DE10117878A1 - Yarn tension monitor has a deflector in the yarn path, which is shifted by the yarn tension to distort a photo-elastic element where an opto-electronic scanner registers light through it and detects changes - Google Patents

Abstract

The yarn tension monitor (M) has a static deflector (D) in the path of the yarn (F). An electronic evaluator (6) takes off the signals (i) corresponding to the mechanical force (K) on the deflector through the yarn tension. A transducer unit (E) is in the mounting (4,5) of the deflector, with a light-permeable photo-elastic element which is distorted by the forces imposed through the yarn tension. The yarn tension monitor (M) has a static deflector (D) in the path of the yarn (F). An electronic evaluator (6) takes off the signals (i) corresponding to the mechanical force (K) on the deflector through the yarn tension. A transducer unit (E) is in the mounting (4,5) of the deflector, with a light-permeable photo-elastic element (S) which is distorted by the forces imposed through the yarn tension. The electronic evaluation unit has an opto-electronic scanner (A) for at least one optical characteristic of light which is varied by changes in the photo-elastic element through forced shifts.

Description

The invention relates to a thread tension meter according to the preamble of the An saying 1.

Thread tension meters have from the very when the thread is at rest or running small load of the thread deflected at the deflector precise information about the thread span supply. From the deformation resulting from the small load of the thread the thread tension in a thread processing system, e.g. B. a Webma machine with weft thread delivery devices, despite work-related vibrations and at lukewarm variable thread of varying friction influences can be determined accurately. In practice Thread tension meters were developed for this purpose measuring elements or piezoelectric elements work from the evaluations circuit can be analyzed. To ensure a clear measurement of the thread tension in within a large measuring range and despite the originating from the thread and the Ensuring external influences is a high level of electronic and device technology African effort required. The well-known thread tension meters are expensive and sensitive devices, which are usually used in large numbers in thread processing systems are installed. With strain gauges or piezoelectric elements, this becomes Used phenomenon that their materials under a mechanical load their elect change its physical properties and draw conclusions about the changes allow mechanical stress conditions causing load. For example, especially the electrical internal resistance or a deformation-induced e electrical voltage. However, for deriving reasonably useful signals high electronic effort necessary.

The invention has for its object a structurally simple and functional cheren, inexpensive to manufacture thread tension meter of a different type create that has a large measuring range and with moderate electronic opening can derive clear output signals.

The object is achieved with the features of claim 1.  

Contrary to the conventional principle, the elastic deformation in the transducer tapping and evaluating the facility directly electronically will be Phenomenon of birefringence of a photoelastic, deformable element to Measuring the thread tension used. From the deformation of the photoelastic E lementes is optoelectronic with polarized light via the change the refractive behavior is sensed on the basis of the intensity of the emerging light, which change with a change in the internal state of tension in the photoelastic E element changes. The photo-elastic element is made of a dielectric material, that is transparent and usually at least largely isotropic. This Ma material becomes anisotropic as soon as it is subjected to a mechanical stress condition becomes. The anisotropy induced thereby results in different refractive indices zes for different lightwave polarization directions with reference to the main neuter tensions inside the element. About the intensity of the leak the voltage condition can be detected in the light. One roughly perpendicular The striking light wave front of polarized light is divided into two waves, which are reflected in the Propagate the interior of the element at two different speeds because there are different refractive indices along the main axes in the element. This results in a phase difference in the emerging light; the element acts like a uniaxial crystal, in which the intensity of the emerging light of an analyti equation follows, which is easy to derive. Since the main stresses in the element in in practice are hardly oriented parallel to the polarization axes, the Conditions of tension based on the emerging light simply by its isoch feel romate. The leads virtually over the entire extent of the element special arrangement for an almost constant phase offset or phase difference, whereby the two continuous light waves influence each other sen. By evaluating the light finally captured in relation to the job The current tension conditions can be reflected in the fotoelasti element with little electronic effort within a wide measuring range judge empire. The thread tension can be derived precisely from this. The The output characteristic is not linear, but square in the first approximation. However, the thread tension can be adjusted by suitable, known linearization methods can be measured with high precision. Since the thread tension is indirect via the internal tension condition of the elastic element determined optoelectronic way  is determined, using the effect of photo elasticity or Birefringence and supported by the geometric requirements, let strong and meaningful useful signals for measuring the thread tension are formed len. This is done with moderate electronic effort. The mechanical opening building the thread tension meter is easy. The thread tension meter can be Producing inexpensively, is insensitive, compact and therefore in thread processing optimal systems to install. According to the invention, the phenomenon is photo elastic material that is used by the mechanical load of the thread chip caused internal tension states its optical properties changed and thus conclusions on the extent of the load and the thread tension allows. This means that photo-elastic material when illuminated or Illumination, for example with polarized light, or its refractive index the ratio between applied and transmitted light with the load än changes, with the geometry of the photo-elastic element also being used, for strong and meaningful output signals within a wide measuring range ches. Because the output signal is strong and within a wide range meaningfully varied and clear relationship between the change in mecha African voltage state and the change in optical properties ge is given, the necessary electronic effort remains to evaluate the evaluation output signal low. In addition, the thread tension meter can be inexpensive design, simple and compact, with the use of light as an extra advantageous for the precise measurement of forces as low as those from the thread tension of a thin thread result, is an advantage. On top of that, that Photoelastic elements as the main active component of the thread chip voltage sensor is only scanned contactlessly by the light, which is the structure Simplified, because there is no direct electrical tap on the photo-elastic element is required.

Measuring devices for large forces using the phenomenon of photoelasticity, Drü Cke or other measured values are known from US 4,466,295 A and US 3,971,934 A.

The thread deflector is expediently attached directly by means of the photo-elastic element in of the bearing, so that any force resulting from the thread tension  is introduced into the photo-elastic element and in this a mechanical Voltage state induced, which varies strictly depending on the load and interferes with light can be scanned insensitively.

Inexpensive is a photo-elastic element in plate form, of which the thread deflector protrudes on one side and thereby has a thread contact area which of the closest plate surface is spaced with a torsion arm. In this way, the photo-elastic element becomes primarily a torsion with a shard subject to loads, possibly in connection with a bend, as the photo elastic element is particularly sensitive to torsion. The optical axis the optoelectronic scanning device penetrates the plate transversely to the plate ver run, preferably approximately perpendicular to the plate surfaces, so that a critical cal collimation within a too long light path in the photo-elastic el ment is avoided. The stored mass of the photoelastic element is there at only a minimum, so specifically for use in thread tension measurement a favorable natural resonance frequency, for example in the order of magnitude of about 1 kHz with good immediate response.

A strip-shaped plate is very practical, on the opposite longitudinal sides which is fixed in the storage, the plate width is a multiple of Plate thickness is. The optical axis of the optoelectronic scanner passes through the strip-shaped plate perpendicular to the plate main plane and at a distance from the thread deflector and a clamped longitudinal end, d. H. in an area in which the mechanical torsional stress in the photo-elastic element almost homo gene is what the positioning of the optical axis of the optoelectronic scanner direction simplified.

Alternatively, the photo-elastic element could be a plate clamped on one side, which is contacted directly by the thread at a distance from the and thus itself forms the thread deflector, or a thread guide for contact with the Thread carries. The plate is under the load from the thread tension in this execution form mainly loaded on bending.  

Isotropic or qua is particularly suitable as the material for the photo-elastic element si-isotropic plastic or isotropic optical glass. For use in the thread However, voltmeters are also suitable for plastic or optical glass with a reasonably defined, preferably production-related, optical light gang sachse. Such materials are usually isotropic and are used in a me chanic stress state anisotropic. A photoelastic is particularly useful shear plastic such as polycarbonate, which is commercially available with the desired material specifications is available. The induced anisotropy results in different Refractive indices for different light polarization directions with respect to that main stresses inside the photo-elastic element. The Span Condition can be detected by measuring the intensity of the exiting Light, the photoelastic element between two linear polarizing elements elements with crossing polarization axes.

Since it is for the use of the photoelastic element in the thread tension knife is important to produce as little as possible in the largely stress-free state One should have tension-related tensions within one of an art fabric film cut out plate at least the free-running cut edges ge be ground to eliminate "frozen" stresses. The plate comes with Cut to size and then at least in the exposed cut edges brought to the necessary plate width by grinding to avoid undesired influences to minimize the measuring accuracy.

In order to minimize the influence of extraneous light or the like., The photo-elastic Element outside the passage area of the optical axis of the optoelektroni rule the scanning device have an opaque cover, for. B. one Paint.

In the optoelectronic scanning device, the light source should be at least quasi emit monochromatic light. A first polarizing element between the Light source and the photo-elastic element takes only a linear polarization of the Light that strikes the photo-elastic element. On the opposite A second polarizing element is placed on the side with its polarizing axis opposite  the polarization axis of the first polarizing element with a predetermined th angle is offset, for example 90%. The receiver is positioned behind it. By coordinating the rotational positions of the first and second polarizing elements rela tiv to each other and relative to the optical light transmission axis of the photo-elastic Elements, a positioning is determined in which the photoelasti is not loaded element or with a minimal load, minimal light transmission occurs while the light transmission occurs within a wide scanning range brought load and increasing thread tension legally up to a maximum increases. It can be expedient to arrange the polarizing elements so as to be rotatable order the best orientation in relation to the photo-elastic element to be able to ask. It is always possible to find two orthogonal positions in which the light quenching between the crossing polarizing elements almost is perfect, e.g. B. better than 0.1%. It is advisable to use the photo-elastic Ele only largely pure torsion, so that the thread tension measurement he shows a low sensitivity to vibration.

A red light LED is useful as the light source, while the receiver takes a photo element like a photo transistor can be. The output characteristic is not linear, but in the first approximation square, d. that is, the intensity of the second Emerging light polarizing element follows an analytical expression, the one subject can be derived. For example, the intensity of the emerging light proportional to the squared value of the torque applied by the load, so that the thread tension directly over the constant torsion arm of the load is determined.

The thread deflector is expediently a ceramic rod or ceramic tube preferably with a round cross section, which is fixed with a holder on the plate and extends approximately perpendicular to the surface of the plate. Has ceramic material good wear resistance to thread abrasion, is light, temperature nsensitive and cushioning.

In a specific embodiment, the plate is edged between two bearings trestles so that it bridges the gap between the pedestals.  The first and the two plate surfaces are facing in a bearing block contain second plate-shaped polarizing elements, the rotational position of which is expedient is partially adjustable. The light source and the receiver, also in this Bearing blocks are housed, define the optical axis of the optoelectronic Scanner which penetrates the plate perpendicular to the plate surface, and at a distance from the point at which the thread deflector twists from the load generated in the plate, and also at a distance from the area of definition of the plate. the This construction concept leads to low vibration sensitivity of the thread tension knife and a good and immediate response behavior of the thread chip tension meter for changes in thread tension.

A bridge-shaped holder from Fa arranged the leaders who with the thread deflector the thread path through the company Set the voltage meter. If necessary, an additional thread guide in placed in the immediate vicinity of the thread deflector, so that the thread detaches the thread Flektor applied at a constant distance from the plate, even if the Ab stands for the thread guides in the thread running direction are chosen to be relatively large. there a small deflection angle of the thread is sufficient, which is its mechanical load (Friction, diffraction) minimized.

Embodiments of the subject matter of the invention are based on the drawings explained. Show it:

Fig. 1 is a schematic perspective view of a thread tension meter,

Fig. 2 is a schematic representation of the thread tension meter of Fig. 1, and

Fig. 3 schematically shows a modified embodiment of a thread tension meter.

A thread tension meter M in FIG. 1 is provided for use in thread processing systems in order to measure the tension in a running or resting thread F or to provide an output signal representing the thread tension, possibly for controlling at least one associated component such as a controllable thread brake ( Not shown). A typical application of the thread tension meter M is the thread path between a thread delivery device and a weaving machine.

The thread tension meter M has a base body 1 and a bridge-like holder 2 for two aligned thread guides 3 , which define a predetermined, straight thread path through the thread tension meter M. The thread F is deflected at a deflector D, in the embodiment shown on a rod or tube 12 , for example made of ceramic material and with a round cross-section. The thread F bears on the thread deflector D in a predetermined contact area 14 , in which the thread F can be held by a further thread guide, not shown.

On the base body 1 17 bearing blocks 4 , 5 are arranged on both sides of an intermediate space. In the bearing block 5 , an optoelectronic scanning device A is arranged, consisting of a light source LS, for example a red light LED 12 , a first polarizing element P _i in the form of a square or round plate which is rotatably adjustable in the bearing block 5 ; a spaced-apart second polarizing element P _O , also in the form of a square or round plate that can be arranged rotatably bar, and a receiver R, for example a Fotoele element or phototransistor 13 . The light source LS and the receiver R are connected via lines to an evaluation circuit 6 which supplies a signal i.

A photo-elastic element E, for example with the shape of an elongated, thin plate S, with a longitudinal end in a fixing area 7 in the bearing block 7 and z. B. as here with the other longitudinal end in a Festlegungsbe rich 8 clamped in the bearing block 5 . Between the definition areas 7 and 8 he stretches the plate S upright here. The plate S has mutually parallel plate surfaces 9 and also mutually parallel plate edge surfaces 10 . On the plate S, the thread deflector D is fixed with a holder 11 in a motion-transmitting manner. Since the thread F imposes a load K on the thread deflector D in the contact region 14 , which is derived as a reaction force from the thread tension, the thread deflector projects freely on one side, and the contact region 14 has a low torsion ratio to the plate S, from the Load K in the plate S generates pure torsion, which causes a torsional stress state in the interior of the plate S, which depends on the load K from the extent. For this purpose, it is expedient to fix the plate S at two opposite end regions and to twist between them.

The plate S consists, for example, of dielectric, transparent, normally at least quasi-isotropic material such as optical glass or plastic (amorphous organic glass, or plastic with cubic crystal lattice) and is used in the case of a anisotropic internal torsional stress condition. From the anisotropy result for different lightwave polarization directions different refractive index dices related to the main stresses inside the photoelastic Element.

If, as in the voltmeter M in Fig. 1, the photoelastic element E Zvi rule two linear Polarisierelementen P _i, P _O arranged such that the optical axis of the optoelectronic scanning device A in the distance from the Festlegungsbe rich 8 and of the bracket 11 and is directed approximately perpendicular to the plate surfaces 9 through the plate S, then the voltage condition can be detected by measuring the intensity of the light that emerges from the illuminated plate. The polarizing elements are arranged so that their polarization axes cross each other. By coordinating the relative rotational positions of the polarizing elements on the light passage axis of the photo-elastic element, extensive light extinction can be set with the condition of the photo-elastic element largely free of tension. With increasing torsional tension inside the photo-elastic element, the intensity of the emerging light increases. This intensity variation is registered by the receiver R and converted in the evaluation circuit 6 into an output signal i from which the thread tension can be determined.

The light intensity is at least approximately proportional to the squared value of the torque applied, which causes the torsional stress, resulting from the load K and the torsion arm of the thread contact area 14 to the plate S.

A polycarbonate, e.g. B. known with the trade name optical LE XAN, can be used with a thickness of, for example, 1 to 2 mm. The polarizing elements P _i , P _O are so-called polaroids. The light source LS generates z. B. a quasi monochromatic light. Sheet polycarbonate is usually not isotropic. Due to the manufacturing process, however, there may be an optical light transmission thing, even if it is not under mechanical tension. By means of the polarizing elements, two orthogonal positions can be found with which the light extinction between the polarizing elements is almost perfect, for example better than 0.1%. Since the photo-elastic element can only be twisted, it works with low sensitivity to vibrations.

The behavior under pure torsional stress is explained with reference to FIG. 2. The plate S, for example made of polycarbonate, has a width h, a length l and a thickness b. It is defined at the left end in definition area 7 . A torque T is applied to the other end. As a result, a uniform stress status appears in the plate S as a stress tensor. This modifies the dielectric sensor so that the plate S gets an anisotropic behavior. The main voltages lie on the XY plane, so that their direction is never parallel to the axes of the two polarizing elements P _i , P _O , the axes of which are mainly oriented in the X direction. Each light wave front that hits the plate S vertically is divided into two waves that propagate in the plate S at two different speeds, as a result of the different refractive indices along two main axes. This results in a phase difference, with the chosen arrangement resulting in a constant phase delay almost over the entire plate extension, at least as far as the isochromates of light are concerned. The light emerging from the second polarizing element P _O follows an analytical equation that can be easily derived.

Since the two wave or vibration components through the plate with one Propagate total phase difference, and the amplitudes from the second polar emerging light waves or light vibrations out easily can be found, there is an interference between the two waves, which ultimately  for the variation of the emerging light registered by the receiver is answerable.

The polycarbonate plate has a length of 50 mm, for example, a width of 20 mm and a thickness of 2 mm and can be with the optoelektroni The scanning device A reliably for deriving a meaningful output signals, in particular by applying a torsional stress, to the company to be able to measure the voltage.

In Fig. 3, another arrangement of the photo-elastic element E is shown schematically. The photo-elastic element E is again a plate S with mutually parallel plate surfaces 9 and plate edge surfaces 10 . As in the embodiment of the plate S in FIGS. 1 and 2, the plate is cut out of a polycarbonate film parallel to its main direction, this main direction should coincide with the main dimension of the film. The plate is cut out with a larger width than required. The correct dimension is produced by grinding at least the longitudinal cut edges in order to eliminate frozen or internal stress states from the production and / or the cutting of the plate. Appropriately, the unused surfaces of the plate are provided with opaque shielding conditions, for. B. with a paint application C in Fig. 1st

In the variant in FIG. 3, the plate S is clamped on one side only in the bearing block 4 in the fixing area 7 . It cantilevers with the other end. The plate S can serve directly as the thread deflector D by deflecting the thread F directly over the plate and in the contact area 14 in order to release the load K. The optoelectronic scanning device A is arranged between the fixing area 7 and the contact area 14 in such a way that its optical axis is approximately perpendicular to the plate surfaces 9 and passes through the plate at a distance from the longitudinal edges.

In the dashed alternative in FIG. 3, a thread guide 15 is fixed at the free end of the plate S directly or with a holder 16 , which forms the contact area 14 for the thread F. In this configuration, the plate is mainly subjected to bending, so that the inner bending stresses are detected with the optoelectronic scanning device A and the thread tension is deduced from the bending stress conditions by varying the intensity of the emerging light. The scanning principle can also be described with the birefringence phenomenon. The evaluation circuit is relatively simple. It also serves to acti vate the light source LS and to polarize the photo element, e.g. B. a photo transistor 13 . The output signal is e.g. B. about an approximately 10 K-Ohm load resistance was read in conjunction with a 10 nF parallel filter capacitor, and can be sent directly to an oscilloscope, without further amplification or conditioning. The visual representation is carried out using 16 average patterns, for example. The connecting lines to Auswerteschal device, and then on, should expediently be well shielded in order to superimpose as little noise as possible on the voltage signal.

An arrangement similar to that in FIG. 1, ie a plate-shaped photoelastic element, which is loaded with the load K from the thread tension essentially purely on torsion and is clamped on both ends, seems to be most suitable for measuring the thread tension. By scanning only the inner torsional tensions, with the short passage of light through the small thickness of the plate and perpendicular to the plate surfaces, with the coordinated alignment of the crossing polarization axes of the linear polarizing elements, and with, for example, red light, the thread tension can be within measure a wide, ie spread, range precisely, with a slight change in the thread tension already leading to a significant change in the intensity of the emerging light. Due to the pure Tor sionss tension in the photo-elastic element, the thread tension meter is relatively insensitive to vibrations oriented differently, as is usually the case in thread processing systems, e.g. B. on a loom are unavoidable. The thread tension meter M is compact, structurally simple and consists of few and inexpensive parts. It is reliable and can be used universally.

Claims (15)

1. Thread tension meter (M) for a thread (F) deflected within a defined thread path on a stationary deflector (D), with an electronic evaluation circuit ( 6 ), which is taken from the deflector (D), mechanical and with the Thread tension (t) corresponding load (K) derives output signals (i), with at least one transducer device (E) deformable as a function of the load and monitored by the evaluation circuit being provided in the load transmission path from the deflector (D) to the bearing ( 4 , 5 ), characterized in that the transducer device (E) has a translucent photoelastic element (S) arranged elastically deformable under the thread tension (t) in the thread tension meter (M) and an optoelectronic scanning device (A.) connected to the evaluation circuit ( 6 ) ) for at least one load-dependent varying optical property of the photo-elastic element (S) exposed to light (L). 2. Thread tension meter according to claim 1, characterized in that the thread deflector (D) is supported by means of the photo-elastic element (S) in the bearing ( 4 , 5 ). 3. Thread tension meter according to claim 1, characterized in that the photo-elastic element (S) is plate-shaped and on at least one plate edge area in the storage ( 4 , 5 ) is fixed that the thread deflector (D) at a distance from the fixing area ( 7 , 8 ) is cantilevered on one side with a direction transverse to the plate course starting from the fixing area ( 7 , 8 ) on the photoelastic element (S) and has a predetermined thread contact area ( 14 ) which is adjacent to the thread contact area plate surface ( 9 ) or plate edge surface ( 10 ) is spaced apart with a torsion lever arm, and that for the measurement of the thread tension (t) on the basis of a torsion (T) generated by the load (K) with shear loads in the photo-elastic element (S), the optoelectronic scanning device (A) has an optical axis ( X), which the photo-elastic element (S) transversely to the plate course and in the direction of the plate course at a distance from the thread -Deflektor (D) and the fixing area ( 7 , 8 ) passes through, preferably approximately perpendicular to a plate surface ( 9 ). 4. Thread tension meter according to claim 3, characterized in that the photo-elastic element (S) is a strip-shaped plate and fixed at opposite longitudinal ends in the storage ( 4 , 5 ) that the thread deflector (D) approximately transverse to the longitudinal direction of the Plate is oriented and held between the longitudinal ends on the plate, and that the optoelectronic scanning device (A) between the holder ( 11 ) of the thread deflector (D) and a longitudinal end of the plate with its optical axis (X) substantially perpendicular to Plate surface ( 10 ) is arranged. 5. Thread tension meter according to claim 1, characterized in that the photo-elastic element (S) as the thread deflector (D) comprises a in the storage ( 4 ) at least on one side fixed plate, either directly through the contacting thread (F) or the load (K) is applied approximately perpendicular to the plate surface ( 10 ) in a bending sense via a thread guide ( 15 ) arranged on the plate. 6. Thread tension meter according to claim 1, characterized in that the Photo-elastic element (S) is made of isotropic plastic or optical glass. 7. Thread tension meter according to claim 1, characterized in that the photo-elastic element (S) made of a plastic or optical glass with a defi niert, preferably manufacturing-related, optical light transmission axis be stands. 8. Thread tension meter according to claim 1, characterized in that the Photoelastic element (S) made of polycarbonate, e.g. B. trade name optical LEXAN, consists.   9. Thread tension meter according to claim 1, characterized in that the photo-elastic element (S) is a cut out of a film, flat and translucent plate, the cutting edge surfaces ( 10 ) extending from the fixing area ( 7 , 8 ) or extending between end-side fixing areas are. 10. Thread tension meter according to claim 1, characterized in that the photo-elastic element (S) outside the passage area of the optical axis (X) of the optoelectronic scanner (A) an opaque cover (C), preferably a color application. 11. Thread tension meter according to claim 1, characterized in that the optoelectronic scanning device (A) a light source (LS) for at least quasi mo still chromatic and / or polarized light (L), between the light source (LS) and the photo-elastic element (S) first polarizing element (P _i ), in the direction of the optical axis (X) and on the opposite surface of the photo-elastic element (S), a second polarizing element (P _O ) with respect to the polarizing axis of the first polarizing element with a predetermined angle around the optical axis (X) twisted polarization axis, which preferably together cause a light birefringence (birefringense) and behind it has a receiver (R). 12. Thread tension meter according to claim 11, characterized in that the light source (LS) a red light LED ( 12 ) and the receiver (R) are a photo element ( 13 ). 13. Thread tension meter according to claim 3, characterized in that the thread deflector (D) is a ceramic rod or tube ( 12 ), preferably with a round cross section, which is fixed with its holder ( 11 ) on the plate and in extends approximately perpendicular to the plate surface ( 10 ). 14. Thread tension meter according to at least one of the preceding claims, characterized in that on a base body ( 1 ) of the thread tension meter (M) two with an intermediate space ( 17 ) spaced bearing blocks ( 4 , 5 ) are seen before that the plate at both ends in is fixed to the bearing blocks ( 4 , 5 ), preferably lying on edge, and extends through the intermediate space ( 17 ) such that the deflector (D) is attached to the plate in the intermediate space and has an end opposite the bearing blocks with the thread contact region ( 14 ) ( 4 , 5 ) protrudes that in a bearing block ( 5 ) the two plate surfaces ( 10 ) facing first and second plate-shaped polarizing elements (P _i , B) are contained, and that the light source (LS) and the receiver (R) in Bearing block ( 5 ) are placed on the first and second polarizing elements (P _i , P _O ). 15. Thread tension meter according to claim 14, characterized in that a bridge-shaped holder ( 2 ) with two aligned thread guides ( 3 ) is arranged on the base body ( 1 ) below the intermediate space ( 17 ) and the end of the thread deflector (D) use the thread deflector (D) to define the thread path through the thread tension meter (M).