5 Meter Characterization
Meter characterization comprises standard deviation, zero flow drift, and flow testing.
5.1 Single Shot Standard Deviation
The standard deviation in dToF (and volume) is often used as a measure for the accuracy with which flow
measurements can be made. Although it is possible to average across several measurements, the amount of
time and power required to do this may not meet application requirements.
Standard deviation testing is typically conducted at room temperature over a period of 30 minutes with a
1 measurement per second rate to ensure a statistically valid average. The standard deviation is reported with
the mean in the "Waveform Tab" of the GUI.
shows the single-shot STD of blocks of 200
measurements. Each plot represents single-shot STD of 200 measurements. The plot clearly shows the variation
of single-shot STD is just ± 2 ps, and the average is < 25 ps.
Figure 5-1. Single Shot Standard Deviation
5.2 Zero Flow Drift Testing
Zero flow drift testing is often used as a measure of the minimum detectable flow of a meter and accuracy in low
flow. The minimum detectable flow of a meter is related to the zero flow drift and the sensitivity of the meter. A
meter with higher sensitivity and lower zero flow drift will have a smaller minimum detectable flow. The minimum
detectable flow is limited by the drift in dToF over temperature. This test is typically conducted in an oven with a
temperature profile ranging from 5°C to 85°C over a period of 4 to 24 hours, depending on the robustness of the
test. These tests are conducted with both the meter and electronics in the oven as well as with just the meter in
the oven to ensure the electronics do not contribute to the drift. More detailed information on zero flow drift
testing can be found in the
Ultrasonic Sensing Metrology Subsystem Reference Design for Water Flow
Meter Characterization
16
Water Flow Meter
SLAU810B – SEPTEMBER 2019 – REVISED SEPTEMBER 2020
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