Energy-efficient sensor temperature control with two Peltier elements

Abstract

Measuring device for optical radiation with a measuring head (1), wherein an optical sensor element (2) is arranged in the optical beam path of the measuring head (1), wherein at least one first Peltier element (4) is provided for temperature control of the sensor element (2), wherein the first Peltier element (4) temperature-controls, stabilizes, or cools the sensor element (2), wherein the resulting waste heat is dissipated by the first Peltier element (4) to a heat sink (5), wherein the heat sink (5) is designed to dissipate heat to the environment of the measuring head (1), wherein at least one second Peltier element (6) is provided, wherein the heat sink (5) thermally connects the first Peltier element (4) to the second Peltier element (6), characterized in that the heat sink (5) has externally arranged cooling fins (13) for dissipating the heat to the environment, wherein a filter element (3) is arranged upstream of the sensor element (2).wherein the at least second Peltier element (6) is provided for temperature control of the filter element (3), wherein the second Peltier element (6) transports the heat from the heat sink (5) to the filter element (3) and thus heats the filter element (3), so that the waste heat from the cooling of the sensor element (2) is used to heat the filter element (3).

Description

[0001] The invention relates to a measuring device for optical radiation with a measuring head, wherein an optical sensor element is arranged in the optical beam path of the measuring head, upstream of which a filter element is connected, wherein at least one Peltier element is provided for tempering the sensor element.

[0002] DE 693 08 469 T2 describes an imaging device, wherein a picture tube is arranged in the optical beam path of the imaging device, with a window plate connected upstream of it. Several Peltier elements are provided in the imaging device. The Peltier elements serve to absorb heat from the photoelectric surface. For this purpose, a heat dissipation region of each Peltier element is attached to an end plate of the device housing, and a heat absorption region of each Peltier element is attached to a copper plate.

[0003] US Pat. No. 6,133,569 A describes a thermal infrared camera. A thermal infrared image pickup element is arranged in the optical beam path of the infrared camera, upstream of which is an infrared transmission window. At least one first Peltier element is provided for controlling the temperature of the infrared image pickup element. Furthermore, a second Peltier element is provided for controlling the temperature of an infrared-blocking body.

[0004] US 4 833 889 A discloses a measuring device for optical radiation with a measuring head, wherein an optical sensor element is arranged in the optical beam path of the measuring head, which sensor element is preceded by a window, wherein at least one first Peltier element is provided for temperature control of the sensor element, wherein the first Peltier element cools the sensor element, wherein the resulting waste heat is dissipated by the first Peltier element to a first heat-conducting base plate, wherein at least one second Peltier element is provided for temperature control of the window, wherein the first heat-conducting base plate connects the first Peltier element to the second Peltier element in a heat-conducting manner, so that the waste heat from the cooling of the sensor element is used to heat the window, wherein the second Peltier element transports the heat from the first heat-conducting base plate to the window and thus heats the window.US Pat. No. 4,833,889 A also discloses cooling fins on a heat sink for dissipating heat to the environment. However, these fins are provided on another heat-conducting base plate, which is provided with a housing cap containing the window. Thus, the temperature of the window depends on the temperature of the heat sink and also the environment.

[0005] In photometry and radiometry, semiconductor sensors, particularly photodiodes, are used to convert a photometric or radiometric measurement into an electrical signal. Optical elements, such as filters, are often installed in the optical beam path of the sensor. The properties of both sensors and filters are temperature-dependent, so that changing temperatures lead to measurement errors. For this reason, such arrangements are usually temperature-stabilized. For this purpose, a Peltier element is known to be provided for the joint temperature control of the sensor element and the filter element. Arrangements are known in which the sensor and filter are heated together to a temperature above the highest expected ambient temperature. However, operating the sensor at higher temperatures (usually 35°C) is associated with disadvantages such as increased noise.Another known option is to cool the sensor element and filter element together using a Peltier element to a temperature below the lowest ambient temperature. Compared to the first approach, this has the significant advantage of reduced noise. However, considerable electrical energy is required for cooling. The electrical energy required for this increases the greater the difference between the ambient temperature and the desired cooling temperature. This electrical energy, along with the heat extracted from the sensor element and the filter element, must be completely dissipated to the environment as waste heat. This may require large heat sinks and possibly also fans, thereby increasing the required installation space of the measuring head and the susceptibility to errors caused by the fan.A considerable amount of energy is required for both heating and cooling the sensor element and the filter element in order to operate the measuring head in a temperature-stabilized manner.

[0006] The object of the invention is therefore to provide a measuring device that eliminates the disadvantages described and enables efficient temperature stabilization.

[0007] This object is achieved by a device according to claim 1.

[0008] According to the invention, at least a second Peltier element is provided for temperature control of the filter element, with a heat sink thermally connecting the first Peltier element to the second Peltier element. In this case, the combination of the two Peltier elements leads to efficient temperature stabilization. Thus, as is already known, a Peltier element temperature-controls, temperature-stabilizes, or cools the sensor element. The waste heat generated here is dissipated by the Peltier element to the heat sink. A second Peltier element mounted on the same heat sink transports heat from the heat sink to the filter, thereby heating it. By temperature-controlling the filter element with the second Peltier element and the thermally conductive connection of the heat sink between the first Peltier element and the second Peltier element, the waste heat from cooling the sensor element can be used to heat the filter element.This makes the proposed temperature stabilization using the two Peltier elements arranged on the heat sink particularly energy-efficient. Furthermore, cooling the sensor element leads to significantly improved noise performance, which increases the precision achievable with the measuring head. Heating the filter element using the second Peltier element also makes it possible to reduce the size of the heat sink, thus saving installation space. Utilizing the waste heat from cooling the sensor element can also eliminate the need for fans that would otherwise be required. Eliminating additional fans for cooling the heat sink further reduces the installation space required for the measuring head and reduces the system's susceptibility to failure. The lower electrical energy required also enables the use of smaller power supply circuits, thus saving further installation space.

[0009] A particular advantage of the inventive design is that the heat sink is designed to dissipate heat to the surroundings of the measuring head. Dissipating heat to the surroundings represents an effective way to reduce the temperature of the measuring head, in particular of the sensor element. To dissipate heat to the surroundings, the heat sink has externally arranged cooling fins.

[0010] The combination of the two Peltier elements ensures efficient temperature stabilization. The first Peltier element regulates or cools the sensor element, while the waste heat is dissipated through the Peltier element to the heat sink. A second Peltier element is mounted on the same heat sink and transports the heat from the heat sink to the filter element, thereby heating it.

[0011] Advantageous embodiments and further developments of the invention emerge from the dependent claims.

[0012] According to an advantageous embodiment of the invention, the first Peltier element is arranged between the sensor element and the heat sink and transfers heat between the sensor element and the heat sink. Such a Peltier element makes it particularly easy to control the temperature of the sensor element. The Peltier element arranged between the sensor element and the heat sink enables precise adjustment of the temperature of the sensor element and effective dissipation of heat to the heat sink. This enables effective temperature control of the sensor element, so that the temperature-dependent properties of the sensor element play a subordinate role in the measurement. The Peltier element can form a structural unit with the sensor element.

[0013] A particularly advantageous embodiment is one in which the second Peltier element is arranged between the heat sink and the filter element and transfers heat between the heat sink and the filter element. With such a Peltier element, the filter element can be temperature-controlled particularly easily. The Peltier element arranged between the heat sink and the filter element enables precise adjustment of the temperature of the filter element and effective heating of the filter element using heat provided by the heat sink. The Peltier element arranged between the filter element and the heat sink cools the heat sink on the one hand and heats the filter element on the other. This enables effective temperature control of the filter element, so that the temperature-dependent properties of the filter element play a subordinate role in the measurement.

[0014] One possible embodiment of the invention is characterized by a controller that senses the temperatures of the sensor element and the filter element, controls the first and second Peltier elements, and thus regulates the temperatures of the sensor element and the filter element to setpoints. With such a controller, the temperature of the sensor element and the filter element can be very easily adjusted and maintained constant by controlling the Peltier elements, so that the temperature-dependent properties of the sensor and the filter do not generate measurement errors for measurements with the measuring head.

[0015] A particularly advantageous embodiment of the invention provides that the setpoint temperature of the sensor element is below the ambient temperature of the measuring head, and the setpoint temperature of the filter element is above it. The first Peltier element cools the sensor element to a temperature set by the controller, with the setpoint being below the lowest expected ambient temperature. The second Peltier element heats the filter element to a temperature set by the controller, with the setpoint being above the highest expected ambient temperature. This enables effective and efficient temperature stabilization of the measuring head, thus eliminating the influence of the temperature-dependent properties of the filter element and sensor element.

[0016] An advantageous embodiment is that the filter element is held in a filter holder, with the filter holder thermally connecting the second Peltier element to the filter element. The thermally conductive connection of the filter element via the filter holder to the second Peltier element ensures that the filter element is effectively heated or tempered. The thermally conductive connection through the filter holder also ensures that the heat distribution across the filter element is as even as possible, so that the filter element is evenly heated by the second Peltier element.

[0017] A preferred embodiment provides that the sensor element with the first Peltier element is held in a sensor housing, wherein the sensor housing connects the first Peltier element to the heat sink in a thermally conductive manner. Such a sensor housing can act as an additional heat sink, dissipating additional heat to the surroundings of the measuring head. For this purpose, the sensor housing preferably has externally arranged cooling fins. Dissipating the heat to the surroundings represents an effective way to reduce the temperature of the measuring head.

[0018] According to a possible embodiment, it is particularly advantageous that the filter element is designed such that the spectral sensitivity of the overall system corresponds to one of the spectral value functions for V(λ), V'(λ), V eq (λ), x(λ̂),y(λ̂),z(λ̂) corresponds to CIE1931.

[0019] Further features, details, and advantages of the invention will become apparent from the following description and the drawings. An embodiment of the invention is illustrated in the drawings and described in more detail below. Corresponding objects are provided with the same reference numerals in all figures. They show: Fig. 1 measuring head according to the invention in sectioned isometry, Fig. 2 measuring head according to the invention in sectional view,

[0020] In the figures, designated overall by reference numeral 1, a measuring head according to the invention is shown. The illustration according to Fig. 1 and according to Fig.2 shows a measuring head 1 for a radiometric or photometric measuring device. A sensor element 2, which is, for example, a photodiode, is arranged in the optical beam path of the measuring head 1. A filter element 3, for example, a spectrally selective optical transmission filter, is provided upstream of this sensor element 2. A first Peltier element 4 is used to control the temperature of the sensor element 2. The sensor element 2 is preferably held in a sensor housing 20 with the first Peltier element 4 located underneath. A second Peltier element 6 is provided to control the temperature of the filter element 3. A heat sink 5 is arranged between the first 4 and the second, preferably annular Peltier element 6, which heat sink creates a heat-conducting connection between the first Peltier element 4 and the second Peltier element 6. The combination of the two Peltier elements 4, 6 ensures efficient temperature stabilization. In this way, the temperature is controlled orThe first Peltier element 4 cools the sensor element 2, with the waste heat being dissipated by the Peltier element 4 to the heat sink 5. A further Peltier element 6 is mounted on the same heat sink 5 and transports the heat from the heat sink 5 to the filter element 3, thereby heating it. The temperature control of the filter element 3 with the second Peltier element 6 and the heat-conducting connection of the heat sink 5 between the first Peltier element 4 and the second Peltier element 6 makes it possible to use the waste heat from the cooling of the sensor element 2 to heat the filter element 3. This makes the proposed temperature stabilization by means of the two Peltier elements 4, 6 arranged on the same heat sink 5 particularly efficient. The cooling of the sensor element 2 also significantly improves the noise behavior.By heating the filter element 3 by the second Peltier element 6, the size of the heat sink 5 can be reduced, thereby saving installation space. The arrangement of the first Peltier element 4 between the sensor element 2 and the heat sink 5 enables the effective transfer of heat from the sensor element 2 to the heat sink 5, so that the sensor element 2 is effectively cooled. By arranging the second Peltier element 6 between the heat sink 5 and the filter element 3, the heat from the heat sink 5 can be excellently transferred to the filter element 3, so that the latter is heated. Temperature stabilization can be achieved particularly effectively by a controller 7, which detects the temperatures of the sensor element 2 and the filter element 3 using sensors, controls the first 4 and the second Peltier element 6, and thus regulates the temperatures of the sensor element 2 and the filter element 3 to setpoints.For particularly effective temperature stabilization of the measuring head 1, several temperature sensors 10, 11, 12 measure the temperatures of the sensor element 2, the heat sink 5, and the filter element 3 or its filter holder 8, in the case of the preferably laterally arranged temperature sensor 10, and an electronic circuit acts as a controller 7, regulating the two Peltier elements 4, 6 such that the sensor temperature is set to a target value below the lowest expected ambient temperature and the filter temperature is set to a target value above the highest expected ambient temperature. The two Peltier elements 4, 6 have independent control circuits. In this stabilized state, the temperature of the sensor element 2 is below, and the temperature of the filter element 3 is above, the ambient temperature of the measuring head 1. The heat sink 5 is designed to dissipate the heat of the sensor element 3 to the environment. For this purpose, the heat sink 5 has cooling fins 13.The sensor element 2, together with the integrated Peltier element 4, is fixed to the heat sink 5 via a retaining ring 19. In the example shown here, the heat sink 5 is additionally formed by a base 9, which also has cooling fins 13. The controller 7 is arranged in this base 9 and is connected to the Peltier elements 4, 6 and the temperature sensors 10, 11, 12 via connections 18. The filter element 3 is held in a filter holder 8, wherein the filter holder 8 connects the second Peltier element 6 to the filter element 3 in a thermally conductive manner. This allows the heat generated by the second Peltier element 6 to be effectively transferred to the filter element 3. For this purpose, the filter element 3 is fixed in the filter holder 8 with a screw ring 14. A housing cap 15 is arranged around the filter holder 8 and has a glass window 16 through which the beam path can enter the measuring head 1.Behind the glass window 16 and in front of the filter element 3, an air cushion space 17 is arranged, which shields the filter element 3 and the filter holder 8 from the environment and thus ensures a uniform temperature of the filter element 3. In order to minimize unwanted heat transfer from the cooled sensor element 2 to the environment or from the heated filter element 3 to the environment, the individual components, sensor element 2 including the connection to the first Peltier element 4, heat sink 5 and housing 15, filter element 3 including the connection to the second Peltier element 6, are thermally insulated from one another, for example by air layers or additional insulating material within the housing cap 15. This enables temperature stabilization of the measuring head 1 within a defined ambient temperature range.For this purpose, the preferably photoelectric sensor element 2 is cooled by a Peltier element 4 to a temperature below the lowest expected ambient temperature, and an optical filter 3 is heated by a second Peltier element 6 to a temperature above the highest expected ambient temperature. Both Peltier elements 4, 6 operate on a common heat sink 5 that is thermally connected to the environment, with at least a portion of the waste heat generated during the cooling of the sensor element 2 being used to heat the filter element 3. List of reference symbols 1 measuring head 2 sensor element 3 filter element 4 first Peltier element 5 heat sinks 6 second Peltier element 7 controls 8 filter holder 9 bases 10 Temperature sensor A 11 Temperature sensor B 12 Temperature sensor C 13 cooling fins 14 Screw ring 15 Housing cap 16 stained glass windows 17 Air cushion room 18 connections 19 Retaining ring 20 sensor housings

Claims

[1] Measuring device for optical radiation with a measuring head (1), wherein an optical sensor element (2) is arranged in the optical beam path of the measuring head (1), wherein at least one first Peltier element (4) is provided for tempering the sensor element (2), wherein the first Peltier element (4) tempers or temperature stabilizes or cools the sensor element (2), wherein the resulting waste heat is dissipated by the first Peltier element (4) to a heat sink (5), wherein the heat sink (5) is designed to dissipate heat to the environment of the measuring head (1), wherein at least one second Peltier element (6) is provided, wherein the heat sink (5) connects the first Peltier element (4) to the second Peltier element (6) in a heat-conducting manner, characterized bythat the heat sink (5) has externally arranged cooling fins (13) for dissipating the heat to the environment, wherein a filter element (3) is arranged upstream of the sensor element (2), wherein the at least second Peltier element (6) is provided for tempering the filter element (3), wherein the second Peltier element (6) transports the heat from the heat sink (5) to the filter element (3) and thus heats the filter element (3), so that the waste heat from the cooling of the sensor element (2) is used to heat the filter element (3). [2] Measuring device according to claim 1, characterized by that the first Peltier element (4) is arranged between the sensor element (2) and the heat sink (5) and transfers heat between the sensor element (2) and the heat sink (5). [3] Measuring device according to claim 2, characterized bythat the second Peltier element (6) is arranged between the heat sink (5) and the filter element (3) and transfers heat between the heat sink (5) and the filter element (3). [4] Measuring device according to one of claims 1 to 3, characterized by a controller (7) which detects the temperatures of the sensor element (2) and the filter element (3) by sensor means, controls the first and the second Peltier element (4, 6) and thus regulates the temperatures of the sensor element (2) and the filter element (3) to setpoint values. [5] Measuring device according to claim 4, characterized by that the setpoint temperature of the sensor element (2) is below and the setpoint temperature of the filter element (3) is above the ambient temperature of the measuring head (1). [6] Measuring device according to one of claims 1 to 5, characterized bythat the filter element (3) is held in a filter holder (8), wherein the filter holder (8) connects the second Peltier element (6) to the filter element (3) in a heat-conducting manner. [7] Measuring device according to one of claims 1 to 6, characterized by that the sensor element (2) with the first Peltier element (4) is held in a sensor housing (20), wherein the sensor housing (20) connects the first Peltier element (4) to the heat sink (5) in a heat-conducting manner. [8] Measuring device according to one of claims 1 to 7, characterized by that the filter element (3) is designed such that the spectral sensitivity of the overall system corresponds to one of the spectral value functions for V(λ), V'(λ), V eq (λ), x(λ̂),y(λ̂),z(λ̂) according to CIE1931.

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