WO1993009584A1

WO1993009584A1 - Open circuit monitor

Info

Publication number: WO1993009584A1
Application number: PCT/AU1992/000484
Authority: WO
Inventors: Keith Arnold Forster; Eric John Forster
Original assignee: Neolite Neon Company Pty Limited
Priority date: 1991-11-01
Filing date: 1992-09-11
Publication date: 1993-05-13
Also published as: AU639405B3; AU2591292A

Abstract

An open circuit monitor (14) is disclosed which is configured to detect an undercurrent condition on the primary winding of a transformer (10) caused by an open circuit condition on the secondary winding. The monitor (14) is configured to mount directly upon terminals (12) of the transformer (10) thus avoiding the need for interconnecting cabling between the monitor (14) and the transformer (10). A main supply is directly connected to input terminals (23) of the monitor (14). Also disclosed is a current sensing monitor (106) which senses the undercurrent condition without the use of a resistor (50) connected in series with the primary winding. The current sensing monitor (106) preferably takes the form of a Hall effect sensor (108). The open circuit monitor is generally configured for use with a high tension transformer of a neon lighting display.

Description

OPEN CIRCUIT MONITOR Field of the Invention The present invention relates generally to electronic safety and protection devices and, in particular, but not exclusively, to an 5 undercurrent protection/monitoring device that can be used with a high tension transformer of a neon lighting display.

Background Art In the art of so-called "neon" lighting displays undercurrent protection devices are generally known as open circuit monitors in that 10 the device detect an open circuit of one winding of a transformer by sensing an abnormal current in another winding of the transformer. A standard configuration for use is shown in Fig. 1 where an open circuit monitor 3 is connected in series between a high tension (H.T.) transformer 2 and a low tension mains supply 8 and is arranged to 15 operate so as to sense the current load drawn by the transformer 2 and to disconnect the supply 6 from the transformer 2 when the high tension output 7, supplying the neon lamp display 1, becomes open circuit. This situation generally arises through the neon tubes of the display 1 being damaged by hail, thrown projectiles, any cable and/or electrode 20 dislodgement or disconnection from the glass tubing, and the like. An open circuit on the secondary of the HT transformer 2 ultimately causes breakdown of the Insulation of the secondary which is generally irrepairable. The open circuit monitor 3 includes input terminals 4 connectable to the mains supply 8 and output terminals 5 which are 25 separately connectable to the low tension input 6 of the HT transformer 2. An earth connection 9 is generally also provided for safety purposes.

Whilst known open circuit monitors such as that described above operate satisfactorily, their configuration on-site can, at times, be 30 untidy due to the open circuit monitor representing a further item being located adjacent to the display 1 and the requirement for further

_ cabling to interconnect the devices.

Summary of the Invention % It is an object of the present invention to substantially 35 overcome, or ameliorate one or all of, the problems identified above. In accordance with one aspect of the present invention there is disclosed an undercurrent monitoring device for a transformer having two input terminals, said device having a pair of input terminals connectable to an AC mains supply and a pair of output terminals, wherein said device is mountable on said transformer by a direct connection between the input terminals of said transformer and the output terminals of said device.

In one preferred form of the device, the device comprises a circuit board upon which an electronic circuit of said device is arranged, said device output terminals comprising pad contacts arranged about apertures through which said input terminals of said transformer are insertable for securing said device to said transformer and electrically connecting said transformer input terminals to said pad contacts.

In another preferred form the device comprises a circuit board upon which an electronic circuit of said device is arranged, said device output terminals comprising connectors extending from said circuit board and arranged for insertion into a connector means comprising said Input terminals of said transformer, said connector means securing said device to said transformer and electrically connecting said input terminals of said transformer to said connectors. In accordance with another aspect of the present invention there is disclosed an undercurrent monitoring device for a transformer, said device being characterized by the absence of a current sensing resistor in series with a winding of said transformer.

In accordance with another aspect of the present invention there is disclosed an undercurrent monitoring device for a high tension transformer in a neon-type lighting system, said device comprising a Hall effect sensor means and associated switching means adapted to detect an undercurrent condition in a winding of said transformer and to disconnect an electrical supply from said transformer in response thereto.

In a preferred form the sensor means comprises a toroid about which is wound a conductor supplying said winding, and a Hall effect sensor arranged in an air gap of said toroid to detect magnetic field fluctuations caused by changes in current in said conductor. In accordance with another aspect of the present invention there is disclosed a neon lighting system comprising a neon lighting display energisable from outputs of a high tension transformer, and an undercurrent monitoring device as identified above. Brief Description of the Drawings A number of preferred embodiments of the present invention will now be described with reference to the remaining drawings in which:

Fig. 2 is an exploded isometric view of the preferred embodiment; Figs. 3A, 3B, 4A and 4B show side and plan views of two printed circuit boards arrangements;

Fig. 5 shows a schematic circuit diagram of one electronic circuit usable in the open circuit monitor.

Fig. 6 shows an exploded isometric view of another embodiment; Fig. 7 is a partial side cross-section of the arrange of Fig. 6; Fig. 8 shows a schematic circuit diagram of a preferred electronic circuit; and

Fig. 9 is a perspective view of a current monitor of the circuit of Fig. 8. Best and Other Modes for Carrying Out the Invention

Referring to Fig. 2, an H.T. transformer 10 is shown which is suitable for use in energising a neon or other gas filled display (not illustrated) from a two terminal high tension output 11 (only one terminal of which is illustrated). The transformer 10 is provided with two input terminals 12 which are configured as insulated bolts extending from a casing of the transformer 10. The terminals 12 are for connection to a mains electricity supply, such as 240V 50Hz, or 120V 60Hz. A further earth connection terminal 13 is provided for earthing of casing of the transformer 10. The transformer 10 is useful in the prior art arrangement of Fig. 1 in which case mains supplying leads are directly connected to the terminals 12 and 13 using nuts 22 as illustrated.

However, this preferred embodiment, an open circuit monitor (0CM) 14 is configured to be mounted upon the terminals 12 to provide direct connection thereto.

The 0CM 14 includes a printed circuit board (PCB) 15 and a housing 16 which encloses an electric circuit 40 (seen in Fig. 5) mounted on the PCB 15. The circuit 40 includes output terminals formed as PCB track pads 18 arranged about apertures 17 that each pass through the PCB 15. The apertures 17 are arranged to permit insertion of the bolts 12 therethrough. In this manner, a pair of nuts 22 can be used to secure the PCB 15 directly to the terminals 12 thus mounting the OCM 14, and for a direct electrical connection between the input of the transformer 10 and the OCM 14. An earth connection can be made using an earth connection lug 21 and a nut 26 in the known manner. The OCM 14 is supplied directly by an active 19 and a neutral 20 lead of a mains supply which connect to a pair of mains connection bolts 23 using lugs 24 and corresponding nuts (not illustrated for clarity). It will be apparent that this arrangement simplifies the configuration of a neon display system in that the OCM 14 is directly electrically connected to, and mounted upon the transformer 10, thus eliminating the need for the installing technician to run additional cable between the OCM 14 and transformer 10, as in the prior art. Accordingly, this configuration can permit savings to be made both in respect of labour costs, and materials, such as cable and lug-type connectors.

Seen in Figs. 3A and 3B is the PCB 15 upon which the circuit 40 is mounted. The circuit 40 outputs to the pair of track pads 18 which surround the apertures 17 through which the bolts 12 are insertable. Accordingly, by screwing the- nuts 22 onto the bolts 12 to contact the pads 18, direct connection to the PCB 15 is made by the input terminals of the transformer 10. Also the mains connection bolts 23 are arranged to similarly pass through mains pads 25 in the manner shown.

An arrangement such as that shown in Figs. 4A and 4B can alternatively be used where a printed circuit board 301s shown having OCM output pads 32 arranged about apertures 31 as before, and vertically oriented mains connection bolts 33 and corresponding pads 35. Such a configuration 1s useful with HT transformers manufactured by Sanyo Corp.

Turning now to Fig. 5, the circuit 40 of the OCM 14 is shown which is specifically adapted for use at 240V 50Hz. Connected to an input active terminal, is a resistor 41 which supplies power, via a capacitor 42 to a zener diode 43. The zener diode 43 is connected to the neutral supply input and, via diode 45 provides a pre-determinable DC supply voltage at the cathode of the diode 45. The DC supply is filtered by a resistor 46 and a capacitor 48. A sensing resistor 50 is connected in series in the neutral link between input and output of the OCM 14. A transistor 51 is arranged to sense the current passing through the resistor 50 and is connected to a load resistor 47 connected to the DC supply provided by the diode 45. A capacitor 49 is arranged to filter the voltage across the transistor 51. A resistor 52 is provided between the base of the transistor 51 and the neutral output of the circuit 40, and operates to prevent the transistor 51 drawing excessive current through its base.

The transistor 51 is configured to provide either a logic HIGH or a logic LOW to the input of an inverter 53 which outputs to a triac triggering device 54. The triggering device 54 provides for an isolated trigger of a triac 55 which allows for switchable connection of the active at the input, to the active of the output.

When power is supplied to the input, the triac 55 is initially off and no current passes to the output for supplying to the transformer input. The diode 45 permits charging of the capacitor 48 which imparts a logic HIGH upon the input of the inverter 53 which provides a triggering LOW output to the triggering device 54. This enables a switching ON of the triac 55 to provide a through connection to energise the primary of the HT transformer 10. Accordingly, the transformer 10 conducts current which establishes a voltage drop across the sensing resistor 50. The resistance value of the resistor 50 is selected so that, under normal operating conditions, the voltage drop across the resistor 50 maintains the transistor 51 ON, thus preventing altering the state of the triac 55.

^" When the secondary (high tension) output of the transformer 10 becomes open circuit of very high Impedance, due to the high magnetic reluctance and large turns ratio.of such transformers, the primary current drops significantly and the transistor 51 is configured to switch the logic state at the inverter 53 when the current sensed by the resistor 50 drops below a predetermined amount. This turns the triac 55 OFF.

The inverter 53 is preferably an MC14584BCP device and is supplied with DC power from terminals connected across the resistor 46. The triac trigger device 54 is preferably an MOC3041 device which connects to a resistor 56 which senses voltage supply to the active output. With this configuration, the trigger device 54 can sense the switching off of the triac 55 due to an open circuit and maintain the triac 55 switched off in spite of the input of the inverter 53 subsequently going HIGH after the switching off of the transformer 10 primary. This arrangement prevents the automatic reconnection of the transformer primary until such time as the fault has been rectified.

Referring now to Figs. 6 and 7 an alternative embodiment is shown in which a transformer 61 is enclosed within a casing 60 which is provided with a terminal block 65 mounted thereon using mounting screws 66. The transformer 61 (seen in Fig.7) includes input leads 62 which extend through the casing 60 into respective connection channels 67 of the terminal block 65. Fixing screws 68 are used to secure the leads 62 within the block 65.

An OCM 70 is shown which includes a housing 71 and a PCB 72 to which the housing 71 is fixed using, usually four, screws 77. Input terminal bolts 73 are also provided to contact input terminal track pads 74 in the manner earlier described. However, in this embodiment rather than having apertures, the PCB 72 Includes two output pins 76 extending through the PCB 72 rearwardly for connection within the channels 67 of the terminal block 65. The pins 76 in this particular embodiment are substantially L-shaped such that they contact output track pads 75. The output pins 76 are also secured within the channel 67 by the fixing screws 68. Alternatively, the pins can be replaced by bolts in which the head is soldered to the track pad 75 and the shank extends rearward through an aperture in the track pad 75 as in the previous embodiments.

With the electronic circuit 40 of Fig. 5, the current sensing resistor 50 provides for the sensing a range of lower limits of current such that if the limit is exceeded, the open circuit monitor operates to protect the secondary of the transformer. For 240V 50Hz systems, a single resistor 50 can be configured to provide a operating low current range of 0.5-1.5 amps, 1.5-2.5 amps, 2.5-3.5 amps, or 3.5-4.5 amps. It will be apparent from the foregoing that the range of minimum currents actually sensed is limited by the value of the resistor 50 and the power it can dissipate. Furthermore, in each of the above examples, the range is only of 1 ampere which in some applications Is considered unduly restrictive. It is desirable therefore to extend the under voltage protection limit to a lower current value thereby permitting the neon lighting system to be more tolerant to under voltage fluctuations in power supply systems. Similarly, an increase in the maximum value will ensure reduced susceptabi 1 ity to over-voltage transients that can cause momentary increases in primary winding current.

An electronic circuit 80, shown in Fig. 8, is configured to provide a substantially larger sensing range through the elimination of the current sensing resistor 50 used In the circuit of Fig. 5.

In Fig. 8, the circuit 80 includes an active input 81 and a corresponding neutral input 82 to which a zener diode 84 and rectifying diode 86 are configured with a coupling capacitor 87 to provide a reference DC voltage across a smoothing capacitor 89. A protection diode 88 is provided to protect the other devices of the circuit 80 from failure of either or both of the diodes 84 and 86.

Connected across the smoothing capacitor 89 is a voltage regulator 90 which outputs a positive supply 91 and a negative supply 92. A transistor 93 is provided which is connected from its collector via a load resistor 95 to the positive supply 91. A biasing resistor 94 Interconnects positive supply 91 with the base of the transistor 93. A resistor 96 interconnects the positive supply 91 to charge a capacitor 99. An inverter 97 is connected to invert the collector output of the transistor 93 which is provided to the cathode of a diode 98, whose anode is connected to the interconnection of the resistor 96 and the capacitor 99. That interconnection also connects to two inverters 100 and 101 which, via a resistor 102 coupled to dlac input of a triac triggering device 103. The triggering device 103 1s configured to switch a triac 104 connected between the active input 81 and an active output 83. A resistor 105 is provided with the triggering device 103 for sensing of an output voltage. The neutral input 82 connects directly to a neutral output.

Open circuit monitoring is provided by a current monitor 106 which is configured using a coil 107 arranged between the active output 83 and the triac 104. The coil 107 generates a magnetic field that interacts with a Hall effect sensor 108. The sensor 108 has a sensing lead output 114 which couples via a capacitor 109 to the base of the transistor 93. As seen in Fig. 9, the current monitor 106 is formed from a toroid 110 about which the coil 107 is wound. The toroid 110 includes an air gap 111 within which is placed the Hall effect sensor 108. When the triac 104 switches ON and current passes through the coil 107, a magnetic field is established within the toroid 110 which is sensed by the Hall effect sensor 108 which outputs a voltage linearly dependent upon the magnetic field. The Hall effect sensor 108 is provided with a positive supply lead 112 and a negative supply lead 113 which connect to the supplies 91 and 92 respectively. The sensing lead 114 is arranged at a DC offset level between positive supply 91 and the negative supply 92. As the circuit 80 is configured to operate with a transformer operating under alternating current, the coupling capacitor 109 Imparts upon the base of the transistor 93 the voltage output from the Hall effect sensor 108.

In operation, when power is supplied to the inputs 81 and 82, the regulator 90 enables each of the supplies 91,92. Because the triac 104 is initially OFF, no current flows is sensed by the current monitor 16. As the capacitor 99 is initially unchanged, the inverters 100 and 101 trigger the device 103. This then enables the triac 104 to turn ON Interconnecting the active input 81 with the active output 83. Under normal operating conditions, the sensed output 114 fluctuates at 50Hz (for 50Hz supplies, 60Hz for 60Hz supplies) to periodically switch the transistor 93 off which causes a periodic LOW output from the inverter 97. This causes discharging of the capacitor 99 through the diode 98.

Should the output current of the active output 83 drop below a predetermined level, the transistor 93 will be biased ON via the resistor 94 which causes the inverter 97 to output a high voltage which is blocked by the diode 98. Accordingly, the charge voltage on the capacitor 99 increases and causes the inverters 100 and 101 to provide a high voltage at the resistor 102 which acts to switch the triggering device 103 to switch the triac 104 OFF.

With the configuration of Fig. 8, the low current operating range of those described previously with the reference to Fig. 5 can be substantially increased such the previous minimum levels can be reduced by approximately 50% and the maximum levels increased to approximately 5 amperes. The actual low current switching level is set by component values that can be determined by those skilled in the art. Overcurrent protection is provided by an air gap in the HT transformer resulting in a high magnetic reluctance and the relatively high resistance of the secondary winding. It will be appreciated by those skilled in the art that the electronic circuits of Figs. 5 and 8, whilst specifically configured for 240V 50 Hz supply, can be easily reconfigured and adapted for 120V 60 Hz supplies such as used in the United States. The foregoing describes only a number of embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto without departing from the scope of the present invention.

Claims

CLAIMS:

1. An undercurrent monitoring device for a transformer having two input terminals, said device having a pair of input terminals connectable to an AC mains supply and a pair of output terminals, wherein said device is mountable on said transformer by a direct connection between the input terminals of said transformer and the output terminals of said device.

2. A device as claimed in claim 1, said device comprising a circuit board upon which an electronic circuit of said device is arranged, said device output terminals comprising pad contacts arranged about apertures through which said input terminals of said transformer are insertable for securing said device to said transformer and electrically connecting said transformer input terminals to said pad contacts.

3. A device as claimed in claim 1, said devlde comprising a circuit board upon which an electronic circuit of said device is arranged, said device output terminals comprising connectors extending from said circuit board and arranged for Insertion into a connector means comprising said input terminals of said transformer, said connector means securing said device to said transformer and electrically connecting said input terminals of said transformer to said connectors.

4. A device as claimed in claim 2 or 3, wherein-said electronic circuit comprises a sensor means that senses an supply current below a predetermined value to a primary.winding of said transformer said sensor means being characterized by the absence of a sensing resistor placed in series with said primary winding.

5. A device as claimed in claim 4, wherein said sensor means comprises a Hall effect means that senses a magnetic field established by current flowing in said primary winding.

6. An undercurrent monitoring device for a transformer, said device being characterized by the absence of a current sensing resistor in series with a winding of said transformer.

7. An undercurrent monitoring device for a high tension transformer in a neon-type lighting system, said device comprising a Hall effect sensor means and associated switching means adapted to - n - detect an undercurrent condition in a winding of said transformer and to disconnect an electrical supply from said transformer in response thereto.

8. A device as claimed in claim 7, wherein said sensor means comprises a toroid about which is wound a conductor supplying said winding, and a Hall effect sensor arranged in an air gap of said toroid to detect magnetic field fluctuations caused by changes in current in said conductor.

9. A neon lighting system comprising a neon lighting display energisable from outputs of a high tension transformer, and an undercurrent monitoring device as claimed in any one of the preceding claims.

AMENDED CLAIMS

[received by the International Bureau on 9 March 1993 (09.03.93); original claims 1 and 6 amended; new claim 10 added; remaining claims unchanged (2 pages)]

1. An undercurrent monitoring device for a transformer, said transformer having two input terminals, said device comprising a pair of input terminals connectable to an AC mains supply and a pair of output terminals, wherein said device is mountable on said transformer by a fastened direct connection between the input terminals of said transformer and the output terminals of said device.

3. A device as claimed in claim 1, said device comprising a circuit board upon which an electronic circuit of said device is arranged, said device output terminals comprising conducting connectors extending from said circuit board and arranged for insertion into a connector means comprising said input terminals of said transformer, said connector means securing and electrically connecting said input terminals of said transformer to said conducting connectors to thereby mount and support said device on said transformer.

4. A device as claimed in claim 2 or 3, wherein said electronic circuit comprises a sensor means that senses an supply current below a predetermined value to a primary winding of said transformer said sensor means being characterized by the absence of a sensing resistor placed in series with said primary winding.

5. A device as claimed in claim 4, wherein said sensor means comprises a Hall effect means that senses a magnetic field established by current flowing in sai primary winding.

6. A device as claimed in claim 2 wherein said input terminals comprise threaded posts and said device is secured thereto by complementary threaded nuts. 7. An undercurrent monitoring device for a high tension transformer in a neon-type lighting system, said device comprising a Hall effect sensor means and associated switching means adapted to detect an undercurrent condition in a winding of said transformer and to disconnect an electrical supply from said transformer in response thereto.

10. An undercurrent monitoring device for a high-tension transformer in a neon-type lighting system, said transformer having a pair of input terminals, said device comprising a pair of input terminals connectable to an AC mains supply, a pair of output terminals adapted to be fastened to said transformer input terminals to provide electrical connection therebetween and physical support and mounting of said device to and upon said transformer, and a Hall effect sensor means and associated switching means arranged on a circuit board upon which said terminals of said device are arranged, said sensor means and said switching means being configured to detect an undercurrent condition in a winding of said transformer and disconnect said AC means supply from said transformer input terminals in response thereto.