CA2216201A1

CA2216201A1 - A load and supply status indicator

Info

Publication number: CA2216201A1
Application number: CA002216201A
Authority: CA
Inventors: Peter P. Pohorily
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-11-14
Filing date: 1997-11-14
Publication date: 1999-05-14

Abstract

A self contained electrical status indicator that can indicate whether a load isoperating or not, it requires no batteries and uses a current transformer with alight to indicate current and another light to indicate voltage. The nature of it's design allows a user to safely connect it between an alternating current (AC) source and an electrical load utilizing plugs and sockets intended for that loadwithin seconds. It can determine whether or not a load is operating as expected and if it isn't, the device conveys the general nature about where the problem lies. The device can be left connected between the source and the load for as long as desired or it can be used temporarily. It runs on the power available from the circuit to which it is connected. One of it's two lights indicates whether or not supply voltage exists and the other indicates whether or not the load is drawingcurrent. Since the supply voltage determines the overall operation of the deviceand of the load any problems with the supply will naturally have to be overcome first. Only then can any problems in the rest of the circuit be addressed. The electrical status indicator's output can be consulted once again in this case.

Description

A self contained electrical status indicator that can indicate whether a load isoperating or not, it requires no batteries and uses a current transformer with alight to indicate current and another light to indicate voltage. The nature of it's design allows a user to safely connect it between an alternating current (AC) source and an electrical load utilizing plugs and sockets intended for that loadwithin seconds. It can determine whether or not a load is operating as expected and if it isn't, the device conveys the general nature about where the problem lies. The device can be left connected between the source and the load for as long as desired or it can be used temporarily. It runs on the power available from the circuit to which it is connected. One of it's two lights indicates whether or not supply voltage exists and the other indicates whether or not the load is drawingcurrent. Since the supply voltage determines the overall operation of the deviceand of the load any problems with the supply will naturally have to be overcome first. Only then can any problems in the rest of the circuit be addressed. The electrical status indicator's output can be consulted once again in this case.
Related to this invention are any devices that use lights to indicate whether or not alternating voltage or alternating current are present. Also related to this device are any other devices that use current transformers to indicate the presence of AC
current.
Devices commonly used to indicate the presence of voltage alone do not indicate whether or not a load connected to a source of electricity is actually working.
Current transformers can be used to detect the presence of AC current however there are difficulties involved with it's connection owing mainly to the necessity of breaking the circuit to install it onto one of the two supply wires. In addition it is easy to see whether or not many electrical devices are operating without the need to detect that AC current exists however there is at least one case where the operating status of the load is not obvious. Automotive block heaters that are powered by alternating current give no practical indication as to whether they are working or not at the time they are plugged in. It happens that it is most important that the operating status of the heater be known as soon as the device is plugged in since it prepares the engine for an important start some time later. It is of no use for the driver to learn that the power wasn't delivered to the heater later when the automobile is needed since it might not start at that time. Status information indicating the presence of voltage alone is insufficient information for this type of load since a problem in the circuit often does not affect the voltage at the source yet a problem with either the device or the connection can yield the device inconspicuously inoperative. In cases like this it is also not practical to determine whether a load is operating by the senses since it may be remote and largely inaccessible. It is also often not practical to break the circuit and check the current with an ammeter, a task left best to only those who are trained to do so.
Given that it is not obvious when some loads are operating, a voltage indicator light alone is not only insufficient but can also be misleading since it alone will imply that a defective load is operating to the user of the equipment.

It was found that the practical difficulties involved with breaking the circuit quickly to detect the operating current could be overcome by using a small current sensing transformer to power a light that indicates the presence of current flowinside of an enclosure that can be safely plugged in and out of the circuit within seconds. The inclusion of a voltage status indicator adds to the device's uniqueability to detect whether the problem lies with the source or with the equipmentbeing powered. The simplicity of the device lends itself to anyone who wishes touse it and no academic understanding of electricity is required to operate it. The meanings of it's output lights can quickly determine whether or not an electrical load is really operating with little or no training in cases where voltage status indicators alone fail to do so. The device is thus capable of removing any doubts about the operation of the equipment that is being powered and about the presence of power at the source. It is able to do this because the information it displays is real with time as long as it is connected. This device is capable ofmaking simply and accurately those preliminary "go, no go" types of trouble shooting steps by an unskilled person that would otherwise have require a specially equipped skilled person to perform. These features give the device a unique ability to reassurance both skilled and unskilled users alike about the operating status of important equipment that is to date unsurpassed.

Drawing References 1. Conceptual Assembly Drawings (Figures 1 through 4)

2. Schematic Diagram (Figure 5) With reference to the drawing titled Conceptual Assembly Drawings, Figures 1 through 4 inclusive are conceptual drawings that can all be possibilities for the assembled electrical status indicator. Plug and receptacles other than the typesshown including types used in different countries having different pin shapes and placements are also possible however they are not shown. Socket P1 and plug P2 allow quick and easy insertion or removal of the device. D1 and D4 are light emitting diodes that indicate the current and voltage status respectively. The body housing the circuitry and lights can be made of molded plastic of the type used in typical plugs in use today.

Figure 5 in the drawing titled Schematic Diagram shows the device's internal circuitry. The voltage and current sensing parts of the circuit can be analyzed independently as follows.

To analyze how the device senses voltage assume that P2 is connected to a live AC receptacle while P1 is left disconnected. In this condition only D4 will shine indicating the presence of voltage since it is part of a series circuit across the live terminals of the receptacle. This series circuit includes D3, D4, optional D5 and R1 across the hot and neutral terminals of P2. R1 is a voltage dropping resistorthat limits the current through D4 to a level that D4 and optional D5 can handle.
D3 is included to rectify half of the AC voltage and this significantly reduces the resistance needed for R1 which in turn reduces the amount of heat generated in R1. If the voltage supplied by the receptacle to which P2 is connected disappears then D4 will extinguish and will thus indicate a problem with the supply voltage.
D5 is included since D4 becomes a capacitive reactance when it is reverse biased. This capacitive reactance will be in series with the capacitive reactance that D3 presents when it is reverse biased along with the resistance in R1. The capacitive reactances that D3 and D4 will exhibit during the AC half cycles thatcause reverse bias voltages to exist will depend on the individual components chosen for D3 and D4. These reactances and the series resistance of R1 will all drop voltages during the half cycles that cause reverse bias voltages across D3 and D4. If measurements show that the reverse voltage across D4 are excessive during the half cycles that cause reverse voltages across D4 then D5 can shunt D4 as shown. It is easy to choose D3 such that reverse voltages across it are never a problem. Light emitting diodes may however be more sensitive to reverse voltages thus the reason for D5. D5 will be forward biased during any instances when a reverse voltage across D4 tries to develop thus clamping the reverse voltage across D4 to a safe level.

To analyze how the device senses current assume that P2 is connected to a live receptacle as explained above with the addition that P1 is connected to a load that is drawing current. D4 will shine as described in the preceding paragraph since voltage is present at the source. D1 is an LED that derives it's power from current transformer T1. It shines because the load current that is also flowing through T1's primary winding causes a voltage across T1's secondary winding that is high enough to turn on D1. The voltage across T1's secondary winding can only exist when current is flowing through it's primary winding. T1's primary winding is made of very few turns of a conductor who's cross sectional area is large enough to deal with the levels of currents that the load demands. T1's secondary winding is made of many turns of very fine wire that produce enough voltage to make D1 shine. The currents that flow in T1 's primary and secondary windings are proportional by the turns ratio in these windings, the current being stepped down on the secondary side. Diode D2 is optional. When it is included itprovides a path for the reverse current when possibly damaging reverse voltages across D1 appear due to the alternating voltage that T1's secondary applies across D1. D2 can be excluded if measurement of the peak reverse voltage across D1 shows that it is within D1's ability to withstand the existing reversevoltage levels. It is interesting to note that no series resistance is used to limit D1's current. None is needed because current transformer T1 is sized such that the current produced in T1's secondary winding will never reach the maximum levels that D1 and (if included) D2 can withstand. If a break anywhere in the load's circuit that is in series with T1 's primary causes the current to disappear then D1 will extinguish and only D4 will continue to indicate the presence of voltage. If the receptacle that is supplying the power loses it's voltage on theother hand then both of the lights will extinguish whether or not a break in thecircuit exists since no power is available to run the device's lights.

The device can be made more sensitive to smaller load currents by choosing an LED with a lower forward voltage drop for D1. The device can also be made more sensitive to lower levels of load currents by changing T1's turns ratio such that the voltage across it's secondary winding is increased. Two or more transformers with secondary windings connected in series can also increase the available output voltage. These changes may require That D1 be protected by use of either D2, a series resistance to limit D1's current or both as previously described.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A self contained electrical status indicator that can be inserted or removed from a circuit typically within seconds using suitable plugs and sockets that are intended to connect an electrical load to an appropriate source of electricity, the device indicates whether the load is operating or not, requires no batteriesand uses a current transformer with a light to indicate the presence of current and another light used to indicate the presence of voltage.

2. A device as defined in claim 1 that includes either one or two cables extending from the body that encloses the necessary circuitry and either of the body's ends where it's plug and/or socket ends for the intended source and/or load are located. The cables can be any length and they contain the necessary wires that connect the plug and/or socket to the rest of the circuitry that is part of the device. In this claim either a plug or a socket can be integral with the body containing the necessary circuitry or the body that encloses the necessary circuitry can use two cables to make connections to the plug and socket ends that will connect between the source and the load. In this latter case the plug and socket that the device requires are not integral with the body that contains the circuitry to the body. These physical assembly possibilities are shown in figures 2 through 4 inclusive in the drawing titled

Conceptual Assembly Drawings.

4. A device as defined in claim 1 that requires no cables extending between the necessary circuitry, plug and socket that integrates the necessary plug and socket into a single body. This claim is shown in Figure 4 in the drawing titledConceptual Assembly Drawings.

5. A device as defined in claim 1 that uses plugs and sockets other than of the type shown in figures 1 through 4 inclusive thus allowing it's use on 240 volt circuits or in different countries that use different voltages, plugs and sockets.