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Hukseflux HFP01SC User Manual

Self-calibrating heat flux sensor
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Hukseflux
Thermal Sensors
USER MANUAL HFP01SC
TM
Self-calibrating heat flux sensor
Copyright by Hukseflux | manual v1624 | www.hukseflux.com | info@hukseflux.com

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  • Page 1 Hukseflux Thermal Sensors USER MANUAL HFP01SC Self-calibrating heat flux sensor Copyright by Hukseflux | manual v1624 | www.hukseflux.com | info@hukseflux.com...

  • Page 2: Warning Statements

    Putting more than 20 Volt across the heater wiring can lead to permanent damage to the heater. Do not use “open circuit detection” when measuring the sensor output. HFP01SC manual v1624 2/39...

  • Page 3: Table Of Contents

    Trouble shooting Calibration and checks in the field Appendices Appendix on cable extension / replacement Appendix on standards for calibration Appendix on calibration hierarchy Electrical connection of HFP01SC supplied by Campbell Scientific USA EU declaration of conformity HFP01SC manual v1624 3/39...

  • Page 4: List Of Symbols

    (soil) surface surface property of the surrounding soil soil property of the heater heater property obtained by self-test selftest property obtained by self-calibration selfcalibration property of the current-sensing resistor current HFP01SC manual v1624 4/39...

  • Page 5: Introduction

    It survives long-term installation in soils. In essence, HFP01SC is a combination of a heat flux sensor and a film heater. The heat flux sensor output is a voltage signal that is proportional heat flux through the sensor. At a regular interval the film heater is activated to perform a self-test.
  • Page 6 Every 6 h, the HFP01SC film heater is switched on to perform a self-test. During the self- test the normal heat flux measurement is interrupted. Analysis of the heat flux sensor response to heating, the self-test, serves two purposes: •...
  • Page 7 Figure 0.2 HFP01SC. The opposite side has a red cover. Standard cable length is 5 m (2 cables). The uncertainty of a measurement with HFP01SC is a function of: calibration uncertainty, use of self-calibration • differences between reference conditions during calibration and measurement •...

  • Page 8: Ordering And Checking At Delivery

    DC voltage measurement, typically the 100 x 10 VDC range or lower. Expose the sensor heat, for instance touching it with your hand, or activating the HFP01SC heater by putting 9 to 12 VDC across the green and brown wires of cable [2]. The signal should read >...

  • Page 9: Instrument Principle And Theory

    Using the heat flux sensor of HFP01SC is easy. For readout the user only needs an accurate voltmeter that works in the millivolt range. To convert the measured voltage, U, , a constant that is to a heat flux Φ, the voltage must be divided by the sensitivity S...
  • Page 10 The exact sensitivity of the sensor is determined at the manufacturer by calibration, and is found on the calibration certificate that is supplied with each sensor. Heat flux sensors such as HFP01SC, for use in the soil, are typically calibrated under the following reference conditions: conductive heat flux (as opposed to radiative or convective) •...

  • Page 11: The Self-Test And Self-Calibration

    2.2 The self-test and self-calibration A self-test is started by switching on HFP01SC’s heater, while recording the sensor output signal and the heater power, and finalised by switching the heater off. During the heating interval a current is fed through the film heater, which generates a known heat flux.
  • Page 12 The signal level during the self-test, multiplied by 2, is used for self- calibration. The newly measured sensitivity compensates for the deflection error, and also for temperature dependence of the sensitivity and non-stability of the sensor. HFP01SC manual v1624 12/39...

  • Page 13: Programming The Self-Test And Self-Calibration

    For accurate measurements the exact value of Rheater must be entered into the equation. The value of A is its nominal heater value. The value of R is its nominal value, assuming use of a 0.1 % resistor. current HFP01SC manual v1624 13/39...
  • Page 14 (of which +5 % due to temperature dependence). 2.3.3 Program summary In case the user writes his own software program for controlling the HFP01SC selft-test, the program flow in table 2.3.3.1 may be used. Table 2.3.3.1 a summary of a program for control of the self-test...

  • Page 15: Specifications Of Hfp01Sc

    Working completely passive, using a thermopile sensor, HFP01SC generates a small output voltage proportional to this flux. HFP01SC is equipped with a film heater. The heater may be used to perform an on-line self-test. Analysis of the self-test results in improved quality assurance and accuracy of the measurement.
  • Page 16 Table 3.1 Specifications of HFP01SC (started on previous page, continued on next page) Sensor diameter including guard 80 x 10 Sensing area 8 x 10 Sensing area diameter 32 x 10 Passive guard area 42 x 10 (a passive guard is required by ISO 9869)
  • Page 17 Table 3.1 Specifications of HFP01SC (started on previous pages) CALIBRATION Calibration traceability to SI units Product certificate included (showing calibration result and traceability, as well as film heater resistance and surface area) Factory calibration method method HFPC01, according to ASTM C1130...

  • Page 18: Dimensions Of Hfp01Sc

    3.1 Dimensions of HFP01SC Figure 3.1.1 HFP01SC heat flux sensor dimensions in x 10 film heater heat flux sensor plus passive guard 2 x cable (standard length 5 m, optionally longer cable in multiples of 5 m, cable above 20 m in multiples of 10 m) Total sensor thickness including heater and covers is 5.6 x 10...

  • Page 19: Standards And Recommended Practices For Use

    The heat flux in the soil at 0.05 m depth is usually between -100 and +300 W/m The measurement of the soil heat flux with HFP01SC using the self-test is more reliable and accurate than without the self-test. However, there still is a large source of uncertainty: 1.
  • Page 20 Figure 4.2.1 typical meteorological surface energy balance measurement system with HFP01SC installed under the soil. Ad 2: For various reasons, practical as well as scientific, the heat flux plate must be installed under the soil, and not directly at the soil surface. First, the self-calibration only works when the sensor is surrounded by soil.
  • Page 21 The heat capacity of water is known, but the other quantities of the equation are difficult to determine and vary with location and time. The storage term may be the main source of uncertainty in the soil energy balance measurement. A typical value for dry soil heat capacity is 840 J/(kg·K) HFP01SC manual v1624 21/39...

  • Page 22: Installation Of Hfp01Sc

    Installation of HFP01SC 5.1 Site selection and installation Table 5.1.1 Recommendations for installation of HFP01SC Location preferably install in a large field which is relatively homogeneous and representative of the area under observation. Orientation recommended orientation is with the red side of the sensor facing upwards.

  • Page 23: Electrical Connection

    5.2 Electrical connection HFP01SC has two separate cables, one for the signal, cable 1, and one for the heater, cable 2. An HFP01SC should be connected to a measurement and control system, typically a so- called datalogger. HFP01SC’s heat flux sensor is a passive sensor that does not need any power.
  • Page 24 3 and 4. The heater current is usually measured using a 10 Ω current sensing resistor (not included with HFP01SC) (3) in series with the heater, and by measuring the voltage across the resistor, at datalogger inputs 5 and 6.

  • Page 25: Requirements For Data Acquisition / Amplification

    5.3 Requirements for data acquisition / amplification The selection and programming of dataloggers is the responsibility of the user. To see if directions for use with HFP01SC are available: contact the supplier of the data acquisition equipment. Table 5.3.1 Requirements for data acquisition, amplification and control equipment for...

  • Page 26: Making A Dependable Measurement

    Statements about the overall measurement uncertainty can only be made on an individual basis, taking all these factors into account. When measuring in soils, we recommend using model HFP01SC to get a higher level of quality assurance and accuracy of the measurement. HFP01SC’s self-test partially compensates for the temperature dependence, non-stability and the deflection error.

  • Page 27: Typical Measurement Uncertainties

    HFP01SC measurement. 6.3 Contributions to the uncertainty budget When measuring in soils, we recommend using model HFP01SC to get a higher level of quality assurance and accuracy of the measurement. HFP01SC’s self-calibration compensates for the temperature dependence, non-stability and the deflection error. We usually assume that the self-check including the self-calibration reduces usual uncertainties related to non-stability, temperature dependence and deflection by 50 %.
  • Page 28 When measuring in soils, we recommend using model HFP01SC to get a higher level of quality assurance and accuracy of the measurement. We usually assume that the self- check including the self-calibration reduces usual uncertainties related to deflection by 50 %.
  • Page 29 6.3.4 uncertainty caused by temperature dependence HFP01SC’s temperature dependence specification is < 0.1 %/°C. This means that for every °C deviation from the 20 °C reference temperature, 0.1 % uncertainty should be added in the uncertainty budget, unless the self-calibration is used.

  • Page 30: Maintenance And Trouble Shooting

    Maintenance and trouble shooting 7.1 Recommended maintenance and quality assurance HFP01SC measures reliably at a low level of maintenance. Unreliable measurement results are detected by scientific judgement, for example by looking for unreasonably large or small measured values of heat flux, response time during the self-test and sensitivity measured during the self-test.

  • Page 31: Trouble Shooting

    VDC range or lower. Expose the sensor heat, for instance touching it with your hand, or activating the HFP01SC heater by putting 9 to 12 VDC across the green and brown wires of cable [2]. The signal should read > 2 x 10 V now.

  • Page 32: Calibration And Checks In The Field

    Usually mounted side by side. Hukseflux main recommendations for field calibrations relative to a reference sensor are: 1) to compare to a calibration reference of the same brand and type as the field sensor 2) to connect both to the same electronics, so that electronics errors (also offsets) are eliminated.
  • Page 33 HFP01SC manual v1624 33/39...

  • Page 34: Appendices

    Appendices 8.1 Appendix on cable extension / replacement HFP01SC is equipped with two cables. Keep the distance between data logger or amplifier and sensor as short as possible. Cables may act as a source of distortion by picking up capacitive noise. In an electrically “quiet” environment the HFP01SC cables may be extended without problem to 100 metres.

  • Page 35: Appendix On Standards For Calibration

    6 that a guarded hot plate, a heat flowmeter, a hot box or a thin heater apparatus are all allowed. Hukseflux employs a thin heater apparatus, uses a linear function according to X1.1 and uses a nominal temperature of 20 °C, in accordance with X2.2.

  • Page 36: Electrical Connection Of Hfp01Sc Supplied By Campbell Scientific Usa

    8.4 Electrical connection of HFP01SC supplied by Campbell Scientific USA Sensors supplied by Campbell Scientific USA have a different wiring diagram. The 10 Ω current sensing resistor is included in the sensor cabling using heat-shrink tubing with hot-melt adhesive. Table 8.4.1 FOR SENSORS SUPPLIED BY CAMPBELL USA ONLY: connections of cable 1 heat flux sensor signal.

  • Page 37: Eu Declaration Of Conformity

    8.5 EU declaration of conformity Hukseflux Thermal Sensors B.V. Delftechpark 31 2628 XJ Delft The Netherlands in accordance with the requirements of the following directive: 2014/30/EU The Electromagnetic Compatibility Directive hereby declare under our sole responsibility that: Product model: HFP01SC...
  • Page 39 © 2016, Hukseflux Thermal Sensors B.V. www.hukseflux.com Hukseflux Thermal Sensors B.V. reserves the right to change specifications without notice.

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