Introduction

HID's RFID products are generally robust and reliable, but problems occasionally appear. The card (or more generally, the tag) and reader are relatively simple but sophisticated. The tag power is provided by the reader and there is a low-power, short-range rf transmission from the tag to the reader to return the code in the tag.

These factors may produce confusing results. This note provides simple guidelines and procedures to isolate the cause of most problems. Detailed understanding of the operation of the tag or reader is not required; qualified installers should be able to isolate most problems with simple procedures.

Most readers will only read a tag whose data falls within a certain range. Tables in the reader memory determine what ranges of tag data is readable. These tables may change according to customer. If some tags read on one reader but not another, it is likely that the problem is caused by a data mismatch. A new batch of tags that do not read may also indicate a data mismatch.

Tag data does not change, so any tag that once read at a reader should always read at that reader unless the tag or reader has failed. Data mismatches will not cause short read range.

Guidelines For Troubleshooting

• If the same tag works well with a different reader, the reader or noise is generally the problem. There may be a data mismatch if the tag does not read at all with one reader but reads at another.
• If tags do not read at any reader or consistently read at reduced distance at any reader, the problem is generally the tag, although noise is not ruled out. Data mismatches cause failure to read but not short reads.
• If results are inconsistent, or if rotating the reader through 90 degrees makes a difference, interference or noise is likely.
• Poor read distance (range) may be due to tags, readers, noise or metal plates or loops very near the reader.

Common Problems And Their Causes

The table below illustrates the relative simplicity of problem types and sources. It also shows that any of the three most common problems may have more than one cause.

Generally, investigate results using the same tags with different readers or using different tags with the same readers.

• If problems are consistent with the reader, but the same tags work well at another reader, there is a problem with the reader or the location.
• Noise often looks like a reader problem; swap the reader if you can. If the problem tracks the location, noise is likely. If the problem tracks the reader unit, the unit is defective.
• If some tags work well with a given reader and others do not, the tags are the problem. Remember that a data mismatch may be the cause. Data mismatches will not read short; they will not read at all.

Preparation

To be able to perform all procedures in this document you will need the following. Some of them require no tools.

1. A dc voltmeter.
2. The installation manual for the reader.
3. Simple hand tools to remove the reader cover and connect or disconnect wires to the reader.
4. A Continuous Read command card; this card is only available from HID on request.

Electrical Noise Problems

General Notes on Noise

Noise is the most frustrating cause of malfunction because it often causes erratic results. It is also a common cause of system malfunction and should always be considered.

Some computer monitors or similar equipment and certain kinds of electrical machinery may produce rf noise that will interfere with the system. Power supplies of certain types, especially switching power supplies, may generate noise on the dc supply wires to the reader. Less frequently, host computer or panel connections may be a problem.

Noise may produce intermittent or slow reading, complete failure to read or short read range. It may produce inconsistent results, with symptoms appearing and disappearing over a long or short period.

Noise sources are generally of two types: radiating or conducting. Radiated noise is transmitted through the air. This is more common than conducted noise. Conducted noise comes into the reader via wires from the power supply or the host. Sometimes, switching power supplies generate enough noise to cause reader malfunction.

Interfering Equipment or Other Radiating Noise Sources

If you suspect that some nearby equipment is the cause, turn it off if possible and test the HID equipment. If that is not possible, try to separate the reader and the possible noise source. Various noise sources produce greater or lesser amounts of noise, so it is not possible to generalize about adequate separation. CRTs such as computer monitors will not usually affect a reader more than six feet away.

Radiating sources are often directional so that rotating them or the reader slowly through 90 degrees while attempting reads may producing convincing results. Not all sources are directional, so this is not a conclusive test if it fails.

Power Supplies and Host Computers or Panels

The first check that should be made on the power supply is to verify that the dc voltage is correct to the reader when the reader is on. Note that noise levels adequate to disrupt reader operation can not be detected with a typical voltmeter, even on AC settings.

Power supply noise may be investigated by substituting a battery temporarily as the power source if a suitable battery is available. A "linear" power supply (laboratory style) of suitable voltage and current capacity may also be substituted.

When substituting a power source, first do so close to the reader. If that is successful, move the substitute power source physically near the intended power source so that noise pickup in power supply wires can be considered. If the reader works using the substitute supply in both locations, the system power supply is likely to be a source of excessive noise. If the reader works only with the substitute supply near the reader, power supply wiring is probably picking up noise. This is unusual, but if it occurs, try rerouting wires away from other equipment or using twisted, shielded wires with the shield grounded at the supply only.

Host computer or panel noise problems are easily isolated by disconnecting the wires to the host at the reader. The reader does not require a host to operate.

Tag Problems

Tag problems will be characterized by consistent results at any given reader. Tag problems may produce short read range or failure to read. Tag problems are likely if:

1. Tags will not read or have short read range on readers that read other tags well. Remember that data mismatch may be a problem and that data mismatch will not cause short read range.
2. The reader reads a Continuous Read command card correctly. Remember that in order to read any command card, reader power must be cycled and the command card must be presented before any data tag.

Reader Problems

Reader problems may exhibit many different symptoms. Incorrect mounting on metal or near closed metal loops may severely reduce range.

Readers are generally reliable and noise or tag problems should be investigated first unless it is easy to try a different reader.

The easiest way to isolate reader problems is to swap readers. Another is to cycle power to the reader and present a Continuous Read command card. If the reader will not read this card immediately after initialization (two indicator light flashes show correct initialization), it is not functioning correctly.

Problem Solutions

In many cases, the solution is clear once the source of a problem is isolated. This note is not intended to provide details for cases for which resolution is not clear. Contact your HID representative who will assist you in a final solution.