How Can We Use Passive RFID to Achieve High Inventory Accuracy in Our Warehouse?


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Ask The ExpertsCategory: QuestionsHow Can We Use Passive RFID to Achieve High Inventory Accuracy in Our Warehouse?
James Maxwell asked 2 years ago

I work in the military, where we effectively employ passive RFID, currently on a large portion of our equipment at some of our logistics bases. The technology has been a game-changer for accountability and auditability. However, we want to expand its use for our smaller "eaches," which leads me to my question. I offer the following background:

We have a large volume of inventory in various packaging/storage/racking configurations in warehouses. Some are on open pallets, while others are inside tri-walls, collapsible containers, etc. Some items also have their own metal cases (which I believe is the challenge). Much of this inventory is static, for reasons I won't get into. While I know we can easily use passive RFID to keep track of our container/pallet locations, I'm more interested in whether or not we can employ the technology to track what is inside those locations to help with inventory accuracy.

The goal is as follows: I have 148 widgets in a container. Remove three, and the warehouse clerk fails to update the WMS record. But a same-day pass by that location with the RFID reader identifies the imbalance and brings it to management's attention for appropriate action.  Does passive RFID technology exist to support this? What would be the limitations, if any? And what the effective range be (i.e., 15 feet up on a high row, two pallets deep)?


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Whether or not you could use passive UHF RFID to achieve high levels of inventory accuracy in the warehouse would depend on the nature of the items being tracked and how densely packed they were. Let's address pallets and plastic containers first.

If the items on the pallets and in the containers were RF-friendly, you would likely be able to read all of them and determine that, say, two items had been removed. However, if the items were made of dense material or metal, then you would not be able to read all the items, particularly those at the center of pallets or containers. Since you only need to know if an item is removed, it might be possible to write a software application that would compare the past inventory taken with RFID to the current inventory, enabling you to determine what's missing.

Let's say you were to read the top nine bags of concrete mix on a pallet. The next time you took inventory with RFID, there would be five tags read from the top row and four from the second row, and you would know four were taken from the top. This would not be ideal, since the system could infer items had been taken when they weren't, but it would get you closer to the current inventory level. Metal containers would pose a challenge, and there would be no way to read their entire contents. But if you could open each container and read the top items only, then the above approach could work.

Another option might be to require folks to walk through a portal with the items removed from inventory. It would depend on the operations of your warehouse, and on whether creating portals and requiring people to walk through them would be too disruptive. But if the tags were read when the items were removed, then inventory could be decremented automatically.

I would recommend you consider attending RFID Journal LIVE! 2022, which will take place on May 17-18 in Las Vegas. There will be companies at the conference that will be able to help you design a solution. Bring photos of the containers and pallets to show them what you are trying to achieve.

Mark Roberti
Founder and Editor
RFID Journal


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