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Enabling better global research outcomes in soil, plant & environmental monitoring.

Hukseflux CRC series

Calibration reference cylinders for thermal needle probes TP02/TP08, TP07 and TP09.

CRC’s contain traceable thermal conductivity reference materials for calibration of Non-Steady-State Probes. There are several different CRC types. The geometry of the different types is adapted to fit needles with a certain diameter.


The heart of the CRC cylinder is a specially manufactured amorphous plastic reference material (5). (See Figure 1). Contrary to other plastics, this material does not have any directionally dependent thermal properties. In the plastic material a hole is drilled (4), with the approximate outer dimensions (ND Needle Diameter and IL Insertion Length) of the needle that needs to be calibrated. The plastic material is incorporated in a metal protection casing (2). A plug (7) is provided for sealing purposes. In order to guarantee perfect contact between needle (1) and reference material (5), the metal casing is filled with a fluid, glycerol (3). An additional hole (6) is provided in order to be able to perform checks of material stability with thin needle probes. The user is recommended to send the CRC to Hukseflux for a check of material stability every 5 years.


Figure 1: Generalised overview of CRC calibration reference cylinder

Hukseflux is a leading supplier of Non-Steady-State Probes, and is the inventor of the CRC calibration method.

NOTE: As a low-cost (lower accuracy) alternative reference material Hukseflux promotes use of glycerol filled with plastic fibre material. This is delivered as a standard with most Hukseflux systems.

Table 1: CRC cylinder types and their application
Type Dimensions Suitability for needle types
CRC01 H = 260
D = 100
IL = 185 – 30
ND = 1.6
TP02, TP08
CRC04 H = 206
D = 100
IL = 137 – 6
ND = 3.6
CRC05 H = 260
D = 100
IL = 190 – 12
ND = 6.6
Test method ASTM D 5334-00 and D 5930-9, IEEE Std 442-1981
Temperature range 0 – 60°C
Thermal conductivity of reference 0.2 W/mK (nominal value)
Traceability to NPL National Physical Laboratory, United Kingdom