Voyantic

Maximizing Tagformance lite Measurement Accuracy with Warm Up

Application Note

Published 12/2014
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1 Introduction

When planning measurements with the Tagformance measurement system, there are several important factors to consider for maximizing the accuracy of the measurement results: how to set up a proper measurement environment where the effects of the reflections and other radio transmitters are minimized; and how to create a proper measurement setup where the path loss and frequency dependent antenna gain are taken into account. Also, for example the measurement distance, the antenna - tag alignment and the measurement unit temperature are possible reasons for uncertainty.

This application note describes how the unit’s temperature effects the Tagformance measurements and how to maximize the measurement accuracy with proper warm up.

2 Temperature and Tagformance lite Measurement Results

The Tagformance measurement unit generates heat when the carrier is on. The measurement device temperature has an effect on the measurement results, but the impact on the system level accuracy is within the technical specifications. Using the Voyantic Wideband Reference Tag as the Device Under Test (DUT), the difference between a cool unit and a hot unit can be up to 1dBm on Transmitted power and Tag sensitivity or 0.5 meter in read range. As can be seen on Figure 1, the difference is practically constant across the 800-1000 MHz frequency band. Therefore, the measurement accuracy is improved by taking the temperature into account while preparing for a test sequence.

The results presented in this application note are measured with a Tagformance unit in three different temperatures. Cool unit is the device immediately after power on in room temperature after the unit had been switched off over the weekend. Warm unit represents the measurement unit in a typical temperature level when measurements are performed – to reach this temperature level a Threshold Sweep is made once per 2 minutes over long period of time. Hot unit is the maximum temperature after running tests continuously for several hours. It is not typical to have unit running this hot.

Figure 1. Temperature effect on transmitted power
Figure 2. Temperature effect on theoretical read range forward

3 Maximizing Measurement Accuracy with Warm Up

To maximize the measurement accuracy, the device should be warmed up. Especially if the “Measure Path Loss” -routine is used to configure the measurement setup, it is important to run this routine approximately at the same device temperature with the final measurements. In a typical situation, a 10 minute warm-up time should be used, as suggested in the user manual. This is the time required to get the unit “warm” to typical level when tags are measured one after another.

If an extensive measurement run is planned and the unit is expected to heat up more, a longer warm-up time may be needed.

There are different ways to warm up the unit depending on the available license options:

  • Run Threshold Sweeps one after another for 10 minutes
  • Start Response Test with constant power of 20dBm and switch on the carrier for 10 minutes
  • Start Protocol Testing Suite and switch on the carrier using 20dBm transmit power for 10 minutes
  • Start Population Editor and search population using 20dBm transmit power for 10 minutes
  • Create and run a script which runs e.g. Threshold Sweeps one after another for 10 minutes.