Using LabVIEW and NI Hardware to Improve the Quality of RFID Tags for Tracking Fish

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"Using NI hardware and LabVIEW software, we provided a fast, reliable system that met all of the client’s functional needs."

- Tom Brass, Saint Bernard Engineering Inc.

The Challenge:
Designing a test system to rapidly sort more than 1.1 million passive integrated transponder (PIT) tags a year to ensure that only quality tags are used for tracking fish.

The Solution:
Creating a fully automated test system using LabVIEW software and an NI PXI controller, motion control, vision, signal generation, and data acquisition to sort tags based on failure criteria such as size and electrical characteristics.

Author(s):
Tom Brass - Saint Bernard Engineering Inc.

To measure the effect of habitat, harvest, hatcheries, and hydropower on the survival of fish in the Columbia River Basin, researchers inject PIT tags – a type of RFID tag – into fish to track their migration. These PIT tags are automatically read and the fish are identified as they pass through one of the many reading stations on their migration.

Due to the variable quality of tags on the market, the Pacific States Marine Fisheries Commission and the PIT TAG Information System (PITAGIS) needed an in-house automated PIT tag test system. Past tag problems included broken ferrite antennas, reduced read range, and variable performance.

The test system had to measure dimensions, evaluate electrical characteristics, perform statistical analysis, and test more than 1.1 million tags a year. To achieve this, the commission and PITAGIS needed a system with sophisticated integration of motion, vision, signal generation, and data acquisition.

Automated PIT Tag Test System

The Automated PIT Tag Test System (APTTS) is fully automated (Figure 1). It accepts PIT tags on one end and returns tags sorted by failure criteria on the other. The resulting data and report are displayed on screen (Figure 2) and also output to Microsoft Excel files.

The system measures and analyzes several tag characteristics, including the following:

• Dimensions (to 0.1 mm)

• Resonant frequency

• Nominal frequency amplitude

• Bandwidth

• Q-factor

• Turn-on voltage (reading the tag ID)

• RF modulation

• Batch weight (to 0.001 gram/tag)

We chose a PXI system for its reliability and high speed. Data is stored on the PXI controller and periodically transferred to the client PC for display and reporting.

Starting the Testing

First, the PIT tags are weighed by placing the batch of tags on a scale. After the tags have been sorted and counted, the final per-tag weight is determined.

Then, the batch of tags is placed in a vibratory bowl controlled by an analog signal. The vibratory bowl guides the tags onto a track (Figure 2). Optical sensors detect the presence of a tag at the end of the track and an actuator lets the tag down onto a carrier. The carrier moves the tag under a line-scan camera and into an antenna (Figure 3). The image from the camera (Figure 4) is analyzed to determine the height and width of the tag.

Electrical Analysis

The PIT tag responds to a specific resonant frequency by sending its identification. Figure 5 shows a portion of the response from a tag. The resonant frequency sine wave is generated by the system using an NI PXI-5421 arbitrary function generator and the response is captured with an NI PXI-5922 24-bit flexible resolution digitizer. The function generator and digitizer are triggered by a motion sensor immediately before the tag enters the antenna. Then, the PIT tag is moved to the position in the antenna where the highest amplitude signal was detected. Once it is in position, the remaining electrical tests are performed.

The resonant frequency is measured by sweeping the frequency and looking for the frequency with the highest amplitude. This data is also used to determine the bandwidth and Q-factor. The turn-on voltage is determined by incrementing the amplitude at the resonant frequency until the ID can be read successfully.

Sorting the Tags

After the electrical tests are complete, the pass bin or appropriate failure bin is moved into place. The carrier moves the tag out of the antenna and an extractor is lowered in front of the tag as it exits the antenna, forcing it off of the carrier and into the bin below. Then the carrier is returned to the start to receive a new tag.

Performance

The system needed to test one tag every 10 seconds. Depending on the testing parameters, the test time for one tag is as short as 9.6 seconds. More refined testing parameters can result in longer test times.

We tested the system using a batch of 1,000 tags. Each failure was verified and the system placed each PIT tag in the correct bin. Failures included a broken tag (Figure 7), tags that failed to respond, and tags that did not have the correct resonant frequency.

Using NI hardware and LabVIEW software, we provided a fast, reliable system that met all of the client’s functional needs.

Author Information:
Tom Brass
Saint Bernard Engineering Inc.
3570 Lexington Ave N Suite 303
Shoreview, MN 55126
United States
Tel: (651) 204-6528
tbrass@saintbernardengineering.com

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