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Measuring the accuracy of real-time clocks (RTCs) in embedded devices is essential for ensuring reliable timekeeping. This process involves comparing the device’s clock against a known reference over a specific period. Accurate measurements help identify drift and improve synchronization methods.
Preparation for Measurement
Before starting, select a stable reference clock, such as an atomic clock or a network time protocol (NTP) server. Ensure the embedded device’s environment remains constant to avoid temperature or power fluctuations affecting the results. Record the initial time from both the device and the reference.
Conducting the Test
Allow the device to run for a predetermined period, typically several hours or days, depending on the required accuracy. During this time, periodically log the device’s clock and compare it with the reference. Note any discrepancies at regular intervals.
Calculating Drift and Accuracy
After the test period, calculate the total time difference between the device’s clock and the reference. Divide this difference by the elapsed time to determine the drift rate, usually expressed in parts per million (ppm). For example, a 1-second discrepancy over 24 hours indicates a drift of approximately 11.6 ppm.
Interpreting Results
Compare the calculated drift against the device’s specifications or application requirements. If the drift exceeds acceptable limits, consider calibration, hardware improvements, or synchronization techniques like periodic updates from a reliable time source.