Dual Needle Algorithm - Decagon Devices KD2 Pro Operator's Manual

7 KD2 PRO THEORY
imize contact resistance that results in water movement away from
the sensor.
Decagon's KD2 Pro design attempts to optimize thermal proper-
ties measurements relative to these issues. Our sensors are relatively
large and robust making them easy to use. The KD2 Pro keeps heat-
ing times as short as possible to minimize thermally induced water
movement and lower the time required for a measurement. We also
limit heat input to minimize water movement and free convection.
Use of relatively short heating times and low heating rates requires
high resolution temperature measurements and special algorithms
to measure thermal properties. The KD2 Pro resolves temperature
to 0.001 C in temperature. It uses special algorithms to analyze
measurements made during a heating and a cooling interval. Algo-
rithms also separate out the effects of the heat pulse from ambient
temperature changes. The KD2 Pro uses two different algorithms,
one for the dual needle sensor and one for the single needle, based
on Carslaw, Jager, and Kluitenberg's line heat source analysis.
7.1

Dual Needle Algorithm

Heat is applied to the heated needle for a set heating time,
temperature is measured in the monitoring needle, 6 mm distant
during heating and during the cooling period following heating. The
readings are then processed by subtracting the ambient temperature
at time 0, multiplying by 4 and dividing by the heat per unit length,
. The resulting data are fit to the following equations using a non-
linear least squares procedure.
where:
8
Carslaw and Jaeger (1959) and Kluitenberg et al. (1993).
= +
0
= + (
0 1
4 (
=
56
2
( )
1
2 2
)
h
)
0
KD2 Pro
8
, and
(1)
(2)
(3)