Telemetry circuit for an a.c. power system

© Beginning of patent period: 15.Feber 1973 Longest possible duration:

© Issued on: 12.November 1973 © Inventor:

© dependence:

311 21 »© Pamphlets considered to delineate the state of the art:

DT-AS 1 262 331 - 2 -

Nr.311218

The invention relates to an electrical arrangement comprising an AC power source, at least one pair of supply or power lines for connecting the power source to a load, a pulse transmitter connected to the supply lines and a pulse detector connected to the supply lines. The pulse transmitter includes a potential breakdown device and a potential storage device. When the alternating voltage potential applied to the two supply lines, which is also the potential applied to the pulse transmitter, changes, the breakdown device responds to the instantaneous potential drop on the supply lines and ignites. Then either a charging or a discharging current flows through the breakdown device and the memory device and this current flow leads to a pulse which appears on the two supply lines. This pulse is picked up by the detector.

Electrical arrangements having an AC power supply circuit and a remote measuring circuit using the supply lines of the supply circuit for relaying signals have been provided. Such a system is described, for example, in US Pat. No. 3,327,167. Another example of such a system is an arrangement in which radio frequency signals are superimposed on an AC supply circuit to transmit information or to put into operation electrical devices connected to the supply circuit.

In the German Auslegeschrift 1262331 a circuit arrangement is described which comprises two control circuits for generating pulses, the latter being sent through one of two AND gates to one of two counters, depending on which gate is closed by means of a switch. The pulse transmitter generates pulses in a selected phase angle of the input alternating current and supplies a binary signal as soon as the phase of the line voltage exceeds a certain point.

While known arrangements of this type are partially useful, they often have the disadvantage of being too costly, too large, or too unreliable over a longer period of time. Another aspect that prevents the use of certain types of telemetry circuitry is the low-impedance load of many AC power supply circuits. For example, a supply circuit comprising a power transformer, supply lines, and an electric motor has a relatively low impedance, and any remote measuring circuit incorporated in such a supply circuit must be able to operate with such a low-impedance load.

The invention relates to a circuit arrangement for an AC power supply having an AC power source, an AC load and a pair of supply lines connecting the load to the power supply to the power source, wherein between the supply lines parallel to the load, a pulse transmitter is connected, which in its operation one at rest discharge capacitor temporarily connected to the supply lines, wherein the resulting current flow results in a pulse which is impressed on the AC voltage on the supply lines, which circuit arrangement is characterized in that the pulse transmitter comprises the capacitor and a potential breaker arranged in series with the latter, which carries current when the voltage in the same on the Ignition voltage rises, and interrupts the current when the voltage in the same drops to the erasing voltage, so that in operation the potential breakdown device ignites and conducts current as soon as the voltage applied thereto reaches the ignition voltage, this Stromzufluß changes the voltage of the capacitor, thereby reducing the voltage drop across the potential breakdown device to the erase voltage.

Further features and technical advantages of the invention will become apparent from the following explanation in conjunction with the drawings. 1 shows a block diagram of an arrangement with a remote measuring circuit according to the rules of the invention, FIGS. 2 to 8 schematically show different embodiments of transmitters for use in the arrangement according to FIG. 1, FIGS. 9 and 11 show schematic representations of a transmitter Part of a three-phase system with a Femmeßschaltung according to the invention, Fig. 10 schematically shows a non-protected full three-phase supply system with a remote measuring circuit according to the invention; Figs. 12-14 are schematic representations of out-of-range receivers or detectors for use in a telemetry circuit according to the invention and Fig. 15 curves; which illustrate the operation of a remote sensing circuit according to the invention.

The arrangement shown in Fig.l comprises a conventional AC source -16-, for example a power transformer, a load -17-, for example one or more electric motors, one or more household appliances or any combination thereof, and two supply lines -18 and 19- connect the load -17- to the power source -16- to form a power supply circuit. Furthermore, the arrangement comprises a transmitter -21-, which is connected by means of a conductor -20- between the supply lines -18 and 19-, and a detector -22-, which is also connected to the two supply lines. A switch -23- is used to start up transmitter -21- and means -24- is connected to respond to or be actuated by detector -22-. In short, the arrangement operates in the following way: When AC current from the power source flows through the supply circuit and the switch -23- puts the switch -21- into operation, generates - 3 -

No.311218 of the transmitter -21- Pulses, which are superimposed on the AC voltage of the supply lines -18 and 19-. The detector -22- responds to the pulses generated by the transmitter -21- and actuates the

Facility - 24--.

The switch -23- may be a manually operated embodiment, or the switch may be configured to automatically respond to an environmental condition. As examples of hand-operated embodiments are push-button switches or switches in a burglar alarm system, which are unintentionally operated by a burglar in attempting to penetrate a house or building called. As an example of automatic switches are switches that respond automatically to temperature, smoke, water, etc., called.

The device -24- may be an audible or visual alarm, a household appliance, eg a coffee maker, a control circuit for disconnecting the load -17- from the power source -16-, etc.

For example, a complete assembly may include an electric motor as a load, the switch being configured and arranged to respond to the temperature of the engine and to operate the transmitter when the engine overheats. In such an arrangement, the device -24- may include an alarm or relay for disconnecting the motor from the power source in the event of overheating. An example of another complete system is an arrangement in which the load or the like is one or more household appliances. The switch -23- is automatically responsive to fire, smoke or intrusion into the house and the device -24- consists of an alarm or indicator of some sort. The supply lines -18 and 19- can be conveniently formed in such a case of the usual electrical wiring system of the house, which is used to power the lighting fixtures and other facilities of the house.

The design of an embodiment of the transmitter -21- is illustrated in Figure 2; this has a potential breakdown device -26- and a potential storage device -27-. In the embodiment shown in Fig. 2, the potential breakdown device -26- comprises a glow lamp and the potential storage device -27- comprises a capacitor. Preferably, the circuit according to Figure 2 further comprises a switch -28- to start up the transmitter; In the present case, the switch is shown in the form of a temperature-responsive switch with a bimetallic element -29-. The switch -28-, which could also be connected in parallel with the glow lamp -26-, is in the illustrated embodiment in series with this and the capacitor -27- in an electrical line -31-, the line -20- shown in FIG .l corresponds and connects these components to the two supply lines -18 and 19-.

To explain the operation of the circuit according to Figure 2, it is assumed that the lamp -26- is a glow lamp with a breakdown or ignition voltage of about 200 V and an erase voltage of about 57 V. Lamps which meet these conditions are commercially available (eg under the trade names "Signalite" lamp No. A258 or No. T2-27-1W760). The capacitor -27- in this example is a 0.1 microfarad capacitor. The size of the capacitor should be such that it can be fully charged in a very short time, and it should be a non-polar type capacitor since it is connected between the AC power supply lines. It is further assumed that the AC power source -16- is a sine voltage having a peak-to-peak value of about 800 V corresponding to 280V_eGives away £ f.

In the curve -A- of Fig. 15, -35- denotes a sinusoid which repeats the voltage of the AC power source. It is assumed that the switch -28- closes at the time when the voltage corresponds approximately to the point -32-; this point is approximately at the voltage zero line and is on the rising branch of the sinusoid -35-. At point -32- no current flows through the transmitter, since the voltage drop across the glow lamp -26- does not reach its ignition voltage of 200V. However, as the voltage on the rising branch of the curve -35- increases, the voltage at the transmitter rises to about 200V, whereupon the glow lamp -26- lights up and becomes conductive. Upon ignition of the glow lamp -26- current flows through it and the capacitor -27- and this current flow gives a pulse -33- which is superimposed on the sinusoid -35-. The current flows through the transmitter until capacitor -27- is charged to a voltage approximately equal to the difference between the ignition voltage and the erase voltage of the glow lamp -26-. In the illustrated example, the capacitor -27- is charged to about 143 V in about 4 Jtsec, and at the same time, the voltage across the glow lamp drops to about 57V. The curve -B- of Fig. 15 indicates the voltage drop across the capacitor -27-, the curve -C- corresponds to the voltage drop across the glow lamp -26-. When the voltage on the glow lamp -26- falls to 57V, the glow lamp -26- stops conducting, thereby breaking the current path through the transmitter, thus preventing the capacitor -27- from being discharged. The voltage across the capacitor -27- thus remains at the 143 V level, as indicated by the reference numeral -34- in the curve -B-. The voltage across the glow lamp -26- represented by the curve trace -C- rises to a 4 indicated by the reference numeral -42-

Nr.311218

Height equal to the ignition voltage of the glow lamp -26-, and then this voltage falls on the

Level -43-, which corresponds to the erase voltage of the glow lamp -26-.

After the formation of the pulse -33-, the slope of the sine curve -35- continues on the rising branch of the curve until the total voltage drop across the transmitter is about 343V. The voltage across the capacitor is then still 143 V and the voltage at the glow lamp has thus risen again to 200 V, which causes the glow lamp ignites again. Again, a current pulse flows through the transmitter, the capacitor -27- to about 286 V, represented by the level -36- in the curve -B-, charged and another pulse -37- is generated.

Then the voltage at the transmitter begins to drop on the descending branch of the sinusoid, and once it has fallen to the level at which the total voltage drop at the transmitter minus the voltage drop across the capacitor -27- is 200V, the glow lamp -26- fires again , The capacitor -27- discharges to the level -39- of the curve -B-, and another pulse -38- is generated.

The above process is repeated continuously as long as switch -28- is closed producing a train of pulses in the AC supply circuit received by detector -22-. Advantageously, the ignition voltage and the erase voltage of the breakdown device should be as far apart as possible in order to obtain as much energy as possible with each pulse. While the magnitude of each pulse is determined by the characteristics of the breakdown device, the amount of energy in each pulse is determined by the capacitor, depending on the amount of time required to charge or discharge. In addition to its obvious function of storing energy, the capacitor 27- also serves to limit the amount of current flowing through the glow lamp and as a coupling element between the transmitter and the AC power supply lines. The breakdown device may be defined as a device that responds to the potential applied thereto and exhibits a sudden increase in conductivity as soon as the voltage applied thereto reaches a given level.

As already mentioned, the curves -Α, B and C- of Fig. 15 illustrate the incoming states when the peak-to-peak value of the AC voltage appearing on the power supply lines -18 and 19- is about 4 times the value of the breakdown potential of the Glow lamp is. The curve -D- will be explained in connection with Fig.12. The total number of pulses generated by the transmitter in each AC cycle depends on the RMS value of the AC voltage relative to the break and erase voltages of the glow lamp. The table below shows the number of pulses generated in each AC voltage period at different supply voltages, with all voltages given as RMS values. The table illustrates the operation of a circuit in which the firing and extinguishing voltages of the glow lamp are 200 and 57 V, respectively, and the capacitor has 0.05 microfarads at 600 V.

<td>Number of pulses</td><td>management tension V_eff</td><td>Voltage at the capacitor V_eff</td><td>Voltage on the lamp V_eff</td>

<td>2</td><td>141</td><td>110</td><td>83</td>

<td>4</td><td>210</td><td>172</td><td>85</td>

<td>6</td><td>275</td><td>242</td><td>85</td>

<td>8th</td><td>325</td><td>300</td><td>85</td>

<td>10</td><td>405</td><td>390</td><td>85</td>

<td>12</td><td>470</td><td>455</td><td>85</td>

Here, the voltage across the capacitor is the maximum voltage -35- and the

Voltage at the glow lamp the voltage - 43-, at which the glow lamp goes out. The voltage across the capacitor largely depends on the internal impedance of the glow lamp when it is not burning. As already mentioned, the extinguishing voltage of the glow lamp is 57 V at DC according to the type specification of the manufacturer. For AC, the erase voltage is higher and at 60 Hz, the specified 83 to 85 V.

FIG. 3 shows a transmitter circuit which can be used in supply networks of relatively low voltages. The transmitter circuit of Figure 3 comprises a glow lamp -46- with an ignition voltage of, for example, 200V, a capacitor -47- connected in series by a conductor -48- to the glow lamp -46-, and a diode -49- which is closed parallel to the glow lamp -46-. The conductor -48- corresponds to the conductor -20- of Fig.l and serves to connect the transmitter to the supply lines -18 and 19-. A switch similar to switches -23 and 28- of Figures 1 and 2 may be incorporated in the transmitter circuit of Figure 3 to operate this transmitter.

No.311218.

At a supply voltage of, for example, 110 V effective, a sine wave voltage appears with a peak-to-peak value of about 300 V at the transmitter. Assuming that capacitor -47- is connected to ground, during the positive half cycle of each sine wave, the anode of diode -49- is positive and the diode is biased in the flux direction. Then, current flows through the diode -49- and the capacitor -47-, charging the capacitor -47- to about the peak value of 150V. During the negative half cycle of each AC sine wave, diode -49- is disabled. When the AC voltage goes negative, the voltage drop across the lamp -46- is equal to the voltage of 150V to which the capacitor is charged, plus the AC supply voltage, and when that sum rises to about 200V, the lamp -46 will fire -. The capacitor -47- discharges through the lamp -46- and a pulse is generated on the supply lines -18 and 19-. The transmitter shown in Fig.3 thus generates in the example given only one pulse for each full cycle of the supply voltage. For example, the capacitor -47- may be a 2 microfarad capacitor.

The circuit shown in Figure 4 comprises two transmitters -49 and 49a-, these transmitters each have thyristors or silicon rectifier -51 and 51a, which are connected in series with capacitors -52 and 52a-, u.zw. by means of conductors -53 and 53a, which correspond to the conductor -20- in Fig.l. In the conductors -53 and 53a-on-off switch -55 or 55a- for putting into operation or switching off the transmitter -49 or 49a- are inserted. Each of the transmitters shown in FIG. 4 further includes a device having a voltage dependent breakdown characteristic, such as a glow lamp or breakdown device, as known in the art as "DIAC" (hereinafter referred to as a DIAC device). A DIAC device is a semiconductor that breaks and conducts at, for example, 30V maximum in each direction, with the voltage drop across the DIAC device dropping to about zero when the line is continued. The conductive properties of a DIAC device are the same for current flow in both directions. The characteristics of a DIAC device are similar to those of a glow lamp, the main differences being that the operating voltages of a DIAC device are lower and a DIAC device is a relatively low power device.

In the present case, transmitters -49 and 49a are provided with DIAC devices -54 and 54a, respectively, connected between the control terminals and the anodes of the respective thyristors. The characteristics of such a thyristor are, of course, such that when the thyristor is forward biased or turned on, a relatively small voltage appearing at its control terminal will render the thyristor conductive and the thyristor will remain conductive even if the control terminal signal disappears until the anode current of the thyristor is interrupted.

In each transmitter circuit -49 and 49a, respectively, the union of thyristor and DIAC device forms a breakdown device whose firing and erase voltages are determined primarily by the characteristics of the DIAC device.

To explain the operation of the transmitters according to Fig. 4, it is assumed that the capacitor -52- is connected to the earth line and that both switches -55 and 55a- are closed. The thyristor -51- is triggered to conduction as soon as the voltage at its cathode becomes negative to ground and, further, when the voltage is greater than the breakdown voltage of the DIAC device -54-. When the voltage at the transmitter -49- is greater than the breakdown voltage of the DIAC device -54-, the DIAC device conducts -54- and triggers the thyristor -51- into the conducting state. The voltage drop across the DIAC device -54- goes back substantially to zero, the thyristor -51- conducts current, the capacitor -52- is charged, and a pulse appears on the supply lines. As soon as the charge on capacitor -52- reaches approximately the breakdown voltage of the DIAC device, the thyristor -51- stops conducting. The transmitter -49- generates one or more pulses until the negative voltage peak is reached, the number of pulses depending on the magnitude of the breakdown voltage with respect to the peak voltage.

Since the thyristor -51- normally conducts current only in a direction, the transmitter 49- shown in Fig. 4 normally generates pulses only during a part of a single half-wave

AC voltage period when the thyristor -51- is forward biased and the voltage rises. If the polarity of the AC supply voltage at the two transmitters in the next half cycle is reversed, the transmitter -49a is powered and generates a pulse. After both transmitters have been operated in a sine passage, a discharge of the capacitors -52 and 52a- by the thyristor -51- or prevents the thyristor -51a-, and the charges on the capacitors prevent the thyristors -51 and 51a- are triggered in the subsequent sine cycles in the conductive state.

To discharge the two capacitors -52 and 52a for subsequent operation of the two transmitters, pushbutton switches -56 and 56a and resistors -57 and 57a, respectively, are parallel to the

Capacitors -52 or 52a- connected. When closing the switches -56 and 56a- unload the

Capacitors -52 and 52a- via resistors -57 and 57a-.

- 6 -

Nr.311218

The transmitter shown in Fig. 4 is intended for arrangements equipped with two detectors, one detector being arranged to respond to pulses generated in the negative half-wave from the transmitter -49- while the detector is in the negative half-wave other detector responds to pulses emanating from the transmitter -49a- in the positive half cycle. Of course, if it is desired to work with only one transmitter and detector, only the switch -55 or 55a of this transmitter closed and the other switch -55a- be opened.

The circuit shown in Fig. 5 is similar in configuration and operation to the circuit of Fig. 4, except that the circuit of Fig. 5 produces a continuous train of pulses during a series of sine waves, while the circuit of Figs .4 delivers a group of pulses only in the course of the first sine wave after the startup. The circuit according to Figure 5 comprises two transmitters -61 and 61a, these transmitters each have thyristors -62 and 62a, which are connected in series with capacitors -63 and 63a and on-off switches -64 and 64a, respectively. Thyristors -62 and 62a have DIAC devices -66 and 66a connected between their control terminals and anodes while diodes -67 and 67a, respectively, are connected in anti-parallel between their anodes and cathodes. The two transmitters -61 and 61a are connected in parallel between two conductors -68 and 69- corresponding to the conductor -20- of Fig.l.

In operation, assume that switch -64a is closed, conductor -68- is connected to ground and the voltage on conductor -69- becomes negative. Looking first at the transmitter -61a, it is blocked by the negative voltage at the anode of the thyristor -62a, but current flows through the reverse connected diode -67a and charges the capacitor -63a- to the peak voltage. Of course, if the thyristor -62a is disabled and bypassed by the diode -67a, no pulse is generated by the transmitter -61a. Subsequently, when the voltage on the conductor -69- goes in the positive direction, this voltage is added to the voltage to which the capacitor -63a is charged, similar to the operation of the circuit according to Fig. 3, and when the breakdown voltage of the DIAC device -66a- is reached, the thyristor -62a- is triggered into the conducting state. With the present voltage polarity, the diode -67a is naturally disabled. The transmitter -61a then generates pulses, similar to one of the transmitters according to FIG. 4, the number of pulses generated by the transmitter 61a in each cycle naturally being dependent on the magnitude of the breakdown voltage of the DIAC component -66a with respect to FIG Peak AC voltage depends. The above process is repeated every AC cycle.

The operation of the transmitter -61- is similar to that of the transmitter -6la-, except that the transmitter -61- generates pulses on the opposite half-wave of each sine wave, since the thyristor -62- and the diode -67- are the other way round Thyristor -62a and the diode -67a- are connected. Thus, the two transmitters -61 and 61a-- generate pulses during the opposite half-waves of each oscillation as explained above. However, should it be desired to generate pulses only during the positive part or only during the negative part of each oscillation, one of the two switches -64 and 64a can be closed and the other opened. Of course, transmitters -61 and 61a should be used in conjunction with two detectors designed to respond to pulses generated in opposite half-waves.

The transmitter shown in Fig. 6 also generates a train of pulses during a continuous series of sine waves. The transmitter of Fig. 6 comprises a semiconductor -71- known in the art as TRIAC "and a capacitor -72- connected through a conductor -73- corresponding to conductor -20- of Fig.l. to which the TRIAC device is connected in series. A device with breakdown properties, eg a glow lamp or a DIAC device is connected between the control terminal -76- of the TRIAC device -71- and a point between the TRIAC device and the capacitor -72-. Again, the union of the TRIAC device -71- and the neon lamp -74- forms a breakthrough device. A switch (not shown) may be incorporated into the circuitry of the transmitter of Fig. 6 to start up or shut down the transmitter.

The TRIAC device -71- has operating characteristics similar to those of the thyristor -51-, except that a thyristor passes current in only one direction, while current can flow in both directions through a TRIAC device. The transmitter shown in Fig. 6 thus operates similarly to each of the transmitters of Fig. 4, but generates pulses on both the rising branch and the falling branch of each sine wave. Each time a voltage drop, no matter what the polarity, is equal to the ignition voltage of the neon lamp -74- on the glow lamp, the glow lamp ignites and triggers the TRIAC device into the conductive state. Then charging current flows through the capacitor -72- and it is generated in the manner explained a pulse.

The transmitter shown in Figure 7 comprises a TRIAC device -81-, a capacitor -82- which is connected in series through a conductor -83- to the TRIAC device -81-, and a battery -84-, which is connected between the control terminal of the TRIAC device -81- and the conductor -83- such that the negative terminal of the battery -84- with the control terminal of the

-7Nr.311218

TRIAC component is connected. The positive terminal of the battery -84- is connected to the conductor -83- on the side of the TRIAC device, which is opposite to the capacitor -82-.

A switch (not shown) may be incorporated in the circuit of the transmitter of Fig. 7 to effect its turn-on and turn-off. Assuming that the current path through the TRIAC device -81- is closed, when the sinusoidal voltage source crosses the zero voltage line on the rising branch of the wave train, the TRIAC device -81- will initially be nonconductive, but it will become conductive triggered as soon as the voltage drop across the TRIAC device in conjunction with the DC voltage at the control terminal of the TRIAC device reaches the ignition voltage of the TRIAC device. At this time, the TRIAC device becomes conductive, the capacitor -82- is charged, and a pulse is generated on the supply line. The charging of the capacitor -82- results in a reduction in the voltage drop across the TRIAC device to the point where it becomes nonconductive, as discussed above. On the falling branch of the sine wave, the TRIAC device is again triggered to conduct, discharging capacitor -82- when the voltage drop across TRIAC device -81- reaches its ignition voltage, regardless of the polarity of the voltage drop across the TRIAC -Bauelement.

The transmitter shown in Figure 8 operates similar to the transmitter circuit of Figure 2; a switch (not shown) may be inserted in the power path to control the turning on and off of this transmitter. The transmitter according to Figure 8 comprises a spark gap -86-, a capacitor -87- and a conductor -88-, the spark gap -86- and the capacitor -87- in series with each other and with the

Feeder lines -18 and 19 - connects. The spark gap -86- (for example, a device such as the one on the

The art is known under the trade name Victoreen Type VX-96) has a pair of axially aligned electrodes -89 and 90- mounted on beams -92 and 93-. Electrodes -89 and 90- are electrically isolated from each other, for example, by making carriers -92 and 93- from an electrically insulating material. The two electrodes -89 and 90- are further adjustable in their axial direction, so that the length of the gap -94- between the mutually facing ends of the electrodes can be changed. In the present case, the electrode -89- is movably guided in a hole through the carrier -92- and a locking screw -96- is used to hold the electrode -89- in the set position with respect to the carrier -92-. The electrical connections between the electrodes -89 and 90- and the conductor -88- preferably comprise flexible leads -97- which allow adjustment of the mutual position of the two electrodes -89 and 90-.

In the operation of the transmitter of Figure 8 this is non-conductive, when the voltage drop at the transmitter is relatively low. However, as soon as the voltage drop across the spark gap -86- is sufficient to cause a flashover through the gap -94-, current flows through the spark gap -86- and charges the capacitor -87- until the voltage applied to the gap - 94- Tension has fallen so far that no spark can be kept up. At this time, the spark gap -86- becomes nonconductive and it remains until the voltage drop across it again rises to a value at which sparking occurs between the two electrodes -89 and 90-. The operation of the transmitter according to Figure 8 is of course the same as that of Figure 2 regardless of the polarity of the voltage applied to the transmitter.

Figure 9 illustrates the connection of a transmitter to the supply lines for a three-phase load, eg a three-phase electric motor -101-. The motor -101- has three-phase windings -102, 103 and 104- which are connected via the three supply lines -106, 107 and 108- to a three-phase power source (not shown). The transmitter is connected via two of the three supply lines, in the illustrated example it lies between the supply lines -106 and 107-. Since the transmitter uses only two supply lines, it is of course also suitable for use in single-phase systems. The transmitter includes a glow lamp -109- and a capacitor -lll-, and a normally-temperature-sensitive electrical switch -112- is inserted in the transmitter circuit to control its turn-on and turn-off. A conductor -113- connects the glow lamp -109- and the

Capacitor - lll - in series between the two supply lines - 106 and 107--, another

Conductor -114- connects switch -112- in parallel to the glow lamp -109-.

The switch -112- may be any temperature responsive switch, in the present case an embodiment having a temperature sensitive bimetal element -116-which bends at a predetermined temperature and opens the switch. The bimetallic element -116- of the switch -112- is arranged in suitable heat transfer relationship with one of the windings -102, 103 and 104- such that the position of the switch -112-, ie whether it is open or closed, is an indication of whether the temperature of the associated winding is above or below a predetermined temperature. In the illustrated example, the bimetallic element -116- is disposed opposite to the winding -103-. The switch -112- is preferably designed to open at a temperature which is considered to be too high or dangerously high for the motor -101-.

- 8th -

Nr.311218

Assuming that the temperature of the motor -101- and the switch -112- is below the predetermined temperature, the switch is closed, alternating current flows through the switch -112- and the capacitor -111-, and the switch -112- closes the glow lamp-short. Now, when it happens that the temperature rises above the aforementioned predetermined temperature, the switch -112- opens and brings the glow lamp -109- in series into the current path with the capacitor -111-. Thereafter, the operation of the transmitter of FIG. 9 is similar to that of the transmitter of FIG. A train of pulses flows through the supply lines -106 and 107-, the two windings -103 and 104- and the current source (not shown). A detector for use in the circuit according to Fig. 9 is preferably connected between the two supply lines -106 and 107-, so that both the transmitter and the receiver use the two same supply lines. However, a detector connected between feed lines -107 and 108- would detect pulses generated on feed lines -106 and 107- if capacitor -111- were very large. Such a capacitor would generate high energy pulses which also appear on the supply lines -106 and 107- because of crosstalk between the windings of the supply transformer.

Figure 10 illustrates a complete three-phase AC system in which a transmitter -121- is arranged to respond to the temperature of an AC load -122-, eg, an electric motor, while a detector -123- is turned on so that it can turn on Separation of the motor -122- from a current source -124- causes when the temperature of the motor -122- rises above a predetermined level. The motor -122- has windings -126, 127 and 128- connected together and to three feed lines -129, 131 and 132-; the latter connect the three windings -126, 127 and 128- to the three-phase power source -124-. Three normally-open supply switches -133, 134 and 135- are inserted into lines -129, 131 and 132- between power source -124- and load -122-, respectively. These three switches allow or disable the supply of power to the load -122-. The three switches -133, 134 and 135- are mechanically connected to the armature of a relay which further comprises a relay winding -136-. Relay winding -136- is in a control voltage which further includes a current source -137-, either AC or DC, two conductors -138 and 139- and a normally closed switch -141- in conductor -138-. The connections are made so that when switch -141- is closed, winding -136- is powered by current source -137- and the three switches -133, 134 and

135- are closed. An alarm 142 - which may be an audible or visual alarm, for example - is connected in series between the two conductors -138 and 139- in series with a current limiting resistor -143- and a normally open switch -144-. The two switches -141 and 144- are mechanically connected to simultaneous actuation by the detector circuit -123-, as will be explained below.

The transmitter circuit -121-, which may be one of the embodiments described above, is between the two feed lines -131 and 132-. A switch -146- is connected to the transmitter and spatially arranged to respond to the temperature of at least one of the windings -126, 127 and 128-. In the example shown, the switch -146- is arranged in front of the winding -128-. Now, when the temperature of winding -128- rises above a predetermined value, switch -146- will turn on, turning on transmitter -121- and causing one or more pulses to go through supply lines -131 and 132- Windings -126 and 128- and the current source -124- can flow. The detector -123- detects the presence of the pulse (s) and operates a device -147- which places switch -141- in its open position and switch -144- in its closed position. The opening of the switch -141- causes the current to flow through the winding -136-, closing the switch -144- causes the alarm -142- to turn on. The cessation of current flow through the winding -136- again results in an opening of the three switches -133, 134 and 135- and thus separation of the load -122- from the three-phase current source -124-. Thereafter, the load remains de-energized until an operator removes the cause of overheating the load -122- and returns the system to working position.

As mentioned in the explanation of Figure 9, the temperature-sensitive switch -112- is adjacent to one of the windings, here the winding -103-, and therefore it will respond quickly to a temperature rise of this winding -103-, but it will not respond immediately to a temperature rise in windings -102 and 104-. Accordingly, the embodiment of Fig. 9 does not provide protection against a single-phase "operating condition in which power is applied to windings -102 and 104- but not to winding -103- since the latter winding, which is not energized, will not overheat experiences. The circuit of FIG. 11 is generally similar to that of FIG. 9, but is designed to also provide protection against a single phase operating condition of the type discussed above.

The circuit shown in Fig.ll comprises a three-phase load, such as an electric motor, with

Windings -151, 152 and 153- connected to three feeders -154, 156 and 157-.

-11No.311218 -231- and one indicator lamp -232- connected. As in the detector of Fig. 12, a control glow lamp -233- and a resistor -234- are connected in parallel to the thyristor -219-, and a test transmitter comprising a glow lamp -236- and a capacitor -237- is interposed between the Heads -211 and 212- switched. When the detector is to be tested, a switch -238- is momentarily closed, thereby producing a train of pulses on the conductors -211 and 212-. The relay -218- is a common embodiment in which the contacts -227 and 228- which occupy one position when the coil -217- is energized and the opposite position when the coil -217- is de-energized ,

To consider the operation of the circuit of Figure 13, assume that a train of pulses appears on the conductors -211 and 212-, these pulses being generated either by the test transmitter or by a transmitter connected to the load. The train of pulses passes through the pulse filter -222- and the positive parts are integrated and stored in the integrator circuit -223-. When the potential of the integrator circuit -223- reaches the Zener voltage of the diode -224-, the thyristor -219- is triggered into the conducting state and rectified current flows through the coil -217-, the thyristor -219- and the contacts of the Switch -221-. The current flow through the coil -217- causes the normally closed contact -227- to open and to turn

Close the normally open contact -228-. When the contact -227 - is closed and the

Coil -229- of the main supply switch is fed by the supply voltage AC voltage, the main supply switch is closed; the opening of the normally closed contact -227- stops the flow of current through the coil -229- and thus leads to an opening of the main supply switch. The closing of the contact -228- leads to turning on the indicator lamp -232-, which is again preferably mounted for example on a control panel together with the switch -221-. An operator who sees the indicator light burned thus becomes aware that the main power switch is open, and is cautioned that the load needs service or maintenance. After the load has been rectified or replaced, the switch -221- is momentarily opened, terminating the flow of current through the thyristor -219-. The coil -217- is then de-energized, contact -227- closes and energizes coil -229-, the main power switch closes, and contact -228- opens to turn off indicator lamp - 232--.

Another pulse detector of the type indicated in FIG. 10 is shown in FIG. The detector of Figure 14 comprises two conductors -241 and 242- which connect the detector to the two feeders, eg lines -131 and 132- of Figure 10. A fuse -243- corresponding to the device -147- of Fig. 10 is connected between the two conductors -241 and 242- in series with a normally open relay contact -244-. The contact -244- is replaced by a

Relay coil - 246 - operated. The detector further comprises a pulse filter - 248 - for the most part

Disable the feeder line frequency. The filter output is connected to an integrator -249- in which the pulses are integrated and stored. When the voltage in the integrator reaches a predetermined level, a zener diode -251- will be conductive and a thyristor -252- will be triggered into conduction. The current flowing through the thyristor - 252 - also flows through the relay coil - 246-- connected in series with the thyristor -252-.

The operation of the detector according to Fig. 14 in the arrangement according to Fig. 10 is in summary as follows: A series of pulses appearing on the supply lines and the conductors -241 and 242- is passed through the pulse filter -248- to the integrator -249 - supplied. When the integrator voltage reaches the zener voltage of diode -251-, diode -251- conducts and triggers thyristor -252- into the conductive state, thereby feeding relay coil -246- and closing contact -244-. By closing this contact -244-, the fuse -243- is switched directly between the two supply lines so that it responds and a pin or piston is actuated, which is mechanically connected to the two switches -141 and 144- (Fig.10) is. As explained above, opening the switch -141- causes the load to be disconnected from the power source, while closing the switch -144- triggers the alarm -142-. As with the other detectors discussed herein, a train of pulses over approximately thirty periods of AC line supply voltage is sufficient to conduct the Zener diode -251- into conduction.

It can be seen from these statements that the invention provides a novel device with excellent operating characteristics. A trained according to the rules of the invention transmitter has the advantages of being relatively simple, small and yet extremely robust and reliable; Moreover, it is cheap to manufacture and install. Due to its small size and the fact that it does not require separate conductors for connection to a detector, the transmitter is excellently suited for use in a protection circuit for electric motors and the like, since the transmitter is easily placed in the stator of the stator because of its small size Motors can be mounted close to the windings. In such a system, the detector may be located at a remote location, such as near the power source or in a central location.

Nr.311218

Control station to be arranged. A transmitter arranged in a motor in the above manner is capable of long-lasting and reliable performance, and operates in a satisfactory manner in the low-resistance

Load on the supply system because of the very short pulses.

In the above explanation, the switch connected to control the turn-on and turn-off of the transmitter has been called a heat-responsive switch in most cases. It will be understood, however, that the transmitter may be operated in conjunction with a switch designed to respond to other environmental conditions. For example, the transmitter may find application in a home or building security system and the switch may be configured to respond to heat or smoke, such as when a fire is occurring in a home or building. The transmitter may form part of a burglar alarm system and comprise a switch which is designed and arranged so that it or the like in case of unauthorized opening of a window, a door. is pressed. In such a home or building security system such a connection is suitably made that the pulses generated by the transmitter flow through the AC power supply lines of the house or building to a detector and an alarm device.