ku-pF Apparatus
The ku-pF MP10 is a laboratory instrument for the automatic determination of any saturated hydraulic conductivity ku and the pF curve (water tension curve) in accordance with the condensation method on up to 10 soil ring samples simultaneously.
The apparatus is designed for UGT soil sample rings with 250 cm3 inner volume and 41 cm2 cross sectional area. These soil sample rings have bore holes at height intervals of 3 cm for the insertion of the tensiometers. The filled soil sample rings are set onto filter plates, saturated and sealed basally in the carrier basket for the test run. The gradient resulting from the condensation on the free ground surface is measured by two tensiometers which record the corresponding water content and the flow rate by periodic weighing.
Air bubbles are easy to recognise and eliminate through the acrylic head with bleed screw. The star shaped carrier, which rotates at the set test interval, permits the examination of 10 samples simultaneously. The sample at the weighing position is lifted from the carrier by the scales such that it is standing free. The weighing data and the tensions are stored on the internal data logger. This automatic measuring produces a continuous measurement series with a minimum of monitoring. The scales are automatically zero balanced between weighings. Drift effects or any foreign bodies on the scales do not cause any interference.
The ku-pF apparatus works independently of a PC due to the integrated data logger and a microcomputer. A computer must only be connected for maintenance, test start and reading data.
Microcomputer aided basic device for 10 soil sample rings consisting of:
– Measuring station for weighing and tensiometer testing
– Datalogger with RS-232 interface and controller unit
– 10 sample rings (250 cm3), 10 sample holders
– 20 electronic tensiometers with pressure transducer
– 1 drill device for tensiometer installation
PROCESS RELEVANT MEASURING TARGETS
– Determination of unsaturated hydraulic conductivity (ku) as function of water content and tension
– Determination of pF-curve
– Recording of the gradient of water movement and flow rate
PC-Software for data logger communication, calibration, trial start and storage of measuring data in tabulated files (ASCII-Files) and analysis of measured data.
The ku-pF Apparatus for measuring the hydraulic conductivity (ku) and the pF curve of soil samples in the unsaturated range is based on a measuring principle according to WIND (1980). For this, soil samples get fully saturated in the sample ring and then sealed at the base. The free surface is exposed to evaporation, and the gradient of the resulting water movement is recorded with a data logger. Using the ku-pF Apparatus, up to ten soil samples can be analysed simultaneously. For this, the sample rings are put onto a star-shaped sample changer and put periodically, with a suitable time interval, onto a scale. Water movement, i.e. the amount of water which per time interval passes through the sample surface, gets weighed, and the gradient of water tension is measured in each sample ring by two tensiometers spaced at a distance of 3 cm.
The tensiometer values are recorded with the time pulse of weighing. An integrated control computer is used for experiment control and primary data logging.
| Sample ring volume | 250 cm3 |
| Cross-sectional area of sample ring | 41 cm2 |
| Number of samples | 1 – 10 |
| Measuring interval per sample | 10 – 40 min |
| Weighing resolution | 0.01g |
| Tension range | 0 – approx. 90 kPa |
| Weight of apparatus | approx. 40 kg |
| Size (L x W x H) | approx. 100x70x40 cm |
| Power consumption | 230V / 1A |
| PC connection | serial interface (115200 Baud) |
| Measuring position of tensiometer | at weighing position |
| Memory | 210 to 840 days |
| Measurement Principle | Evaporation method |
ku-pF Single Place |
ku-pF Multi Place |
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| The ku-pF SP measures one sample at a time, measurement is completely automated. | The ku-pF MP10 measures up to 10 samples at the same time. Measurements are completely automated. Depending on sample homogeneity, 6 to 12 samples are necessary |
| Corresponding Systems | |
| Hood Permeameter according to HARTGE, and Soil LT. Samples can be used in a saturated state without changes. Soil LT can be used to determine surface area and volume change caused by shrinking during drying through the use of laser triangulation. |
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| Who needs which system? | |
| Intermittent use | Large numbers of samples, regular use |
| Bachelor/Master studies, lectures | Soil labs, scientific use |
| Small budget | Medium budget |