Temperature Effects in a Tensiometer‐Pressure Transducer System

Watson, K. K.; Jackson, R. D.

doi:10.2136/sssaj1967.03615995003100020006x

Cited by 18 publications

(10 citation statements)

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“…They attributed these effects primarily to temperature changes in the soil and the effects on soil water movement caused by the metal parts of the tensiometer. Later, Watson and Jackson [1967] reported on temperature effects in a tensiometer-pressure transducer system. However, their study was conducted in a laboratory with small temperature fluctuations.…”

Section: Introductionmentioning

confidence: 99%

Diurnal fluctuations of tensiometric readings due to surface temperature changes

Warrick

Wierenga

Young³

et al. 1998

Water Resources Research

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Abstract. Pressure fluctuations in tensiometers in response to temperature changes are examined. Mechanisms considered include temperature variation within an air gap at the top of the tensiometer, the air gap size, saturated water vapor pressure, and hydraulic conductivity of the soil. Pressures measured in a tensiometer generally fall between two simplified, limiting cases. The first limiting case assumes that the tensiometer cup is impermeable for water. This leads to very high fluctuations as air and soil temperatures change. For a cyclical temperature of 35 ___ 15øC, variations in water pressure inside the cup can be ___70 cm water head. For the second limiting case the water moves freely between the tensiometer and the soil, which leads to more stable readings, within _+ 1 cm for the above 15øC fluctuation. While cup impedance was found to be a negligible factor for all cases considered, the analysis presented here suggests that conductivity of the soil immediately around the cup is the main factor governing temperature-induced pressure fluctuations inside the cup. BackgroundTensiometers are widely used to evaluate soil water potentials in the wet range. Documentation and criteria for successful operation are extensive and well known [cf. Cassel and Klute, 1986]. An assumption for using tensiometers is that the soil water is in equilibrium with water inside of the device where the pressure is measured, either within standing water inside of the cup or in a gas phase existing at the upper end of the column. For the older style tensiometers the gas phase is minimized by servicing the device to remove gases which enter by leaking through the cup or coming out of solution in the water.The newer "puncture-type" tensiometer [Martbaler et al., 1983] is designed to include an air gap of ---2 cm at the top of the device to allow insertion of a needle to measure the pressure with a portable transducer. The air gap allows for a more gradual (seconds instead of milliseconds) change in pressure at the transducer membrane, and thus it eliminates membrane rupture. It also prevents the needle from filling with water and leads to a device which requires less servicing. An increase in air pressure due to insertion of the needle can be taken into account by a "double-puncture technique" [Greenwood and Daniel, 1996]. An intentional air gap can also be used for monitoring in the deep vadose zone by measuring the soil water pressure using a pressure transducer beiow the standing water level. In this case, a considerable air gap can be used, but the soil water pressure at the cup follows as long as the pressure transducer is below the standing water level.

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Section: Introductionmentioning

confidence: 99%

Diurnal fluctuations of tensiometric readings due to surface temperature changes

Warrick

Wierenga

Young³

et al. 1998

Water Resources Research

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“…It has been recognized for some time that tensiometer systems are sensitive to thermal loading (Watson and Jackson, 1967;Schuster, 1974). In our system, the large excursions in millivolt output observed during temperature calibrations (Figure 2) represent the net effect of thermal loading on all components, electrical and mechanical.…”

Section: Discussionmentioning

confidence: 99%

“…Although highly accurate readings are achievable in transducer/tensiometer applications (Rice, 1975;Long and Huck, 1980), several investigations have shown the sensitivity of these systems to thermal loadings, resulting in potentially large deviations in the millivolt output (Watson and Jackson, 1967;Trotter, 1984). However, very few field applications have evaluated the sources of uncertainty in their systems (Lowery et al, 1986).…”

Section: Introductionmentioning

confidence: 99%

“…Pressure transducers are widely used in soil hydrology investigations (Fitzsimmons et al, 1972; Anderson and Burt, 1978;Marthaler et al, 1983;MacVicar and Walter, 1984;Hoover, 1987) and are generally accepted as the most effective and efficient means of measuring soil water potentials. Although highly accurate readings are achievable in transducer/tensiometer applications (Rice, 1975;Long and Huck, 1980), several investigations have shown the sensitivity of these systems to thermal loadings, resulting in potentially large deviations in the millivolt output (Watson and Jackson, 1967;Trotter, 1984). However, very few field applications have evaluated the sources of uncertainty in their systems (Lowery et al, 1986).…”

Section: Introductionmentioning

confidence: 99%

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The calibration and use of pressure transducers in tensiometer systems

Hoelscher

Nuttle

Harvey

1993

Hydrological Processes

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The uncertainty in a transducer/tensiometer system was assessed with temperature and pressure calibrations. A reference transducer/tensiometer pair was used to factor out temperature related deviations from two monitoring pairs. The reference pair removed most of the deviations, resulting in a high estimate of precision. In contrast to earlier reports of high accuracy, these estimates of accuracy were considerably reduced by a time correlated residual pattern. The calibrations suggested that the electronic components may be responsible for these residual errors and illustrated the need for experimentation which isolates the error among groups of components. The complexity of transducer/ tensiometer networks, and the differing response of each component to thermal loading, demonstrated the necessity of using a reference system, which when properly designed can yield reliable pressure readings for soil water.

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“…Miller (195 1) and Klute and Gardner (1962) have considered the theory of the limiting cases in which either the instrument or the soil controls the overall response time. Subsequently, Watson (1965, 1967 and Watson and Jackson (1967) have applied the theory assuming the soil to be non-limiting. However, the actual conditions under which the soil can be so regarded have not been examined.…”

Section: Introductionmentioning

confidence: 99%

Theory of Time Response of Tensiometers

Towner¹

1980

Journal of Soil Science

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Summary The time taken for a tensiometer to reach equilibrium with the soil‐water pressure is a function not only of the tensiometer characteristics but also of the soil‐water transport properties. When. in an appropriate system of units. the numerical value of the conductance of the tensiometer cup is small compared with that of the hydraulic conductivity of the soil, and the sensitivity of the pressure ‘gauge’ is large compared with the differential water capacity of the soil. then the precision of the measurements is such that the observed response may be indistinguishable from that of a tensiometer in bulk water. referred to as ‘tensiometer limited’. The theory developed in this paper for a hemispherical tensiometer cup shows that tensiometer‐limited conditions can be achieved in practice. Moreover. such conditions would often correspond to a rapid response system. It is suggested that it might be advantageous in the design of a field recording system to choose a tensiometer‐limited system even if it is not the fastest realisable one in order that its response is completely predictable from the known tensiometer characteristics. independent of the unknown soil properties. which may be changing.

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Temperature Effects in a Tensiometer‐Pressure Transducer System

Cited by 18 publications

References 0 publications

Diurnal fluctuations of tensiometric readings due to surface temperature changes

Diurnal fluctuations of tensiometric readings due to surface temperature changes

The calibration and use of pressure transducers in tensiometer systems

Theory of Time Response of Tensiometers

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