Tags are available as read-only, and read/write. Read/write tags can be classified as reusable and disposable. A reusable tag typically would be used within the plant for tracking and reworking purposes. A disposable tag may follow the product from manufacture to distributor to retailer to end user.
In general, read-only tags have the lowest memory capability—often 20 bits or so. Active read/write tags can often hold as much as 32 Kbytes or more. Read/write speeds depend on several factors: length of data to be transmitted, the physical range between the transponder and controller, the radio frequency on which the system operates, modulation technique used, etc.
Generally speaking, higher-frequency radio systems can send data faster, but may have shorter range than lower frequencies. The most commonly used ranges are: 125/134.2 kHz, 13.56 MHz (ISO 15693), 900 MHz (typically for EPC), and 2.45 GHz. There is a tradeoff between frequency usage and noise. Lower frequencies should have longer ranges than higher frequencies, but noise at lower frequencies can degrade operation. The higher frequencies often can penetrate metal enclosures better than lower frequencies, but higher frequencies are susceptible to standing wave nulls, which can cancel shorten reliable distances. Greg Breuckman, Colder’s business development manager, explains how his company’s technology is solving customer production issues: "Our new Smart Coupling series integrates RFID technology into a host of standard couplings and package inserts to automatically exchange product data at the exact time and location of connection using contactless technology (see Figure). We get numerous requests for mechanical keying to enable a customer to prevent the connection of incompatible fluids in process. RFID technology can be used as an electronic key, offering millions of unique codes versus a handful of mechanical options. Beyond electronic keying, RFID chips enable a customer to store process information on the container fitment such as date codes, lot codes, product identification and product parameters."
By storing product parameters on the container, says Breuckman, Colder’s customers can access this information for auto-calibration. "Instantaneous adjustments can be made in process by having the control system change pump speeds and flow rates depending on the process recipe and the information stored on the RFID tag."
Imagine Extreme Variety
RFID applications are as varied as you can imagine. For example, Accusort () deploys RFID for CD production process control, ingredient verification in the baking products industry, and lights-out tracking of photo-sensitive emulsions and films during processing.
Within Accusort’s CD manufacturing technology an RFID system provides reliable verification of metal spindles as they carry CDs through the various CD manufacturing processes including injection molding, reflective plating, lacquer coating and screen printing. A rewriteable tag is mounted to the bottom of the spindle, and is read prior to entering the processing machine. Once this data is read by the RFID system and transmitted to a PLC-based system, a CD is released into the machine. If an invalid CD is read, the PLC does not allow the spindle to enter the machine.
To help control the accurate batch processing of baking ingredients Accusort’s RFID system monitors the filling of containers with dry ingredients (salt, sugar, flour, etc.) and makes sure the ingredients match the recipe list before mixing and baking. Each dry ingredient station holds four containers, and each container a different ingredient. To track the containers, adhesive RFID tags are applied to each container with a blank ingredient label placed over the tag. Each container labeled with an RFID tag is placed in a vibrating dry-ingredient delivery tray, and the RFID system reads the container’s contents. Fifty trays are designated for only a particular ingredient. A reader antenna is located in the back of the tray and is connected to the reader through a 6-ft cable. The reader transmits container data to a PC, and the PLC/PC determines if the correct container is placed in the tray before any ingredients are loaded.
At a plant in Colorado, customer uses Accusort’s RFID technology to track conveyor trays transporting photo-sensitive materials for processing in total darkness. The challenge was to retrofit the existing 0.25-in. thick aluminum conveyor trays with the reusable read/write RFID tags. Since the trays were solid aluminum, placing the tags directly on the metal would kill the signal, and nothing could protrude from the bottom of the tray. A 3- in. hole was drilled through the center of the plate, and a non-metallic PVC tag spacer was fabricated to hold the 13.56 MHz tags inplace. This enabled the readers, located between the rollers on the conveyor system, to sense the tags with no loss of signal. The RFID system readers—coupled to a PLC via DeviceNet—track the products throughout the process, and provide updated information to process engineers.
Reduces Equipment Failure
RFID tags from Northern Apex (www.northernapex-rfid.com) are being used by a solids imaging machine vendor to verify that its customers purchase the right thermopolymer for their machines. According to Northern Apex’s product manager, Rick Rayber, the tags help the imaging machine vendor reduce equipment failures caused by customers using the wrong polymer. The tags also reduce bogus warranty claims, which saves money as well.. It’s a little analogous to buying an inkjet printer and using those "cheap" non-OEM inks, which often voids the manufacturer’s warranty. Only in this case, while a good photo-quality printer may cost around $200, solids imaging machines sell in $750,000+ range.
So, in process automation, if you handle multiple-ingredient batches, you must adhere to CFR21 Part 11 record keeping practices, or need a better handle on quality control, it looks like RFID is in your future.
Wayne Labs is a process automation veteran with more than 15 years engineering experience and 20 years in senior editorial positions. You can reach hime at www.waynelabs.com.