FI20175029A1 - Measurement device with motion sensing - Google Patents

Measurement device with motion sensing Download PDF

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Publication number
FI20175029A1
FI20175029A1 FI20175029A FI20175029A FI20175029A1 FI 20175029 A1 FI20175029 A1 FI 20175029A1 FI 20175029 A FI20175029 A FI 20175029A FI 20175029 A FI20175029 A FI 20175029A FI 20175029 A1 FI20175029 A1 FI 20175029A1
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FI
Finland
Prior art keywords
measurement
sensor
probe
material
parameter values
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FI20175029A
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Finnish (fi)
Swedish (sv)
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FI20175029A (en
Inventor
Janne Kivijärvi
Timo Heikkinen
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Farmcomp Oy
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Priority to FI20165877A priority Critical patent/FI20165877L/en
Application filed by Farmcomp Oy filed Critical Farmcomp Oy
Publication of FI20175029A publication Critical patent/FI20175029A/en
Publication of FI20175029A1 publication Critical patent/FI20175029A1/en

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01CMEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C1/00Measuring angles
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01KMEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K1/00Details of thermometers not specially adapted for particular types of thermometer
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01KMEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K13/00Adaptations of thermometers for specific purposes
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means
    • G01N27/02Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material
    • G01N27/04Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material by investigating resistance
    • G01N27/048Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material by investigating resistance for determining moisture content of the material
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means
    • G01N27/02Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material
    • G01N27/22Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material by investigating capacitance
    • G01N27/223Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material by investigating capacitance for determining moisture content, e.g. humidity
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01PMEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom

Abstract

The disclosure relates to a measurement device for penetrable materials (151) which comprises an elongated measurement probe (12) configured to penetrate the penetrable material (151). The elongated measurement probe (12) comprises one or more first sensors (19, 110, 120) configured to measure one or more material parameter values in the penetrable material (151). These material parameters may include permittivity, electrical conductivity, moisture concentration or salinity. The measurement device also comprises a second sensor (19, 110, 121, 200, 33-37) configured to measure probe motion parameter values which express the movement of the elongated measurement probe (12) in relation to the penetrable material (151). The measurement device is configured to time the measurement of material parameter values in response to receiving probe motion parameter values, or to indicate the reliability of measured or predicted material parameter values in response to receiving probe motion parameter values.

Description

MEASUREMENT DEVICE WITH MOTION SENSING

FIELD OF THE DISCLOSURE

The present disclosure relates to measurements performed with measurement probes in penetrable materials, and more particularly to a method and apparatus for improving the reliability of such measurements.

In this disclosure the term “penetrable material” refers to any material body which an elongated and rigid measurement probe can penetrate when it is pushed against the surface of the body with sufficient force. The body may be a pile of small particles or a unitary solid material in one piece. It may also be a body of pressed material which has been converted into a more or less solid body through pressing. Before pressing the body may comprise material in particulate form, or thin objects such as straws.

In this context the adjective “penetrable” means that the material is sufficiently pliable to allow the tip of the probe to compress or move aside the material when it penetrates the body of penetrable material. The probe can thereby create a channel through one section of the body of penetrable material without breaking the material and without altering other sections in the same body of penetrable material. The body of penetrable material may also be soft and easily compressible, which allows the probe to penetrate the body.

BACKGROUND OF THE DISCLOSURE

Examples of penetrable materials include pressed biomaterials such as hay, straw, silage, haylage or baleage, which may, after harvesting, be pressed, baled and stored in tightly packed bales, or alternatively pressed and stored in a silage pit. After a storage period the pressed biomaterial may, for example, be used as animal feed, bedding for domestic animals or as fuel in bioenergy-based power generators. The silage, haylage, baleage hay or straw may include plants such as alfalfa, timothy grass, clover, fescue, maize, reed canary grass, elephant grass or cereal grains such as barley, wheat or rice.

Pressed biomaterials also include materials such as peat, cotton, tobacco, hemp or hops. These materials can be pressed and packed tightly for storage, transportation or consumption. In some circumstances, such as naturally occurring peat bogs, the materials may have been pressed without human intervention.

All of the above biomaterials may also be converted into chopped form by chopping, hacking or grounding before they are pressed and stored. Alternatively, they may be pressed and stored in unchopped form.

The apparatus and methods described in this disclosure are applicable in measurements performed in both chopped and unchopped biomaterial in pressed form. Biomaterial chop may have a fine composition, that is, it may contain small particles and/or short straws. Biomaterial chop may also have a rough composition, that is, it may contain large particles and/or long straws.

Some penetrable materials may be stored without pressing, and the apparatus and methods described in this disclosure are also applicable for performing measurements in such materials when they are stored, for example, in silos, sacks, boxes, containers, jars or other comparable storage equipment, or even when the material is simply collected in a heap. Penetrable materials which could be collected in this way include, for example, wood chips, logging residue and sawdust, particulate biomaterials such as grain, seed, fruit and other small food items for human or animal consumption, as well as soil, compost and manure. Piles or stacks of inorganic particulate material such as sand and gravel, as well as particulate trash material such as plastic residue, may also be collected, stored, and measured with probe-type measurement devices which penetrate the pile or stack.

In the present disclosure, the term “coarseness” will be used as a general adjective for describing how fine or rough the composition of any particulate material is. For example, very finely chopped material has low coarseness, whereas unchopped material has high coarseness. A particulate material with small particles has low coarseness, whereas a particulate material with large particles has high coarseness.

One further example of a penetrable material is meat. The state of a piece of meat may be monitored with probe-based measurements at any stage of processing, transport, storage and food preparation.

In all embodiments described in the present disclosure, the penetrable material is stationary in relation to the point of measurement. The material is not, for example, flowing or moving past the measurement point on an automated processing line when the measurement is performed. This means that a motion sensor which detects relative movement between the probe and the body of penetrable material will allow detection of sudden changes in the measurands due to repositioning of the probe.

The body of penetrable material will often be stationary not only in relation to the point of measurement, but also in relation to the earth, and it will often remain sufficiently stationary even when it is penetrated by a measurement probe. One example of such an application is the measurement of a pile of grain. Whenever the body of penetrable material may be assumed stationary, any motion sensor which detects the motion of the probe will also effectively detect the relative movement between the probe and the body of stationary penetrable material.

Document US6088657 discloses a measurement probe for measuring moisture concentration in hay bales. Document US2014334523 discloses a measurement probe for measuring the core temperature of frozen products. A problem with prior art probe measurement devices is that measurements conducted while the probe is in motion, or just after the probe has been in motion, may be subject to measurement errors which are not present when the probe has been stationary for a longer time. It is not always easy for a human operator to distinguish between reliable and unreliable measurements, especially if the settling time required for a reliable measurement is long.

Probe-based electrical measurements typically involve two metallic electrode sections near the tip of the probe, separated by an insulating section. The permittivity and electrical conductivity of the penetrable material around the tip of the probe can be measured with capacitive and resistive measurements, respectively, between the two electrodes.

Measured permittivities and electrical conductivities can in some penetrable materials be used as indicators of local moisture concentration or salinity around the tip of the probe, because both permittivity and conductivity are influenced by the amount of water and/or salt present in the material. Calibration experiments, specific to each material and each degree of coarseness, are required for correlating a certain measured capacitance or electrical conductivity with a certain moisture concentration or salinity.

If electrical measurements are performed when the probe is in motion, the resulting measurement values may often fluctuate because the electrical environment around the probe is changing. If the measurement device performs continuous measurements and stores or displays results even when the probe is moving, then these results may not be at all comparable to measurement results obtained from a stationary probe. Calibrated correlations may also be reliable only for stationary probes.

If electrical measurement values are averaged before they are stored or displayed, averages may be erroneous if some of the averaged values were obtained in motion. Low-pass filtering of the measurement signal, or slow A/D conversion of the signal, may also lead to settling time requirements where the probe has to remain stationary for a certain time before the measurement result can be considered valid.

Probe-based temperature measurements typically involve a temperature sensor near the tip of the probe. If the penetrable material is dense, the probe which penetrates it must usually contain sizable metallic structures to ensure sufficient rigidity. These metallic structures give the probe a large heat capacity. A lot of heat may be stored in the metallic parts of the probe.

Before a temperature measurement begins, the probe will typically be at the ambient temperature. If this ambient temperature differs significantly from the internal temperature of the penetrable material, a lot of heat transfer may immediately occur between the probe and the section of penetrable material which surrounds it. The difference between ambient temperature and internal temperature may be particularly strong when temperature measurements are performed in frozen penetrable materials or in penetrable material which is or has been cooked in an oven. In dense materials the probe may be heated by friction when it moves in the penetrable material.

When the temperature of the probe differs from that of the surrounding penetrable material, there will be heat transfer between the probe and the material. The rate of heat transfer depends on the heat conductivity of the penetrable material. The temperature measured by the probe may not be representative of the true internal temperature of the penetrable material until there is thermal equilibrium around the tip of the probe. If the penetrable material has low heat conductivity, as many do, then it may take several minutes or longer before the probe and the penetrable material reach thermal equilibrium sufficiently near the temperature the penetrable material had before it came into contact with the probe.

To prevent the measurement result from being excessively skewed by the initial thermal energy of the measurement probe, the thermal capacity of the body of penetrable material should preferably be much greater than that of the measurement probe.

Measurement arrangements which take into account temperature settling are well-known from medical thermometers, which typically refrain from showing any measurement results until a predetermined settling time has passed. Medical thermometers also commonly employ predictive algorithms which use the time-dependence of early temperature measurements to calculate what the eventual equilibrium temperature (i.e. the true body temperature of the patient) will be. Settling time delays or predictive algorithms may also be employed in probe-type measurement devices for penetrable materials. Some medical thermometers also employ heaters which immediately heat the tip to approximately 37°C when a measurement begins, thus reducing the settling time considerably. However, this form of anticipation is not generally applicable because the internal temperature of most penetrable materials cannot be approximately guessed before measurement.

Another important difference between medical thermometers and probe-type measurement devices is that human operators tend to keep medical thermometers still during measurement, whereas operators of probe-type devices may not be so inclined. In a medical temperature measurement the thermometer is placed in an orifice or pressed against the skin. The thermometer is held in one place and there is no need to perform measurements at multiple depths or many locations because the temperature is the same across the body. In contrast, when temperature measurements are performed in a penetrable material with a probe, the operator is often interested in the temperature distribution within the material. The probe may therefore be repeatedly pushed inward in multiple steps in several locations.

It is well-known that sources of measurement error can be tested and settling times can be experimentally determined. It is also known that measurement devices may be programmed to refrain from displaying any measurement results, or from storing any measurement results, before the settling time has passed or before a predictive algorithm has finished its calculation.

However, a common problem in probe-based moisture concentration and temperature measurement devices is that the human operator who uses the measurement device has to be well-informed about measurement details, such as settling times and predictive algorithms, in order to conduct reliable measurements.

Probe-type measurement devices typically start the measurement, and optionally start running the predictive algorithm, when they obtain a start signal. The operator may, for example, press a button on the measurement device to give the start signal. The device could be programmed to start a timer from this moment and then wait until the predetermined settling time has passed before performing a measurement and displaying results. However, prior art probe-type measurement devices have no way of detecting if the operator moves the measurement device before the settling time has expired or before the predictive algorithm has finished.

To avoid errors arising from premature probe movement, the operator would have to receive a series of instructions on how the device should be used in order to ensure that the measured values are valid. The operator could, for example, be instructed to keep the probe stationary for a specific settling time after giving the start signal. However, since this settling time will depend on the type of material and its coarseness, and on the measurement being performed, the instructions would have to include a complex table where the operator should look up the correct values. Furthermore, if the operator wishes to perform measurement at multiple depths, he or she would have to be instructed to give new stop and start signals every time the probe is pushed to a new depth.

If the operator would fail to follow the instructions correctly, the values obtained from the measurement may be unreliable. It would therefore be preferable to automate the measurement protocol instead of relying on the operator to execute it correctly.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a method and an apparatus which solve the above problems.

The objects of the disclosure are achieved by a method and an apparatus which are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of incorporating a sensor configured to measure motion parameters in a probe-type measurement device for penetrable materials. The motion parameters express how the probe moves in relation to the penetrable material.

An advantage of the method and apparatus of the disclosure is that the measurement device can be programmed to monitor if, when and how the probe moves in relation to the penetrable material. The measurement device may thereby also be programmed to automatically reset or reprogram measurement operations if the probe is moved before a settling time has expired, or before a temperature prediction algorithm has calculated a reliable value. The measurement device may also be programmed to instruct the operator to wait until reliable measurement results have been obtained. Should the operator move the probe too early, the measurement device may be programmed to instruct the operator to keep the probe stationary until a reliable measurement value has been obtained.

When motion parameters are monitored, the operator does not have to follow predetermined instructions on how the device should or should not be moved. Instructions can instead be given as needed, based on what the operator does.

The device may be programmed to autonomously determine whether or not a measurement was reliable. Unreliable values may not be displayed or stored at all, or they may be stored with a marker which indicates that they may be unreliable. In other words, quality control can be programmed into the device and will not be dependent on the operator using the device exactly in a prescribed manner.

In this disclosure, the term “motion parameters” refers to velocity variables, such as depth or distance measured as a function of time. Sensors which measure such variables in conjunction with probe-type measurement devices include, for example, proximity sensors. The term “motion parameters” also refers to acceleration variables, such as velocity measured as a function of time. Sensors which measure such variables include acceleration sensors of various kinds.

Further, the term “motion parameters” also refers to secondary variables which are indirect indicators of probe motion. Force is one such variable. Force transducers of various kinds may be used to measure the force by which the probe is being pushed or pulled when it is inside the penetrable material. It may then be estimated from the measured force whether the probe is in motion or not. The capacitance or electrical conductivity measured by an electrical sensor placed in the probe may also be employed as an indirect indicator of motion in many penetrable materials. In other words, the second sensor may be an electrical sensor. If the probe is stationary, the values of these electric variables typically remain constant around the probe, at least during the relatively short time which is required for a measurement. Therefore, if capacitance or electrical conductivity is continuously monitored, a marked change in either value may be interpreted as an indirect indicator of probe motion.

The “motion parameter” does not have to be a continuous parameter which can assume a range of different values. It may instead be interpreted as a binary value which only reveals that a certain limit has been exceeded, and that the probe is therefore likely to be in motion, without measuring the magnitude of the motion. For example, a metal ball vibration sensor, where a small metallic and mobile mass closes an electric circuit if the sensor undergoes an acceleration which exceeds a certain threshold, may be employed to detect if motion has occurred. A change in capacitance or electrical conductivity, described above, may also be interpreted as a binary (yes/no) motion indicator, because the measured capacitance or electrical conductivity does not in itself provide any quantitative information about the extent or speed of the motion.

Further examples of motion parameter sensors include piezoelectric vibration sensors and mercury switches.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 shows a measurement device according to a first device embodiment.

Figure 2 shows a measurement device according to a second device embodiment.

Figure 3 shows a measurement device according to a third device embodiment.

Figure 4 illustrates a general measurement method.

Figure 5 illustrates a measurement protocol according to a first method embodiment. Figure 6 also illustrates a measurement protocol according to a first method embodiment. Figure 7 illustrates a measurement protocol according to a second method embodiment.

DETAILED DESCRIPTION OF THE DISCLOSURE

General description of measurement device

This disclosure relates to a measurement device for penetrable materials, which comprises an elongated measurement probe configured to penetrate the penetrable material. The elongated measurement probe comprises one or more first sensors configured to measure one or more material parameter values in the penetrable material. The measurement device also comprises a second sensor configured to measure probe motion parameter values which express the movement of the elongated measurement probe in relation to the penetrable material. The device also comprises a control unit configured to read measurement values from the one or more first sensors and from the second sensor. The control unit is also configured to time the measurement of material parameter values with the one or more first sensors in response to receiving probe motion parameter values from the second sensor, or to indicate the reliability of measured or predicted material parameter values in response to receiving probe motion parameter values from the second sensor.

In this disclosure the term “material parameter value” refers primarily to a measured temperature value or electrical value. Measured electrical values may include permittivity or electrical conductivity values. Embodiments for measuring these material parameters will be described in more detail below.

Secondary material parameter values, such as moisture concentration or salinity, can be inferred from permittivity or electrical conductivity values after appropriate calibration experiments have been conducted and the calibration data which correlates to the measured electrical value with the secondary material parameter value has been obtained and stored in the measurement device. Calibration experiments typically have to be conducted separately for each penetrable material and each degree of coarseness. Salinity is of interest especially in the case of soil. Separate calibration experiments may be conducted for soil samples comprising differing amounts of clay.

Technical features common to all three device embodiments will first be described with reference to Figure 1. The illustrated components have not all been drawn to the same scale. A dotted line separates the inside of a body of penetrable material 151 from its surroundings 150. In Figure 1 the device comprises a main unit with an inside and an outside. The main unit is in this case coextensive with the casing 11. The measurement device may in some embodiments be implemented even without a casing, but this alternative will not be separately illustrated.

An elongated measurement probe 12 consists of an inside portion which is inside the main unit, that is, inside the casing 11, and an outside portion which is outside the main unit, that is, outside of the casing 11. The outside portion of the elongated measurement probe 12 can be pushed into a body of penetrable material 151, as illustrated in Figure 1.

The measurement device illustrated in Figure 1 is primarily intended to be a handheld device. A human operator may grab the main unit by wrapping one or two hands around the casing 11, and thrust the probe 12 into a body of penetrable material. The main unit may also comprise a handle attached to the casing to facilitate a more secure grip.

However, the measurement can also be implemented with a machine. In this case the device may not have the kind of casing illustrated in Figure 1. Instead the main unit in the measurement device may be incorporated with the machine. The main unit will nevertheless still comprise an inside and an outside and the probe will consist of a corresponding inside portion and an outside portion.

The outside portion of the elongated measurement probe 12 comprises at least one first sensor configured to measure a material parameter value in the penetrable material 151 which surrounds the probe 12 after it has penetrated the material. The first sensor may be either a temperature sensor or an electrical sensor. In this disclosure, the term “electrical sensor” means a sensor configured to measure permittivity in a capacitive measurement, or to measure electrical conductivity in a resistive measurement, or to perform both of these measurements. The measurement device may comprise only one of these sensors, or one of each. Alternatively, the measurement device may comprise multiple electrical sensors and/or multiple temperature sensors. Both types of sensors will be described in more detail below.

The first sensors are preferably placed close to the tip 18 of the probe 12 to maximize the available measurement depth, but they can be placed anywhere along the length of the probe.

An electrical sensor may, for example, be implemented with a first measurement electrode 19 on the outer surface of the probe and a second measurement electrode 110 at the tip of the probe. These two electrodes may be separated by a dielectric tube 111. The dielectric tube 111 may be made of glass fibre. It should preferably not absorb any moisture. The dielectric tube 111 preferably contains an internal electric wire 117 which facilitates electric contact and measurement between the two electrodes 19 and 110.

The operation principle of this electrical sensor when it used as a moisture sensor will be briefly described. A section 112 of penetrable material surrounds the tip of the probe 12 where the electrical sensor is located. This section may be called the “local” section of penetrable material. The local section consists of the material which affects the electrical measurement performed by the sensor. The physical extent of the local section will vary from one material to another, and it may also depend on the coarseness and density of the material. The sensor can be calibrated for moisture measurements in a specific penetrable material, with a specific coarseness and/or density, without knowing how far the local section extends in each case.

The electrical sensor may perform a capacitive measurement where the surrounding section of biomaterial 112 is used as a dielectric between the two measurement electrodes 19 and 110. The dielectric constant of many penetrable materials changes as a function of moisture concentration.

Alternatively, the electrical sensor may be used as an electrical conductivity sensor which uses the surrounding section of biomaterial 112 as the resistor between the two measurement electrodes 19 and 110. The resistance of many penetrable materials also changes as a function of moisture concentration. The conductivity may be measured either with direct current or alternating current.

Electrical sensors which convert an electrical value into a salinity value operate on the same principle. In this case the permittivity or electrical conductivity of the penetrable material changes as a function of salinity.

The measurement device may comprise a control unit. The control unit may be a part of a computer device which is preferably located inside the casing 11 in Figure 1. The control unit may, for example, comprise several circuit boards 118, 319, 120 in various parts of the moisture concentration measurement device. The probe 12 is preferably hollow, to facilitate transmission of measurement signals. Communication links, such as wires 116, may connect the circuit board 120 in the probe to circuit boards in the main unit.

Circuit board 120 may comprise measurement electronics for sampling the electrical sensor. Alternatively, electrical wires from the electrical sensor may be drawn through the probe to the main unit. The measurement electronics could in this case be located on circuit boards in the main unit.

The temperature sensor may, for example, be a resistive temperature detector, a thermocouple or a diode, which may be placed in direct contact with the inner surface of the hollow probe. The sensor may be glued or soldered to the inner surface. Alternatively, the temperature sensor may be placed on the circuit board 120 in the probe. The measurement electronics for sampling the temperature sensor may again be located either on circuit board 120 in the probe or on a circuit board in the main unit, and electronic connections or communication wires can be drawn through the probe to the main unit as required.

The measurement device may also comprise an interface unit. The interface unit may comprise a display 113, a keyboard 114, a touchscreen, microphones, loudspeakers, or other devices which facilitate user interaction. When the operator starts a measurement, the control unit may prompt the operator to select the type of penetrable material where the method is about to be performed, and possibly also the coarseness of the material.

The control unit may comprise circuitry for implementing audio/video and logic functions on the interface unit. The control unit may also comprise one or more data processors. The control unit may be connected to a memory unit where computer-readable data or programs can be stored. The memory unit may comprise one or more units of volatile or non-volatile memory, for example EEPROM, ROM, PROM, RAM, DRAM, SRAM, firmware or programmable logic. The memory unit may be located on circuit boards in the device.

In addition to the aforementioned components, the measurement device may comprise mechanical components which provide rigidity and structural support. It is especially important that the probe is so strongly supported against the casing, so that it cannot be tilted or bent in relation to the casing. Structural supports are important because the forces which act on the probe when it is pushed into a body of penetrable material can be on the order of a thousand Newtons. However, since these components are not central to the described measurements, they will not be described further in this disclosure.

First device embodiment

In a first device embodiment, the second sensor configured to measure probe motion parameter values is a proximity sensor 121, which may be located on the front side of the casing which faces the body of penetrable material 151, as illustrated in Figure 1. The proximity sensor may, for example, be an infrared sensor which sends infrared pulses toward the body of penetrable material 151 and records their back-and-forth transit time to point 122, where the light is reflected. The proximity sensor 121 is connected to circuit boards in the main unit with communication links.

The proximity sensor determines the proximity distance d, which is illustrated in Figure 1. The control unit may be programmed to sample the proximity sensor at certain time intervals, thereby producing a motion signal which expresses the proximity distance as a function of time. The motion signal may be stored in the memory unit. From the motion signal the control unit may determine whether or not there is/was relative motion between the probe 12 and the penetrable material 151 at any given moment. Alternatively, the control may use the motion signal to determine absolute distance values, such as the penetration depth D, as a function of time. When the length of the probe 12 is L, the penetration depth D equals L - d.

If the penetration depth is to be measured, the operator may be instructed to give a start signal to the control unit when the tip 18 of the probe touches the outer surface of the body of penetrable biomaterial 151, so that the control unit can initiate penetration depth tracking at the right time. Alternatively, if the first sensor is an electric sensor, the control unit may be programmed to initiate penetration depth tracking when the values measured from the first sensor differ from the values which are expected when the probe is surrounded by air. The penetration depth may then be calculated from the proximity data.

When penetration depth tracking is initiated, the control unit may also initiate any of the measurement protocols described below. Alternatively, these measurement protocols may be continuously executed even before the penetration depth tracking is initiated. If penetration depth is not tracked at all, the measurement protocols may also be continuously executed, for example from the moment when the device is turned on.

Second device embodiment

In a second device embodiment, illustrated in Figure 2, the second sensor configured to measure probe motion parameter values is an acceleration sensor. The acceleration sensor may, for example, be a MEMS sensor. The acceleration sensor may be placed on circuit board 120 within the probe, or on any circuit board in the main unit. In Figure 2, acceleration sensor 200 has been placed on circuit board 120.

The control unit may be programmed to sample the acceleration sensor at certain time intervals. The resulting acceleration signal (acceleration as a function of time) may be stored in the memory unit. The control unit may use the acceleration signal to determine whether or not there is/was relative motion between the probe 12 and the penetrable material 151 at any given moment. The control unit can also convert the acceleration signal into a velocity signal (velocity as a function of time) and motion signal (position as a function of time) through numerical integration, and use either of these signals as an indicator of relative motion.

The control unit may also use any of the mentioned signals to calculate absolute distance values. The start signal for the motion measurement may be given by the operator when the tip 18 of the probe touches the outer surface of the body of penetrable biomaterial 151. Alternatively, the control unit may be programmed to initiate the motion measurement automatically when the acceleration signal exceeds a certain threshold value in the direction of the probe 12, in other words acceleration along the x-axis in Figure 2, and in the absence of acceleration in other directions. Especially in dense penetrable materials the static resistive forces which resist the initial break through the 150/151 interface may be larger than the dynamic resistive forces which resist the movement of the probe inside the penetrable material once the probe has broken through the interface. The probe may therefore accelerate quickly in the beginning of a thrust, and the control unit can be programmed to interpret this acceleration peak as the starting point from which absolute distance values, such as penetration depth, can be calculated.

If penetration depth is to be measured, the operator may be instructed to give a start signal to the control unit when the tip 18 of the probe touches the outer surface of the body of penetrable biomaterial 151, so that the control unit can initiate the motion measurement at the right time and calculate the penetration depth. Alternatively, if the first sensor is an electric sensor, the control unit may be programmed to monitor the first sensor continuously and initiate penetration depth tracking when the values measured from the first sensor differ from the values which are expected when the probe is surrounded by air. The penetration depth may then be calculated from the acceleration data.

When the penetration depth tracking is initiated, the control unit may also initiate any of the measurement protocols described below. Alternatively, these measurement protocols may be continuously executed even before the penetration depth tracking is initiated. If penetration depth is not tracked at all, the measurement protocols may also be continuously executed, for example from the moment when the device is turned on.

Third device embodiment

In a third device embodiment, illustrated in Figure 3 the second sensor configured to measure probe motion parameter values is a force transducer. The inside portion of the elongated measurement probe 12 is connected to the main unit through a force transducer which is configured to measure the force acting between the probe and the main unit. To facilitate force measurements, the probe 12 must be at least to some extent mobile along the measurement axis (the x-axis in Figure 3) in relation to the main unit.

The force transducer may include a spring 33 with a known spring constant. The spring 33 may encircle a portion of the probe 12 inside the main unit, as illustrated in Figure 3. A first end 331 of the spring may be fixed to a support structure 34, which may in turn be fixed to the casing 11. A second end 332 of the spring, which may be mobile in relation to the support structure 34, and thereby also mobile in relation to the main unit, may be in contact with the probe 12 for example through a small metal plate 35 which has been welded to the probe 12. The plate 35 may compress the spring 33 in the negative x-direction when the probe 12 is thrust into a body of penetrable material 151. In addition to transmitting the forces acting on the probe 12 to the spring 33, metal plate 35 may be used to prevent the probe 12 from rotating around the x-axis.

The force transducer illustrated in Figure 3 can also be converted to measure the pull force required to withdraw the probe 12 from the body of penetrable material 151. The plate 35 may, for example, be permanently attached to the second end 332 of the spring and the spring may be given more room to expand in the positive x-direction. Alternatively, the plate 35 or an equivalent structure could be placed in contact with two separate springs, one for measuring the pushing force during a thrust, and another for measuring the pull force during withdrawal. The two springs could both encircle the inside portion of the probe 12. Alternatively, one or both of them could be placed aside from the inside portion of the probe 12 and mechanically linked to the probe with suitable mechanical means.

The force transducer may include a magnet 36 which is attached to the probe 12 and thereby at least partly mobile in relation to the casing. The force transducer may further include a Hall sensor 37 for detecting the movement of the magnet 36. The Hall sensor 37 may be fixed to the casing or to a support structure such as 34, so that it is not mobile in relation to the casing. The movement of the magnet 36 is detected by Hall sensor 37. Since the spring constant of the spring 33 is known, the momentary force acting on the probe 12 along the measurement axis can be calculated.

The control unit may read a force measurement value from the force transducer. This force measurement value may be converted into a binary motion parameter value. A threshold force measurement value, specific to each type of penetrable material and each degree of coarseness, may be experimentally determined and then programmed into the control unit. The control unit may be programmed so set the binary motion parameter value to a value which corresponds to “moving probe” when the force measurement value exceeds the threshold. The control unit may be programmed so set the binary motion parameter value to a value which corresponds to “stationary probe” when the force measurement value is below the threshold. The motion signal may comprise this binary motion parameter value as a function of time.

In this third device embodiment the force transducer may also be used as the start indicator in a similar manner as the acceleration sensor in the second device embodiment. After the device has been turned on, the control unit may continuously monitor the force transducer and interpret a force measurement value which exceeds a certain threshold as an indicator of penetration, and thereby initiate other measurements. Other methods described above for initiating measurements may also be used. However, it may be noted that the force transducer data can generally not be used for penetration depth tracking, so there may be no need to start any measurement precisely when the probe is at the surface of the penetrable material.

Measurement methods

This disclosure also relates to a method for performing measurements in a body of penetrable material, wherein a device comprising a main unit is provided, the device comprising an elongated measurement probe. One or more first sensors configured to measure one or more material parameter values in the penetrable material are provided in the elongated measurement probe. A second sensor configured to measure probe motion parameter values, which express the movement of the elongated measurement probe in relation to the penetrable material, is provided in the measurement device. A control unit which is configured to read measurement values from the one or more first sensors and from the second sensor is also provided and at least a part of the elongated measurement probe is pushed into the body of penetrable material. The control unit times the measurement of material parameter values in response to receiving probe motion parameter values, or indicates the reliability of measured or predicted material parameter values in response to receiving probe motion parameter values. The control unit stores the material parameter value and/or presents it to a user.

This method is illustrated in its general form in Figure 4.

First method embodiment

The first method embodiment relates to temperature measurements. The control unit may be programmed to monitor motion parameter values measured by the second sensor and to regulate the temperature measurements, and the display of results, based on the measured motion parameter values.

As explained in the background section, a probe-type measurement device which performs a temperature measurement requires a certain settling time after penetration before it reaches thermal equilibrium with the surrounding material. Predictive algorithms may be used to predict the temperature at equilibrium before it is reached. Even when predictive algorithms are used, a certain settling time (shorter than the settling time to equilibrium) is needed before the prediction reaches a given level of reliability.

If the temperature sensor is not in direct physical contact with the probe surface, there may be a temperature difference between them, and the sensor may respond to changes in probe surface temperature with a small delay. This may affect the predictive algorithm especially if frictional forces heat the probe significantly when it is in motion. If a probe is thrust into a penetrable material whose temperature is below that of the probe, then the measured temperature values may at first show an increasing trend as the frictional heat stored at the probe surface makes its way towards the sensor. Only after a delay will the measured temperature values reverse direction and show decreasing values. This change of direction may lead the predictive algorithm to calculate erroneous predictions. The problem can be overcome by enforcing a settling time which is sufficiently long to allow thermal transfer between the probe surface and the sensor, or by configuring the control unit to reset the predictive algorithm if the measured temperature time series reverses direction.

The motion signal indicates when the probe is in motion. As explained above, in dense penetrable materials frictional forces can warm the probe significantly when it moves in the material. The settling time counter, which determines when the settling time has passed, may therefore have to be reset every time the motion signal indicates that the probe has moved to a new location. When the measurement device is used in less dense penetrable materials the heating due to friction may be insignificant, but the settling time counter may nevertheless be reset every time the probe moves. The temperature at the new location may not be equal to the temperature at the previous location.

The control unit may be programmed to continuously display and update temperature measurement values on the interface unit after the start signal has been received (regardless of what values the motion signal obtains). This displayed value may be the most recently measured temperature value, an average of the most recently measured temperature values, or a prediction based on recent temperature values. However, since measurements and predictions obtained when the probe was in motion, or soon after the probe was in motion, can be unreliable, the control unit may be programmed to indicate this unreliability to the operator. This indication can, for example, be performed by showing the value in red colour on the interface unit. The control unit may be programmed to show reliable values in black colour. With the help of the motion signal and a settling time countdown, the control unit may be programmed to determine when the colour of the colour of the temperature values shown on the interface unit can be turned black.

An exemplary temperature measurement protocol for this method is illustrated in Figure 5. The illustrated method is one where the temperature is displayed continuously. The control unit first receives a start signal (51). The start signal can, for example, be automatically generated when the operator turns on the device. In this case the control unit starts to execute the temperature measurement protocol immediately when it is turned on. Alternatively, the control unit may instruct the operator to give a start signal when the tip of the probe has been placed at the surface of the penetrable material, ready to be thrust in. Another alternative is that the control unit instructs the operator to give a start signal when the tip of the probe is already inside the body of penetrable material.

After receiving a start signal, the control unit may be programmed to initiate the temperature measurements immediately and display the initial measurement results or predictions while indicating their unreliability (52), for example with the colour coding discussed above. The control unit may be programmed to then monitor the motion signal (53), obtained from one of the second sensors described above, until the probe comes to a halt (53, 54). When the motion signal indicates that the probe is stationary, the control unit may be programmed to initiate a settling time count (55) which measures the elapsed time since the control unit determined that the probe was stationary.

The settling time T required for a reliable temperature measurement or prediction may be experimentally determined and programmed into the control unit before or after the measurement device is put into operation. Separate experiments may be conducted to determine the required settling time for each type of penetrable material and each degree of coarseness.

The control unit may be programmed to check the motion signal while the settling time count is in progress (56, 57, 58). It may be programmed to return to step 53 if the probe is moved before the settling time count has expired (in other words, if the probe is moved before the probe has remained stationary for the entire settling time).

The control unit may be programmed to reset or extend the settling time count if it returns from step 57 to step 53. The measurement protocol is strict if the control unit always resets the settling time count to its initial value T in step 55, even when only a small movement was detected in steps 57, 53 and 54. It may be preferable in some applications to reset the settling time in step 55 to another value Τ’, which may be a function on how much probe motion was detected in steps 57, 53 and 54.

For example, say that the settling time T was initially set to 2 minutes in step 55, but after 1 minute and 30 seconds had elapsed in steps 56-58, the probe was moved 5 cm inward. In this case it may not be necessary to reset the settling time count back to 2 minutes again since the movement was so small. The control unit may therefore be programmed to detect if the movement was small, and then to extend the settling time to a new settling time Τ’, which may, for example, be 1 minute. In other words, if the probe is moved only a short distance, the control unit may be programmed to merely lengthen the time which remains of the initial settling time, instead of entirely resetting the settling time counter back to its initial value.

The decision to reset the settling time entirely upon movement, or merely to lengthen the remainder, can also be based on experimental studies conducted before or after the measurement device is put into operation. As mentioned above, frictional forces may significantly heat the probe in dense penetrable materials, especially if the probe moves at high speed for a fairly long distance. Threshold distances, threshold speeds, and/or threshold force measurement values, which are considered to necessitate a complete reset of the settling time, may be experimentally determined for each material.

When the settling time count expires, without the probe having been moved during the count, the control unit may be programmed to switch the reliability indicator (the colour, for example, as mentioned above) of displayed temperature values or predictions from “unreliable” to “reliable”, to show that the indicated values or predictions are now reliable (59). The measured temperature values may be stored in a memory unit, with associated reliability/unreliability indicators.

The control unit may then be programmed to continuously display and/or store the measured temperature values or predictions as reliable until the probe is again put into motion (510). If the motion signal again indicates that the probe has been set in motion, the control unit may be programmed to switch the reliability indicator back to “unreliable” (511) and return to step 53.

An alternative to continuous displaying of measured temperature values and the use of reliability indicators is that the control unit may be programmed to refrain from displaying any measured temperature values or predictions on the interface unit unless it has determined from the motion signal and the settling time countdown that the most recently measured temperature values or predictions are reliable. In other words, after the control unit has received a start signal, the screen on the interface unit may remain blank until reliable measurement values or predictions have been obtained. No reliability indication by colours or other means is necessary in this case, because unreliable results are not displayed at all.

An exemplary temperature measurement protocol for this method is illustrated in Figure 6. Steps 61-67 and 610 in this protocol are the same as steps 51, 53-58 and 510 in the measurement protocol presented in Figure 5. In the protocol presented in Figure 6 the control unit has been programmed to refrain from displaying measurement results or predictions before the settling time has passed, at step 68. The control unit has also been programmed to cease displaying measurement results or predictions when it retrieves a motion signal which indicates that the probe is again in motion (611). If the control unit is programmed to display measurement results directly, the control unit may also be programmed to start the temperature measurement at step 68 and pause the measurement at step 611. Alternatively, the control unit may be programmed to continuously perform temperature measurements even in steps 62-67, but to display results or predictions only at step 68 and cease displaying them at step 611. The latter approach may be adopted especially if the displayed value is a prediction which requires a time series of measured values.

Second method embodiment

The second method embodiment relates to electrical measurements, which may be converted into moisture concentration or salinity measurements with appropriate calibration data, as already described above. The control unit may be programmed to monitor motion parameter values measured by the second sensor and to regulate the electrical measurement, and the display of results, based on the measured motion parameter values.

Similarly to the first method embodiment, the control unit may be programmed to continuously display and update electrical measurement values, or corresponding moisture concentration I salinity values, on the interface unit after the start signal has been received (regardless of what values the motion signal obtains). This displayed value may be the most recently measured value, or an average of the most recently measured values. The control unit may be programmed to indicate the reliability of each measured value. Unreliable values can, for example, be indicated by showing them in red colour on the interface unit. The control unit may be programmed to show reliable values in black colour. With the help of the motion signal, the control unit may be programmed to determine when the indication colour can be turned from red to black.

An exemplary measurement protocol is illustrated in Figure 7. After receiving a start signal (71) the control unit initiates electrical measurements and motion measurements (72). The electrical measurement may take a moment if, for example, several data points are needed to calculate one measurement value. The control unit monitors the motion signal during the measurement (73). When the control unit concludes the measurement (74), it checks if the probe moved during the measurement (75). If it did not move, the measurement value may be displayed and it may be indicated that it is a reliable value (76). If it did move, the result may be displayed and it may be indicated that it is an unreliable value (77). Alternatively, the control unit may be programmed to refrain from displaying any electrical measurement values, or corresponding moisture concentration or salinity values, unless the control unit has determined from the motion signal that the most recently measured electrical values are reliable. This alternative is not separately illustrated.

Claims (14)

1. A measurement device for penetrable materials, which comprises - an elongated measurement probe configured to penetrate the penetrable material, the elongated measurement probe comprising one or more first sensors configured to measure one or more material parameter values in the penetrable material, characterized in that - the measurement device also comprises a second sensor configured to measure probe motion parameter values which express the movement of the elongated measurement probe in relation to the penetrable material, and that - the measurement device also comprises a control unit configured to read measurement values from the one or more first sensors, and from the second sensor, and that - the control unit is configured to time the measurement of material parameter values with the one or more first sensors in response to receiving probe motion parameter values from the second sensor, or to indicate the reliability of measured or predicted material parameter values in response to receiving probe motion parameter values from the second sensor.
2. The device according to claim 1, characterized in that the one or more first sensors includes a temperature sensor and the one or more material parameters include temperature.
3. The device according to claim 1, characterized in that the one or more first sensors includes an electrical sensor and the one or more material parameters include permittivity, electrical conductivity, moisture concentration or salinity.
4. The device according to any of claims 2-3, characterized in that the second sensor is a proximity sensor.
5. The device according to any of claims 2-3, characterized in that the second sensor is an acceleration sensor.
6. The device according to any of claims 2-3, characterized in that the second sensor is a force transducer.
7. The device according to any of claims 2-3, characterized in that the second sensor is an electrical sensor.
8. A method for performing measurements in a body of penetrable material, wherein - a measurement device comprising an elongated measurement probe is provided, one or more first sensors configured to measure one or more material parameter values in the penetrable material are provided in the elongated measurement probe, characterized in that - a second sensor configured to measure probe motion parameter values, which express the movement of the elongated measurement probe in relation to the penetrable material, is provided in the measurement device, - a control unit which is configured to read measurement values from the one or more first sensors, and from the second sensor, is provided, - at least a part of the elongated measurement probe is pushed into the body of penetrable material, - the control unit times the measurement of material parameter values in response to receiving probe motion parameter values, or indicates the reliability of measured or predicted material parameter values in response to receiving probe motion parameter values, - the control unit stores the material parameter value and/or presents it to a user.
9. The method according to claim 8, characterized in that the one or more first sensors includes a temperature sensor and the one or more material parameters include temperature.
10. The method according to claim 8, characterized in that the one or more first sensors includes an electrical sensor and the one or more material parameters include permittivity, electrical conductivity, moisture concentration or salinity.
11. The method according to any of claims 9-10, characterized in that the second sensor is a proximity sensor.
12. The method according to any of claims 9-10, characterized in that the second sensor is an acceleration sensor.
13. The method according to any of claims 9-10, characterized in that the second sensor is a force transducer.
14. The method according to any of claims 9-10, characterized in that the second sensor is an electrical sensor.
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