Returnable Asset Tracking: Measure Dwell Time and Size Your Pool

What is returnable asset tracking?

It means knowing where each reusable container is, and how long it has been there. The industry calls these units returnable transport items, or RTIs. Stainless kegs, IBC totes, steel stillages, roll cages, gas cylinders and reusable shippers all count. The same job is also called returnable packaging tracking.

How long units stay out decides how many you have to own. A unit that sits at a customer for weeks is one more unit in the pool. The Reusable Packaging Association's value calculator asks for the numbers behind that. They include units in the pool, the share lost each year, the average days one cycle takes and the shortest cycle possible.

Purchase records give you the pool, and write-offs give you the losses. Days out are harder to pin down, and where those days are spent is harder still. That is the part a tag fills in.

How returnable container tracking works with no reader on site

A tag on each unit is reported at the customer's site as well as your own, with no reader at either. It is small and needs no wiring or data plan, which matters on a keg or tote with no power of its own. It broadcasts a Bluetooth signal, and any phone that passes reports where it heard the tag. These networks are large (Apple counts over a billion iPhone, iPad and Mac devices, and Google over a billion Android devices).

Its battery lasts up to six years, depending on its size, so one tag stays on a unit for many round trips. Each report carries a place and a time. A unit's history then shows when it reached a customer and when it left.

A barcode or RFID read dates a unit only where there is a reader, which is usually your own dock. The days at the customer then hide inside the round trip. A tag is reported at the customer's site too, so the trip splits into days on the road and days on site.

How to measure dwell time at each customer site

You measure dwell time from two dates: when a unit entered a customer site and when it left. A geofence around each site logs both. Draw one around your own plant too, so the days back home count as well. The geofence guide shows how to draw one.

Read the median dwell per site, not the average. One unit held for three months pulls an average up and hides the pattern. The median shows what a normal visit to that site looks like. For pool size, use the average, because the long holds tie up units too.

Count the units that have not left yet as well. A site still holding units past its normal visit is part of the answer, even though those visits have no end date. History playback shows each unit's trips on the map, and the export and API guide covers getting the dates into a spreadsheet.

How many returnable containers does your pool need?

Your pool needs your daily dispatches multiplied by the average days of one full loop, from leaving your plant to leaving it again. That is Little's Law applied to containers. Days back at your plant for washing, filling and waiting count too, which is why the plant gets its own geofence.

Losses come on top. Each lost unit has to be bought again to keep the pool at that size. Yearly write-offs are the second number to watch.

The Reusable Packaging Association's calculator also asks for the shortest loop possible. Take the gap between the average loop and the shortest, and multiply it by your daily dispatches. The result is the units tied up beyond what the loop itself needs.

Tags show which sites hold that gap, so you know which customers to call first. Each day you take off the average loop frees one day of dispatches, and those are units you do not have to buy. Before you order more, ask for the units that have sat longest at customer sites.

How to start returnable asset tracking at the wash station

Start at the wash line, inspection bay or repair station, where every unit stops on its way back out. You do not need to tag the whole pool to measure its cycle time. A 2016 study of returnable transport items examined this in the International Journal of Production Research. Its cycle time and return rate estimates were satisfactory when not all containers were tagged.

1. Pick the customer sites you want to measure first. Cover those that take a large share of your dispatches, plus any route you already suspect.
2. Tag units at the wash or inspection station as they head out to those sites. The surface is clean there, and the unit goes straight back into circulation.
3. Record which tag sits on which unit number, so the history joins your issue and return records.
4. Draw a geofence around your plant and around each of those customer sites. Each entry and exit is then logged with a time.
5. Let the tagged units run for longer than one round trip, so most of them come back at least once.
6. Export the geofence entries and exits as a spreadsheet, join them to your issue records, and read the median dwell per site. The units still out at the end are part of the answer.

Every unit that comes back passes the same station, so the rest of the pool can be tagged there as it returns.

Demurrage and units held past the agreed days

Demurrage is a daily rental a customer pays for each returnable unit it holds. Gas cylinders are the familiar case. The University of Southern California's compressed gas terms charge it per cylinder per day. Empty cylinders keep incurring it until they are returned.

Your delivery note shows when a unit arrived. The tag shows the rest: each report while the unit stays on the customer's site, and the date it left. Open the unit's history, and each report is listed with a time. Agree with the customer beforehand that these records count, then send the dates with the invoice.

A reminder on your plant geofence flags units away longer than you chose, for holds of up to two weeks. It fires once, and resets when the unit comes back. Count the usual days in transit into that setting. For longer terms, export the geofence entries and exits, and invoice the units past the agreed days.

Where to mount a tag on a returnable container

Mount the tag on a fixed part of the unit, out of reach of forks and straps. Keep it off lids, caps and anything else that is swapped between units. On a stackable unit, keep it off the faces that touch the next unit.

Steel blocks the signal, so put the tag on an outside face. On a keg, fix it to the chime or a handle. On a gas cylinder, use the neck ring, and never drill into the shell that holds the pressure.

Units that go through a washer every trip need a mount the wash cannot loosen. Wash chemicals reach an adhesive pad first, so use the screw mount or a tie. The Standard and Extended tags are sealed to IP68, which covers rain and a dunk but not a pressure jet up close. Place the tag where the jets do not hit.

The Compact Tag is not IP rated, so keep it for totes and shippers that stay dry indoors. The asset tracking tags guide covers mounting on steel and plastic. Pallets and pallet boxes run on the same loop, and the pallet tracking guide covers them.

What to expect from tags on returnable containers

A tag gives each unit a dated trail of the sites it visits. Its updates follow people.

• Updates come from passing phones. Docks, yards and busy customer sites update through the working day. A unit in storage updates when people work near it again. A unit on a truck updates as it passes people or a busier road.
• Building-level position. Expect the right plant, depot or customer site, not the right rack. The unit number does the rest.
• Location, not condition. A tag reports where a unit is and when it came and went. Temperature, fill level and contents stay on your own records.
• Where, not who. A tag shows which site holds a unit, not who moved it there. Your issue records stay the custody record.

Once hundreds of units carry a tag, managing multiple tags as a fleet covers grouping them so the map stays readable.