Calibration of capacitance probe sensors using electric circuit theory

T. J. Kelleners, R. W O Soppe, D. A. Robinson, Marcel Schaap, J. E. Ayars, T. H. Skaggs

Research output: Contribution to journalArticle

73 Citations (Scopus)

Abstract

Capacitance probe sensors are an attractive electromagnetic technique for estimating soil water content. There is concern, however, about the influence of soil salinity and soil temperature on the sensors. We present an electric circuit model that relates the sensor frequency to the permittivity of the medium and that is able to correct for dielectric losses due to ionic conductivity and relaxation. The circuit inductance L is optimized using sensor readings in a modified setup where ceramic capacitors replace the sensor's capacitance plates. The three other parameters in the model are optimized using sensor readings in a range of nonconductive media with different permittivities. The geometric factor for the plastic access tube gp is higher than the geometric factor for the medium gm, indicating that most of the electromagnetic field does not go beyond the access tube. The effect of ionic conductivity on the sensor readings is assessed by mixing salts in three of the media. The influence is profound. The sensor frequency decreases with increasing conductivity. The effect is most pronounced for the medium with the lowest permittivity. The circuit model is able to correct for the conductivity effect on the sensors. However, as the dielectric losses increase, the frequency becomes relatively insensitive to permittivity and small inaccuracies in the measured frequency or in the sensor constants result in large errors in the calculated permittivity. Calibration of the capacitance sensors can be simplified by fixing two of the constants and calculating the other two using sensor readings in air and water.

Original languageEnglish (US)
Pages (from-to)430-439
Number of pages10
JournalSoil Science Society of America Journal
Volume68
Issue number2
StatePublished - Mar 2004
Externally publishedYes

Fingerprint

capacitance probes
electronic circuits
sensors (equipment)
calibration
probe
sensor
permittivity
conductivity
capacitance
ceramics
electromagnetic field
soil salinity
soil temperature

ASJC Scopus subject areas

  • Soil Science
  • Earth-Surface Processes

Cite this

Kelleners, T. J., Soppe, R. W. O., Robinson, D. A., Schaap, M., Ayars, J. E., & Skaggs, T. H. (2004). Calibration of capacitance probe sensors using electric circuit theory. Soil Science Society of America Journal, 68(2), 430-439.

Calibration of capacitance probe sensors using electric circuit theory. / Kelleners, T. J.; Soppe, R. W O; Robinson, D. A.; Schaap, Marcel; Ayars, J. E.; Skaggs, T. H.

In: Soil Science Society of America Journal, Vol. 68, No. 2, 03.2004, p. 430-439.

Research output: Contribution to journalArticle

Kelleners, TJ, Soppe, RWO, Robinson, DA, Schaap, M, Ayars, JE & Skaggs, TH 2004, 'Calibration of capacitance probe sensors using electric circuit theory', Soil Science Society of America Journal, vol. 68, no. 2, pp. 430-439.
Kelleners TJ, Soppe RWO, Robinson DA, Schaap M, Ayars JE, Skaggs TH. Calibration of capacitance probe sensors using electric circuit theory. Soil Science Society of America Journal. 2004 Mar;68(2):430-439.
Kelleners, T. J. ; Soppe, R. W O ; Robinson, D. A. ; Schaap, Marcel ; Ayars, J. E. ; Skaggs, T. H. / Calibration of capacitance probe sensors using electric circuit theory. In: Soil Science Society of America Journal. 2004 ; Vol. 68, No. 2. pp. 430-439.
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