Measurement load and data precision
by
Atle Lohrmann
—
last modified
Mar 21, 2005 10:31 AM
| Quote |
| I want to measure puv data at 1Hz continuously for at least one week (before running out of battery/memory). What is the effect of decreasing the measurement load on the data? |
The effect is two-fold. By increasing the measurement load, the precision in the velocity measurements increase, but alas at the expense of battery consumption. By decreasing the measurement load it is the other way around.
The exact relationship is shown in the Advanced tab in the Deployment planning menu. Just try and vary the measurement load, click on Apply and watch the change in the Battery utilization (for a specified assumed measurement duration) and the velocity precision. As you will see this is a trade-off between need for precision and need for duration.
A 100% measurement load means that the instrument pings as fast as it is able to. Consequently, a measurement load of 50% means that the instrument pings at half that rate.
From signal theory we know that the more pings there are within an averaging period, the better the estimate of the true value we're measuring will get.
A high ping rate will thus reduce the standard deviation, (which is called Precision in the Deployment planning menu).
To illustrate what we are talking about, consider the below list which provides the maximum internal sampling rate of some of our instruments:
Aquadopp profiler
2 MHz:23 Hz
1 MHz: 7 Hz
0.6 MHz: 4Hz
AWAC
1 MHz: 7 Hz
0.6 MHz: 4Hz
Continental
470 kHz: 5 Hz
190 kHz: 2 Hz
Gustav
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As a follow questions to Gustav's post on measurement load and battery utilization, what type of battery does the battery utilization function assume you are using, i.e. small internal alkaline - internal lithium - external large alkaline pack? Also, does the battery utilization function assume the battery is new at the time of programming? and if so are there any ways of estimating battery life through the battery utilization function if the battery is not new, especially the lithium type since they generally do not show a drop in voltage after being used?
Current state:
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Dear ccimaglia,
The assumed type of battery is the one that is supplied with the instrument. Its total watthour [Wh] capacity is listed in the Deployment planning menu of the setup program that comes with your Nortek instrument.
The program assumes that your battery is fully charged and that it behaves like a new battery.
The simplest way of estimating what's left in the battery is to examine your previous setup(s) and the deployment time(s) elapsed. What's left should then be 100% minus the percentage already spent. Other ways of doing this will easily get complicated without yielding much more accuracy than you get by this simple method.
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- gustav
The assumed type of battery is the one that is supplied with the instrument. Its total watthour [Wh] capacity is listed in the Deployment planning menu of the setup program that comes with your Nortek instrument.
The program assumes that your battery is fully charged and that it behaves like a new battery.
The simplest way of estimating what's left in the battery is to examine your previous setup(s) and the deployment time(s) elapsed. What's left should then be 100% minus the percentage already spent. Other ways of doing this will easily get complicated without yielding much more accuracy than you get by this simple method.
" />'> - gustav
Current state:
Being created
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