Q-Card

Jitter: A Failed Transaction

2008-09-08T11:27:00.000-07:00

When you swipe a card and nothing happens or the reader responds with a "card read error" message, one of the most common problems for the failure is jitter. Jitter negatively affects the ability of the card reader to correctly decode the information on the magnetic stripe into readable information. Sources of jitter include the encoding process, the card reader, and normal customer use.

The magnetic stripe on a card stores data like a computer stores data, in binary format. Binary just means that the information is encoded into sequences of 1s and 0s. When the clerk at a store swipes a credit card, for example, the reader decodes the sequence of 1s and 0s into human readable information, such as credit card number, name, and address.

Why Does Jitter Occur

In order for the reader to accurately read the information stored on the card, each bit needs to be encoded to a consistent length. When the card is encoded, the iron or barium ferrite that coats the tape is magnetized to create flux changes, otherwise known as zones.

When the card passes through a card reader, it measures the distance between flux changes to determine if the encoded bit is a 1 or 0. If the flux changes happen sooner or later than expected, the card reader has trouble decoding the information on the magnetic stripe. As a result, the card misreads and the transaction fails.

Common Causes

Sources of jitter during the encoding process include:
Defective Tape Out of spec card properties The card moves during the encoding process Electrical or mechanical noise At the point of the transaction, the card reader may introduce jitter through one of the following problems:
Vibration Sticking Slipping Worn or dirty magnetic read head End users also introduce jitter by using the card in day-to-day activities. As the card bends and the magnetic stripe incurs abrasions, jitter increases.

Why Test

On the date you issue a card, jitter is at the lowest level it will ever be for that card, which underscores the need to start with a card that has low jitter levels.

We calculate jitter as the percent change in bit length from one bit to the next. A card may be unreadable with a jitter range that exceeds 15%. Ideally, we want new cards to have a 0% jitter, which helps ensure quality transactions for our customers.

In my next Q-Card Hotline article, I’ll discuss how we test for jitter.

An Introduction to Card Testing

2008-08-15T08:00:00.000-07:00

Ultimately, the magnetic stripe on a card exists for one reason: to store data for later use. If the data can not be retrieved when your customer swipes the card, you negatively impact customer satisfaction. Testing your magnetic stripe before the cards you ship meets the expectations of your customers.

We measure the quality of magnetic stripe against two ISO standards. ISO/IEC7811-2 provides the specification for low coercivity (loco) tape, and ISO/IEC7811-6 provides the specifications for high coercivity (hico) tape.

The magnetic stripe on a loco card is 300 Oersteds, and the hico cards range between 1250 and 4000 Oersteds. Examples of loco cards include ID, access, and mass transit cards while the financial industry uses hico cards for bank cards.

Types of Tests

Since we have separate ISO reference standards to test loco and hico cards, we can expect different tests for each standard. To test loco cards, we perform window, resolution, and erasure tests.

The window test verifies the amplitude on the stripe falls within acceptable levels. The resolution test ensures that stripe output maintains an acceptable level at higher bit densities. The erase tests intentionally erases the stripe and makes sure the residual amplitude remains low after the erasure.

To test hico cards, we check for demagnetization and distortion. To pass, a magnetic stripe should resist erasure when exposed to a household magnetic, such as a refrigerator magnet. Loco cards because they are encoded with a lower Oersteds value are vulnerable to accidental demagnetization and data loss.

Distortion tests the stripe for parity errors that arise from extra bits. Jitter is another form of distortion that happens when the encoded bits on the stripe appear out of order.

Your Testing Needs

The decision to test your cards to ISO standards should be an easy one to make. Perhaps the biggest decision is whether or not you buy your own equipment or outsource your testing services to a neutral lab.

Q-Card offers solutions to help you ensure total card quality in your lab or in ours. Future installments of the Q-Card Hotline will discuss the benefits of testing in your lab versus outsource. Plus we’ll cover many of the concepts we outlined in this article with more detail.

Welcome to Q-Card Hotline

2008-07-30T18:02:00.000-07:00

At Q-Card, we take card testing seriously, and we believe that ensuring card quality saves money and makes happy customers. We're relaunching Q-Card Hotline as a periodic publication to provide you with updates, tips, and answers to commonly asked questions.

We'll talk about magnetic stripe, contactless, and RFID technologies. In addition, we'll cover and comment on industry news when appropriate.

My name is Terry Schindler, Chief Engineer at Q-Card, and I'll be your host on Q-Card Hotline. I am the chair of ANSI/NCITS B10.11 working group for card test methods. I attend all ISO and ANSI/NCITS meeting. For 15 years, I have attended the ISO WG1 test methods group and held a secretary position in WG1 for at least 6 of those years.

I look forward to hearing from you.