Filtering The Signal When Used In A Mixer Application; Figure 6: Typical Moisture Curve; Figure 7: Graph Showing Raw Signal During Mix Cycle - Hydronix Hydro-Probe Configuration And Calibration Manual

Chapter 2

7 Filtering the Signal When Used in a Mixer Application

Due to high levels of noise caused by the mixer blades, the signal will require a certain amount of
filtering to make it usable for moisture control. The default settings are suitable for most
applications however they can be customised if required.
It is not possible to have default filtering settings that are ideally suited to all mixers because
every mixer has a different mixing action. The ideal filter is one that provides a smooth output
with a rapid response.
Figure 6 is a typical moisture curve during a batching cycle of concrete. The mixer starts empty
and as soon as material is loaded, the output rises to a stable value, Point A. Water is then
added and the signal rises and stabilises at Point B. The batch is completed and the material is
discharged. Stability in the readings at points A and B signify that all of the ingredients within the
mixer are homogenously mixed together.
The degree of stability at points A and B can have a significant effect on accuracy and
repeatability. Most automatic water controllers measure the dry moisture and calculate how
much water to add to the mix based on a known final reference in a particular recipe. It is vital to
have a stable signal in the dry mix phase of the cycle at point A. This enables the water
controller to take a representative reading and make an accurate calculation of the water
required to be added. For the same reasons, stability at the wet end of the mix (Point B) will give
a representative final reference indicating a good mix when calibrating a recipe.
Figure 7, shows the Raw Unscaled data recorded from a sensor over an actual mix cycle, clearly
indicating the large peaks and troughs caused by the mixing blade action.

Figure 7: Graph showing Raw Signal during Mix Cycle

22 Configuration and Calibration Guide HD0679 Rev 1.2.0
Dry
mixing
time
Mixer
loaded
with
material
A

Figure 6: Typical Moisture Curve

Wet mixing
Water
time
Addition
B
Raw Signal
Configuration
Mixer
discharge
Time
Time(s)