Abstract:
With the E-I or E-E transformer, signals which are independent of each other are to be transferable simultaneously, without the signals interfering with each other. The E-I transformer has an E core (e, E′), which has two outer legs (ES 1 , ES 2 ) and an inner leg (EM), and a yoke ( 1 ) which combines with the E core to form a double closed magnetic circuit. A first coil and a second coil are wound around the inner leg (EM), and a third coil and a fourth coil are wound around one (ES 1 ) of the outer legs. The E-E transformer has a first E core (E 1 , E 1 ′) and an identical second E core (E 2 , E 2 ′); each E core has two outer legs (ES 11 , ES 21 , ES 11 ′, ES 21 ′; ES 12 , ES 22 , ES 12 ′, ES 22 ′) and an inner leg (EM 1 , EM 1 ′; EM 2 , EM 2 ′); the E cores together form a double closed magnetic circuit and two outer links (ST 1 , ST 1 ′, ST 2 , ST 2 ′) as well as an inner link (STM, STM′). A first coil and a second coil are wound around the inner link, and a third coil and a fourth coil are wound around the outer link ST 1 , ST 1 ′). The coils on each leg or link may be wound side by side or one above another. The coils on the inner leg or link and those on the outer leg or link form part of different AC power transmission paths.

Description:
This application claims the benefit of provisional application No. 60/314,629, filed Aug. 27, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to E-I and E-E transformers. 
     BACKGROUND OF THE INVENTION 
     The magnetic circuit of an E-I transformer commonly comprises a ferromagnetic E core, which has two outer legs and an inner leg, and a ferromagnetic yoke in the form of a straight bar, the E core and the yoke being so arranged that a doubly closed magnetic circuit is obtained. 
     The magnetic circuit of an E-E transformer commonly comprises a first ferromagnetic E core, which has two outer legs and an inner leg, and a second ferromagnetic E core, which is identical to the first E core and also has two outer legs and an inner leg, the two E cores being so arranged that a doubly closed magnetic circuit is obtained. The respective two outer legs then form two outer links, and the two inner legs form an inner link. 
     The aforementioned magnetic circuits become electric power transformers if at least two coils, each of which is placed on one of the outer legs or outer links, or one of which is placed on an outer leg or outer link and the other on the inner leg or inner link, or both of which are placed on an outer leg or outer link or on the inner leg or inner link, interact with the magnetic circuit. 
     Such transformers serve to provide isolation between primary and secondary circuits for, e.g., AC signals, DC/DC converters, etc. So far, a special transformer has been used for each of these applications. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to design E-I transformers and E-E transformers in such a manner that signals which are independent of each other can be transferred simultaneously, without the signals interfering with each other. To attain this object, a first variant of the invention consists in an E-I transformer comprising 
     a ferromagnetic E core, having a first and a second outer leg and an inner leg, 
     a ferromagnetic yoke in the form of a straight bar which is so arranged that it and the E core form a doubly closed magnetic circuit, 
     a first coil, wound around the inner leg, 
     a second coil, wound around the inner leg, 
     a third coil, wound around the first outer leg, and 
     a fourth coil, wound around the first outer leg. 
     To attain the above object, a second variant of the invention consists in an E-E transformer comprising 
     a first ferromagnetic E core, which has a first and a second outer leg and a first inner leg, 
     a second ferromagnetic E core, which is identical to the first E core, has a third and a fourth outer leg and a second inner leg, and is so arranged 
     that it and the first E core form a doubly closed magnetic circuit 
     which has a first outer link, a second outer link, and an inner link, 
     a first coil, wound around the inner link, 
     a second coil, wound around the inner link, 
     a third coil, wound around the first outer link, and 
     a fourth coil, wound around the first outer link. 
     In a first preferred embodiment of each of the two variants of the invention, the first coil is placed beside the second coil. 
     In a second preferred embodiment of the invention, which can also be used with the first preferred embodiment, the third coil is placed beside the fourth coil. 
     In a third preferred embodiment of the invention, which can also be used with the first and second preferred embodiments, the first coil and the second coil are, respectively, a primary coil and a secondary coil of a first AC power transmission path, and the third coil and the fourth coil are, respectively, a primary coil and a secondary coil of a second AC power transmission path. 
     According to a further development of the third preferred embodiment of the invention, the frequency of the first AC power is substantially less than the frequency of the second AC power, with the first coil and the second coil preferably being a primary coil and a secondary coil, respectively, of a DC/DC converter, and the third coil and the fourth coil serving to accomplish an electrically separated transfer of digital signals. 
     In another preferred embodiment of the invention, a transformer according to any one of the above-mentioned embodiments is used in a physical-to-electrical transducer with on-board evaluation electronics. 
     In a further preferred embodiment of the invention, the transformer is used in a physical-to-electrical transducer with on-board evaluation electronics, with the third coil having an external two-wire field bus connected thereto, and the fourth coil interacting with a digital circuit of the on-board evaluation electronics. 
     One advantage of the invention is that one and the same transformer can be used for two different functions, which saves material and space. The space saving is of particular importance if at the locations of the transformers, only little space is available for electronic components; that is frequently the case with industrial measuring devices, because the forms of their housings are generally standardized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and further advantages will now be explained in greater detail with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic and perspective view of a first embodiment of an E-I transformer with two coils arranged side by side on the inner leg and two coils arranged side by side on one of the outer legs; 
     FIG. 2 is a schematic and perspective view of a second embodiment of an E-I transformer with two coils wound one over another on the inner leg and two coils wound one over another on one of the outer legs; 
     FIG. 3 is a schematic and perspective view of a first embodiment of an E-E transformer with two coils arranged side by side on the inner link and two coils arranged side by side on one of the outer links; 
     FIG. 4 is a schematic and perspective view of a second embodiment of an E-E transformer with two coils wound one over another on the inner link and two coils wound one over another on one of the outer links; and 
     FIG. 5 shows schematically in block-diagram form a preferred use of a transformer as illustrated in FIGS. 1 to  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows schematically and in perspective a first embodiment of an E-I transformer. An E-I transformer  10  has a ferromagnetic E-core E and a ferromagnetic yoke I in the form of a straight bar. The E core E has a first outer leg ES 1  and a second outer leg ES 2  as well as an inner leg EM. E core E and yoke I are so arranged that two closed magnetic circuits are obtained. 
     The first magnetic circuit comprises the outer leg ES 1 , the portion of yoke I connecting the outer leg ES 1  with the inner leg EM, the inner leg EM, and the portion of E core E connecting the inner leg EM with the outer leg ES 1 . The second magnetic circuit comprises the outer leg ES 2 , the portion of yoke I connecting the outer leg ES 2  with the inner leg EM, the inner leg EM, and the portion of E core E connecting the inner leg EM with the outer leg ES 2 . 
     E-I transformer  10  has a first coil  1  wound around inner leg EM, a second coil  2  wound around inner leg EM, a third coil  3  wound around outer leg ES 1 , and a fourth coil  4  wound around outer leg ES 1 . Coil  1  has terminals  11 ,  12 , coil  2  has terminals  21 ,  22 , coil  3  has terminals  31 ,  32 , and coil  4  has terminals  41 ,  42 . In FIG. 1, coils  1  and  2  on inner leg EM are arranged side by side, preferably in close proximity to each other. 
     FIG. 2 shows schematically and in perspective a second embodiment of an E-I transformer. An E-I transformer  10 ′ has a ferromagnetic E core E′ and a ferromagnetic yoke I′ in the form of a straight bar. E core E′ has a first outer leg ES 1 ′ and a second outer leg ES 2 ′ as well as an inner leg EM′. E core E′ and yoke I′ are so arranged that two closed magnetic circuits are obtained. 
     The first magnetic circuit comprises the outer leg ES 1 ′, the portion of yoke I′ connecting the outer leg ES 1 ′ with the inner leg EM′, the inner leg EM′, and the portion of E core E′ connecting the inner leg EM′ with the outer leg ES 1 ′. The second magnetic circuit comprises the outer leg ES 2 ′, the portion of yoke I′ connecting the outer leg ES 2 ′ with the inner leg EM′, the inner leg EM′, and the portion of E core E′ connecting the inner leg EM′ with the outer leg ES 2 ′. 
     E-I transformer  10 ′ has a first coil wound around inner leg EM′, a second coil  2 ′ wound around inner leg EM′ and over the first coil, a third coil wound around outer leg ES 1 ′, and a fourth coil  4 ′ wound around outer leg ES 1 ′ and over the first coil. Since the first and third coils are covered, they cannot be seen in FIG.  2 . The first coil has terminals  11 ′,  12 ′, coil  2 ′ has terminals  21 ′,  22 ′, the third coil has terminals  31 ′,  32 ′, and coil  4 ′ has terminals  41 ′,  42 ′. 
     FIG. 3 shows schematically and in perspective a first embodiment of an E-E transformer. An E-E transformer  20  has a first ferromagnetic E core E 1  and a second ferromagnetic E core E 2 . E core E 1  has a first outer leg ES 11  and a second outer leg ES 12  as well as an inner leg EM 1 . E core E 2  has a first outer leg ES 21  and a second outer leg ES 22  as well as an inner leg EM 2 . The two E cores E 1 , E 2  are so arranged that two closed magnetic circuits are obtained. 
     The first magnetic circuit comprises the outer leg ES 11 , the outer leg ES 12 , the portion of E core E 2  connecting the outer leg ES 12  with the inner leg EM 2 , the inner leg EM 2 , the inner leg EM 1 , and the portion of E core E 1  connecting the inner leg EM 1  with the outer leg ES 11 . 
     The second magnetic circuit comprises the outer leg ES 21 , the outer leg ES 22 , the portion of E core E 2  connecting the outer leg ES 22  with the inner leg EM 2 , the inner leg EM 2 , the inner leg EM 1 , and the portion of E core E 1  connecting the inner leg EM 1  with the outer leg ES 21 . 
     In the assembled condition, outer legs ES 11 , ES 12  form a first outer link ST 1 , outer legs ES 21 , ES 22  form a second outer link ST 2 , and inner legs EM 1 , EM 2  form an inner link STM. 
     E-E transformer  20  has a first coil  6  wound around inner link STM, a second coil  7  wound around inner link STM, a third coil  8  wound around outer link ST 1 , and a fourth coil  9  wound around outer link ST 1 . Coil  6  has terminals  61 ,  62 , coil  7  has terminals  71 ,  72 , coil  8  has terminals  81 ,  82 , and coil  9  has terminals  91 ,  92 . 
     In FIG. 3, coils  8 ,  9  on outer link ST 1  are arranged side by side, preferably in close proximity to each other. Coils  6 ,  7  on inner link STM are arranged side by side but spaced a selectable distance apart; however, they may also be arranged in close proximity to each other like coils  8 ,  9 . 
     FIG. 4 shows schematically and in perspective a second embodiment of an E-E transformer. An E-E transformer  20 ′ has a first ferromagnetic E core E 1 ′ and a second ferromagnetic E core E 2 ′. E core E 1 ′ has a first outer leg ES 11 ′ and a second outer leg ES 21 ′ as well as an inner leg EM 1 ′. E core E 2 ′ has a first outer leg ES 12 ′ and a second outer leg ES 22 ′ as well as an inner leg EM 2 ′. The two E cores E 1 ′, E 2 ′ are so arranged that two closed magnetic circuits are obtained. 
     The first magnetic circuit comprises the outer leg ES 11 ′, the outer leg ES 12 ′, the portion of E core E 2 ′ which connects the outer leg ES 12 ′ with the inner leg EM 2 ′, the inner leg EM 2 ′, the inner leg EM 1 ′, and the portion of E core E 1 ′ which connects the inner leg EM 1 ′ with the outer leg ES 11 ′. 
     The second magnetic circuit comprises the outer leg ES 21 ′, the outer leg ES 22 ′, the portion of E core E 2 ′ which connects the outer leg ES 22 ′ with the inner leg EM 2 ′, the inner leg EM 2 ′, the inner leg EM 1 ′, and the portion of E core E 1 ′ which connects the inner leg EM 1 ′ with the outer leg ES 21 ′. 
     In the assembled condition, outer legs ES 11 ′, ES 12 ′ form a first outer link ST 1 ′, outer legs ES 21 ′, ES 22 ′ form a second outer link ST 2 ′, and inner legs EM 1 ′, EM 2 ′ form an inner link STM′. 
     E-E transformer  20 ′ has a first coil wound around inner link STM′, a second coil  7 ′ wound over the first coil, a third coil wound over outer link ST 1 ′, and a fourth coil  9 ′ wound over the third coil. The first coil has terminals  61 ′,  62 ′, the second coil  7 ′ has terminals  71 ′,  72 ′, the third coil has terminals  81 ′,  82 ′, and the fourth coil  9 ′ has terminals  91 ′,  92 ′. 
     In FIG. 4, the coils on outer link ST 1 ′ are located approximately in the middle of the link, while the coils on inner link STM′ are placed on inner leg EM 1 ′; any other position on the inner and outer links are also possible. 
     In the embodiments of FIGS. 1 to  4 , E core E, E′, yoke I, I′, and the two E cores E 1 , E 2 , E 1 ′, E 2 ′ may be laminations of ferromagnetic steel sheets or corresponding ferrite components, for example. For simplicity, the respective coils in the embodiment of FIGS. 1 to  4  are shown as air-core coils, i.e., as coils without a coil form. It is also possible, of course, to wind individual coils or all of the coils onto suitable coil forms and then place them on the legs or links. 
     It is also possible to place two separate coils on one of the legs or links as in FIG. 1 or  3 , while two coils wound one over another are placed on the associated leg or link as in FIG. 2 or  4 . 
     FIG. 5 shows schematically in block-diagram form a preferred use of a transformer as illustrated in FIGS. 1 to  4 . The first coil and the second coil are, respectively, a primary coil and a secondary coil of a first AC power transmission path W 1 , and the third coil and the fourth coil are, respectively, a primary coil and a secondary coil of a second AC power transmission path W 2 . Preferably, the frequency of the first AC power is substantially less than the frequency of the second AC power. 
     That being presupposed, the first coil and the second coil are, respectively, a primary coil and a secondary coil of a DC/DC converter DCW, and the third coil and the fourth coil serve to accomplish the electrically separated transfer of digital signals as is described in EP-A 977 406, corresponding to U.S. patent application Ser. No. 09/354,689 of Jul. 16, 1999. 
     A primary circuit  51  of DC/DC converter DCW has one end connected to a first DC voltage to be converted, U 1 , and to circuit ground SN, and the other end is coupled to coil  1  of FIG. 1; the corresponding first coils of FIGS. 2 to  4  may also be chosen, of course. Since this choice also applies for the other coils, this is indicated in the following by the corresponding reference characters behind a dash. 
     A secondary circuit  52  of DC/DC converter DCW has one end connected to coil  2 - 2 ′,  7 ,  7 ′ and delivers at the other end a converted second DC voltage U 2 , which may be greater than, equal to, or less than DC voltage U 1 . Since the specific design of DC/DC converters has been in the prior art for a long time and may be quite varied, DC/DC converter DCW is shown as consisting only of subcircuits  51 ,  52  and coils  1 ,  2 , etc. DC/DC converters usually oscillate at frequencies of 20 to 100 kHz. 
     The third coil  3 - 3 ′,  8  is located on the primary side, and the fourth coil  4 - 4 ′,  9 ,  9 ′ on the secondary side, of a subcircuit TS for electrically separating digital signals as disclosed in the above-mentioned EP-A 977 406. A digital signal D 1  is applied to terminal  31 - 31 ′,  81 ,  81 ′ of coil  3 - 3 ′,  8 . Connected to terminal  32 - 32 ′,  82 ,  82 ′ of coil  3 - 3 ′,  8  is an output of a delay element  53 , in this embodiment a series combination of four inverters. 
     Terminal  41 - 41 ′,  91 ,  91 ′ of coil  4 - 4 ′,  9 ,  9 ′ is connected to an input of an inverter  54 , while terminal  42 - 42 ′,  92 ,  92 ′ of coil  4 - 4 ′,  9 ,  9 ′ is the output of the secondary of subcircuit TS, which provides a digital signal D 2  that is virtually identical with, but electrically separated from, the digital signal D 1 . 
     An output of inverter  54  is connected to one terminal of a capacitor K, another terminal of which is grounded, SN, through a resistor R. The junction of capacitor K and resistor R is connected to an input of an inverter  55 , whose output is coupled to terminal  42 - 42 ′,  92 ,  92 ′ of coil  4 - 4 ′,  9 ,  9 ′. The two inverters  54 ,  55 , capacitor K, and resistor R form a monostable multivibrator. For further details, reference is made to the above-mentioned EP-A 977 406. 
     Since digital signals are square-wave signals whose pulse repetition frequency is substantially greater than the frequency of DC/DC converters, the above-mentioned frequency condition can be easily satisfied. 
     The invention can be used to advantage with conventional physical-to-electrical transducers, such as transducers for pressure, level, temperature, flow rate—i.e., the fluid volume or fluid mass flowing through a given cross-sectional area per unit time—, or pH value, etc. 
     Such transducers generally have on-board evaluation electronics; the latter condition a signal from a physical-to-electrical transducer such that it conforms to a standard, e.g., to the conventional 4- to 20-mA current standard or to a frequency standard. “On-board” means that the evaluation electronics are located close to the physical-to-electrical transducer, i.e., in the transducer case. 
     In the case of such transducers, it is particularly advantageous if the third coil is connected to an external two-wire field bus, e.g., HART, FIELDBUS, PROFIBUS, etc., and the fourth coil interacts with a digital circuit of the on-board evaluation electronics, or vice versa.