Various types of interrogators exist on the commercial market. They differ not only by their function, but also by their form, design, and suitability for specific applications. The main kinds are fixed interrogators-for dock doors, conveyors, and personnel doorways-and mobile interrogators such as vehicle-mounted interrogators and handheld interrogators.
Fixed interrogators are intended to be mounted onto a portal or a wall. They need to be locally connected to a power source and often to a network through appropriate cables. They come in a sturdy metal case, usually in dimensions roughly the size of a laptop (about 30 × 25 × 5 cm [12 × 10 × 2 inches]), but many manufacturers are working on developing smaller units. Usually the case has openings for easy attachment via screws. Other features of fixed interrogators include the following:
Operate in temperatures around -20°C to 50°C (-4°F to 122°F).
Withstand a certain amount of dust or moisture, but do not expect that you can splash these devices with water.
Carry various LEDs to indicate different conditions. (Some readers do not have this option.)
Usually support up to four antennas and have four or eight ports for antenna connections (four ports for mono-static antennas, eight ports for bi-static antennas). You can also find a fixed interrogator with an embedded antenna.
Provide reading and writing capabilities and usually support multiple protocols (such as EPC Class 0, 1, and Gen 2; ISO; and so forth).
Include I/O port(s) to connect various low-voltage I/O devices such as light stacks or motion sensors.
Provide network interfaces through a serial port (RS-232), Ethernet port (RJ-45), or USB port.
Can communicate wirelessly. Some manufacturers include this feature in the interrogator itself; in other cases you have to connect the interrogator to a wireless bridge through an Ethernet connection. Wireless local area networks (LANs) have some limitations in bandwidth, and therefore this type of networking is not always suitable in dense reader environments, but works well when used with vehicle-mounted or other mobile readers. (The various readers differ greatly in the amount of data they send out on the network, so this should be taken into consideration when choosing a reader for yourself or your client.)
Require access to a grounded power source.
Are used with dock door portals, conveyor portals and tunnels, door portals for access control, and many other applications.
Mobile interrogators are specially designed to be "on the move," often with interfaces that support wireless communication. They do not have to rely on the plug in the wall and are usually ruggedized to withstand rough handling by personnel or a vehicle. Mobile interrogators can be vehicle mounted, handheld, or come in various forms such as small PDAs, cell phones, or plug-in units.
Vehicle-mounted interrogators have the following characteristics:
Are specially designed to be mounted onto a vehicle such as a forklift, clamp truck, or trolley.
Usually come in slightly smaller sizes or different shapes than fixed interrogators in order to be easily integrated or mounted onto a vehicle without obstructing its functions. They are usually plugged into an on-board computer (or connected wirelessly); sometimes they come in the form of a tablet computer with a touch screen.
Are more robust than fixed interrogators, and withstand vibrations, shock, and sometimes even high-pressure washing.
Provide reading and writing capabilities. Most of the time they support various protocols such as EPC Class 0, 1, and Gen 2, or ISO.
Usually communicate through a wireless LAN. They can have the wireless capability integrated or can use a wireless bridge.
Are usually powered by the vehicle's battery or can have their own.
When used on a forklift, are usually mounted together with antennas between the forks and connected wirelessly to the on-board computer or to the network. Sometimes interrogators are mounted on a vehicle, and the antennas are affixed to the forks. Therefore, the cables connecting these devices have to be integrated either into the hydraulic cables used for moving the forks or in a way that the cables do not get damaged.
Handheld interrogators have these features:
Come in the shape of a "hand gun," tablet PC, or PDA, and are relatively light and compact compared to fixed and vehicle-mounted interrogators.
Usually have the ability to read bar codes, as well as RFID tags. Most of the handhelds used today provide writing capabilities, but sometimes you can find a handheld that is read-only.
Support various protocols such as EPC Class 0, 1, or Gen 2, and ISO.
Can function entirely wirelessly through a wireless LAN and be powered by an integrated rechargeable battery. This type of handheld provides great mobility but relies on the battery life.
Can be tethered allowing the power and/or communication to run through a fixed cable. This type of handheld does not have as great mobility as the wireless kind because of the limited length of the tethered cable, but you do not have to worry about the battery life.
Have an antenna integrated into the unit, unlike the fixed and vehicle-mounted interrogators. They can come with a linear as well as a circular antenna.
Are often used for exception processing because of their mobility.
When you are looking at purchasing handheld interrogators, be aware that some manufacturers base their pricing on the basic handheld barcode reading unit plus the price of an RFID module.
Other forms of mobile interrogators include the following:
RFID modules integrated into cell phones (for example Nokia's NFC phone)
RFID modules in the form of a Personal Computer Memory Card International Association (PCMCIA) card that can be inserted into a laptop or a PC
RFID modules intended for OEM manufacturers