DE202004004402U1 - Temperature device for measuring the temperature on elongated objects like wires, fibers, pipes and tapes with any cross sections and forms guides the object to be measured in a hollow space - Google Patents

Abstract

Heat radiation (3) created in a hollow space (HS) is detected through a hole and decoupled by means of a fiber optical wave-guide (5). The fiber connects to a standard trade radiation detector (4) located in the HS. Temperature in the walls of the HS is recorded by a probe. A portion of radiation emitted from the walls is correspondingly adjusted as an object's temperature is determined.

Description

The The invention relates to an arrangement for contactless measurement of the temperature of elongated objects, especially wires, fibers and thin Pipes using infrared radiation pyrometry.

The contactless Temperature determination of fibers and wires using infrared pyrometry different problems. On the one hand, bare metal surfaces have one very low emissivity, so essentially the ambient temperature is detected.

To the others, optical pyrometers have a measurement spot of finite Size up.

Wires with fill a smaller diameter therefore the measuring field is not complete out. Slight fluctuations in position, e.g. through vibrations at lengthways moving objects excessive deviations of the displayed temperatures.

The Using a background emitter, which is regulated to the target temperature of the wire brings a some improvement but limits due to its thermal mass, the response time of the measuring arrangement on. A background emitter is behind or next to it measuring object and the temperature of the object with a Infrared radiation pyrometer measured. The measurement object fills the measurement spot not completely and the lamp temperature deviates from the measured value, so the background emitter is readjusted until the object and Background heaters have the same temperature again.

in the Patent DE4114367 is the position fluctuation of the wire fixed that an elongated measuring field by means of a cylindrical lens is generated, its longitudinal axis is aligned perpendicular to the wire. Position fluctuations due to of vibrations have no influence on the temperature determination. Since commercial pyrometers cannot process emissivities <0.1 this technique only for Objects with high emissivity and at higher temperatures can be used.

in the Patent EP0058806 describes an arrangement in which the wire in a blackened Cavity led becomes. The cavity is with 2 openings provided, by means of which the object is alternated by means of a chopper is measured directly and indirectly.

in the Patent DE2326465, DE2241310 the object to be measured is in one hemispherically trained Cavity led, that acts as a background emitter. With the help of a rotating arranged in the cavity or oscillating mirror alternately becomes object and background measured and the signal difference evaluated.

in the Utility model DE20022572 becomes a thread through a mirror segment enlarges that it the effective measuring spot of a pyrometer arranged opposite equivalent. This arrangement is sensitive to shifts the fiber from the field of optical imaging. The temperature measurement highly reflective metal wires is not possible with it.

The Using a ratio pyrometer that described the above If there are no problems, it is limited to temperatures above 300 ° C for technical reasons. Bare metal wires, the emissivities <0.1 possess, are not to be measured with it, since the height of the absolute Signal is no longer sufficient.

To the They are also used frequently Systems in which the heat flow by means of a heat flow sensor determined between object and a reference with known temperature becomes. The reference is regulated until the heat flow comes to a standstill. The measurement is basically contactless, whereby the heat transfer from object to reference Heat conduction, Radiation and convection takes place. These are also known under the collective term 'Convective Heatflow' (CHF) Systems are very sluggish due to the thermal mass of the reference in the order of magnitude of several seconds.

The The present invention eliminates the problems described by encased the object to be measured with a highly mirrored surface becomes. There are multiple reflections inside the resulting cavity, leading to an increase of the effective emissivity. The exact shape of the cavity plays a subordinate role, e.g. round, rectangular or elliptical cross sections simply realize. However, the ratio of the optically effective surfaces of object and casing if possible be kept small so that the highest possible amplification of the Emissivity or the highest possible Number of multiple reflections is reached.

A Defined optical imaging should be avoided so that the measurement signal largely independent from the position of the wire.

Due to the scattering that occurs on each surface, a homogeneous radiation distribution is formed within the cavity. If necessary, this can be done by a roughened Surface, eg sandblasted surface, are supported. However, experiments show that this is not necessary.

The radiation field building up in the interior of the cavity a suitable measuring instrument (e.g. an infrared radiation pyrometer) measured and according to Planck's formula into a Converted temperature.

There the response time is the radiation is directly detected and evaluated of the system is limited only by the characteristics of the detector and is a few milliseconds.

The intensity of the radiation within the cavity can be estimated on the assumption that a homogeneous radiation field is formed within the cavity and that only the surface of the wire and the enveloping cavity contribute to this radiation. The power emitted by the two surfaces is then: Φ str = ε Obj · Φ (T Obj ) · A Obj + ε H · Φ (T H ) · A H 1)

• Mean:
• Φ _Str : radiated power
• Φ (T): Radiance at the temperature T according to Planck
• ε: emissivity
• A: area
• Obj: Index object
• _H : index cavity

This increases the intensity of the radiation within the cavity. At the same time, both surfaces extract energy from the radiation field through absorption: Φ Section = Φ gl · (Α Obj A Obj + α H A H ) 2)

• α: absorptance
• Φ _Abs : absorbed power
• Φ _Gl : radiance in equilibrium

und entsprechend ergibt sich aus Gleichung 2: ΦGl = εeffObj·Φ(TDr)+(1–EeffObj)·Φ(TH) 4) After an equilibrium has been established, both amounts are the same; furthermore, according to Kirchhoff's law, α = ε. The radiation intensity Φ _{Gl is} measured by the detector. Now define an effective emissivity according to:

and accordingly equation 2 gives: Φ gl = ε effObj · Φ (T Dr ) + (1-E effObj ) · Φ (T H ) 4)

The Temperature of the cavity is known or can easily be done with a temperature sensor be determined. Modern radiation pyrometers offer the possibility to read in an externally recorded reference temperature and according to 4) the calculation of the object temperature.

example

Measurement of a copper wire with a diameter of 0.6 mm, which was guided in a cavity with a round cross section and a diameter of 2 mm. The following then result: A Dr = 2π · r Dr · 1 5) A H = 2π · r H ·1

equation 3.) becomes:

The Inner surface the cavity is mirrored with gold and has an emissivity from 0.04 to. According to the literature, the emissivity of copper is 0.04. The effective emissivity depends then only from the diameter of the wire and the cavity and results to 0.23.

at Comparative measurements with a CHF system were carried out on a pyrometer set emissivity of 0.2 a match of the displayed Temperature of CHF and the infrared radiation pyrometer determined. While Rapid changes in wire temperature with the infrared radiation pyrometer the CHF system was unable to detect it more to follow.

Technically reflectivities> 0.995 generate, which corresponds to an emissivity of 0.005. The effective one The emissivity is then based on the above Geometry to:

The Using a sheathed, highly reflective surface works so as an emissivity amplifier and thus also measures highly reflective materials possible.

explanation of the pictures:

1 shows a wire ( 1 ) with a tubular jacket ( 2 ) is surrounded. The measuring radiation ( 3 ) is opened ( 5 ) decoupled and from an IR pyrometer ( 4 ) detected.

2 basically shows the same arrangement only the casing is designed spherical here.

3 shows an arrangement in which the sheath was again chosen to be tubular, but the coupling of the radiation via an optical fiber ( 9 ) he follows. The light guide directs the radiation to an infrared radiation pyrometer ( 4 ) or a suitable detector ( 4 ) further.

4 shows an arrangement in which the temperature of the walls of the cavity with a temperature sensor ( 6 ) is recorded and by means of a signal converter ( 7 ) is read into the infrared radiation pyrometer. The background radiation emanating from the cavity walls is then taken into account in the calculation of the wire temperature in accordance with Eq. 4.

Claims (5)

Device for measuring temperatures on elongated objects such as wires, fibers, tubes, tapes of any cross-sectional shape ( 1 ), the shape that the object to be measured is in a cavity ( 2 ) is led, the walls of which consist of highly reflective surfaces. Device according to claim 1 with an opening ( 5 ), through which the thermal radiation formed in the cavity ( 3 ) is detected. Device according to Claim 1, in which the thermal radiation ( 3 ) using an optical fiber ( 5 ) is coupled out. The fiber is attached to a commercially available radiation detector ( 4 ) connected. Device according to claim 1 with one or more detector (s) located in the cavity. Apparatus according to claim 1 to 4, in which additionally the Cavity wall temperature by a feeler is recorded and the radiation component emanating from it the determination of the object temperature is corrected accordingly.