Mace HVFlo XCi, Product Manual

Page: 165 / 255

"Depth" - channel type
This channel type MUST be used whenever the resultant depth measurement will be used in a flow rate
calculation. It MUST be used whenever a MACE Doppler ultrasonic sensor is used to measure depth.
So, what are "Slope" and "Offset"?
Most environmental sensors have a linear relationship between the measuring range and the electrical output
range of the sensor.
For a depth sensor this relationship can easily be described using the well known equation of a straight line
Y
= mX + B
Where:
l
Y = Depth
l
m = Slope
l
X
= Sensor output
l
B
= Offset
Or in other words:
Depth = Slope x (Sensor output) + Offset
Where:
l
Depth = measured value
l
Slope = Sensor measuring range / Span (difference between the sensor output at the top of the
measured range and the sensor output at zero)
l
x = Sensor raw value output
l
Offset
= - (Slope X Sensor output at zero)
For example, a typical ceramic depth sensor incorporated into the MACE Area/Velocity sensor, has a sensing
range of 4 metres and a frequency output range of approx. 1.5 kHz to 14.5 kHz. Therefore:
l
Sensor measuring range = 4 metres
l
Sensor span = 14.5 kHz - 1.5 kHz = 13 kHz
l
Slope = 4/13 = 0.30769
l
Offset = -(0.30769 X 1.5) = - 0.46154
l
The final equation - Depth = 0.30769X - 0.46154
Or. for a graphical representation of this equation:
MACE XCi User Manual - 165 -