Durable Asset Tag Test with GPS enabled Handheld RFID Reader

Last Updated on Monday, 28 March 2011 21:52

Maximum Read Range Outdoors with a GPS enabled Handheld RFID Reader

Test Overview and Configuration

The purpose of these tests is to determine the maximum distance an RFID tag can be read using a GPS enabled handheld RFID reader in an outdoor environment. This is the most practical method of locating and inventorying assets in industrial, construction, shipping, or yard environments. By capturing the GPS location of the tag and sending that information via a GSM/GPRS cellular connection, real time asset visibility in remote locations is possible.

During the tests the environmental conditions measured a temperature of 75.9°F (26°C) with a humidity of 32 percent.

For these tests, we used a Convergence Systems Limited CS101 handheld reader (pictured right). Additionally, our team attached a CS501 add-on module that adds quad-band GSM/GPRS cellular communication and global positioning technology (GPS) to the hand-held. This plug-in enables the CS101 handheld reader to capture the GPS location of RFID tag reads in outdoor environments and then send the data using the same technology as a mobile phone.

Our CS101 has a linear polarized antenna which provides longer read range than a circular polarized antenna, but is more orientation sensitive. If the tags are not in the optimum orientation, the handheld must be rotated up to 90 degrees in one direction or the other to achieve maximum read range.

Handheld RFID Reader Configuration

Our team used three different CS101 handhelds, all certified for US FCC, during the tests. For each handheld:

The firmware was the latest available as of date of testing;
The CS101 comes pre-installed with applications for tag reading, tag ranging, and tag inventory, which we used for these benchmarks;
The transmit power was set to the maximum of 1W (30dBm);
During the test, we did not let the battery charge go below 25% without replacing it with a fully charged battery.

In the first set of tests, our team used a section of steel that is similar to a durable goods part or raw material. The tag is mounted in the center and slightly inset (see photo, right). This may negatively impact performance but this placement helps prevent the tag from being damaged or ripped off as an item moves and is common in real-world implementations. Although we did not bolt the tags in place, this is a good example of when it is appropriate to do so.

In our second set of tests, we mounted the tags on a shipping container. We positioned our RFID enabled handheld reader at a distance outside the read zone. We then started the tag search function and slowly moved towards the tag. Once three (3) seconds of continuous tag read was achieved, we recorded the distance.

For each distance measurement, we performed three trials, each trial using multiple tags, and did this with each of our handhelds. That’s over 150 different tests.

While reading the tags, we used the CS501 module to capture our GPS location. Once we finished a trial, we sent the location information to a PC via a GSM/GPRS cellular connection.

The average of all recorded measurements is presented in the results below.

Frequently Asked Questions:

Q: Should we use a linear or circular polarized antenna?

A: In the real world, when you are looking for an RFID tagged item, you’re going to move your handheld reader around to try to find what it is you’re looking for. In most cases, it is better to have directional reads because it provides a longer read range. Typically, handhelds are used in applications with stacked items so orientation is known. For example, file folders are all stacked properly with the tags in the same orientation. Ultimately, always carefully consider your use-cases before choosing an antenna type.

Q: How do you accurately measure the RFID read distances?

A: When measuring the distance between the reader antenna and a tag, our team uses professional-grade laser distance measures (pictured right). This allows us to align the front of the meter directly next to the reader antenna, place the laser dot on the face of the tag and with the press of a button, we have an accurate distance measure with a precision of 1/16". It also accounts for angles and open spaces between the reader and the tag that a standard tape measure cannot. Plus, the range of the distance meter is up to 195 ft.