JPS5853877B2 - High sensitivity pyranometer - Google Patents

Description

[Detailed Description of the Invention] Various types of pyranometers have already been put into practical use to measure shortwave radiation caused by solar radiation without being affected by fluctuations in various meteorological factors such as temperature and wind power over a long period of time, but the accuracy is limited. Not enough.

For example, it is impossible to accurately measure the total solar radiation amount by wavelength, which has recently become popular, using conventional solar radiation detectors (see, for example, Japanese Patent Publication No. 49-39037).

In other words, when solar radiation is divided into wavelengths, the output for each wavelength obtained from a pyranometer that is sensitive to each wavelength will be as low as about -1, and the errors included in the Fuyuyama 0 force will be superimposed and the measurement results will have no meaning. disappears.

There are two causes of errors in conventional solar radiation detectors: one is noise that changes the output due to weather factors other than solar radiation, such as ambient temperature and wind, and the other is differences in spectral characteristics for each wavelength band. It is.

The present invention relates to a structure of a pyranometer to eliminate these two factors.

FIG. 1 schematically shows the structure of a pyranometer, which is the basis of the present invention.

A heat receiving plate having an area AI and a heat capacity C1 and an absorption rate α in the direction in which radiation is incident: P.

put

A heat receiving plate Pl forming a hot junction of the thermopile stack is supported by a base plate 1-B which is mounted on a support having a heat transfer coefficient of 1 and forming a cold junction of the thermopile.

The temperature of the heat receiving plate P1 is θ2, and the temperature of the base plate is θ8.
and calculate the radiation amount.

Then, heat receiving plate: P. Here, if the temperature θ8 of the base plate is constant, the temperature difference θ1, -θ3 is the radiation amount I in a steady state, that is, when the time term in the right side () becomes zero.

gives an output proportional to .

Equation (2) is established on the condition that the temperature difference θ2-θ8 is always zero due to weather conditions E other than the amount of solar radiation.

In other words, it means that the temperature of the base plate and the temperature of the heat receiving plate must always be the same even in a transient manner despite fluctuations in weather conditions, that is, external factors E.

In an actual pyranometer, the base plate (B) and the heat receiving plate are connected by a support and are located at different positions, so the temperature of each does not change equally by the same amount at the same time due to the thermal influence from the surroundings, which causes noise. appears as.

In order to reduce this noise level, the present invention provides another heat receiving plate P2 having a different area as shown in FIG.

Although the two heat receiving plates have different areas and heat capacities, they have the same absorption rate and are arranged so that the heat receiving plate P1 in the center and the surrounding heat receiving plate P2 are concentric so that the thermal influence from the external weather factor E is the same. and connected to a common base plate with the same heat transfer coefficient.

For the heat receiving plate P2, a heat balance equation corresponding to equations (1) and (2) and an equation indicating a temperature difference also hold true.

The formula showing the temperature difference is shown here.

Since this is a formula for the heat receiving plate P2, the subscript is 2.

Here, as mentioned earlier, the absorption rate is equal to α
, = α2 yo α, and the heat transfer coefficients are also equal, that is, they are 1- and 2-3, but only the area is different, A1) and A2.

Now, when the two plates P1 and P2 are connected by a thermoelectric stack, the resulting temperature difference θP1-θP2 is shown below.

In other words, it is the difference between equations (2) and (3).

becomes.

What is meant by equations (4) and (5) is that the measured temperature difference θ2□−θP2 is caused by the difference in area between the two.

In other words, even if the absorption rate is the same, there will be a temperature difference between the two, resulting in the amount of solar radiation I.

It is possible to obtain an output proportional to .

Furthermore, when comparing equation (no) and equation (4), the temperature θ8 of the base plate, which was the cause of the noise explained earlier, is completely irrelevant.

In other words, in FIG. 1, in response to a change in the external factor E, the temperature of the exterior casing C changes, and the heat transfer coefficient K changes.

Although the temperature of the base plate B connected to the base plate B changes, this change is no longer related to equations (4) and (5).

Furthermore, both hot plates P1. If P2 is placed in a position where it is thermally affected by the same amount as the exterior C, for example, concentrically as shown above, the temperature change on the drawing board due to external factor E will be the same amount, and the temperature difference on the drawing board will be much smaller. Discrete solar radiation I.

This means that the noise level will decrease depending only on the

In other words, the S/N ratio is greatly improved.

Also, a comparison of the time-dependent terms shown in equations (2) and (2) shows the same response as equation 2.

As described above, a pyranometer can be obtained in which the S/N ratio is greatly improved and heat receiving plates having the same absorption rate can be used.

In a conventional pyranometer using two heat receiving plates, α1
)α2, that is, the color of each heat receiving plate is black and white respectively, and this contrast creates a temperature difference between the heat receiving plates and eliminates noise, but the existing white paint has a uniform absorption rate for all wavelengths of solar radiation. Therefore, this pyranometer could not be used if it was necessary to measure each wavelength.

In order to measure the amount of solar radiation in a specific wavelength range using the pyranometer of the present invention, in the case of simultaneous measurement, the difference output of two pyranometers each equipped with a filter dome with a different transmission wavelength band is calculated as the output of the difference in the transmission band of these filters. It can be extracted as the amount of solar radiation in the difference band.

In theory, if solar radiation is received through a dome made up of two layers of these two filters, it is possible to determine the amount of solar radiation in a specific wavelength range using a single pyranometer.

Another feature of the present invention is that the size of the sensitive word of the pyranometer of the present invention is 1/7th that of conventional pyranometers.
~1/8.

This makes it possible to significantly reduce the size and weight of the pyranometer itself.

In particular, the above-mentioned filter dome is very difficult to process, and if it becomes large, it becomes practically impossible to process it and the manufacturing cost becomes extremely high.

A more detailed explanation of this structure is as follows.

If the area of the heat receiving plate is large, the incident energy will be proportionally large, and a large output can be obtained.However, in the pyranometer of the present invention, in order to obtain approximately the same output with a small light receiving area, the two heat receiving plates are connected. The heat capacity and heat transfer coefficient of the thermoelectric stack were made extremely small, and the structure was designed to create a temperature difference between them as shown in equation (4).

Normally, the thermopile composed of wire strands 2 does not have mechanical strength, so it is wound and fixed on the bobbin 1 as shown in FIG. 2A to give it strength, but in the present invention, as shown in FIG. 2B Instead of being held by a bobbin, the wires 2 constituting the thermoelectric stack are simply fixed to each other with a strong adhesive 3, and electrical insulation between the wires is also made possible.

According to this configuration, since the amount of heat transmitted through the thermopile itself is small and the heat capacity is small, the temperature difference between the two heat receiving plates is large, that is, a pyranometer with high sensitivity and high response speed can be obtained.

FIG. 3 shows a cross-sectional view of a pyranometer in accordance with the present invention.

Reference numeral 6 denotes a filter dome for transmitting only solar radiation in a specific wavelength range, and a quartz dome 7 for cutting heat rays is provided inside the filter dome.

These two domes are fixed to the main body 11 via an upper O-ring 10 bonded to the holder 9.

A base plate B and a sensing section S shown in FIG. 1 are integrally fixed onto the main body 11.

Furthermore, the main body 11 is made of cast metal and includes parts necessary for the function of the pyranometer, a desiccant container 12, a level 13, an output connector 14, a horizontal adjustment foot 15, a fixed foot 16, a back cover 17,
A sensitivity adjustment potentiometer 18 is attached.

Note that the heat receiving plates P1 and P2 are also integrated into the sensing section S.

4A and 4B show details of the structure of the sensing section S shown in FIG. 3, where A is a sectional view and B is a plan view.

FIG. 4B shows that the heat receiving plates P1 and P2 have circular and annular shapes, respectively, and are arranged concentrically.

Moreover, the ratio of the areas is 10:1.

Solar radiation incident on the heat receiving plates P1 and P2 is absorbed by the black coating material film on the surface, raising the temperature of each.

The heat receiving plate P1 is fixed to the upper surface of the base plate B via a heat transfer member 19 (for example, a metal support).

On the other hand, the heat receiving plate P2 is bent downward and thermally connected to the cold contact plate 20 at a junction 21.

Since the heat receiving plate P2 and the cold contact plate 20 are each made of a metal with good conductivity, such as an Al plate, there is almost no temperature difference between the surface exposed to sunlight and the lower cold contact plate 20.

The cold contact plate 20 is fixed to the lower surface of the base plate B via a heat transfer member 19' having the same structure as the heat transfer member 19.

Since the heat receiving plates P1 and P2 are connected to the base plate 1-B, which is a common hot melt, in this way, the amount of heat escaping is the same and the amount of heat coming in is different based on the difference in area. As a result, the temperature of the heat receiving plate P1 becomes higher than that of the heat receiving plate P2.

The rows of hot junctions 4 and cold junctions 5 of the thermopile 2 without a bobbin shown in FIG. 2B correspond to rows 4.5 of FIG. are combined as follows.

The hot and cold junctions 4.5 are arranged in the diametrical direction of the heat receiving plate P1.

In the thermopile stack 2 shown in FIG. 2B, the thick portion indicates the copper portion of the thermopile stack made of copper-constantan.

In this way, the output of the thermoelectric stack 2 is proportional to the temperature difference between the heat receiving plates P1 and P2, and as a result, it can be taken out from the connector 14 shown in FIG. 3 as an output proportional to the amount of incident solar radiation.

[Brief explanation of the drawing]

Fig. 1 is a thermal schematic diagram explaining the pyranometer of the present invention, Fig. 2A is a perspective view of a general thermopile for a pyranometer, Fig. 2B is a perspective view of a thermopile used for implementing the invention, and Fig. 3 4A and 4B are a longitudinal sectional view showing an embodiment of the pyranometer of the present invention, and FIGS. 4A and 4B are a sectional view and a plan view showing details of the sensing section of FIG. 3. ■o... Incident solar radiation, Pl, P2...
Each heat receiving plate, A1, A2... each heat receiving area, C1, C2... each absorption rate, C0, C2...
...Each heat capacity, K1, K2... Heat transfer coefficient by the pillar, B... Base plate (
cold junction), Ko...Heat transfer coefficient from the base plate to the exterior, C...Exterior, E...External weather factors, 1...Bobbin, 2 ...Thermopile wire, 8...Adhesive, 4...Hot junction, 5...Cold junction, H...Heat direction of flow.

Claims (1)

[Claims] 1. Heat receiving plates with the same solar radiation absorption rate and different areas are placed close together on the same plane, and heat is transferred to a common hot melt through separate heat transfer members having the same heat transfer coefficient. Each heat receiving plate is connected to the thermoplastic so as to release heat, and the temperature difference proportional to the solar radiation incident on each of the heat receiving plates is transferred to a thermoelectric pile whose hot and cold junctions are thermally connected to the respective heat receiving plates. A pyranometer characterized by having a solar radiation sensitive part that measures solar radiation. 2. Claim 1 in which a thermoelectric stack is used as the sensing portion, in which a large number of wires for the thermoelectric stack are stacked and fixed together with an adhesive.
Pyranometer as described.