Sensor Integration and Material Calibration
Configuration and Calibration Guide HD0679 Rev 1.2.0 31
3 SSD Coefficient and SSD Moisture Content
In practice it is only possible to obtain oven dried moisture (total moisture) values for calibration.
If the surface moisture content (free moisture) is required the Saturated Surface Dry (SSD)
coefficient must be used. In some industries SSD is also known as the Water Absorption Value
(WAV).
Absorbed
moisture
+ Free moisture
= Total moisture
The SSD coefficient used in Hydronix procedures and equipment is the Saturated Surface Dry
offset, which is the water adsorption value of the material. The SSD value can be determined
using industry standard procedures or obtained from the material supplier.
The surface moisture content refers
only
to the moisture on the surface of the aggregate, i.e. the
‘free water’. In certain applications such as concrete production only this surface water is used in
the process, which is why it is this value that is generally referred to in concrete mix designs
Oven dried
moisture %
(Total)
- water adsorption value %
(SSD offset in the sensor)
=
surface moisture %
(free moisture)
4 Storing Calibration Data
There are two ways of storing the calibration data, either in the control system or in the sensor.
Both methods are shown below.
Calibration inside the sensor will involve updating the coefficient values using the digital RS485
interface. A value that is directly proportional to moisture will then be output by the sensor. To
communicate using the RS485 interface, Hydronix have a number of PC utilities, most notably
Hydro-Com which contains a dedicated material calibration page.
To calibrate outside of the sensor, the control system will require its own calibration function and
the moisture conversion can then be calculated using the linear Unscaled output from the sensor.
For guidance on setting the output see Figure 2.
4.1
Calibration inside the Sensor
Figure 16: Calibration inside the Sensor
Summary of Contents for Hydro-Mix
Page 4: ...4 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 6: ...6 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 8: ...8 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 10: ...10 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 14: ...Chapter 1 Introduction 14 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 28: ...Chapter 2 Configuration 28 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 42: ...Chapter 4 Best Practices 42 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 48: ...Chapter 5 Sensor Diagnostics 48 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
Page 52: ...Appendix A Document Cross Reference 52 Configuration and Calibration Guide HD0679 Rev 1 2 0 ...
