SandAlert Lite 2
nd
Edition
Page
6
The electrical signal or sensor output is converted into a digital signal by the ADC in the SandAlert
Lite. The sensor output is then processed to provide a sand impact rate (SIR) in impacts per second
(IPS).
To be counted as a sand impact the peak amplitude of the pulse must exceed the low threshold but
not exceed the high threshold. Therefore, referring to Figure 3, pulse 1 is not counted as the low
threshold > peak amplitude.
Figure 3 Sensor Output
Pulse 2 is counted as 1 sand impact, pulse 3 is not counted as the peak amplitude > high threshold
and is therefore excluded. This is to prevent high energy events, e.g. excessive pipe vibration from
being counted as sand impacts. Pulse 4 counts as 2 sand impacts as it is generated by two sand
particles impacting almost simultaneously. Pulse 5, like pulse 1 does not have sufficient energy to
be counted as the peak amplitude < low threshold.
The SandAlert Lite unit can calculate the lower threshold automatically. This is done by examining
the signal and eliminating the flow related noise in the signal, and counting the number of sand
impacts. To illustrate this, different signals under conditions of high and low flow rates, both with
and without sand impacts are shown below.
Threshold
Threshold
a - Low Flow, No Sand
b - Low Flow, With Sand
