted Shadow Coin.

Tip #3
When an Unwanted Shadow Coin is programmed into (learned by) the Xeptor, the Xeptor also takes this information to mean that there is a threat out there and that it should automatically raise its other defenses against various slug threats, including:

1.      Automatically raising the X-Mark detection threshold (same setting Bit-4 of SysConfig, first available in V3.0m and made smarter in V3.0s)

2.      Automatically requiring detection of the X-Mark on both the leading and trailing edges of the coin (same as setting Bit-5 of SysConfig, first available in V3.0p)

3.      Automatically tightening the tolerance on the ensemble of three alloy readings by 40% (same as setting Bit-6 of SysConfig, first available in V3.0s)

Tip #4
If your Unwanted Shadow Coin is too identical to the Valid Coin, it may not be possible to eliminate the Unwanted Shadow Coin. You will know this is the case if you have followed all of the instructions above and find that the accept rate for the Valid Coin becomes excessively poor.