Heat pulse sensor

HP-SDI12-NANO · Digital twin · 12 V · 17 × 3.3 Ω

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Ready 0.0 / 175 s

Sensor

100%
Heater currentLogic powerSignals

Electronics powered · run to show current flow

Temperature rise

TH1 · TH3 side needlesTH2 tip

Readings

Live · PWM average
TemperatureNowRise
22.000 °C+0.000
22.000 °C+0.000
22.000 °C+0.000
22.00 °C+0.00
Sensor estimateSensorSoil
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Available when cooling ends.
PowerNow
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0.000 W0.0 mW each
0.00 J
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References

Methods and data behind the thermal model, the sensor estimate and the soil library. The twin uses these solutions in their ideal form: uniform soil, perfect contact, and no heat stored in the needles, epoxy or board.

  1. Blackwell, J. H. (1954). A transient-flow method for determination of thermal constants of insulating materials in bulk. Part I—Theory. Journal of Applied Physics, 25, 137–144. doi:10.1063/1.1721592The line-source theory behind transient needle probes: a long, thin heater warming the surrounding material.
  2. Carslaw, H. S., & Jaeger, J. C. (1959). Conduction of heat in solids (2nd ed.). Oxford University Press.The temperature field around the heater. Each of the 17 heater resistors is a point source in uniform soil, switched on for the heating time; summing them gives the soil colormap and the TH1, TH2 and TH3 curves.
  3. Campbell, G. S., Calissendorff, C., & Williams, J. H. (1991). Probe for measuring soil specific heat using a heat-pulse method. Soil Science Society of America Journal, 55, 291–293. doi:10.2136/sssaj1991.03615995005500010052xThe dual-probe idea: a heater needle and a temperature needle a fixed distance apart.
  4. Kluitenberg, G. J., Ham, J. M., & Bristow, K. L. (1993). Error analysis of the heat pulse method for measuring soil volumetric heat capacity. Soil Science Society of America Journal, 57, 1444–1451. doi:10.2136/sssaj1993.03615995005700060008xThe pulsed infinite line-source solution for a heat pulse of finite length, and why the needle spacing dominates the heat-capacity error.
  5. Bristow, K. L., Kluitenberg, G. J., & Horton, R. (1994). Measurement of soil thermal properties with a dual-probe heat-pulse technique. Soil Science Society of America Journal, 58, 1288–1294. doi:10.2136/sssaj1994.03615995005800050002xThe sensor estimate: conductivity and heat capacity from the side-needle temperature rise.
  6. Kluitenberg, G. J., Bristow, K. L., & Das, B. S. (1995). Error analysis of heat pulse method for measuring soil heat capacity, diffusivity, and conductivity. Soil Science Society of America Journal, 59, 719–726. doi:10.2136/sssaj1995.03615995005900030013xHow errors in needle spacing, timing and heat input carry into all three properties that the sensor estimate reports.
  7. Bristow, K. L., Bilskie, J. R., Kluitenberg, G. J., & Horton, R. (1995). Comparison of techniques for extracting soil thermal properties from dual-probe heat-pulse data. Soil Science, 160, 1–7. doi:10.1097/00010694-199507000-00001How the properties are extracted: the twin fits the whole temperature-rise curve by nonlinear least squares.
  8. Knight, J. H., & Kluitenberg, G. J. (2004). Simplified computational approach for dual-probe heat-pulse method. Soil Science Society of America Journal, 68, 447–449. doi:10.2136/sssaj2004.4470Simplified calculation of the pulsed line-source solution used to analyze dual-probe data.
  9. Knight, J. H., Kluitenberg, G. J., Kamai, T., & Hopmans, J. W. (2012). Semianalytical solution for dual-probe heat-pulse applications that accounts for probe radius and heat capacity. Vadose Zone Journal, 11(2). doi:10.2136/vzj2011.0112What the ideal line source leaves out: the needles' own radius and heat capacity, which the twin neglects.
  10. de Vries, D. A. (1963). Thermal properties of soils. In W. R. van Wijk (Ed.), Physics of plant environment (pp. 210–235). North-Holland.Converting heat capacity to water content: C = ρb·cs + θ·Cw.
  11. Parker, N., Kluitenberg, G. J., Redmond, C., & Patrignani, A. (2022). A database of soil physical properties for the Kansas Mesonet. Soil Science Society of America Journal, 86, 1495–1508. doi:10.1002/saj2.20465The Kansas Mesonet soil cores and their KD2 Pro readings in Select soil.

Parts list

Select soil

One dot per Kansas Mesonet core. Pick a core, then a water state: the twin runs on that reading's measured conductivity and heat capacity.