Patent Description:
As a measuring instrument for measuring the intensity of a sunlight (amount of solar radiation / solar irradiance), an article is known which detects the solar emitted light by a prescribed detector, and measures the meteorological amount regarding the solar radiation. Especially, a device called an pyranometer has been widely used. For example, with the pyranometer described in Patent Document <NUM>, a thermal type sensor is used for the detector.

With such a pyranometer, dew or frost is deposited on the dome according to external environment, so that the amount of an emitted light passing through the dome is increased or decreased. The pyranometer described in Patent Document <NUM> is configured such that a heat generating component is brought into thermal contact with at least a part of the dome in order to suppress generation of dew or frost generated at the dome, thereby heating the dome. Further, Patent Document <NUM> describes a pyranometer in which the air inside the pyranometer is heated, and the heated air is circulated in a dome of a double structure by a ventilator, thereby suppressing generation of dew or frost generated at the dome. <CIT> discloses an improved net radiometer that measures the total net difference between incoming solar and surface reflected radiant short-wave solar energy flux, and inclusive of the down and upwelling long-wave infrared terrestrial radiant energy flux, within the combined short-wave and long-wave far infrared spectral range is disclosed. Disclosed are net radiometers with thermal absorbers structured to reduce wind sensitivity while maintaining or improving response time. Also disclosed are net radiometers that are configured in a novel way to reduce moisture and water accumulation on the thermal absorber surfaces. In addition, net radiometers are disclosed where the components are configured and thermal absorber structured to reduce unit-to-unit inconsistencies and minimize absorber sensitivity asymmetry effect between the upper and lower instrument absorbers. <CIT> discloses a to a Pyranometer with a housing, a sensor in said housing, an inner window and an outer window both overlying the sensor. The invention is characterized in that the outer window has a relatively high transmission coefficient below an upper wavelength value that is larger than the upper wavelength value of the inner window, wherein the outer window has a thermal conductivity which is at least <NUM> times higher than the thermal conductivity of the inner window, preferably at least <NUM> times higher and most preferably at least <NUM> times higher, an internal heating member (<NUM>) being enclosed by the housing for transferring heat to the housing and to the inner and outer window for prevention of deposition of - and removal of moisture and/or ice. <CIT> discloses a orced ventilation cover for a photo-thermal total radiation meter. A ventilation cover support tray is fixedly arranged on the upper end surface of a ventilation cover installation platform through ventilation cover support stand columns. A blower fan is fixedly arranged on the lower end surface of the ventilation cover support tray. A filtration dust cover is fixedly arranged outside the blower fan. A heating component is fixedly arranged on the upper end surface of the ventilation cover support tray. Photo-thermal total radiation meter fixation screws for the photo-thermal total radiation meter are fixed to the upper end surface of the heating component. A ventilation cover housing is covered outside the photo-thermal total radiation meter and the ventilation cover support tray and is fixed to the photo-thermal total radiation meter fixation screws through ventilation cover housing fixation screws. The technical effects of the forced ventilation cover for the photo-thermal total radiation meter are that: the influence on the temperature due to cold weather in the measuring process of the radiation meter is reduced; reliability of the photo-thermal total radiation meter working in severe weather is improved; and working maintenance-free period of the radiation meter is greatly prolonged.

Herein, with the pyranometer described in Patent Document <NUM>, the heat generating component is brought into thermal contact with the dome. For this reason, the heat of the heat generating component is merely supplied to the dome by local thermal conduction. At this step, for example, when the temperature of the housing is decreased by external environment, the heat from the heat generating component escapes to the housing, which makes it difficult to continuously supply a heat to the dome with stability. As a result, dew or frost may have not been sufficiently suppressed from being generated.

On the other hand, such a pyranometer as described in Patent Document <NUM> has a movable part referred to as a ventilator, and hence is inferior in durability, and the movable part requires a driving electric power, and hence consumes energy. As a result, undesirably, others than the heat generating component also generate a heat.

Under such circumstances, it is an object of the present invention to provide a pyranometer capable of measuring the precise amount of solar radiation continuously and stably while suppressing generation of dew or frost by a simple configuration even in changing external environment.

The dependent claims defined embodiments of the invention.

In accordance an embodiment the heat generating component is provided opposite to the opening at which the dome is provided in a housing. The heat generated by the heat generating component is first conducted to the housing having thermal conductivity, thereby heating the whole housing. Further, the heat of the heated housing is propagated to the dome provided at the opening of the housing. Further, the radiant heat from the housing heats the air around the dome. As a result, the dome and the air around the dome are warmed, so that generation of dew or frost is suppressed. With the pyranometer in accordance with the embodiment, the heating component heats the whole housing with a large heat capacity. For this reason, the temperature of the whole housing is less likely to be changed even when external environment is changed, so that the dome is heated continuously and stably.

The present invention can provide a pyranometer capable of measuring the precise amount of solar radiation continuously and stably while suppressing generation of dew or frost by a simple configuration even in changing external environment.

By reference to the accompanying drawings, preferred embodiments of the present invention will be described. Incidentally, in respective drawings, the ones given the same reference numerals and signs have the same or similar configuration. Incidentally, in the following description, the upper side of the drawing is referred to as "upper"; the lower side, as "lower"; the left side, as "left"; and the right side as "right".

<FIG> shows a cross sectional view of a pyranometer <NUM> in accordance with the present embodiment. The pyranometer <NUM> is a device for measuring solar irradiance with respect to the incident light from the hemispheroidal range as seen from the pyranometer <NUM>. The pyranometer <NUM> has, for example, a housing <NUM>, a dome <NUM>, a diffuser <NUM>, a sensor part <NUM>, and a heat generating element <NUM>.

The housing <NUM> has a barrel part <NUM>, a ceiling part <NUM>, a bottom part <NUM>, and a leg parts <NUM>, <NUM>, and <NUM>. The housing <NUM>, particularly, the barrel part <NUM>, the ceiling part <NUM>, and the bottom part <NUM> are preferably formed of a material having a prescribed or more strength, and a thermally conductive material having a prescribed or more thermal conductivity, and is preferably formed of, for example, a metal material such as aluminum, brass, or alloy iron.

The barrel part <NUM> has, for example, a cylindrical shape, is connected at the upper end thereof with the ceiling part <NUM>, and is connected at the lower end thereof with the bottom part <NUM>.

The ceiling part <NUM> has, for example, a truncated conical shape, and has an opening <NUM>. The opening <NUM> is provided at the top of the ceiling part <NUM>. The opening <NUM> penetrates from the upper surface to the lower surface of the ceiling part <NUM>. The opening <NUM> is stepped in the vicinity of the upper surface, and has a dome adhesion surface <NUM> at the stepped portion.

The bottom part <NUM> has, for example, a flat-sheet shape, and is connected with the lower end of the barrel part <NUM>. The bottom part <NUM> has a function as the base of the pyranometer <NUM>.

The leg parts <NUM>, <NUM>, and <NUM> are provided at the bottom part <NUM>. The pyranometer <NUM> is set at the installation surface (not shown) via the leg parts <NUM>, <NUM>, and <NUM>.

The dome <NUM> has, for example, a hemispheroidal shape, and is provided at the opening <NUM>. The dome <NUM> is glued at the circumferential edge thereof to the dome adhesion surface <NUM>, and thereby is mounted at the housing <NUM>. The shape of the dome <NUM> may not be necessarily a perfect hemispheroidal shape, and may only be a shape capable of taking in a light from all directions of the sky. The dome <NUM> can be formed of, for example, a material having a light transmittance such as glass.

The side surface inside the barrel part <NUM>, the upper surface of the bottom part <NUM>, and the inner surface of the dome <NUM> form the internal space S in the housing <NUM>.

The diffuser <NUM> is an optical component configured so as to diffuse and transmit an incident light therethrough. The diffuser <NUM> is arranged at a position opposed to a sensor element <NUM> described later, and is configured such that a light passing though the dome <NUM> is diffused and transmitted through the diffuser <NUM>, and is made incident upon the sensor element <NUM>.

The sensor part <NUM> includes a sensor element <NUM> and circuit boards <NUM> and <NUM>. The sensor element <NUM> is provided at a position opposite to the dome <NUM> across the diffuser <NUM> in the internal space S of the housing <NUM>. The sensor element <NUM> is a detecting means capable of outputting an electric energy in accordance with the light amount of the solar radiation, and is, for example, a thermal type sensor. As the thermal type sensor, for example, a thermocouple, a thermistor, a Peltier element, or a thermopile can be used. When the sensor element <NUM> is a thermocouple, the sensor element <NUM> is configured such that an incident light (light energy) is converted into a heat (heat energy), and an electric signal corresponding to the heat is outputted.

The circuit boards <NUM> and <NUM> are provided in the internal space S of the housing <NUM>. The circuit boards <NUM> and <NUM> are connected with the sensor element <NUM> and the heat generating element <NUM> via a wire (not shown). The circuit boards <NUM> and <NUM> are each provided with a circuit for performing signal processing and control at the pyranometer <NUM>. For example, each circuit (described later) provided at the circuit boards <NUM> and <NUM> processes an electric signal from the sensor element <NUM>, and calculates the amount of solar radiation, or the like. Each circuit of the circuit boards <NUM> and <NUM> is connected with an external device and a power supply (not shown). The pyranometer <NUM> can communicate with the external device, and can be supplied with power supply via the circuit. Incidentally, the number of the circuit boards is not required to be two as shown in <FIG>, may be one, and may be more plural.

The sensor element <NUM> and each circuit provided at the circuit boards <NUM> and <NUM> form the sensor part <NUM> for calculating the solar irradiance, or the like in a functionable manner.

The heat generating element <NUM> is a circuit element as a component for generating a heat according to the electric power consumption (heat generating component). The heat generating element <NUM> is provided opposite to the opening <NUM> across the internal space S so as to be in contact with the bottom part <NUM>. Incidentally, the wording "opposite across the internal space S" does not mean the geometrically exactly opposite position, and is a wide concept including the inner surface region of the housing <NUM> such that the opening <NUM> and the heat generating element <NUM> are separated from each other by the internal space S. The region is, at least, the region except for the vicinity of the opening <NUM>. For example, the region is the central part of the bottom part <NUM> at the position opposite to the ceiling part <NUM> having the opening <NUM>. The heat generating element <NUM> is provided in a manner enabling the thermal conduction to the housing <NUM> via the bottom part <NUM>. The heat generating element <NUM> is, for example, screwed and mounted to the bottom part <NUM> so as to be thermally connected with the housing <NUM>. Further, the heat generating element <NUM> may be mounted to the bottom part <NUM> using a heat dissipating seal or a heat dissipating adhesive. The heat generating element <NUM> is preferably a circuit element having a relatively large heating value, and capable of controlling the heating value, and is, for example, a MOS-FET. Further, the heat generating element <NUM> may be an element such as a bipolar transistor, a J-FET, an IGBT, or a diode.

The heat generating element <NUM> is, for example, connected to a power supply common with the power supply for driving the sensor part <NUM>. The heat generating element <NUM> is supplied with a power supply, and generates a heat according to the electric power consumption in the heat generating elements <NUM>. The heat generated by the heat generating element <NUM> is first transmitted to the bottom part <NUM>. The heat transmitted to the bottom part <NUM> is transmitted to the barrel part <NUM>, and is transmitted to the ceiling part <NUM>. As a result, the whole housing <NUM> is heated by the heat generating element <NUM>. The housing <NUM> transmits a heat to the dome <NUM> via the ceiling part <NUM>. As a result, the dome <NUM> is heated. Further, the radiant heat radiated from the ceiling part <NUM> warms the air in the periphery of the dome <NUM>. The dome <NUM> and the air around the dome <NUM> are heated, resulting in an increase in the temperature of the dome <NUM> and the temperature of the air in the periphery of the dome <NUM>. This suppresses the generation of dew or frost at the dome <NUM>.

With the pyranometer <NUM>, heating of the whole housing <NUM> increases the stability of the temperature of the dome <NUM> against the change in external environment such as wind or rain. This is because the housing <NUM> is larger in size than the dome <NUM>, and is sufficiently larger in heat capacity than the dome <NUM>. Therefore, when the decrease in temperature due to external environment is caused at each of the housing <NUM> and the dome <NUM>, the temperature reduction amount of the housing <NUM> relative to the temperature reduction amount of the dome <NUM> is reduced. Accordingly, a heat is continuously supplied from the housing <NUM> to the dome <NUM>, so that the stability of the temperature of the dome <NUM> against a change in external environment is increased. As a result, it becomes possible to measure the precise solar irradiance continuously and stably while suppressing the generation of dew and frost even in changing external environment.

The heating control of the heat generating element <NUM> will be described by reference to <FIG> shows the circuit diagram of a circuit <NUM> including the heat generating element <NUM> and each circuit provided at the circuit boards <NUM> and <NUM>. <FIG> illustrates, as one example, the heat generating element <NUM> as a MOS-FET. For the heat generating element <NUM>, the gate is connected with an operational amplifier <NUM>, the drain is connected with a power supply, and the source is connected with a ground via a resistance element <NUM>.

The circuit <NUM> has the heat generating element <NUM>, the CONTROL UNIT <NUM>, the communication unit <NUM>, the DC/DC converter <NUM>, the resistance element <NUM>, the operational amplifier <NUM>, the D/A converter <NUM>, and the A/D converters <NUM> and <NUM>.

The CONTROL UNIT <NUM>, the D/A converter <NUM>, and the A/D converters <NUM> and <NUM> are implemented as a circuit in a microcontroller. Incidentally, for example, the D/A converter <NUM>, and the A/D converters <NUM> and <NUM> are not necessarily required to be provided at the microcontroller, and may be respectively independent elements.

The CONTROL UNIT <NUM> is a functional block implemented by executing a software program including a microcontroller stored in a memory. The CONTROL UNIT <NUM> can calculate, for example, the solar irradiance based on a signal from the sensor element <NUM>. The solar irradiance calculated based on a signal from the sensor element <NUM> can be used, for example, for calculation of the integrated solar irradiance in a given day by a computer connected to the outside of the pyranometer <NUM>.

Further, in the memory of the CONTROL UNIT <NUM>, the calibration factor for calculating the solar irradiance is stored. The CONTROL UNIT <NUM> measures the solar irradiance by using a common calibration factor in any of a first state in which the heat generating element <NUM> generates a heat and a second state in which the heat generating component does not generate a heat. This is the advantage resulting from the arrangement of the heat generating element <NUM> with respect to the sensor part <NUM> across the internal space S in the pyranometer <NUM>. As a result, the heat from the heat generating component becomes less likely to be supplied to the sensor part. This eliminates the necessity of differently using the calibration value only for at the time of heat generation and the calibration value for not at the time of heat generation in the measurement by the pyranometer. Thus, it becomes possible to use the same calibration factor not depending upon on or off of the heat generating function of the heat generating component. Further, as distinct from the case using the calibration factor only for at the time of heat generation, it is not necessary to normally turn the heat generating function of the heat generating component on all the time. Furthermore, the heat generating function of the heat generating component can be automatically turned on or off based on the temperature of external environment and the solar irradiance measured with the pyranometer <NUM>. In this manner, it is possible to enhance the reliability of the measurement. Specifically, it is possible to perform measurement having the exactness ensuring the class A precision in the standard of the pyranometer of ISO9060.

The communication unit <NUM> is a communication circuit for performing communication between the pyranometer <NUM> and the external device. The communication unit <NUM> is, for example, connected with a communication cable, and performs communication with an external device (e.g., a data logger or a personal computer) via the communication cable. The solar irradiance calculated by the CONTROL UNIT <NUM> is transmitted to an external device via the communication unit <NUM>.

The DC/DC converter <NUM> converts the power supply voltage (Vin) of the power supply supplied to the pyranometer <NUM> into a voltage necessary for the operations of the CONTROL UNIT <NUM> and the communication unit <NUM>.

The resistance element <NUM> is provided between the source of the heat generating element <NUM> and the ground.

For the operational amplifier <NUM>, the input is connected with between the heat generating element <NUM> and the resistance element <NUM>, and the output of the D/A converter <NUM>, and the output is connected with the gate of the heat generating element <NUM>. The operational amplifier <NUM> applies a control voltage Vcont to the gate of the heat generating element <NUM> based on the terminal voltage on the heat generating element <NUM> side of the resistance element <NUM>, and the voltage supplied from the D/A converter <NUM>. The operational amplifier <NUM> performs feedback control so as to make the heating value of the heat generating element <NUM> constant.

The D/A converter <NUM> is provided so that the input of the operational amplifier <NUM> and the CONTROL UNIT <NUM> are connected The D/A converter <NUM> converts a digital signal SG1 from the CONTROL UNIT <NUM> into an analog signal, and supplies the voltage based on the converted analog signal to the operational amplifier <NUM>.

The A/D converter <NUM> is provided so that a point between the power supply voltage and the drain of the heat generating element <NUM> and the CONTROL UNIT <NUM> are connected with each other. The A/D converter <NUM> acquires, for example, the power supply voltage Vin as an analog signal, converts the acquired analog signal into a digital signal SG2, and outputs the digital signal SG2 to the CONTROL UNIT <NUM>.

The A/D converter <NUM> is provided so as to connect a point between the heat generating element <NUM> and the resistance element <NUM>, and the CONTROL UNIT <NUM>. The A/D converter <NUM> acquires, for example the voltage between the heat generating element <NUM> and the resistance element <NUM> as an analog signal, converts the acquired analog signal into a digital signal SG3, and outputs the digital signal SG3 to the CONTROL UNIT <NUM>.

A description will be given to the control of the operation of the heat generating element <NUM> by the CONTROL UNIT <NUM>. First, an electric power consumption P in the heat generating element <NUM> is set according to a prescribed heating value of the heat which should be generated by the heat generating element <NUM>. The value of the electric power consumption P is stored in, for example, the memory of the CONTROL UNIT <NUM>. The CONTROL UNIT <NUM> outputs a digital signal SG1 so that operation voltage in the heat generating element <NUM> × current I1 = electric power consumption P. The digital signal SG1 is determined by a digital signal SG2 based on a power supply voltage Vin. The control voltage Vcont supplied to the heat generating element <NUM> is controlled based on the digital signal SG1. The heat generating element <NUM> is connected with a power supply common with the power supply (power supply for driving the sensor part) of the CONTROL UNIT <NUM>. This eliminates the necessity of separately providing a power supply to the heat generating element <NUM>. For this reason, the configuration of the circuit is simplified.

When the current I1 is varied, the voltage drop amount at the resistance element <NUM> is varied. In other words, the voltage on the side to be connected with the resistance element <NUM> of the operational amplifier <NUM> is varied. In this case, the operational amplifier <NUM> outputs a control voltage Vcont corresponding to the difference between the voltage from the D/A converter <NUM> and the voltage on the side to be connected with the resistance element <NUM>. For example, when the current I1 is increased, the operational amplifier <NUM> reduces the control voltage Vcont. Thus, the operational amplifier <NUM> performs feedback control of the control voltage Vcont, which enables electric power control so as to make constant the heating value of the heat generating element <NUM>. As a result, supply of a heat to the dome <NUM> is performed with stability.

Further, the CONTROL UNIT <NUM> may determine whether the supply current falls within a prescribed current range, or not, for example, based on the digital signal SG3. The CONTROL UNIT <NUM> may determine that, when the supply current does not fall within a prescribed current range, an abnormal condition such as breakage of an element is caused at the heat generating element <NUM>. The determination results may be outputted via the communication unit <NUM>, to be informed to the administrator of the pyranometer <NUM>. In this manner, the convenience of the pyranometer <NUM> is improved.

Referring to Fig. <NUM>, a description will be given to the measurement results of the daily integrated solar irradiance by the pyranometer <NUM>. The bar graph of Fig. <NUM> shows the daily integrated solar irradiance in each day. The bar graph surrounded by a dotted line is the daily integrated solar irradiance measured by the pyranometer not having the heat generating element <NUM> (first daily integrated solar irradiance). The bar graph surrounded by a solid line is the daily integrated solar irradiance measured by the pyranometer <NUM> (second daily integrated solar irradiance). At the time of measurement by the pyranometer <NUM>, the measurement was performed while the heat generating element <NUM> was generating a heat. The white circle of Fig. <NUM> is the ratio of the daily integrated solar irradiance in each day. The ratio of the daily integrated solar irradiance is calculated as ((second daily integrated solar irradiance) - (first daily integrated solar irradiance))/(first daily integrated solar irradiance) × <NUM> [%]. The ratio of the daily integrated solar irradiance shows the difference between the first daily integrated solar irradiance and the second daily integrated solar irradiance, namely, a change in measured value due to whether heating by the heat generating element <NUM> has been performed or not. As shown in Fig. <NUM>, in each day of dates of from D1 to D9, the ratio of the daily integrated solar irradiance falls within the range of ±<NUM> %. This means that the difference between the first daily integrated solar irradiance and the second daily integrated solar irradiance is very small, indicating that, also with the pyranometer <NUM>, the measurement equal to that with a pyranometer not having the heat generating element <NUM> is possible. Accordingly, the pyranometer <NUM> can perform the measurement of the amount of solar radiation with precision while suppressing generation of dew and frost.

Herein, a description will be given to the dew suppressing effect and the frost suppressing effect by the pyranometer <NUM>. Table <NUM> is the table for illustrating one example of the dew suppressing effect and the frost suppressing effect under environmental conditions of the weather, occurrence or non-occurrence of dew condensation, and occurrence or non-occurrence of frosting in different dates. Table <NUM> shows respective dew suppressing effects and frost suppressing effects of the pyranometer <NUM> and the pyranometer for comparison not having a heat generating element. As shown in Table <NUM>, the pyranometer <NUM> has the dew suppressing effect and the frost suppressing effect.

Referring to Fig. <NUM>, a description will be given to a pyranometer 10A in accordance with Modified Example of the present embodiment. With the pyranometer 10A, in the inside of a ceiling part <NUM>, a heat generating element <NUM> is provided so as to surround a dome <NUM>. The heat generating element <NUM> is, for example, a resistance heater for generating a heat according to the current passing the heat generating element <NUM>. As with the pyranometer 10A, the heat generating element <NUM> may be provided close to the dome <NUM> in addition to the heat generating element <NUM>. Alternatively, the heat generating element <NUM> may be provided, for example, at the side surface of a barrel part <NUM>. Provision of additional heat generating element <NUM> enables such heating as to more stabilize the temperatures of the housing <NUM> and the dome <NUM>.

Claim 1:
A pyranometer (<NUM>, 10A) comprising:
a housing (<NUM>) having a ceiling part (<NUM>), a barrel part (<NUM>), a bottom part (<NUM>), and an opening (<NUM>) at the ceiling part (<NUM>) of the housing, and having thermal conductivity;
a dome (<NUM>) provided at the opening (<NUM>), and having light transmittance;
a sensor part (<NUM>) provided in an internal space formed by the housing and the dome (<NUM>), and for measuring an intensity of a sunlight made incident through the dome; and
a heat generating component (<NUM>) provided heat conductably to a part of the housing (<NUM>), said heat generating component (<NUM>) being located opposite to the opening (<NUM>) across the internal space such that the heat generating component (<NUM>) is located at the inner surface region of the housing (<NUM>) such that the opening (<NUM>) and the heat generating component (<NUM>) are separated from each other by the internal space (S), and the region where the heat generating component is located is on the bottom part (<NUM>) of the housing at the position opposite to the ceiling part (<NUM>) of the housing having the opening (<NUM>),
wherein the heat generating component (<NUM>) is arranged across the internal space with respect to the sensor part (<NUM>).