IDENTITY CARD AND PROCEDURES FOR ITS VERIFICATION

Description

[0001] The present invention relates to an identity card comprising a hologram area that includes a first volume reflection hologram and a second volume reflection hologram. The invention further relates to a method for verifying the authenticity of a valuable or security product in the form of an identity card.

[0002] Valuable or security documents can be, for example, an identity document, a check card, a non-personalized authorization card such as a ticket or means of payment, or a valuable or security element intended for product security.

[0003] It is known from the prior art to integrate holograms as security elements into security documents or valuable documents. Security elements are entities that possess at least one feature that makes it difficult to unauthorizedly duplicate, imitate, and / or falsify an object in which the security element is integrated. Holograms are used as security elements, for example, in passports or identity cards. However, they are also used in banknotes, driver's licenses, visas, other tokens, labels or tickets, credit cards, bank cards, telephone cards, and similar items.

[0004] Volume holograms represent a special group of holograms. In a volume hologram, a diffractional structure of the hologram is stored within the volume of the holographic recording material. Holographic exposure films, usually supplied on rolls, are typically used as recording materials for volume holograms in valuable and / or security documents. These exposure films are suitable for storing interference patterns whose characteristic dimensions lie in the range of the wavelength of the light used to record or reconstruct the hologram.

[0005] In a contact printing process, the holographic exposure film is positioned in front of a master containing diffraction patterns that are to be "transferred" to the holographic exposure film. In this process, the diffraction patterns of the master are thus copied into the holographic film. For this purpose, coherent light is shone through the holographic film, which is positioned in close proximity to or in contact with the master, and onto the master. The diffraction patterns in the master diffract the light, causing it to be reflected back into the holographic film. There, it interferes with the coherent light used to illuminate the master. An interference pattern is thus formed in the holographic film, determined by the light diffracted by the master.When the holographic film is developed and reconstructed, the reconstruction is similar to that observed when the master is illuminated. A hologram, also known as a Denisyuk hologram, is stored in the holographic film; this is a volume reflection hologram. It is understood that the incident light must have a suitable wavelength (or wavelengths) and a suitable direction (or directions) of incidence so that diffraction at the diffraction pattern occurs as desired.

[0006] For security or valuable documents, the use of holographic features formed from volume holograms is particularly suitable, as they are especially well-suited for verification, for example, by viewing the exposed and developed holographic film perpendicularly. The reconstruction light is preferably irradiated at an acute angle, for example, at 45 degrees to the perpendicular. The angle between the direction of incidence of the reconstruction light and the direction of reflection of the light diffracted by the generated volume hologram, which reconstructs the hologram's information, is essentially determined during the production of the master.

[0007] DE 10 2007 052 ​​952 A1 describes a safety document that includes two adjacent volume reflection holograms, of which a first volume reflection hologram is formed from a more strongly scattering layer and a second volume reflection hologram is formed from a less strongly scattering layer.

[0008] In both layers, the intensity of the reconstruction increases as one approaches the angle of exposure loss. This security document has proven effective in practice and offers adequate protection against product counterfeiting.

[0009] German patent application DE 10 2018 217 560 A1 describes an identity card according to the preamble of claim 1. It shows a security document with a security element that has several diffraction patterns which are optically detectable at different angles of incidence and reconstruction. A first diffraction pattern is made visible by the first diffraction pattern, and a second diffraction pattern is optically detectable by the second diffraction pattern.

[0010] US 2006 / 0181077A1 describes a security document in the form of a banknote that incorporates a security feature. This document explicitly describes the interplay between the reconstructive and non-reconstructive parts of the security feature, whereby the parts can also complement each other.

[0011] From DE 10 2006 057 123 A1 a safety element with two different patterns is known, one pattern being found in the other pattern in the form of omissions.

[0012] There is a need to be able to reliably read holographic features by machine.

[0013] It is therefore the object of the present invention to provide an identity card and a method for its production which take into account the aforementioned disadvantages.

[0014] The aforementioned problems are solved by an identity card with the features of claim 1 and a method with the features of claim 10. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0015] The value or security product formed according to the invention as an identity card is characterized in that the first volume reflection hologram is designed to be reconstructed at a first reconstruction wavelength and a first reconstruction direction, and that the second volume reflection hologram is designed to be reconstructed at a second reconstruction direction that differs from the first reconstruction direction.

[0016] In this way, machine-verifiable security of the personalization data, especially the photograph, can be achieved, since a reading device with different lighting devices or with a device for changing the angular position of the valuable or security product can recognize the holographic security feature, especially optically.

[0017] The security product can be a document or security element, i.e., an element that is attached to an item to be protected against counterfeiting, forgery, or falsification, such as a sticker, label, or the like. Examples of security products that qualify as such include a passport, identity card, driver's license or other ID card or access control card, vehicle registration certificate, vehicle title, visa, check, other means of payment, in particular a banknote, check, bank card, credit or debit card, customer card, health insurance card, chip card, company ID card, certificate of authorization, membership card, or other ID document, provided that it includes or has a portrait photograph attached.

[0018] Preferably, the valuable or security product is in ID 1, ID 2, ID 3, or any other format, for example, in booklet form, similar to a passport-like item. The valuable or security product is generally a laminate of several document layers that are precisely bonded together under heat and increased pressure.

[0019] These products should meet standardized requirements, for example ISO 10373, ISO / IEC 7810, ISO 14443.

[0020] Preferably, the product layers consist of a carrier material suitable for lamination. The value or safety product, however, may preferably be formed from a polymer selected from the group comprising polycarbonate (PC), in particular bisphenol A polycarbonate or a polycarbonate formed with a geminal disubstituted bis(hydroxyphenyl) cycloalkane, polyethylene terephthalate (PET), its derivatives such as glycol-modified PET (PETG), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polyimide (PI), polyvinyl alcohol (PVA), polystyrene (PS), polyvinylphenol (PVP), polypropylene (PP), polyethylene (PE), thermoplastic elastomers (TPE), in particular thermoplastic polyurethane (TPU), acrylonitrile butadiene styrene copolymer (ABS) and its derivatives, and / or paper and / or cardboard and / or glass and / or metal and / or ceramics.Furthermore, the product can also be made from several of these materials. Preferably, it consists of PC, PVC, and PET. The polymers can be either filled or unfilled. In the latter case, they are preferably transparent or translucent. If the polymers are filled, they are opaque. The foregoing refers both to films to be bonded together and to liquid formulations that are applied to a precursor, such as a protective or topcoat. Preferably, the product is made from three to twelve, more preferably four to ten films. The films can also bear printed layers. A laminate formed in this way can finally be coated on one or both sides with the protective or topcoat or with a film. The film can, in particular, be a volume hologram, a film with a surface hologram (for example, a kinegraphic element), or a scratch-resistant film.Overlay layers formed in this way protect a security feature located underneath and / or give the document the necessary abrasion resistance.

[0021] To improve the security of the valuable or security product while simultaneously improving machine readability, it has proven advantageous if more than two, and thus in particular at least one third, volume reflection hologram is present in the hologram area, which is designed to reconstruct with a third reconstruction direction that differs from the first reconstruction direction and the second reconstruction direction.

[0022] When more than two volume reflection holograms are used, the security feature formed from the multiple volume reflection holograms becomes more independent in its position on the substrate or card body. This independence is increasingly enhanced by increasing the number of possible reconstruction angles / incident beam directions; thus, by increasing the number of volume reflection holograms.

[0023] Many card readers – especially those designed for reading ID1-format cards – allow the card to be placed "freely" on the reader. This means there is no stop on the card itself to define its position for reading. Therefore, the card is initially positioned at an undefined angle when the light is projected onto the reader. The card's position relative to the reader can then be determined based on the position of a reconstructing volume reflection hologram. If multiple different volume reflection holograms are used for the security feature, the position of the feature can be deduced from the (partial) volume reflection hologram that reconstructs under illumination. It can then be specifically checked whether and which of the other (partial) volume reflection holograms reconstruct under different angles.The higher the number of (partial) volume reflection holograms, the higher the probability that at least one of them will be reconstructed, even if the location of the hologram area containing the security feature is initially unknown.

[0024] Further improved readability can be achieved by providing at least one reference point and arranging the hologram area to be read in a predefined relation to this reference point of the product. In this context, it is advantageous if the reference point is formed by at least one edge of the product card. Preferably, at least two mutually perpendicular edges are specified as reference points, so that the hologram area to be checked is located, for example, in one of the four quadrants of an identity card.

[0025] It is possible that the volume reflection holograms have an identical shape, which improves their machine recognition, since a verification computer must always check for the presence of the same pattern in order to verify the authenticity of the majority of volume reflection holograms.

[0026] In this context, it is advantageous if the volume reflection holograms are formed as directly adjacent polygons. These can be, for example, triangles or quadrilaterals, especially rectangles or squares.

[0027] However, machine evaluation is also facilitated if the volume reflection holograms are formed as immediately adjacent circular sectors whose tips lie at a common point.

[0028] To keep the complexity of testing and evaluating the volume reflection holograms as low as possible, it is advantageous if the volume reflection holograms are designed to reconstruct at the same reconstruction wavelength.

[0029] However, it is possible for the first volume reflection hologram to be designed to be reconstructed at a first reconstruction wavelength, for the second volume reflection hologram to be designed to be reconstructed at a second reconstruction wavelength that differs from the first, and for the third volume reflection hologram to be designed to be reconstructed at a third reconstruction wavelength that differs from both the first and second reconstruction wavelengths. This increases counterfeit protection, as at least three different wavelengths would have to be used in a counterfeiting attempt to imitate the holograms.

[0030] It has proven to be particularly counterfeit-proof if the valuable or security product is provided with a (printed) portrait image, and if the portrait image is secured with a security feature formed from volume reflection holograms.

[0031] In a first embodiment of the invention, the hologram area is precisely defined by the dimensions of the portrait image. In this way, the hologram area can be identified and read very precisely and with minimal effort based on the visible portrait image.

[0032] Alternatively or additionally, it is possible that at least one (for example, printed) data field with personalization data is present, and that the data field is secured with a security feature formed from the volume reflection holograms.

[0033] In a second embodiment of the invention, the hologram area is precisely defined by the dimensions of the data field containing personalization data. In this way, the hologram area can be identified and read very precisely and with minimal effort based on the visible data field.

[0034] The inventive method for verifying the authenticity of the valuable or security product comprises in particular the following steps: Providing the valuable or security product with a hologram area to be checked, specified at a fixed position on one of its surfaces; irradiating the hologram area from a first reconstruction beam direction and checking whether a first volume reflection hologram is reconstructed; irradiating the hologram area from a second reconstruction beam direction that differs from the first and checking whether a second volume reflection hologram is reconstructed; irradiating the hologram area from a third reconstruction beam direction that differs from the first and second reconstruction beam directions and checking whether a third volume reflection hologram is reconstructed; and determining product counterfeiting if at least one of the volume reflection holograms in the hologram area has not been reconstructed.

[0035] This method also offers the advantage of improved machine readability of the valuable or security product. The advantages and beneficial embodiments associated with the valuable or security product according to the invention apply equally to the method according to the invention.

[0036] However, it is preferred if the shape of each of the volume reflection holograms includes at least one edge that extends in the form of a line, in particular a test line, along an edge of one of the other volume reflection holograms, and if product counterfeiting is detected even if the test line is not present or is incomplete.

[0037] A test line is a line that can be traced with a pen and that appears on an authentic, high-value or security product when the individual images from each optical inspection of the three volume reflection holograms are superimposed in perfect registration (congruence). A test line formed in this way can therefore be specifically checked for tampering attempts, because if steps, edges, or corners appear on the line formed by the edges of several volume reflection holograms, a counterfeit is detectable.

[0038] The present invention is explained in more detail below with reference to the figures, the examples shown being merely illustrative and not representing any limitation as to the scope of the described invention. Specifically, the figures show: Fig. 1 a schematic isometric representation of a security product in the form of an identity card, Fig. 2 a schematic sectional view of the identity card along line II, Fig. 3 the highly schematic security product whose hologram area is provided with three square volume reflection holograms, and which is irradiated from a first reconstruction beam direction such that the first volume reflection hologram is reconstructed, Fig. 3b the highly schematic security product made of Figure 3a , whose hologram area - due to the illustrated tilt - is irradiated from a second reconstruction beam direction in such a way that the second volume reflection hologram is reconstructed, Fig. 3c the highly schematic value or security product from Figure 3a, whose hologram area - due to the illustrated further tilting - is irradiated from a second reconstruction beam direction in such a way that the third volume reflection hologram is reconstructed, Fig. 4a, the highly schematic value or security product, whose hologram area is provided with three pie-shaped volume reflection holograms, and which is irradiated from a first reconstruction beam direction in such a way that the first volume reflection hologram is reconstructed, Fig. 4b, the highly schematic value or security product from Figure 4a , whose hologram area - due to the illustrated tilt - is irradiated from a second reconstruction beam direction in such a way that the second volume reflection hologram is reconstructed, Fig. 4c, the highly schematic value or security product from Figure 4a, whose hologram area - due to the illustrated further tilting - is irradiated from a second reconstruction beam direction in such a way that the third volume reflection hologram is reconstructed, Figure 5 a schematic representation of a device for reconstructing and detecting the security feature of the valuable or security product formed from holograms, Fig. 6 the resulting test lines of the holograms from Figures 3a to 3c , and Fig. 6b the resulting test lines of the holograms from Figures 4a to 4c .

[0039] In Figure 1 A security product 100 bearing a security feature 500 is shown. The security document 100 can be a personal document such as a passport, identity card, access card, or similar. All subsequent examples are described using such a card as a representative example of other document types.

[0040] In the Figures 1 and 2The valuable or security product 100 is represented in the form of an identity card, which, for example, has been assembled as a laminate from several internal polymer layers 140. For example, the polymer layers can consist of PC and / or PET. The individual layers can be unfilled or filled with fillers. In the latter case, they are opaque; otherwise, they are transparent. The layers can preferably be bonded together in such a way that they form a monolithic block that is practically impossible to split.

[0041] In Figure 2The layers shown before lamination are for illustrative purposes only. The interfaces are no longer visible in the finished laminate. The outer layers 150 of the card can be a final protective plastic film or consist of a protective varnish applied to the card after lamination. The protective plastic film or varnish is transparent, allowing information underneath to be seen. In particular, one or more printed layers 140a, for example, of a portrait image 110, remain visible, preferably located directly next to or behind the outer layer 150.

[0042] The security product 100 has a top side 101 and a bottom side 102. The top side 101 contains the cardholder's face or portrait image 110, as well as data fields, namely, for example, a first data field 120 and a second data field 130 containing card and holder data in plain text. The data in the first and second data fields 120 and 130 are produced by printed layers located on an outer layer of the document, but directly beneath the outer protective layer 150. The data in a third data field 125 and a fourth data field 135 reproduce the personalization data, which is already printed in plain text, in Braille.

[0043] It can be seen that the portrait image 110 is assigned a security feature 500 for its protection, which in this case is formed from several holograms in the form of an Identigram (a registered trademark of the applicant). However, the security feature 500 can also be used to protect other personalization data, for example in one of the data fields 120, 125, 130, or 135.

[0044] To enable machine reading of the identity card, a hologram area 502, depicted with dashed lines, is defined. A device for detecting the security feature 500 expects the presence of this feature within this area. The position of the hologram area 502 is defined in relation to a fixed reference point of the security product 100. This fixed reference point is defined in this case by the position of the portrait image 110. Several such reference points may exist, and at least one edge of the product card can also be used as a reference.

[0045] This hologram area 502 is accessed using the Figures 3 to 5This will be discussed in more detail. In hologram area 502, there is a first volume reflection hologram 500a, a second volume reflection hologram 500b, and a third volume reflection hologram 500c. All volume reflection holograms 500a, 500b, and 500c have an identical shape. As shown in the example, they are... Figures 3a to 3c formed from polygons, in particular from immediately adjacent squares. As shown in the example above. Figures 4a to 4c The volume reflection holograms 500a, 500b, 500c are formed from immediately adjacent circular sectors whose vertices lie at a common point. The position of this point can, in turn, be a predefined position of the value or security product 100 and, as such, itself represent a security feature.

[0046] The first volume reflection hologram 500a is configured to reconstruct a first reconstruction wavelength and a first reconstruction angle from a first reconstruction beam direction, and the second volume reflection hologram 500b is configured to reconstruct a second reconstruction angle from a second reconstruction beam direction that differs from the first reconstruction angle and the first reconstruction beam direction. The third volume reflection hologram 500c is configured to reconstruct a third reconstruction angle from a third reconstruction beam direction that differs from the first reconstruction angle, the first reconstruction beam direction, the second reconstruction angle, and the second reconstruction beam direction. In the Figures 3a to 3c and in the Figures 4a to 4cThis is illustrated by the hatching, which represents the respective reconstructing volume reflection hologram 500a, 500b, 500c; each at a different angular position of the value or security product 100.

[0047] In the present embodiment, the volume reflection holograms 500a, 500b, and 500c are configured to be reconstructed at the same reconstruction wavelength. In another embodiment, the first volume reflection hologram 500a is configured to be reconstructed at a first reconstruction wavelength, the second volume reflection hologram 500b is configured to be reconstructed at a second reconstruction wavelength that differs from the first, and the third volume reflection hologram 500c is configured to be reconstructed at a third reconstruction wavelength that differs from both the first and second reconstruction wavelengths.

[0048] Figure 5Figure 1 shows a schematic representation of a device 200 for reconstructing and capturing the security feature 500 of the valuable or security product 100, which is formed from holograms. The device 200 comprises an image sensor 205, a lighting device with a light source 225, a holder 213 for the valuable or security product 100, and a processor 215 which is in communication with the image sensor 205. The light source 225 is configured to illuminate the security feature 500 with visible or invisible light from different angles and / or from different reconstruction directions. Alternatively or additionally, a second light source 225 may be provided to offer a further angle or direction of illumination. Alternatively or additionally, a third light source 225 may be provided to offer yet another angle or direction of illumination.

[0049] To verify the authenticity of the valuable or security product 100, the valuable or security product 100, with its fixed hologram area 502, is first positioned on one of its surfaces. The hologram area 502 is then illuminated from a first reconstruction beam direction at a first reconstruction angle with respect to the surface normal, and it is checked whether the first volume reflection hologram 500a is reconstructed. Subsequently, the hologram area 502 is illuminated from a second reconstruction beam direction that differs from the first, in particular at a second reconstruction angle with respect to the surface normal that differs from the first, and it is checked whether the second volume reflection hologram 500b is reconstructed.Subsequently, the hologram area 502 is irradiated from a third reconstruction direction that differs from the first direction and the second direction, in particular at a third reconstruction angle that differs from the first and the second reconstruction angle, and it is checked whether the third volume reflection hologram 500c is reconstructed, whereby a product counterfeit is detected if at least one of the volume reflection holograms 500a, 500b, 500c in the hologram area 502 was not reconstructed.

[0050] According to Figures 6a and 6b The holograms shown have another special feature, which arises because the volume reflection holograms 500a, 500b, 500c are directly adjacent to each other.

[0051] When the images of the respective reconstructing volume reflection holograms 500a, 500b, and 500c, captured during the respective test, are superimposed, they form at least one test line 504, which is highlighted in bold in the figures. This line is formed without steps, corners, or edges, thus indicating that no attempt to manipulate the security feature formed by the three holograms has been made. While in the Figures 3a to 3c The holograms shown depict two parallel and straight test lines 504; the test line 504 of the Figures 4a to 4c The holograms shown are arc-shaped.

[0052] This test line 504 offers a further possibility for improving counterfeit protection, because the shape of each of the volume reflection holograms 500a, 500b, 500c includes at least one edge which continues in the form of the test line 504 on an edge of one of the further volume reflection holograms 500a, 500b, 500c, whereby a product counterfeit is also detected if the test line 504 is not present or is present with interruptions.

[0053] The design of the holograms according to Figures 3a to 3c offers a further advantage that contributes to security, because if the test lines 504 do not run at a predetermined fixed distance from each other, it can also be concluded that the valuable or security product 100 is counterfeit.

[0054] The design of the holograms according to Figures 4a to 4coffers another advantageous possibility for the additional safeguarding of the valuable or security product 100. Here, the distance of the point of the tip to the circular arc test line 504 is fixed as a security feature. REFERENCE MARK LIST

[0055] 100 Value or security product 101 Upper substrate surface, upper card surface, top side 102 Lower substrate surface, lower card surface, bottom side 110 Face image 120 First data field 130 Second data field 125 Third data field 135 Fourth data field 140 Internal polymer layers 140a Printing layer 150 Outer protective layer 500 Security feature 500a First volume reflection hologram 500b Second volume reflection hologram 500c Third volume reflection hologram 502 Hologram area 504 Verification line

Claims

1. An identity card comprising a hologram area (502) comprising a first volume reflection hologram (500a) and a second volume reflection hologram (500b), wherein the first volume reflection hologram (500a) is designed to be reconstructed at a first reconstruction wavelength and a first reconstruction beam direction, and that the second volume reflection hologram (500b) is designed to reconstruct at a second reconstruction beam direction that differs from the first reconstruction beam direction, characterized in that a portrait image (110) is present, and that the portrait image (110) is secured with a security feature (500) which is formed from the volume reflection holograms (500a, 500b, 500c), wherein the hologram area (502) is precisely defined by the dimensions of the portrait image (110), or that at least one data field (120, 125, 130, 135) with personalization data is present, and that the data field (120, 125, 130, 135) is secured with a security feature (500) which is formed from the volume reflection holograms (500a, 500b, 500c), wherein the hologram area (502) is precisely defined by the dimensions of the data field (120, 125, 130) containing personalization data.

2. The identity card according to claim 1, characterized in that at least one third volume reflection hologram (500c) is present in the hologram area (502), which is designed to reconstruct at a third reconstruction beam direction that deviates from the first reconstruction beam direction and the second reconstruction beam direction.

3. The identity card according to claim 1 or 2, characterized in that at least one reference point is present and that the hologram area (502) is arranged in a predetermined relation with respect to the at least one reference point of the product.

4. The identity card according to claim 3, characterized in that the at least one reference point is formed by at least one card edge of the product.

5. The identity card according to any one of claims 1 to 4, characterized in that the volume reflection holograms (500a, 500b, 500c) have an identical shape.

6. The identity card according to claim 5, characterized in that the volume reflection holograms (500a, 500b, 500c) are formed as polygons directly adjacent to one another.

7. The identity card according to claim 6, characterized in that the volume reflection holograms (500a, 500b, 500c) are formed as circular sectors directly adjacent to one another, whose vertices lie at a common point.

8. The identity card according to any one of claims 1 to 7, characterized in that the volume reflection holograms (500a, 500b, 500c) are designed to reconstruct at the same reconstruction wavelength.

9. The identity card according to any one of claims 2 to 8, characterized in that the first volume reflection hologram (500a) is designed to reconstruct at a first reconstruction wavelength, the second volume reflection hologram (500b) is designed to reconstruct at a second reconstruction wavelength that differs from the first reconstruction wavelength, and that the third volume reflection hologram (500c) is designed to reconstruct at a third reconstruction wavelength that differs from the first and second reconstruction wavelengths.

10. A method for verifying the authenticity of an identity card according to any one of claims 2 to 9, comprising the steps of: - providing the identity card with a hologram area (502) to be verified which is predetermined at a fixed position on one of its surfaces, - irradiating the hologram area (502) from a first reconstruction beam direction and checking whether a first volume reflection hologram (500a) is reconstructed, - irradiating the hologram area (502) in a second reconstruction beam direction that differs from the first reconstruction beam direction and checking whether a second volume reflection hologram (500b) is reconstructed, - irradiating the hologram area (502) under a third reconstruction beam direction deviating from the first and second reconstruction beam directions and checking whether a third volume reflection hologram (500c) is reconstructed, and - detecting a counterfeit product if at least one of the volume reflection holograms (500a, 500b, 500c) has not been reconstructed in the hologram area (502), characterized in that that a portrait image (110) is present on the identity card, and that the portrait image (110) is secured with a security feature (500) formed from the volume reflection holograms (500a, 500b, 500c), wherein the hologram area (502) is precisely defined by the dimensions of the portrait image (110), or that at least one data field (120, 125, 130, 135) with personalization data is present on the identity card, and that the data field (120, 125, 130, 135) is secured with a security feature (500) which is formed from the volume reflection holograms (500a, 500b, 500c), wherein the hologram area (502) is precisely defined by the dimensions of the data field (120, 125, 130) containing personalization data.

11. The method according to claim 10, characterized in that the shape of each of the volume reflection holograms comprises at least one edge which continues in the form of a test line (504) at an edge of one of the other volume reflection holograms (500a, 500b, 500c), and that product counterfeiting is also detected if the test line (504) is not present or is present with interruptions.