High voltage sensor assembly

Details High voltage sensor assembly High voltage sensor assembly

1999-12-03

2001-11-06

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Internal-combustion engine ignition system or device

In situ testing of spark plug

C324S122000, C340S660000, C340S654000

Reexamination Certificate

active

06313635

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to static eliminators that use high voltage alternating current to ionize air and thereby produce mobile ions that are attracted to electrically charged articles until those articles are electrically neutral and, more specifically, to a high voltage sensor that can monitor the power supply used with static eliminators, as well as other high voltage devices.
Alternating current static eliminators have been widely used to eliminate or suppress static electricity on electronic equipment, sheets and webs of nonconductive material, plastic parts and food containers, fluid and bulk solids, and on many other uninsulated or ungrounded articles. The source of alternating current for AC static eliminators is known as a “high voltage power source,” or a power unit, which is usually a current limited or ferroresonant transformer. The “high voltage power source” is supplied with alternating electric current from conventional mains, typically conditioned to be within the range of 100-440 volts alternating current and cycling at either 50 or 60 Hertz. The secondary windings of the high voltage power source operate at between 4,000 and 10,000 volts, with the current being limited to about five milliamperes to protect users from receiving severe shocks.
There are many alternating current static eliminating designs. The lower voltage designs usually have the ionizing electrodes and the passive electrodes directly connected to the alternating current power source ferroresonant transformer. The higher voltage designs use a resistance (as shown in U.S. Pat. No. 3,760,229) or capacitance (as shown in U.S. Pat. No. 3,120,626) in series with the alternating current power source to limit the electrode current and protect workers from shock or ignition of hazardous vapors. Most designs maintain the ionizing electrode at a high voltage while the remaining designs use an ionizing electrode that is maintained at ground potential (as shown in U.S. Pat. No. 3,369,152). Other designs have both electrodes isolated from ground (as shown in U.S. Pat. Nos. 4,053,770 and 5,307,234) that use the voltage difference between electrodes to drive the ionization process. The above designs can be incorporated into “single point ionizers,” “static bars” that are linear rays of single point ionizers, blow-off guns and nozzles (as shown in U.S. Pat. Nos. 3,156,847 and 3,179,849), ionizer fitted air movers (as shown in U.S. Pat. No. 4,440,553), or the like. The variety of electrode designs and operating voltages requires that a high voltage sensor be capable of use with the various usable designs and electrode voltages.
Typically, the high voltage power source on a static eliminator is provided with an indicator light, which is intended to indicate that the alternating current static eliminator is “on.” In other words, the indicator light indicates that the static eliminator is being supplied with electric current from the mains. The problem with this approach is that it reveals only that power is connected to the primary windings of the high voltage transformer. This can be problematic as it is the voltage across the secondary windings of the transformer that drives the ionization from the electrodes. Thus, the sensor can generate misleading information when there is a failure in the secondary winding or in the electrode system connected to that winding. Accordingly, when the sensor is attached to the primary windings, it is possible that even though the indicator light is in the “on” condition, the ionizing apparatus may be essentially non-functioning. Thus, ideally, a high voltage sensor should be able to establish whether the output (i.e., secondary winding) of the transformer is shorted out by the failure of the ionizer, the high voltage wire, or the transformer insulation systems.
An alternating current static eliminator uses an oscillating voltage that is the same at all ionizing electrode sets and along all connecting wires to the alternating current source. The conductor system is an equipotential system. The amplitude of the voltage depends upon the load and ionizer design. In monitoring the potential for ionization, it is therefore sufficient to use one sensor to monitor the entire ionizer system. Accordingly, the sensor should be placed at the most convenient location on the high voltage power source for monitoring the static eliminator system. Thus, ideally, the high voltage sensor should be designed to be sufficiently flexible with respect to being positionable at various locations along the combination high voltage power source and static eliminator system, including being positionable along the wires connecting the alternating current source with the AC static eliminators. This allows the sensor to be placed at the most convenient location for monitoring the system.
The insulation system of a static eliminator, including cables, is normally exposed to hostile industrial environments and consequently has a finite life. As such, failure detection circuits are important to alert equipment operators when static elimination is no longer occurring. Accordingly, an ideal high voltage sensor should match and preferably exceed the durability of the other components of the ionizer system. Additionally, the high voltage sensor should be replaceable separately from the other components of the ionizer system.
High voltage sensors can be generally classified as either directly coupled or capacitively coupled. Directly coupled high voltage sensors are attached directly between the high voltage terminals. Some directly coupled high voltage sensors operate from current drawn from the secondary windings of the high voltage power source, while others rely on current drawn from the mains to drive the electrical circuitry. The use of power from the mains permits brighter visual indications of failure, allows the use of relays to operate control circuits, and makes possible the use more sophisticated provisions for interpretation of failure modes. The sensing and relay circuits of the mains-powered circuits are generally located inside the high voltage power source.
Typical direct coupled sensors, such as the SK-4/7 from Simco Japan, include a failure detection circuit to turn “off” the high voltage and inform the operator when there is a high voltage electrode or cable failure. The sensing circuits are mounted inside the high voltage high voltage power source and include a voltage divider across the output of the transformer. Simco Japan manufactures an optional, external monitor that uses red and green lights and a buzzer with its failure detection circuit. The dual-phase high voltage power source with a trip circuit manufactured by Simco USA demonstrates another approach for designing sensing circuits which determine the secondary voltage from the cap-coil of the ferroresonant transformer. The detection signal is used to operate a relay that turns “on” a flashing light and disconnects power to the transformer. The circuit can only be used with ferroresonant transformers and must be part of the high voltage power source. The threshold for voltage trip-out, and delay before the full trip-out, can be adjusted, but are fixed in practice. The trip circuit is also commercially available as a stand-alone unit or as an integral part of a single phase high voltage power source. Sophisticated sensors (such as that shown in U.S. Pat. No. 3,584,258) discriminate between a streamer corona and the non-carbonizing sparks within the dielectric, high leakage currents, and arcs. Other similar circuits are available in the industry.
Capacitively coupled sensors obtain signals that are used to detect high voltage through the capacitance of the insulation system. This approach has an advantage in some applications where the sensor is to be incorporated in the capacitively coupled ionizer. Such ionizers are often compact in design and thus require that the insulation system remain unbroken while securing measurements. In these compact ionizers, breaks in the insulation system becom

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