CA1220262A - Electronic safety and heat control means - Google Patents
Electronic safety and heat control meansInfo
- Publication number
- CA1220262A CA1220262A CA000435824A CA435824A CA1220262A CA 1220262 A CA1220262 A CA 1220262A CA 000435824 A CA000435824 A CA 000435824A CA 435824 A CA435824 A CA 435824A CA 1220262 A CA1220262 A CA 1220262A
- Authority
- CA
- Canada
- Prior art keywords
- load
- current
- measuring
- temperature
- winding
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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- Control Of Resistance Heating (AREA)
Abstract
ELECTRONIC SAFETY AND TEMPERATURE CONTROL MEANS
ABSTRACT OF THE DISCLOSURE
This invention relates to an electronic safety and heat controlling means, mainly for heat mats and concreting cassettes to be used on building sites. It comprises a temperature regulating device, fuses operating as overload protection, a setting device, a testing device and an indicator to indicate the operative condition of the means.
This electronic means is characterized in that a differ-ential current measuring and control means has been disposed to control the main circuit over a relay on the basis of the difference between the current going to and that returning from the load. A switching means has been disposed to isolate the load from the means when a fuse responds or when one of the mains conductors or the ground conductor breaks.
ABSTRACT OF THE DISCLOSURE
This invention relates to an electronic safety and heat controlling means, mainly for heat mats and concreting cassettes to be used on building sites. It comprises a temperature regulating device, fuses operating as overload protection, a setting device, a testing device and an indicator to indicate the operative condition of the means.
This electronic means is characterized in that a differ-ential current measuring and control means has been disposed to control the main circuit over a relay on the basis of the difference between the current going to and that returning from the load. A switching means has been disposed to isolate the load from the means when a fuse responds or when one of the mains conductors or the ground conductor breaks.
Description
;22~2 Eii2 Electronlc safety and eemperature control means The present lnvention concerns an electronlc ~afety and temperature control means, malnly for heat mats and concreting cassettes to be used on building slte~, as has been stated in the preamble of c]aim 1.
Electromechanlcal safety means of prior art have been found to be unsatlsfactory particularly in outdoor use in adverse conditions, such as for instance in connectlon with heatlng appliances employed on bullding sites, owlng to the tcndency of the heating means to suffer damage, to the humid condieions and to heavy service. When conventional fuses or other overcurrent protection means are u~ed, these interrupt the current ln one lead only, whereby ground con-tact may be established e.g. between another current lead and ground or ground connection, with harmful consequences. Moreover, standard fuses are slow in operation, nor are conventlonal fault current protection switches, their triggering current values usu-ally 30 mA, able in instances of overheating to isolate the heating mat from the mains before the mat has been destroyed. A sltuation like this is encountered when under the carpet is left thermal lagging material, peat, a board stump or other material in such disposition that there la no mechanical thermal cut-out ln th$ heat mat adJacent to it. The rate of increase of the fault current de-pends on the size of the piece of lagging and on the temperature, but its ascent up to the value of 30 mA usually takes more than an hour even though the temperature at the hottest point of the mat i6 over 200 C (F*g~=~t. Such temperatures are dangerous in view of fire safety.
In addition, the mechanical temperature sensors commonly employed in connection with said heating appliances are unsatisfactory since the temperatures of heating means fltted with such vary very con-siderably; moreover, mechanical temperature sensors tolerate no great numbers of switching operations. It may be observed in gener-al that existing safety devices are applicable primarily on dry premises, that being based on a mechanical triggering mechanism
Electromechanlcal safety means of prior art have been found to be unsatlsfactory particularly in outdoor use in adverse conditions, such as for instance in connectlon with heatlng appliances employed on bullding sites, owlng to the tcndency of the heating means to suffer damage, to the humid condieions and to heavy service. When conventional fuses or other overcurrent protection means are u~ed, these interrupt the current ln one lead only, whereby ground con-tact may be established e.g. between another current lead and ground or ground connection, with harmful consequences. Moreover, standard fuses are slow in operation, nor are conventlonal fault current protection switches, their triggering current values usu-ally 30 mA, able in instances of overheating to isolate the heating mat from the mains before the mat has been destroyed. A sltuation like this is encountered when under the carpet is left thermal lagging material, peat, a board stump or other material in such disposition that there la no mechanical thermal cut-out ln th$ heat mat adJacent to it. The rate of increase of the fault current de-pends on the size of the piece of lagging and on the temperature, but its ascent up to the value of 30 mA usually takes more than an hour even though the temperature at the hottest point of the mat i6 over 200 C (F*g~=~t. Such temperatures are dangerous in view of fire safety.
In addition, the mechanical temperature sensors commonly employed in connection with said heating appliances are unsatisfactory since the temperatures of heating means fltted with such vary very con-siderably; moreover, mechanical temperature sensors tolerate no great numbers of switching operations. It may be observed in gener-al that existing safety devices are applicable primarily on dry premises, that being based on a mechanical triggering mechanism
2~;~
they are unrel.iable in operation, in particular at the opposed extreme temperatures and in moist environment.
Earlier attempts to elminate the drawbacks mentioned have the following disadvantages. The principle of fault current measurement is not applicable with low enough fault currents, owing to the sensitivity to disturbances of the measuring principle, if the protection lead is cut off from the mains or there is none, it is stil.l. possibl.e to connec-t the device to the mains and the risk of potential overheating is obvious, the means is not fit to be enclosed in a water--tight housing on account of the heat dissipation of the triac, the means fails to meet the requirements of the fail-safe principle in its operation, because of its measuring principle.
In the art is further known, through the American Patent No.
they are unrel.iable in operation, in particular at the opposed extreme temperatures and in moist environment.
Earlier attempts to elminate the drawbacks mentioned have the following disadvantages. The principle of fault current measurement is not applicable with low enough fault currents, owing to the sensitivity to disturbances of the measuring principle, if the protection lead is cut off from the mains or there is none, it is stil.l. possibl.e to connec-t the device to the mains and the risk of potential overheating is obvious, the means is not fit to be enclosed in a water--tight housing on account of the heat dissipation of the triac, the means fails to meet the requirements of the fail-safe principle in its operation, because of its measuring principle.
In the art is further known, through the American Patent No.
3,727,105, a safety means based on the use of fuses, where in the event of a conductor break on the load side the fuses in one or several current leads will blow. However, the means consumes quite many fuses, and the operation of the means is imperfect inasmuch as the means is not capable of operation if, for instance, the neutral lead breaks on the mains side, nor does it elimina-te the risk of el.ectric shock if in the event of the glass being broken the heating resistance is not cut off. It should also be noted that the operation of the means is not based on measuring the fault current and on triggering in accordance with its intensity.
The object of the present invention is to eliminate -the drawbacks presented in the foregoing. In particular, the object of the invention is to provide a safety and temperature control means for heating appl.iances which is substantially more reliable in use, and better appl.icabl.e in humid or even wet, and severe and wearing, condi-tions, than those of prior art and in which the values of the fault curren-t and of the temperture are steplessly adjustable to be proper for each instance of application.
Regarding the features which are characteristic of the invention.
~ 3 - ~Z~2~2 reference is made to the claims section.
The eletronic safe~y and heat controlllng means of the invention affords substantially greater safety than any of prior art, partic-ularly as regards fire protectlon. In the event of impending fire or other danger, the means takes care of enforced control. No in-terference is caused since the temperature coneroller operates according to the neutral point switch principle. In the event that a phase, neutral or ground conductor of the malns network supplying the means is interrupted or a fuse blows, the safety device compo-nent will totally disconnect the load from the mains.
The inventlon is described in the following in detail with the aid of an embodiment example, wlth reference belng made to the attached drawings, wherein:-Fig. 1 illustrates graphically the local heating up of con~entionalheatiQg mats when the point sub~ect to temperature rise is isolated from its environment, and the equlvalent fault current, Fig. 2 prescnts a block diagram describing the mode of operation of the means, and Fig. 3 presents a block diagram of the circuitry of the means.
In Fig. 1 has been shown, ln the top part, the normal temperature of a conventional heating mat with an interrupted line, and that of a point of the mat isolated from the environment, by a solld line, during the heating phase. As the figure reveals, the temperature of a point of the mat isolated from the environme~t, e.g. whe~ under the mat there is thermal lagging material, peat, a board stump, etc., tends to rise slgnificantly past the normal operating temper-ature of the mat. But this causes the fault current to begin to rise. The rate of the rise of the fault current depends on the size of the insulatlng body and on the temperature, and the growth of the fault current up to e.g. 30 m~ usually takes several hours, although the temperature at the hottest point of the mat (E~olid line) ls higher than 200C, becau~e the ~rowth of the fau~t current 22(~2~2 wltll time i9 only regular, owing to the fast change of temperature, up to a few milliamp6 and the fault current may instead be constant e.g. at 15 mA even for several hours. Such overheatlng naturally entalls the risk of deseruction of the mat, and general fire hazard, and the power supply to the mat ~ust therefore be lnter-rupted at a very low fault current already, e.g. at 0.5 mA. In the lower part of Fig. 1 is also seen how the fault current increases, as a function of tlme, in the instance ~ust considered (dot-and-dash line).
~lg. 2 displays the safety ~eans 15 for controlling a heatlng means 16, such as a heating mat or a concreting cassette. The power supply 17, that i9 current from the mains, is introduced in the control device constituted by the means, and further as operating power 18, controlled by the means, to the heating appliance 16 proper. The operation of the heating appliance 16 i3 monitored by the aid of observing l9 the difference of the current going to the heating appliance and that returning therefrom, i.e. the differen-tial current~ and observing 20 ehe temperature. The safety and tem-perature controlling means comprises a pilot lamp 21 indicating when the apparatus is in operation, a buzzer 22 notifying of a dis-turbance condition, a test button 23, by the aid of which the proper functionlng of the means is tested, a reset push-button 24 by the aid of which the me~ns i5 set to be operative, and a temper-ature regulating means 25, by the aid of which the temperature of the heating appliance 16 is ad~usted.
The safety device part 15 has been arranged to lnterrupt the power supply to the heating appliance 16 in the event of disturbance.
Furthermore, the 3afety device part has been dlsposed to switch the heating power 18 on again after the potential disturbance of power supply 17 has ceased to exist.
Fig. 3 shows in detail the principle de3ign of the safety and temperature control means.
In Fig. 3 is seen the means of the invent~on, disposed in connec-tion with a heating mat A~ intended to serve a ground frost thawing _ 5 - ~ 2 ~ ~ 2 ~ 2 application. The safety mean5 comprlses a safety device 8etting me3ns 7, a testlng means 7', an indicator, such a~ a pilot llght 8, to 1ndicate that the device is operating, a temperature ad~usting means 9 and main circuit cut-out means, i.e. fuses 10. As taught by the invention, the means further includes a current transformer Ml measuring the difference between the current golng to the load and that returning therefrom and in which the differential current of the phase and zero leads is compared ~lth a reference current pro-duced in the winding 3. When the current difference between the windings 1 and 2 exceeds or equals the current in the winding 3, the phase of the current in the measuring winding 5 will shift through 180 or the amplitude will fall to zero. The transformer M2 forms a reference signal coinciding in phaQe with the current de parting from the winding 3. For the appliance to be connected to the malns and for current to begin to flow ln the windings 3, cur-rent is to begln with bri~fly applied to the winding 4, so that a negative voltage is obtained and the cut-out relay 11 attracts its armature. Damage of any compor.ent whatsoever in the circuit causes no voltage across the relay. The reference current < 1 mA passing through the windings 3 is supplied to the ground lead, and in case the ground lead is broken, no signal w~ll be obtained from the transformer Ml and the appliance will not become connected to the network. The controller 9 i~ composed of a micro circult intended for neutral point switching.
With a~vie~ to reducing the heat dissipation of the triac 12, a relay JhS has been added in parallel with the triac. By this circuit is obtained a connection free of interference, and interruption always at the neutral point, as ~ell as an extremely long ser~ice life for the relay, since it is not required to make or break con-nection under voltage. Information concerning the true temperature of the load,~ is obtained Erom a sensor member 13 placed outside the load.
Prevention of overheating ha~ also been ensured by means of a me-chanical thermal cut-out 14, mounted in con~unction with the load 6, for lnstance coinclding in location with the sensor element 13.
2~2 The safety and heat control apparatus of the ~nventlon i9 preferab-ly built to be waterproof, whereby its use becomes possible even in humid and wet location3. The means affords complete user safety because no live parts are acce~sible. Slnce the temperature control means operates according to the neutral polnt 8witchlng principle, the means will cause no lnterference in the environ~ent. The tem-perature i3 controllable with very hlgh accuracy, enabling the thermal durability of the materials entering the construction of the load to be optimally utlllzed. As output stage, a relay has been used, whereby two-pole or multiple-pole circult breaking action can be implemented. The means operates reliably at any oper-ating temperature and in any operating conditlons.
As will be obvious to a person skllled ln the art, the indlvldual operative blocks of the mean~ can be carried out in many different ways lndeed, as regards circuit technology, without departing from wlthin the protective ~cope of the clalms.
The object of the present invention is to eliminate -the drawbacks presented in the foregoing. In particular, the object of the invention is to provide a safety and temperature control means for heating appl.iances which is substantially more reliable in use, and better appl.icabl.e in humid or even wet, and severe and wearing, condi-tions, than those of prior art and in which the values of the fault curren-t and of the temperture are steplessly adjustable to be proper for each instance of application.
Regarding the features which are characteristic of the invention.
~ 3 - ~Z~2~2 reference is made to the claims section.
The eletronic safe~y and heat controlllng means of the invention affords substantially greater safety than any of prior art, partic-ularly as regards fire protectlon. In the event of impending fire or other danger, the means takes care of enforced control. No in-terference is caused since the temperature coneroller operates according to the neutral point switch principle. In the event that a phase, neutral or ground conductor of the malns network supplying the means is interrupted or a fuse blows, the safety device compo-nent will totally disconnect the load from the mains.
The inventlon is described in the following in detail with the aid of an embodiment example, wlth reference belng made to the attached drawings, wherein:-Fig. 1 illustrates graphically the local heating up of con~entionalheatiQg mats when the point sub~ect to temperature rise is isolated from its environment, and the equlvalent fault current, Fig. 2 prescnts a block diagram describing the mode of operation of the means, and Fig. 3 presents a block diagram of the circuitry of the means.
In Fig. 1 has been shown, ln the top part, the normal temperature of a conventional heating mat with an interrupted line, and that of a point of the mat isolated from the environment, by a solld line, during the heating phase. As the figure reveals, the temperature of a point of the mat isolated from the environme~t, e.g. whe~ under the mat there is thermal lagging material, peat, a board stump, etc., tends to rise slgnificantly past the normal operating temper-ature of the mat. But this causes the fault current to begin to rise. The rate of the rise of the fault current depends on the size of the insulatlng body and on the temperature, and the growth of the fault current up to e.g. 30 m~ usually takes several hours, although the temperature at the hottest point of the mat (E~olid line) ls higher than 200C, becau~e the ~rowth of the fau~t current 22(~2~2 wltll time i9 only regular, owing to the fast change of temperature, up to a few milliamp6 and the fault current may instead be constant e.g. at 15 mA even for several hours. Such overheatlng naturally entalls the risk of deseruction of the mat, and general fire hazard, and the power supply to the mat ~ust therefore be lnter-rupted at a very low fault current already, e.g. at 0.5 mA. In the lower part of Fig. 1 is also seen how the fault current increases, as a function of tlme, in the instance ~ust considered (dot-and-dash line).
~lg. 2 displays the safety ~eans 15 for controlling a heatlng means 16, such as a heating mat or a concreting cassette. The power supply 17, that i9 current from the mains, is introduced in the control device constituted by the means, and further as operating power 18, controlled by the means, to the heating appliance 16 proper. The operation of the heating appliance 16 i3 monitored by the aid of observing l9 the difference of the current going to the heating appliance and that returning therefrom, i.e. the differen-tial current~ and observing 20 ehe temperature. The safety and tem-perature controlling means comprises a pilot lamp 21 indicating when the apparatus is in operation, a buzzer 22 notifying of a dis-turbance condition, a test button 23, by the aid of which the proper functionlng of the means is tested, a reset push-button 24 by the aid of which the me~ns i5 set to be operative, and a temper-ature regulating means 25, by the aid of which the temperature of the heating appliance 16 is ad~usted.
The safety device part 15 has been arranged to lnterrupt the power supply to the heating appliance 16 in the event of disturbance.
Furthermore, the 3afety device part has been dlsposed to switch the heating power 18 on again after the potential disturbance of power supply 17 has ceased to exist.
Fig. 3 shows in detail the principle de3ign of the safety and temperature control means.
In Fig. 3 is seen the means of the invent~on, disposed in connec-tion with a heating mat A~ intended to serve a ground frost thawing _ 5 - ~ 2 ~ ~ 2 ~ 2 application. The safety mean5 comprlses a safety device 8etting me3ns 7, a testlng means 7', an indicator, such a~ a pilot llght 8, to 1ndicate that the device is operating, a temperature ad~usting means 9 and main circuit cut-out means, i.e. fuses 10. As taught by the invention, the means further includes a current transformer Ml measuring the difference between the current golng to the load and that returning therefrom and in which the differential current of the phase and zero leads is compared ~lth a reference current pro-duced in the winding 3. When the current difference between the windings 1 and 2 exceeds or equals the current in the winding 3, the phase of the current in the measuring winding 5 will shift through 180 or the amplitude will fall to zero. The transformer M2 forms a reference signal coinciding in phaQe with the current de parting from the winding 3. For the appliance to be connected to the malns and for current to begin to flow ln the windings 3, cur-rent is to begln with bri~fly applied to the winding 4, so that a negative voltage is obtained and the cut-out relay 11 attracts its armature. Damage of any compor.ent whatsoever in the circuit causes no voltage across the relay. The reference current < 1 mA passing through the windings 3 is supplied to the ground lead, and in case the ground lead is broken, no signal w~ll be obtained from the transformer Ml and the appliance will not become connected to the network. The controller 9 i~ composed of a micro circult intended for neutral point switching.
With a~vie~ to reducing the heat dissipation of the triac 12, a relay JhS has been added in parallel with the triac. By this circuit is obtained a connection free of interference, and interruption always at the neutral point, as ~ell as an extremely long ser~ice life for the relay, since it is not required to make or break con-nection under voltage. Information concerning the true temperature of the load,~ is obtained Erom a sensor member 13 placed outside the load.
Prevention of overheating ha~ also been ensured by means of a me-chanical thermal cut-out 14, mounted in con~unction with the load 6, for lnstance coinclding in location with the sensor element 13.
2~2 The safety and heat control apparatus of the ~nventlon i9 preferab-ly built to be waterproof, whereby its use becomes possible even in humid and wet location3. The means affords complete user safety because no live parts are acce~sible. Slnce the temperature control means operates according to the neutral polnt 8witchlng principle, the means will cause no lnterference in the environ~ent. The tem-perature i3 controllable with very hlgh accuracy, enabling the thermal durability of the materials entering the construction of the load to be optimally utlllzed. As output stage, a relay has been used, whereby two-pole or multiple-pole circult breaking action can be implemented. The means operates reliably at any oper-ating temperature and in any operating conditlons.
As will be obvious to a person skllled ln the art, the indlvldual operative blocks of the mean~ can be carried out in many different ways lndeed, as regards circuit technology, without departing from wlthin the protective ~cope of the clalms.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Electronic safety and heat control means for a load connected to a power supply, including a temperature regulat-ing device connected to the load, fuses connected between the load and the power supply for overload protection, a setting device, a testing device, an indicator to indicate the opera-tive condition of said means and a differential current meas-uring and control means measuring the difference between cur-rent flowing to and returning from the load and having a measuring transformer including first and second windings in the phase and neutral conductors, characterized by a refer-ence winding and a measuring winding in said measuring trans-former arranged so that the current difference between the first and the second windings is compared to a reference cur-rent in the reference winding and when said current differ-ence exceeds or equals said reference current, the phase of the current in the measuring winding will shift through 180°
or the amplitude will fall to zero.
or the amplitude will fall to zero.
2. The invention claimed in claim 1, characterized in that it includes a second measuring transformer comprising corresponding reference and measuring windings and forming a reference signal of the same phase with the current in the reference winding so that by comparing the phases of measur-ing transformers interruption is carried out.
3. The invention claimed in claim 1 or 2, character-ized by a bimetalic pick-up arranged to sense the temperature of the load and connected to said temperature regulating device.
4. The invention claimed in claim 1 or 2, character-ized by a semiconductor component connected in one of said mains conductors and a thermal fuse arranged to prevent over-heating of the semiconductor component in the event of a mal-function.
5. The invention claimed in claim 1 or 2, character-ized in that said temperature regulating device operates in accordance with the principle of neutral point switching.
6. The invention according to claim 1 or 2, character-ized by a semiconductor component connected in one of said mains conductors and a relay adapted to short-circuit said component except in switching situations, in order to reduce power losses due to heating.
7. The invention claimed in claim 1, characterized by an external pick-up for detecting the temperature of the load and connected to said temperature regulating device.
8. The invention claimed in claim 7, characterized in that the load is a heat mat having a power supply cable, and in that said pick-up is disposed in said cable.
9. The invention claimed in claim 8, characterized in that said pick-up has a time constant matched to the heating characteristics of the heat mat.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000435824A CA1220262A (en) | 1983-08-31 | 1983-08-31 | Electronic safety and heat control means |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000435824A CA1220262A (en) | 1983-08-31 | 1983-08-31 | Electronic safety and heat control means |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1220262A true CA1220262A (en) | 1987-04-07 |
Family
ID=4125985
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000435824A Expired CA1220262A (en) | 1983-08-31 | 1983-08-31 | Electronic safety and heat control means |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1220262A (en) |
-
1983
- 1983-08-31 CA CA000435824A patent/CA1220262A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |