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The Elimination of Zero & Cal from Power Sensor Measurements
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.
of Zero & Cal from Power Sensor Measurements
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.
Posted December 18, 2013
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