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Instrumentation iv.

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Rotimi Dinrifo, PhD
Rotimi Dinrifo, PhD

This document discusses various methods for measuring soil water and flow. It begins by describing common flow measurement devices like orifice plates, venturis, and turbines and their accuracy, rangeability, advantages, and disadvantages. It then covers methods for monitoring soil water content including soil feel and appearance charts, gravimetric sampling to determine water content by weight, and instruments like tensiometers, porous blocks, and neutron probes. The last section provides a brief overview of different types of workshop measuring instruments for tasks like measuring length, angles, surface finish, and deviations.

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AET 314 INSTRUMENTATION HND 1 AGRIC & BIO- ENGINEERING (FARM POWER & SOIL + WATER) R R Dinrifo, Ph.D MODULE 1V Flow Measurement Soil Water Monitoring & Measurement Workshop Measuring Instruments:

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Sensor Rangeability1 Accuracy2 Dynamics Advantages Disadvantages orifice 3.5:1 2-4% of full span - -low cost -extensive industrial practice -high pressure loss -plugging with slurries venturi 3.5:1 1% of full span - -lower pressure loss than orifice -slurries do not plug -high cost -line under 15 cm flow nozzle 3.5:1 2% full span - -good for slurry service -intermediate pressure loss -higher cost than orifice plate -limited pipe sizes elbow meter 3:1 5-10% of full span - -low pressure loss -very poor accuracy annubar 3:1 0.5-1.5% of full span - -low pressure loss -large pipe diameters -poor performance with dirty or sticky fluids turbine 20:1 0.25% of measurement - -wide rangeability -good accuracy -high cost -strainer needed, especially for slurries vortex shedding 10:1 1% of measurement - --insensitive to variations in density, temperature, pressure, and viscosity -expensive positive displacement 10:1 or greater 0.5% of measurement - -high reangeability -good accuracy -high pressure drop -damaged by flow surge Flow Measurement devices

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Orifice flow meter venturi Elbow meter Pitot tube

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SOIL WATER MONITORING & MEASUREMENT • Efficient irrigation requires a systematic water management program. Such a program answers the questions of when to irrigate, how much water to apply during irrigation and how best to apply the water (rate of application, method, etc.). • Accurate assessment of the soil water-holding characteristics along with periodic soil water monitoring and measurement are required. Monitoring and measuring soil water available to irrigated crops is part of an integrated management package.

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Among the most common approaches are: • soil feel and appearance • gravimetric sampling • tensiometers • porous blocks • neutron scattering

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Soil texture Available water Coarse (sand, loamy sand) Moderately coarse (sandy loam, fine sandy loam) Medium (loam) Fine (silt loam, clay loam) 100% (field capacity) Leaves wet outline on hand when squeezed. (0.0) Appears very dark, leaves wet outline on hand; makes a short ribbon. (0.0) Appears very dark, leaves wet outline on hand: will ribbon out about 1". (0.0) Appears very dark, leaves slight moisture on hand when squeezed: will ribbon out about 2". (0.0) 70%-80% Appears moist: makes a weak ball. (0.2-0.3) Dark: makes a hard ball. (0.3-0.4) Quite dark: makes tight plastic ball: ribbons out 1/2". (0.4- 0.6) Quite dark ribbons and slicks easily: makes plastic ball. (0.5-0.7) 60%-65% Appears slightly moist: forms weak brittle ball. (0.4) Fairly dark: makes a good ball. (0.8) Fairly dark: forms firm ball: barely ribbons. (0.8) Fairly dark: forms firm ball: ribbons 1/4"-1/2". (0.9) 50% Appears dry: forms very weak ball or will not ball. (0.5) Slightly dark: forms weak ball. (0.8) Fairly dark: will form ball: slightly crumbly. (1.0) Balls easily: small clods flatten out rather than crumble: ribbons slightly. (1.1-1.2) 35%-40% Dry: will not ball. (0.6- 0.7) Light color: will not ball or forms brittle balls. (0.9-1.0) Slightly dark: forms weak ball: crumbly. (1.2-1.3) Slightly dark, forms weak balls: clods crumble. (1.4-1.5) Less than 20% (wilting point) Very dry: loose, flows through fingers. (0.8-1.0) Dry: loose, flows through fingers. (1.3-1.6) Light color: powdery, dry. (1.6-2.0) Hard, baked, cracked, light color. (1.6-2.3) Soil feel and appearance chart for estimating available soil water.

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• Soil sampling involves taking soil samples from each of several desired depths in the root zone and temporarily storing them in water vapor-proof containers. The samples are then weighed and the opened containers oven-dried under specified time and temperature conditions (104°C for 24 hours). • Percent soil water content on a dry mass or gravimetric basis, Pw, is determined with the following formula Pw = [(wet sample weight-dry sample weight) / dry sample weight] x 100

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Tensiometry Soil water tension, soil water suction, or soil water potential are all terms describing the energy status of soil water. Soil water potential is a measure of the amount of energy with which water is held in the soil. A soil water characteristic or water release curve shows the relation between soil water content and soil water tension

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Sketch showing typical electrical resistance block installation. Porous blocks are made of materials such as gypsum, ceramic, nylon, and fiberglass. Similar to tensiometers, the blocks are buried in intimate contact with the soil at some desired depth and allowed to come to water tension equilibrium with the surrounding soil. Once equilibrium is reached, different properties of the block which are affected by its water tension may be measured.

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Neutron Scattering Neutron scattering is a time-tested technique for measuring total soil water content by volume. This method estimates the amount of water in a volume of soil by measuring the amount of hydrogen present. A neutron probe consists of a source of fast or high energy neutrons and a detector, both housed in a unit which is lowered into an access tube installed in the soil. The probe is connected by cable to a control unit which remains on the surface. Clips on the cable allow the probe to be set at pre-selected depths in the soil profile. Access tubes should be installed at least to the depth of the expected rooting zone. The control unit includes electronics for time control, a counter, memory, and other electronics for processing readings

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WORKSHOP MEASURING INSTRUMENTS classification of measuring instruments: • Length measuring Instruments. • Direct measuring. • Indirect measuring. • Angle measuring Instruments. • Instruments for surface finish. • Instruments for deviations.

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WORKSHOP INSTRUMENTS

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Instrumentation iv.

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Instrumentation iv.

  • 1. AET 314 INSTRUMENTATION HND 1 AGRIC & BIO- ENGINEERING (FARM POWER & SOIL + WATER) R R Dinrifo, Ph.D MODULE 1V Flow Measurement Soil Water Monitoring & Measurement Workshop Measuring Instruments:
  • 2. Sensor Rangeability1 Accuracy2 Dynamics Advantages Disadvantages orifice 3.5:1 2-4% of full span - -low cost -extensive industrial practice -high pressure loss -plugging with slurries venturi 3.5:1 1% of full span - -lower pressure loss than orifice -slurries do not plug -high cost -line under 15 cm flow nozzle 3.5:1 2% full span - -good for slurry service -intermediate pressure loss -higher cost than orifice plate -limited pipe sizes elbow meter 3:1 5-10% of full span - -low pressure loss -very poor accuracy annubar 3:1 0.5-1.5% of full span - -low pressure loss -large pipe diameters -poor performance with dirty or sticky fluids turbine 20:1 0.25% of measurement - -wide rangeability -good accuracy -high cost -strainer needed, especially for slurries vortex shedding 10:1 1% of measurement - --insensitive to variations in density, temperature, pressure, and viscosity -expensive positive displacement 10:1 or greater 0.5% of measurement - -high reangeability -good accuracy -high pressure drop -damaged by flow surge Flow Measurement devices
  • 4. SOIL WATER MONITORING & MEASUREMENT • Efficient irrigation requires a systematic water management program. Such a program answers the questions of when to irrigate, how much water to apply during irrigation and how best to apply the water (rate of application, method, etc.). • Accurate assessment of the soil water-holding characteristics along with periodic soil water monitoring and measurement are required. Monitoring and measuring soil water available to irrigated crops is part of an integrated management package.
  • 5. Among the most common approaches are: • soil feel and appearance • gravimetric sampling • tensiometers • porous blocks • neutron scattering
  • 6. Soil texture Available water Coarse (sand, loamy sand) Moderately coarse (sandy loam, fine sandy loam) Medium (loam) Fine (silt loam, clay loam) 100% (field capacity) Leaves wet outline on hand when squeezed. (0.0) Appears very dark, leaves wet outline on hand; makes a short ribbon. (0.0) Appears very dark, leaves wet outline on hand: will ribbon out about 1". (0.0) Appears very dark, leaves slight moisture on hand when squeezed: will ribbon out about 2". (0.0) 70%-80% Appears moist: makes a weak ball. (0.2-0.3) Dark: makes a hard ball. (0.3-0.4) Quite dark: makes tight plastic ball: ribbons out 1/2". (0.4- 0.6) Quite dark ribbons and slicks easily: makes plastic ball. (0.5-0.7) 60%-65% Appears slightly moist: forms weak brittle ball. (0.4) Fairly dark: makes a good ball. (0.8) Fairly dark: forms firm ball: barely ribbons. (0.8) Fairly dark: forms firm ball: ribbons 1/4"-1/2". (0.9) 50% Appears dry: forms very weak ball or will not ball. (0.5) Slightly dark: forms weak ball. (0.8) Fairly dark: will form ball: slightly crumbly. (1.0) Balls easily: small clods flatten out rather than crumble: ribbons slightly. (1.1-1.2) 35%-40% Dry: will not ball. (0.6- 0.7) Light color: will not ball or forms brittle balls. (0.9-1.0) Slightly dark: forms weak ball: crumbly. (1.2-1.3) Slightly dark, forms weak balls: clods crumble. (1.4-1.5) Less than 20% (wilting point) Very dry: loose, flows through fingers. (0.8-1.0) Dry: loose, flows through fingers. (1.3-1.6) Light color: powdery, dry. (1.6-2.0) Hard, baked, cracked, light color. (1.6-2.3) Soil feel and appearance chart for estimating available soil water.
  • 7. • Soil sampling involves taking soil samples from each of several desired depths in the root zone and temporarily storing them in water vapor-proof containers. The samples are then weighed and the opened containers oven-dried under specified time and temperature conditions (104°C for 24 hours). • Percent soil water content on a dry mass or gravimetric basis, Pw, is determined with the following formula Pw = [(wet sample weight-dry sample weight) / dry sample weight] x 100
  • 8. Tensiometry Soil water tension, soil water suction, or soil water potential are all terms describing the energy status of soil water. Soil water potential is a measure of the amount of energy with which water is held in the soil. A soil water characteristic or water release curve shows the relation between soil water content and soil water tension
  • 9. Sketch showing typical electrical resistance block installation. Porous blocks are made of materials such as gypsum, ceramic, nylon, and fiberglass. Similar to tensiometers, the blocks are buried in intimate contact with the soil at some desired depth and allowed to come to water tension equilibrium with the surrounding soil. Once equilibrium is reached, different properties of the block which are affected by its water tension may be measured.
  • 10. Neutron Scattering Neutron scattering is a time-tested technique for measuring total soil water content by volume. This method estimates the amount of water in a volume of soil by measuring the amount of hydrogen present. A neutron probe consists of a source of fast or high energy neutrons and a detector, both housed in a unit which is lowered into an access tube installed in the soil. The probe is connected by cable to a control unit which remains on the surface. Clips on the cable allow the probe to be set at pre-selected depths in the soil profile. Access tubes should be installed at least to the depth of the expected rooting zone. The control unit includes electronics for time control, a counter, memory, and other electronics for processing readings
  • 11. WORKSHOP MEASURING INSTRUMENTS classification of measuring instruments: • Length measuring Instruments. • Direct measuring. • Indirect measuring. • Angle measuring Instruments. • Instruments for surface finish. • Instruments for deviations.