CHAPTER 4 COLLECT
4-6
never stops swaying, the Dipstick will only be able to collect data very slowly, and only at those
instances when the structure stops and changes direction.
Under these circumstances, you'll want to use the “Averaging” mode of data collection. You
select the number of internal readings to average (either 2, 4, or 8) and you select the “allowable
difference,” and the Dipstick does the rest. By doing this, the Dipstick will “damp out” the
vibrations or swaying.
Here's how “Averaging” works:
The Dipstick collects a series of “internal readings” and holds them in its internal memory. It does
this very quickly, many times per second. Then it averages these readings to get a “mean” or
“average” value. It then checks to see how far each of the internal readings is from the mean or
average. If all the readings are close to the average, it knows that this is a valid reading and stores
it in memory, then Beeps to let you know it is time to turn the Dipstick and collect another reading.
If any one of the 2, 4, or 8 readings is farther from the average than the “allowable difference” you
specify, the Dipstick knows that the average may be skewed by the “bad” reading, and discards it.
The Dipstick discards only the “bad” internal reading and any internal readings collected before
the “bad” reading, retaining the readings that came in after the bad one, and collects however many
readings it needs to get the 2, 4, or 8 that you have asked for. When it has collected a total of 2, 4,
or 8 readings (whatever you specified) it will re-average those readings, then check each of those
readings to see whether they are all close to the average. If they are close to the average, it saves
the average reading as the next “reading” in the Run, and Beeps again to tell you it is time to turn
the Dipstick. This all happens very very quickly. Data collected using the AVERAGING mode
have been shown to be essentially identical to the data collected using the “2 identical” mode,
particularly if you use a reasonably small number for the “allowable difference.” Similarly,
selecting a larger number of readings to average will also reduce the variability of a profile. There
is no hard and fast rule about what number of readings to average and what value of “allowable
difference” to use. It depends on how much the building or structure is swaying, and how quickly
you can get an average reading that meets the criteria you set.
We recommend that you try 0.004 as an allowable difference, averaging 4 readings. This
means that each of the four readings must be within 0.004" of the average. The worst reading can
only be 0.004" away from the average. Because it is averaging 4 readings, the reading that is
stored on the computer is likely to be within 0.0015" of the correct value, or even closer. If the
Dipstick collects data rapidly using 0.004 and 4 readings, the structure is only swaying a small
amount and this is a good setting. If the structure is moving rapidly, and the Dipstick is still slow
collecting data, try using a larger “allowable difference" and collect 4 readings. For example, try
0.008 allowable and 4 readings. If it is still slow to collect readings because the structure is
moving a lot, use a larger “allowable" value, but average more readings. You'd use 8 readings
instead of 4. If you are working on a bridge or if there is excessive vibration in the road due to
construction, averaging is probably the better way to collect data. If you are on a stable road where
sway and vibration are non-existent, then "2 identical" readings will probably be a better choice.
Number of Readings to Average
When you select the averaging mode, you must also select how many readings in a row the
Dipstick must average. You can select 2, 4, or 8 readings. You must also determine the allowable
difference in the readings. Averaging 4 readings is a good choice and is the recommended normal
setting.
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