What do I need to check if data stops recording during a measurement?
Check the cable connection to the USB port. Change the energy management of your computer to Continuous Operation (which is standard when using a laptop). If using a USB hub, make sure it is properly powered.
What might be an explanation for this behavior of the pressure curves?
It could be that the tensiometer shafts are not screwed in tightly enough.
How do expansive soils impact the HYPROP measurement process?
In expansive soils, the water content/water potential relationship has to be interpreted as the amount of water per mass of soil. To convert it to a volumetric retention curve, you can either act on the assumption of a constant volume (which happens during the integrated HYPROP evaluation and is wrong, in this case) or convert it in volumetric water content by knowing the shrinking characteristic. There are three aspects to this conversion:
If the formation of gaps due to shrinkage is large, the retention curve should be interpreted in relation to gravimetric water content rather than volumetric water content
The second aspect concerns the position of the tensiometer ceramics, as they could no longer be positioned symmetrically in the soil sample. This also causes an error, especially when calculating the conductivity values. The error from calculating the retention data is less serious.
The third aspect is the problem of water vapor, which escapes laterally from the gaps. This also will cause an error (especially when calculating the conductivity) as this acts on the assumption that the total water loss from the lower half of the sample happens only in a vertical direction.
Can two HYPROPs be degassed at the same time using the refill unit?
Yes, more than one HYPROP can be degassed at the same time. Though the instruments are designed to use one vacuum pump with one vacuum mount and one beaker mount for one HYPROP and four tensiometer shafts, there is no problem to connect more devices by using another tube, as long as the system is tight. You can check this using a manometer.
The scale is turned on and connected to the software, but it is marked grey and "not available." What can be the problem?
The scale may be measuring with an unsupported unit. With HYPROP balances it can only be measured in grams, because measuring in other units is not supported by the HYPROP-VIEW Software. You can fix this issue by pressing the “function” button. Please be sure that the following settings are set right, especially the last one (number 7). This should say F. 1.
Using single balance mode, the weighing screen pops up continuously even though the HYPROP is connected. Why?
The software could be assuming that the HYPROP is not connected. Please check the connection of HYPROP to the tensioLINK adapter to ensure it is not loose or malfunctioning.
Why does the scale not record the weight during the measurement?
There are three possible explanations for this issue:
The scale is not switched on. Because of this, the scale will be detected by the software but cannot log any data. You will know that the scale is switched on when the weight appears on its display.
The scale is being used in a wrong mode and therefore cannot log the weight.
One balance for many HYPROPs: No automatic measurement of the weight is possible. The weight changes have to be taken manually (see manual).
One balance per HYPROP: The weight changes will be recorded automatically. Weights cannot be taken manually.
The default settings on the scales were changed. Check to ensure that the scale settings match the defined settings shown in the user manual (see section “Preparing a Measurement” under “Default Settings”).
How can a typical HYPROP measuring curve of pure fine and middle sand (Ss) be described?
The following measuring curve is typical for sand with narrow particle size distribution and without fines:
The tensions rise immediately and spontaneously after the start of the measurement until they reach a level that corresponds to the air entry point.
The tensiometer shafts run completely parallel for a long time and differ only around a hydrostatic pressure difference of 2.5 hPa.
After draining the main pore portion, the tensiometer shaft value of the upper tensiometer shaft rises extremely steep. The dropping out of the tensiometer shaft is now very quick.
At the end of the measurement, the lower tensiometer shaft is still completely unaffected by the extreme dehydration front, and the difference of water tensions is very high.
Hydraulic conductivities can be calculated only for a short period of time.
The measurement is completed due to the dropout of the upper tensiometer shaft after a water loss of approximately 35 percent.
How can a typical HYPROP measuring curve of slightly loamy sand (Sl2) be described?
The measuring curve of S12 can be described with the following parameters:
The tensions rise immediately after the start of measurement until the level of the air entry point is reached.
A soft jerking at the beginning of the measurement can be an indication that the air enters the system sporadically, rather than uniformly. This will be reflected in the evaluation of the retention curve. The tensiometers will be performing completely parallel for a long time, with only the 2.5 hPa hydrostatic pressure difference between each other.
The upper tensiometer first rises exponentially only after the drainage of the main pore portion. The dropping out of the tensiometer follows very fast and the air entry point of the ceramic cup is reached shortly after that. The lower tensiometer is still in the regular measuring area.
The difference of the tensions is big enough for the hydraulic conductivity to be calculated only after reaching the exponential rise.
The measurement is finished with the dropping out of the upper tensiometer, after the withdrawal of nearly 30 percent of the water.
How can a typical HYPROP measuring curve of clayey silt (Ut3) be described?
The following measuring curve is typical for very fine-grained substrates:
The tensions rise immediately and spontaneously, steep and continuous after the start of the measurement. This reflects a very small coarse porosity. pF 2.0 is reached after a few hours (under evaporation conditions with fan). The water loss until the time pF 2.0 is reached is approximately 4 percent. The jerking, which occurs at the beginning of the measurement, shows the discontinuous entry of the air in the soil.
After reaching approximately 100 hPa (pF 2.0), the difference between the tensiometers (which have been parallel until this point) is big enough to determine the hydraulic conductivity.
Both tensiometers rise unabated as time progresses and drop out quite soon. The clayey silt has just a few big medium pores. The finer middle pores area is still filled with water at the time the tensiometer drops out and the water content is accordingly high.
The dispersion of the tensiometer values is moderate over the whole measurement process, which indicates a relatively high, unsaturated conductivity.
The measurement is finished when the upper tensiometer drops out after less than one day. At this point, the water loss of the sample is approximately 20 percent.
How can a typical HYPROP measuring curve of sandy clay (Ls3) be described?
The following measurement curve is typical for clay with a wide pore size distribution:
The tensions rise continuously with a moderate increase for about two days. This reflects a coarse pore portion of about 10 percent.
Both tensiometer values proceed parallel until about 50 hPa (pF 1.7). From this point on, the tensiometer values are apart enough that the hydraulic conductivity can be determined.
After about two days, the tensiometer values rise with greater increase but still weak bending. The measurement limit is reached just one day later. This indicates a limited and simultaneously diversified middle pore portion.
The dispersion of the tensiometer values is moderate, which indicates a relatively high hydraulic conductivity in this area. In this case, the measurement is finished when the upper tensiometer drops out (after about three days). At this point, the water loss of the sample is approximately 17 percent.
What if my HYPROP shows a constant value of 4000 hPa (400 kPa)?
If your HYPROP shows a constant value of 4000 hPa (400 kPa), the pressure sensor is damaged. Please contact METER Group support or your local dealer to send the device in for checking and repair. We will repair it fast and with cost-efficiency.