We seek a solution for container yard management in real time. We need to be able to determine the exact location of a container in the yard, which covers 65,000 square meters [700,000 square feet]. We move around 250 to 300 containers per day, and capacity is for 2,000 containers. All containers are kept in stacks of four.
We plan to use passive ultrahigh-frequency (UHF) tags. The readers will have GPS/GPRS capabilities, and we plan to affix them to the crane shafts, so that when a crane moves to pick up a particular container, it will read that container’s tag information and send that data, as well as reader location (determined via GPS) to the server. GPS will be used for mapping.
My question is this: Will noise and vibration from the crane affect the UHF reader’s performance? We cannot fix poles in the yard to mount readers and collect the data, due to the cranes’ movement, and we do not want to use an active solution, due to high price. Is our approach to using UHF a viable alternative solution?
—Jignesh
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Dear Jignesh,
To answer your question about whether vibration from the crane would interfere with the UHF system, I reached out to the experts at Motorola. Mike Koch responded: “I don’t see any reason why Gen 2 would not work in the application, and do not see vibration as affecting the reader-to-tag communication. The real question would be whether the chosen reader that is mounted to the crane can survive the harsh environment.”
Another question might be whether GPS will be accurate enough for your needs. I’m no expert, but as I understand the technology, GPS accuracy is affected by a number of factors, including the position of the satellites being communicated with, any interference with the receiver-to-satellite communication, and atmospheric conditions. This can create errors of up to 10 meters (33 feet), and sometimes up to 30 meters (99 feet).
If that is not precise enough, or if the GPS fees are too high, an alternative would be to embed tags in the ground at key locations, and to mount readers under the cranes. When the crane passes over a tag, its location is communicated to a back-end system, which links that location with the ID number of the container being lifted. But, as Mike Koch says, the key might be to encase the interrogator in a box that enables it to survive harsh conditions.
—Mark Roberti, Editor, RFID Journal