The GT series guiding tubes are accessories for Non-Steady-State Needle probes. They are intended to facilitate measurements in hard soils, concrete, cement and bentonite. Also in case of measurements on large quantities of samples one can use several guiding tubes and one single needle.
Non-Steady-State Probes are used to determine the thermal conductivity of the surrounding medium. The method can applied in various substances such as sludges, fluids, foodstuff. The most frequent application however is in soils. A recurring problem is that insertion into hard soils, bentonites and cements is quite difficult. The main problem is that it is quite difficult to insert needles into these hard materials. The use of guiding tubes in many cases can solve this problem; The guiding tube should be inserted into the medium, and the needle can be inserted at a later stage.
Hukseflux is a leading supplier of Non-Steady-State Probes, and is the inventor of this guiding tube technology.
In case of bentonites and cement the guiding tubes are cast into the material and experiments can be carried out later. In case of hard soils, a typical approach is to pre-drill a hole, insert the guiding tube, compact the soil again, and perform a measurement. In case of dryout experiments guiding tubes are inserted into the samples, dryout can then take place at high temperature (the needle is not inserted).
It has been verified that the addition of a guiding tube does not have a significant impact on the measurement accuracy; when inserting a needle to a guiding tube, essentially a larger diameter needle is created. This results in a larger transient time; one has to wait longer before the desired linear behaviour (of temperature versus the logarithm of time) is occurring. This is normal behaviour for thicker needles. In case it is possible, it is recommended to add a small quantity of glycerol into the guiding tube (before inserting the needle) to minimise the contact resistance. This improves the repeatability of the measurement. One should however be careful not to pollute the soil with the glycerol.
TP08 can be obtained as a separate probe for incorporation in the user’s measurement and control system. It is suitable for operation with the Campbell Scientific CR10X.
|Test method||ASTM D 5334-00 and D 5930-9, IEEE Std 442-1981|
|Delivery||sets of 5 tubes, including caps|
|Protection tube with cap||IP 67|
|Type||Dimensions||Suitability for needle types|
|GT01||L = 90
OD = 2
|GT02||L = 170
OD = 2.38
|GT03||L = 150
OD = 4.50