The selection of an RFID reader is guided by the selection of the RFID tags. Once you select a tag that will be the most suitable for your solution, half of your work is done as far as criteria for selecting an RFID reader.
Besides the factors common to tags and readers (the reader must be able to read the tag) such as type (active, passive), frequency (LF, HF, UHF and Microwave) and protocol (Gen 2, HF, NFC, Mifare, etc.), most distinguishing factors that apply to readers only are:
- 1.Form factor
- 2.Country regulations
- 3.Read distance (based on reader transmit power)
- 4.Network and power connection
Fixed interrogators are designed to be bolted to walls near doorways or attached to wire racks near doors, integrated into stands and dock door portals, and attached to conveyor portals and the like .
Vehicle-mounted interrogators, which can automate shipping and receiving of goods, are usually integrated into material handling devices such as forklifts, paper trucks, cargo trucks, and pallet jacks. These interrogators usually have a special shape for easier installation onto the vehicle and a rugged design to survive the vibrations and other environmental conditions.
Mobile interrogators, such as handheld interrogators, are often used for low-volume reading or writing in exception processing, quality assurance, and mobile shipping receiving units. Handheld interrogators come in a variety of forms and have a vast selection of options for communications. They can be tethered, receiving power and accomplishing data transmission via a nearby base unit using an extensible cord. Other types of handhelds can be wireless, depending on wireless networks or Bluetooth communications for data transfer, limiting operational time to battery life between charges. Newer renditions of handheld interrogators are appearing in forms of cellular phones and personal digital assistants (PDAs).
Handheld interrogators are usually monostatic, with integrated linear antennas. The monostatic design keeps their size to a minimum since only one antenna is used, while the linear antenna polarization is used to get the best read range. The interrogator’s orientation can be changed simply by turning your wrist.
Because the radio spectrum across the world is not allocated in the same way, each country has its own regulations regarding the spectrum usage. While tags usually work globally, even if they are specifically tuned to particular region, readers are the transmitters and they must operate within the regulatory conditions. Because of this, you will see several country specific versions of the same reader, which will differ by frequency used (865 – 868 MHz for Europe under ETSI regulations or 902 – 928 MHz for US under the FCC regulations), transmitted power (2 ERP for Europe and 4 EIRP for US) and various rules like frequency hopping, listen before talk and other. For more information on regulations click here.
Read distance is related to the transmitted power from the interrogator. Simplistically explained, the higher transmitted power, the higher the read distance (barring interference and adverse environmental conditions). Of course, the transmitted power is capped by the country regulations. The effective transmitted power is also related to he antenna, as antenna efficiency and a cable loss can also reduce the power and therefore the read distance. Some readers do not utilize the full allowed power setting due to restrictions on their power source, if they are powered by the battery and therefore, you can expect a shorter read range.
Network and Power Connection
In order to receive data from the reader, it has to be connected to a network. There are several options. Fixed readers usually utilize:
- Serial interface
- POE (Power Over Ethernet – both power and network connection)
- Battery powered (seldom)
Handheld readers usually feature:
- USB (when tethered)
- Battery powered (Li-Po, Li-On)
You can learn more about readers/interrogators here.