The Elimination of Zero & Cal from Power Sensor Measurements

LadyBug Technologies

Orwill Hawkins, of LadyBug Technologies, submitted this short note on the advantages of modern power sensor circuit techniques for eliminating the need for internal zeroing & calibration. Sophisticated factory calibration and a smart sensor allows fully qualified operation across all rated power and temperature ranges.

The Elimination of Zero & Cal from Power Sensor Measurements

With almost all electronic devices, temperature impacts performance. This is particularly critical when the device is part of a measuring instrument. To be useful, RF & mW power sensors need to provide accurate power measurements across broad frequency ranges and power levels. However, power sensor measurement accuracy has always been very susceptible to minor variations in temperature. These errors are mitigated by requiring the user to manually zero and calibrate the sensor before use. This process hasn't changed in over 50 years. It must be performed any time ambient temperature changes by just a few degrees centigrade.

The zero & calibration (cal) process for traditional power sensors involves disconnection from the test system measurement point or device under test and connection to an external calibration source. Newer sensors that have an internal zero & cal capability and don't require an external calibration source are much more convenient but will still exhibit sensitivity to temperature. The internal zero & cal is periodically and automatically performed but not for each measurement. Additionally, the ability of a power sensor to adapt to changes in temperature is limited to how rigorous of a factory calibration was performed and the ability of the sensor to accurately know its operating temperature.

This obsolete process makes conventional power sensors unusable for a variety of critical applications. These would include embedding power sensors in an operational system or a rack of test equipment to monitor critical test points. It also includes applications a where a sensor is used remotely in what may be a harsh environment. In general, it would include any situation that requires a constant stream of unattended measurements over an extended time period.

Most USB power sensors require an internal zeroing & calibration periodically. The line of USB sensors from Lady Bug Technologies has made the internal zero & cal processes obsolete with the ability to make highly accurate measurements without the need for zero & cal. They undergo the most rigorous factory calibration in the industry including a calibration across the full operational temperature range. Then during use, the sensor measures the temperature for each power reading, employing a patented technique to ensure that the correct factory temperature calibration factor is always applied to each measurement.

LadyBug Technologies

Posted  December 18, 2013