FR2490436A1 - METHOD AND DEVICE FOR APPLYING POWER FROM A FIRST CAMERA UNIT TO A SECOND, THROUGH A TRANSMISSION LINE, WITH A TRIAXIAL CABLE SECURITY CIRCUIT - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A METHOD AND A DEVICE FOR APPLYING CURRENT FROM A FIRST CAMERA UNIT TO A SECOND, BY A TRANSMISSION LINE WITH A SAFETY CIRCUIT. ACCORDING TO THE INVENTION, IF THE CURRENT IS INTERRUPTED, THE CURRENT IS NO LONGER APPLIED TO THE TRIAXIAL CABLE 15 AND A CHOSEN AND NOT NULL IMPEDANCE 46 IS APPLIED TO THIS CABLE 15 AT THE HEAD 10 OF THE CAMERA; IF IMPEDANCE 46 CAN BE DETECTED AT PROCESSING UNIT 12, CURRENT IS REAPPLIED TO CABLE 15; IMPEDANCE 46 MAY BE FORMED AS A DIODE WHICH HAS DIFFERENT EFFECTS DURING DIFFERENT ALTERNATE POLARITIES. THE INVENTION APPLIES IN PARTICULAR TO REMOTE-CONTROLLED TELEVISION CAMERAS.

Description

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  The present invention relates to safety circuits, and more particularly to circuits for

  security used with remote controlled television cameras.

  As shown in Figure 1, it is frequently desirable, in certain situations, such as in the case of sports or political events, to have a TV camera head (CH) 10 at a considerable distance (sometimes as much as 3 km) of a control and processing unit (CPU) 12 of the camera. A transmission line 14

  interconnection is used both to feed (typically

  280 volts AC) and control the CH head by the CPU. In addition, line 14 forms audio and video channels. One type of line used for this purpose has 81 conductors. This is expensive, impractical to handle and thick. In the RCA TK-47 camera manufactured by RCA Corporation, Commercial Communication Systems Division, Camden, NJ 08102, USA, time division multiplexing is used to reduce the required number of drivers to 30. This reduces the price and the mass compared to 81-conductor cables. To maximize safety, both in the 81-conductor and lead-in cable, screw-in connectors are used with the "hot" side (side of the cable having the current) having a female connector. As another safety measure in the 30-conductor cable, a driver,

  called "sensing wire" is connected to ground at the head 10.

  If the cable is broken or disconnected, a "high" level of logic voltage is applied to this wire, which logic high level activates a logic circuit to trigger a relay in the unit 12. The tripped relay prevents the current from being

  longer applied to the cable 14.

  Recently, to further reduce the weight and cost of the cable, the triaxial cable ("Triax") 15 has been used, as shown in FIG. 3. This cable 15 comprises an inner conductor 16, an insulating layer 18, an inner shield 20, an insulation layer 22, an outer shield 24, and finally an outer insulation layer 26. The shield

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  external 24 is connected to the skin (housing) of the unit 12 and the head 10. The alternating current and the signals are all transmitted by using the internal shielding 20 and the internal conductor 16 by using the interface circuits. of triax 28 and 30 shown in FIG.

  28 and 30 are shown in more detail in FIG. 4.

  In this arrangement, the signals at the unit 12 are multiplied by frequency distribution by filters (not shown) and applied to an RF high frequency modulator 32. The resulting modulated signal is applied to a low pass filter.

  34 and the resulting filtered signal is applied to a condensate

  The Cl capacitor has a high nominal frequency and a low reactance for high frequency signals, and therefore serves to block the alternating current so as to prevent it from entering the high frequency circuits as it is will explain below. Thus, the filtered signal is applied to the inner conductor 16. To the conductor 16 and the inner shield 20 is also applied the alternating current of a source (not shown) by isolation coil inductance LI and L2. These inductance coils block the high frequency signals of the AC power source while leaving the alternating current

  cross them. Triax 15 transmits current signals -

  alternatively and at high frequency at the head 10 o they are applied to a blocking capacitor C3 and isolation coils L3 and L4. It should be noted that isolation capacitors C2 and C4 are connected to the inner shield 20 and the ground of the high frequency source to the unit 12 and to the head 10 respectively. At the head 10, the high frequency signals pass through the blocking capacitor C3 and are applied to the low pass filter 36 and the high pass filter 38. However, as the high frequency signals have passed through the low pass filter 34, they pass only through the low-pass filter 36 and not through the high-pass filter 38. From the low-pass filter 36, the high-frequency signals are applied to a demodulator (not shown) and then to the on-band filters. basic (not shown) to separate them. Moreover, the signals

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  at high frequencies can not pass through the induction coils.

  Isolation rate L3 and L4. The alternating current can not pass through the capacitor C3 but it passes through the inductance coils L3 and L4 to feed the rest of the head 10 (not shown). At the head 10, the high frequency signals of a high frequency modulator (not shown) are applied to the high-pass filter 38 and then pass through the capacitor C3. The high frequency signals can not pass through the low-pass filter 36 or the inductance coils L3 and L4, and thus substantially all the high frequency signals are applied between the inner conductor 16 and the inner shield 20. The triax 15 transmits the high frequency signals to the unit 12 where they pass the capacitor

  C1 then the high pass filter 40 for application to the demodula-

  The high frequency signals of the head can not pass through the inductance coils LI and L2 or the low-pass filter 34. From the demodulator 42, the demodulated signals are applied to baseband filters.

  (not shown) for their separation.

  It can be seen that no detection wire (as explained above) is present in the system

to triax of Figure 4.

  It is therefore desirable to increase

  the safety of a triaxial cable system.

  According to the principles of the invention, a method and apparatus for applying current from a first camera unit to a second, through a transmission line, comprises applying a current to the transmission line at the first unit, detecting whether the current is interrupted, stopping the application of current to the line when detecting that this current has been interrupted, applying a selected and non-zero impedance to the line to the second unit, detecting the selected impedance and non-zero at the first unit and reapplied current at the line to the first unit upon detection at that first unit of

the impedance chosen non-zero.

  The present invention will be better understood and other characteristic details and advantages thereof

  will become clearer during the description

  explanatory text which follows, with reference to the accompanying schematic drawings given solely by way of example, illustrating an embodiment of the invention and in which: FIGS. 1 and 2 give block diagrams showing a typical camera unit and control

  according to the prior art using multicore cables

  Figure 3 shows a triaxial cable. Figure 4 shows partially block-like and partly schematic details of Figure 2; FIG. 5 shows partially in the form of a block and partially in schematic form, a safety circuit according to the principles of the invention; Figure 6 is a schematic diagram of Figure 5;

  FIGS. 7 to 12 are voltage diagrams

  useful times to explain the operation of the figures and 6; and

  - Figure 13 is a detailed diagram of the present

the invention.

  In figure 1, A indicates video of red, Bevidéo of green, Cvidéo of blue, D? 3 x audio, E% 280 volts AC, Fp camera control, G,

  Syna.camera, H. 3 x audio and I "video search.

  Figure 5 shows a modification of Figure 4 o is incorporated a safety circuit 44 according to a preferred embodiment of the invention. Relays RE1 and RE2 are also added to the unit 12 and to the head 10, respectively, as well as a combination of passive elements

46 to the head 10.

  When the relays REI and RE2 are at the positions indicated in FIG. 5, the AC current path is from the input 48 to the unit 12 by the relay REI, the internal conductor 16 and the internal shielding 20, the relay RE2 to the output 51 of the alternating current. Thus, the path of the alternating current is closed (conducting). A current sensing coil 50 is inductively connected to one of the lines connected to the AC input 48 and applies the resulting induced voltage to the safety circuit 44. The circuit 44 applies a signal through an output line 52 to the relay coil (not shown) of the relay REI in order to maintain the relay contacts S1 and S2 at the position shown in FIG. 5. The coil 54 of the relay RE2 is supplied directly by the internal conductor 16 and the inner shield 20 and maintains the relay

RE2 at the position shown.

  If for some reason the AC path is interrupted, for example by disconnecting the triax cable at one of its ends, the alternating current can no longer flow, and therefore no induced voltage is applied. by the coil 50 to the safety circuit 44. A lack of voltage at the line 52 then forces the relay contacts Si and 52 to move to the opposite position with respect to that illustrated in FIG. 5, thus interrupting the application of the current alternating with triax 15. As the alternating current is no longer applied to the coil 54 of the relay RE2, the contacts S3 move to the opposite position to that shown in FIG. 5, thus disconnecting the output 51 of the alternating current and the internal conductor 16. The upper end of the

  combination 46 is then connected to the inner conductor 16.

  The other end (bottom) of the combination 46 is

  permanently connected to the outer shield 24.

  Due to the above-described switching of the relay RE1, the output A of the safety circuit 44 is connected by the contacts S2 of the relay RE1 to the internal circuit 16 of the triax 15. If the triax 15 is connected again, the outputs A and 56 of the circuit 44 can "see" the combination 46 by the contacts S2, the internal conductor 16

  and the outer shield 24 of the triax 15, and the contacts S3.

  The circuit 44 then produces a pulse to switch the

  relay RE1. This connects the alternating current to the triax 15.

  If the outputs A and 56 can not "see" the combination 46 because the cable is disconnected, short-circuited or touched by a human finger, no pulse is generated and the alternating current can never be applied to the triax 15. The application of the alternating current forces the contacts S3 to switch because the coil 54 of the relay RE2 is powered by the triax 15. The switching of the contacts S3 connects the alternating current to the power supply

  (not representative) of the head 10 which is connected to the outlet 51.

  The current sensing coil 50 in the unit 12 then causes a continuous current to be applied to the REI relay coil to maintain the contacts continuously.

  SI and S2 at the position shown in FIG.

  FIG. 6 shows details of the security circuit 44 which will be described with reference to FIGS. 7 to 12. The oscillator 60 produces a square-wave signal as shown in FIG. 7 (a) at a frequency of 100 Hz. The signal is applied to the divider-decoder 62 where it is divided by 10 (see Figure 7b). The split signal, which has alternating polarities of +5 and 0 volts, is applied to the inverting amplifier 64 and is sufficient to saturate this amplifier. OR gate 66 has inputs connected to the outputs of stages four and nine of divider 62, and applies the sample pulses of FIG. 7 (c) to switch 68. Amplifier 64 is connected to the output resistor RI and the shunt resistors R2 and R3. As can be seen in FIG. 7 (d), the signal 740 at the output of the amplifier 64 is a slot alternating between +5 volts (before to and between t1 and t2) and -10 volts (between t0 and t1). and after t2). These

  two voltages are the voltages of the two feed rails

  In this way, the amplifier 64 is saturated in both states and the output signal is applied by the resistor R1 to the output point A. The signal at the output A is applied by the relay contacts. 52 and the inductance L1 (as can be seen in FIG. 5, none being represented in FIG. 6), to the inner conductor 16. If the triax 15 is connected, to the head 10 the signal is applied to the combination 46 which is formed of the series combination of the resistor R4 and the diode CR1. At point A, the diode CR1 of the combination 46 only affects the negative parts of the signal 740 at the output of the amplifier 64. In particular, the negative parts are limited to -5 volts (before t1 and after t2) while the positive parts are unaffected and

  remain at +5 volts (between t1 and t2), see figure 8 (a).

  By a suitable choice of the resistors R1, R2, R3 and R4, the waveform at the junction of the resistors R2 and R3 (indicated by the point X) is + 1, 66 volts DC, when the point A is either at +5 or -5 volts, see Figure 8 (b). The point X is connected to a window detector 70 and more particularly to the positive input of a voltage comparator 72 and to the negative input of a voltage comparator 74. The comparators 72 and 74 have reference potentials. of + 1.8 and + 1.5 volts which are

  applied respectively to their negative and positive inputs.

  Consequently, the outputs of comparators 72 and 74 are high if the potential at point X is greater than + 1.8 volts or less than + 1.5 volts. The OR gate 76 has inputs which are respectively connected to the outputs of the comparators 72 and 74, and it applies, by its output Y, a signal at a logic low level to the switch 68.

  if the X signal is between +1.5 and 1.8 volts.

  A low signal (0 volts) from the window detector to the output Y (see FIG. 8c) causes the switch 68 to apply sampling pulses from the OR gate 66 to the clock input C of the divider 78 by 64 while a high signal (+5 volts) at the output of the detector 70 causes the sampling pulses to be applied to the recovery input S. If the Y-signal has been low for the duration of the sampling pulses, the divider 78 produces an output signal for triggering a monostable multivibrator 80. The multivibrator 80 in turn applies a 200 millisecond pulse to the coil 84 of the relay RE1 through the OR gate 82. This 200 msec pulse is long enough to connect the input 48 of the alternating current of FIG. 5 to the triax, which switches the relay RE2 of the head 10 and consequently applies the alternating current to the power supply in the head 10. As the current flows, the coil 50 detection current applies a signal to the relay coil 84 by the gate 82 and therefore the current

  alternative continues to be applied "after the end of the impulse

  200 ms, as explained above.

  If the potential in X is outside the range of + 1.5 to + 1.8 volts, then a high signal is present at the output Y and the divider 78 is restored, and therefore

  no pulse is produced by the multivibrator 80.

  Thus, there is no application of alternating current to triax 15. It can easily be seen that if the voltage at point A is in a chosen "window" (+ 1.5 to 1.8 volts)

  for a selected time (64 pulse periods of sample

  calibration), alternating current is applied to triax 15.

  Figures 9a, b and c show the potentials mentioned above at points A, X and Y respectively

  when the triax 15 is not connected (in open circuit).

  Since the diode CR1 is not connected to the point A by the triax, the potential at the point A before t1 and after t2 is -10 volts, that is to say the total-negative potential at the output of the 64 amplifier and it is + 5 volts

  between t2 and t ', as can be seen in Figure 9a.

  Point X is therefore only at 1.66 volts when the potential at point A is +5 volts and it is

  O volt elsewhere, as can be seen in Figure 9b.

  Thus, the potential at point Y is low during the interval between t1 and t2 'see FIG. 9c, and since this interval represents less than 64 sampling pulse periods,

  no alternating current is applied to the triax 15.

  When the triax 15 is short-circuited (conductive

  internal carrier 16 connected to the internal shield 20), the potential at the point A is, by definition, always of the order of 0 volts (exactly 0 volts if the resistance of the triax 15 is not considered), see Figure 10a. When the potential at the output of the amplifier 64 is + 5 volts between t1 and t2, the potential at the point X is i Ovolt When the potential at the output of the amplifier 64 is -10 volts before t and after t2 the voltage at point X is +3.33 volts, see Figure lob. In each case, the potential at point X is outside this window, and therefore the potential at point Y is always high, see Figure 10c. As in

  the case of the open circuit of Figure 9, no alternating current

  native is applied to triax 15 in the case of short-circuit

cooked shown in Figure 10.

  Figure 11 shows waveforms in the

  case where the cable is touched by the finger of a human being.

  "Finger resistance" can vary from several KM (wet) to several Ma (dry). When the potential at the output of the amplifier 64 is -10 volts before t1 and after t2, the potential at the point A is somewhat less negative than -10 volts, whereas when the potential at the output of the amplifier 64 is + 5 volts between t1 and t2, the potential at point A is less than +5 volts, see figure lla. The potential at point X in Figure llb is

  undetermined, but will probably not be in the window

  Given the required time and therefore the potential at point Y will be continually high, see figure lie. Thus, no alternating current is applied to the triax 15. Even when the potential at the output of the amplifier 64 is +5 volts between t1 and t2, the potential at point X is in the window because of a resistance chance of a finger, the potential at point Y is low for a time insufficient to activate

  the application of alternating current as in the case

  Figure 9 (unconnected triax). This is true because the -10 volt voltage of the amplifier 64 can never be made positive, and in any case not in the window, by any resistance value of a finger from O to

unlimited value of ohms.

  The waveforms of Figures 7 to 11 have been idealized. Figure 12 shows practical waveforms when the triax cable 15 is connected. It can be seen in Figure 12a that the flanks of the pulses at point A are rounded. This is due to the inherent capacitance of the cable, which can become considerable for long cables and this is also due to the value of the resistance R. For this reason, the sampling pulses of FIG. 12d are delayed with respect to the beginning of the pulses at point X (which can be seen in FIG. 11b) at t0 t1, t2, and the like, so that the sampling takes place during the horizontal right portion of the pulses X. Moreover, the frequency of the signal A The divider 78 inserts a delay of 3.2 seconds after the cable has been connected. Instead of using a diode resistor for the combination 46, similar or more complex combinations can be used, but then the elements R1, R2 and R3 must also be adapted. A complete detailed circuit is shown on

  Figure 13. Resistor R4 is 4700 ohms.

Claims (11)

  A method for applying current from a first camera unit to a second, via a transmission line, said method of applying a current to said transmission line to said first unit, detecting whether said current is interrupted, and stopping the application of said current to said line upon detecting that said current has been interrupted, characterized by applying a selected and non-zero impedance to said line (15) at said second unit (10), detecting said impedance selected at said first unit (12), and reapplication of the current at said line (15) to said first unit (12) upon detection at said first unit (12) of said impedance chosen non-zero.   2. Method according to claim 1, characterized in that the impedance chosen and non-zero above comprises a substantially unidirectional conductor means (CR1) and in that the second detection step mentioned above consists in applying to the line (15) above, a signal (740) having different polarities alternating, deriving a signal according to said applied signal and said conducting means and detecting at the first unit, the effects   different from the said conductive means   different values of the applied signal.   3. Method according to claim 2, characterized   in that the above-mentioned step of detecting consists in deter-   undermine if the derivative signal is at a chosen value of   potential for at least one selected time.   4. Device for carrying out the method according to claim 1, characterized by first   and second camera units (12, 10) and a transmission line   connection (15) interconnected, said first unit (12) comprising means (RE1) for applying a current to said transmission line (15), means (50) for detecting whether said current is interrupted, and for stopping said applying said current to said line (15) upon detection that said current has been interrupted, said second unit (10) comprising means (RE2) for applying a selected and non-zero impedance (46) to said line (15) when said interruption; and said first unit (12) further comprising means (44) for detecting said selected and non-zero impedance, said application means (RE1) reapplying current to said line (15) when said detecting means <44) detects said impedance chosen non-zero (46).   5. Device according to claim 4, characterized   in that the impedance chosen and non-zero aforementioned   comprises a substantially unidirectional conductive means -   (CR1) and that said impedance detecting means 44 includes means (62, 64) for applying to said   line, a signal having alternating and different polarities   rents, means (R1, R2, R3, R4) for deriving a signal according to the applied signal and said conductive means (46) and means (70) for detecting the different effects that said conductive means have on the different polarities of said derived signal.   6. Device according to claim 5, characterized   characterized in that said sensor means (70) comprises means for determining whether said derivative signal is within a selected value of potential less a chosen time.   7. Device according to claim 6, characterized   characterized in that said sensor means (70) comprises two voltage comparators (72, 74) for determining whether the derived signal is below and above above and below reference voltages respectively, an OR gate (76) having two connected inputs at the outputs of said comparators a switch (68) having a control input connected to the output of said OR gate, a signal input for receiving sample pulses (through 66), and a pair of outputs; and a divider (78) having clock and erase inputs respectively connected to the outputs switches.   8. Device according to claim 5, characterized   in that the unidirectional conductive means (46) aforementioned comprises a diode (CRI).   9. Device according to claim 5, characterized   in that the means for applying an alternating polarity   device (62, 64) comprises a pulse source (62) and an amplifier (64) connected to a pair of current supplies having opposite polarities (+ and -), and in that the aforementioned branching means comprises an output resistor (RJ) connected to the output of the amplifier (64) and two shunt resistors connected in series (R2, R3) connected between the input of the amplifier (64) and its output; and in that the detection means (70) comprises   a voltage window detector connected to said resistors these bypass.   10. Device according to claim 4, characterized in that the first and second camera units comprise a television camera processing unit and a camera head respectively and in that   that the aforementioned line comprises a triaxial cable.   11. Device according to claim 4, characterized in that each said application means comprises a relay (RE1, RE2) and in that the aforementioned interruption detecting means (50) comprises a coil current detection.