TP-02-ATX is very often used with Campbell Scientific CR10X. A
manual on application of TP-02-ATX with CR10X is
obtainable here. For
a smaller version of TP-02-ATX, see TP-08-ATX.
Figure
1: TP-02-ATX Non-Steady-State Probe consists of a needle
with 2 thermocouple junctions (3), (4) (the tip acts as a reference) and a
heating wire, (2). It is inserted into the medium that is investigated. In the
base, (6), a temperature sensor, (1), is mounted. Advantages of this design: an
optimal accuracy independent of the medium temperature, a minimal sensitivity to
thermal gradients, a high sensor stability and the possibility to use normal
cables and connectors. All dimensions are in mm.
Introduction
The standards of the American Society for
Testing and Materials (ASTM) and Institute of Electrical and Electronics
Engineers (IEEE) describe proven methods for determining the thermal
conductivity of materials.
ASTM D 5334-00 and D 5930-97 and IEEE Std
442-1981 " Standard Test Methods" specify the use of Non-Steady-State Probes
(NSSP) in various applications. In general a NSSP consists of a heating wire,
representing a perfect line source, and a temperature sensor capable of
measuring the temperature at this source. The probe is inserted in the medium
that is investigated. The NSSP principle relies on a unique property of a line
source: after a short transient period the temperature rise, ∆T, only depends on
heater power, Q, and medium thermal conductivity, λ:
∆T = (Q / 4 π λ) (ln t + B)
With ∆T in K, Q in W/m, λ in W/mK, t the
time in s and B a constant. By measuring the heater power, and tracing the
temperature in time (for TP-02-ATX typically during 2 minutes), λ can be calculated.
The sample size is not critical, as long as a 20 mm radius around the needle is
covered.
The measurements of Q, t and ∆T are all
direct measurements of power, time, and temperature respectively. These are done
without need of reference materials. The measurement with TP-02-ATX is absolute.
TP-02-ATX 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.
TP-02-ATX Design
The Hukseflux TP-02-ATX is designed to be able to
cover a wide range of applications. Design considerations are as
follows:
- Optimal Accuracy: TP-02-ATX incorporates 2 thermocouple junctions in the
needle producing a voltage output, U, that is proportional to ∆T. The one in
the tip is not heated, and serves as a reference junction.
- In this configuration the voltage before
starting the measurement is always small, independent of the medium
temperature. In designs with only one sensor in the needle, the signal U will
appear on top of a larger signal.
- The two junction design has a superior
accuracy when measuring at high and low temperatures.
- In addition, by having both the reference- and
the hot junction in the needle, the sensitivity to temperature changes of the
medium is minimised.
Temperature
sensor in the base: The sensor in the base
(Pt1000) serves as a cold junction measurement for establishing the absolute
medium temperature T. (As required by ASTM). This is used for temperature
correction of the thermocouple sensitivity, again offering superior accuracy
across the temperature range.
Temperature and
moisture resistance: All the materials in TP-02-ATX
are highly temperature resistant. It has a full stainless steel needle and base,
with a welded tip (IP68) and a potted cable (IP67). The needle is 100%
waterproof.
Standard cables
and connectors: Putting the Pt1000 temperature
sensor in the base allows the use of normal copper core cables and connectors
for cable extension of TP-02-ATX.
Long term
stability: The fully sealed construction is
essential for prevention of internal corrosion and maintaining stability of the
sensor over time.
Data
processing: the data obtained with TP-02-ATX can be
processed in any normal spreadsheet program.
Figure
2 The signal of TP-02-ATX as a function of the natural
logarithm of time (ln(t)). After a transient period the graphs show linear
behaviour. In this phase the slope of the graph is inversely proportional to the
thermal conductivity λ.
Calibration/ ISO 9000
Verification of the stability of the total
probe can be done by repeated (yearly) testing in glycerol, preferably at
several temperatures. Alternatively Calibration Reference Cylinders (CRC)
traceable to NPL can be purchased at Hukseflux. TP-02-ATX is suitable for use by ISO
certified labs.
Suggested use
More information/ Options
Standards: ASTM standards can be obtained
from ASTM at http://www.astm.org.
Alternative designs: Hukseflux is
specialised in NSSP design. Alternative models, for instance smaller, more
robust or temperature resistant have been manufactured on request.
Permanent installation in soils: The
dedicated model TP01 is specifically designed for long term monitoring. A
separate brochure is available.
Solutions for measurement and control: See
the TP-02-ATX manual or inquire at Hukseflux. A program for Campbell Scientific CR10X
is available. Turn key systems are offered for sale: see TPSYS.
Manuals: The TP-02-ATX manual
is available free of charge as a PDF file via e-mail.
NEW!
- For high accuracy calibration CRC Calibration
Reference Cylinders are available.
- For insertion into hard soils GT Series Guiding tubes can be applied.
TP-02-ATX Specifications
-
Test method: ASTM D 5334-00 and
D 5930-97 IEEE Std 442-1981
-
Needle length: 150 mm
-
Traceability: NPL
-
Range (λ): 0.1 to 6 W/m.K
-
Sensitivity (∆T): Thermocouple K, ANSI MC96.1-1982
-
Temperature range (total sensor
-55 to +180 °C including cable):
-
Accuracy (@ 20 °C): +/- (3% + 0.02) W/mK
-
Temperature dependence of the
accuracy: +/- 0.02 %/K (additional)
-
Measurement cycle duration: 200 s
(typical)
-
Power requirements (switched) : 3 V, 1 Watt
(max)
-
Medium / sample requirements:
Granular materials, powders, slurries, gels, pastes. Some samples require
pre-drilling. Sample size: Min 20 mm radius. Smaller samples: consult HUkseflux.
Caution: please consult the product manual for more details.
-
Protection needle and base: IP 68
-
Protection total sensor: IP 67