STP01 Soil temperature profile
The STP01 is a sensor for very
accurate measurement of temperature versus depth (also called “temperature
gradient”) in the soil. A heating wire offers the possibility of self-testing,
increasing the level of quality assurance. An experimental option is to
determine soil thermal conductivity as a function of depth.
See also the scientific section on non-steady
state probe science.
Free: For a nice clear print of the original product
brochure (PDF) click here.
INTRODUCTION
The measurement of soil temperature
profiles has many applications, particularly in determining soil energy
balance.
STP01 contains 5 thermocouples, tc, (at
2, 5, 10, 20 and 50 cm depth, A to E) and one reference Pt100 temperature sensor
(at 50 cm, E). The key item in the design is the central copper-nickel (CuNi) wire
(5). By having the reference tc junction in the sensor and only measuring
differential tc voltages (relative to the reference tc junction at 50 cm), the
gradient accuracy is record breaking (down to +/- 0.02 degrees C) and cabling
can be simple all copper (Cu) wire. As an extra, there is a heating wire
incorporated (6) from I to II. The reaction of the tc’s to sudden heating (tc
pulse response) is a test for sensor performance in the inaccessible
environment.
- Figure 1 Layout
of STP01
- 1 soil surface
- 2 sensor foil (0.6 mm thickness, 2.5 at
Pt 100)
- 3 cables (5 m), extendable
- 4 copper leads
- 5 constantan wire for thermocouples
- 6 constantan wire for heater
- 7 Pt 100 (4 wire connection)
- I and II: end of heating wire (2 times
2 wire connection) A, B, C, D and E: tc junctions
-
- Wiring schedule:
- 1 heater power
- 2 heater measure
- 3 thermocouple 2 cm
- 4 thermocouple 5 cm
- 5 thermocouple 10 cm
- 6 thermocouple 20 cm
- 7 thermocouple 50 cm
- 8 Pt100 +
- 9 Pt100 +
- 10 Pt100 –
- 11 Pt100 –
- 12 heater power
- 13 heater measure
- All dimensions are in mm.
STP01 ADVANTAGES
The STP01 has several advantages over
existing designs:
- high accuracy gradient measurement by
accurate positioning of the tc joints (+/- 1mm), and measurement of tc voltage
relative to the junction at 50 cm (+/- 0.02 K is achievable)
- high accuracy and stability of the
relative distance between sensors (+/- 0.5 mm)
- thin, 0.6 mm only, (non disturbing)
construction (contrary to conventional stick designs) does not disturb the
thermal flow pattern
- sensor to logger cabling is all copper;
easily extendable.
- easy quality assurance & servicing:
self-test is possible by heating and looking at the pulse response, saving
servicing time.
*EXPERIMENTAL USE: SOIL THEMAL CONDUCTIVITY MEASURMENT
When using the heater, the tc pulse
response can be used to calculate soil thermal conductivity at 3 depths; 5, 10
and 20 cm. The well established thermal needle or non-steady-state probe
technique is applicable. For more theory on this method, see ask for the
Hukseflux TP02 manual. (T = A.ln(t) +B, with T temperature, t time, A a
function of geometry, power and thermal conductivity). The possibility to
perform this measurement is an experimental option and the measurement accuracy
is not specified by Hukseflux.
DATA ACQUISITION AND CONTROL
Solutions for measurement and control:
See the STP01 manual or inquire at
Hukseflux. Example programs for Campbell Scientific CR10X
and CR1000 is
available.
MANUALS
The STP01 manual is available free of charge as a PDF file via
e-mail.
SUGGESTED USE
SENSOR SPECIFICATIONS
-
Thermocouples, tc: Cu-CuNi,
type T
-
Temperature range: -30
to +70
°C
-
Depths below soil surface: 2, 5, 10, 20 & 50
+/- 1 mm
-
Reference
junction: Pt100 DIN class B
-
Thickness (nominal): 0.6 mm (2.5 at Pt100)
-
Required readout: 4 diff
volt, 1 common ground, Pt100-4 or 3 wire
HEATER SPECIFICATIONS
-
Resistance (nominal):
200 W
-
Voltage input: 9-15 VDC
-
Duration
of the self test: ± 10 min at 0.3 Watt
-
Average power
consumption: 0.05 Watt
-
Required readout:
1 diff volt
-
Self-test
recommendation: once every 3
hours, at least every 24 hours
OPTIONS
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