GB2495349A - Heating cable having a calibration wire - Google Patents
Heating cable having a calibration wire Download PDFInfo
- Publication number
- GB2495349A GB2495349A GB1203998.8A GB201203998A GB2495349A GB 2495349 A GB2495349 A GB 2495349A GB 201203998 A GB201203998 A GB 201203998A GB 2495349 A GB2495349 A GB 2495349A
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- heating
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- electrical power
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 277
- 238000000034 method Methods 0.000 claims description 17
- 230000035876 healing Effects 0.000 claims description 5
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- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 16
- 229910045601 alloy Inorganic materials 0.000 description 7
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 229910000990 Ni alloy Inorganic materials 0.000 description 4
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 3
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- 229910000599 Cr alloy Inorganic materials 0.000 description 3
- 229910000881 Cu alloy Inorganic materials 0.000 description 3
- 239000011651 chromium Substances 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 239000010949 copper Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 239000004020 conductor Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000003139 buffering effect Effects 0.000 description 1
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- 229910052804 chromium Inorganic materials 0.000 description 1
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- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
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- 238000010276 construction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 239000008236 heating water Substances 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
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- PXHVJJICTQNCMI-OIOBTWANSA-N nickel-56 Chemical compound [56Ni] PXHVJJICTQNCMI-OIOBTWANSA-N 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B1/00—Details of electric heating devices
- H05B1/02—Automatic switching arrangements specially adapted to apparatus ; Control of heating devices
- H05B1/0227—Applications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/0019—Circuit arrangements
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/0033—Heating devices using lamps
- H05B3/0038—Heating devices using lamps for industrial applications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/34—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater flexible, e.g. heating nets or webs
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/40—Heating elements having the shape of rods or tubes
- H05B3/54—Heating elements having the shape of rods or tubes flexible
- H05B3/56—Heating cables
Landscapes
- Control Of Resistance Heating (AREA)
Abstract
A heating controller includes a source of electrical power for outputting electrical power to a heating cable which includes at least one heating element 150,152 and a calibration wire 156 that is substantially the same length as the heating element and has a substantially temperature independent resistance. The cable heating controller (fig 1, 102) includes a controller that determines the resistance of the calibration wire; calculates from it the length of the heating element; and controls the electrical power source to deliver power to the heating element according to its length. The resistance can be determined using a voltage divider, a low pass filter and an analogue to digital converter input to a microprocessor. The controller can calculate the resistance of the element from a resistance per unit length and the calculated length and can measure the ambient temperature using a sensor (fig 1, 122). The source of power can be controlled by its duty cycle and can deliver a higher power depending on whether the temperature is below a threshold. Different power settings can be input by a user. By determining the length of cable attached to it the controller can be used with different lengths of cable.
Description
Cable Heating The present invention relates to a cable heating and in particular to a single controller for a cable heating system which can be used with healing cables of different lengths.
Cable heating systems are generally known and comprise a controller and a heating cable in which the controller includes an electrical power supply which applies a voltage to at least one conductive element within a cable which generates heat via ohmic heating owing to the finite resistance of the conductive element. For example a cable heating system is described in U.S. Patent Application Publication No. 2008/0251509 owned by the applicant.
There are a wide variety of app}ications for cable healing systems. Some of these involve the use of different lengths of heating cable. For example, as described in the above reference US Patent Application, when used in electric blankets of different sizes, different length cables may be used. As another example, cable heating systems can be used to heat pipes, such as water pipes, to prevent damage to the pipes owing to low temperatures, such as damage by frozen water. Again, depending on the length of pipe to be heated a different length of cable may be required.
It is preferable to be able to provide a single controller which can be used with different lengths of heating cable. Different lengths of heating cable will typically present a different total resistance to the controller and so the controller needs to be able to determine the resistance of the cable attached to it in order to ensure that the correct electrical power is supplied by the controller to the cable. Also, it is often desirable for a cable heating system to be able to deliver different amounts of power, to the same length of cable, so as to optimise the heat delivered by the cable to the environment through which the cable will pass. The resistance of the heating element of the cable will vary with temperature. However, it cannot be known in advance exactly what environment the heating cable is going to be used in, what temperatures the heating clement is going to experience and hence what the resistance of the heating element is going to be, even if its length were kept fixed and only a single power level were provided by the controller.
Hence, the controller needs to have some mechanism for determining the resistance of the heating element or elements without foreknowledge of the environment in which the cable is going to be used.
Also, if the environment experiences particularly low temperatures, it can be preferable to provide increased heat so as to reduce the time taken to increase the heat of the entity being heated by the cable. Again, in order to determine the appropriate electrical power to supply tG the cable, the controller needs to be able accurately to determine the actual resistance of the heating element or elements.
It would therefore be beneficial to provide a mechanism by which a cable heating controller can easily determine the resistance of the heating element of the cable attached to it in situ.
A first aspect of the invention provides a cable heating controller for a cable heating system, including a source of electrical power for outputting electrical power to a heating cable. The heating cable includes at least one heating element and a calibration wire. The calibration wire and heating element have substantially the samc length. The calibration wire has a substantially temperature independent resistance. A controller is configured to determine the resistance of the calibration wire, calculate the length of the heating element from the determined resistance, determine the electrical power to output to the heating element using the calculated length and control the source of electrical power to deliver the determined electrical power to the heating element.
Thc controller can reliably determine the length of the heating element, at any temperature, as the resistance of the calibration wire does not change with temperature, and has same length as the heating element. Once the length of the heating element is known, the controller can deteni-uine what electrical power is required to provide a desired heating effect and hence control the power supply to meet that target heating effect.
The calibration wire can have a temperature coefficient of resistance of less than 0.3% per °C, preferably less than 0.1% per DC, more preferably less than 0.05 per DC and most preferably not more than 0.01% per °C.
The calibration wire can be made from an alloy. The alloy can include nickel. Preferably the alloy is an alloy of nickel/chromium/iron or nickel/copper. Prefcrably the calibration wire is made of an alloy comprising approximately 80% nickel and 20% cluomium or approximately 44% nickel and 56% copper. The nickel/copper alloy has good temperature independent resistance but its resistance range is less good and it is more costly than the nickel/chromium alloy which can therefore he preferred in some applications.
The controller can store the resistance per unit length for the calibration wire.
Determination of the length of the heating element can use the resistance per unit length of the calibration wire and the determincd resistance of the calibration wire.
The controller can be further conflgjircd to determine a resistance per unit length associated with the calculated length. The controller can further be configured to calculate the resistance of the heating element using the determined resistance per unit length.
The controller can store a plurality of different values of resistance pcr unit length, each associated with a different range of heating clcment lengths. This allows the sainc controller to be used with a plurality of heating cables of different lengths.
The controller can fUrther be configured to determine a duty cycle corresponding to the determined electrical powcr to output to the heating element. The duty cycle can be used to control the source of electrical power.
The controller can further he configured to determine a first electrical power to output to the heating element at a temperature above a first temperature and/or a second electrical power to output to the heating element at a temperature below the first temperature. The second electrical powcr can bc greater than the first electrical power.
The controller can further be configured to determinc that no electrical power should be output to the heating element at a temperature above a second temperature. The second temperature can be peater than the first temperature. The controller can further be configured to control the supply of electrical power to not supply electrical power to the heating element when the ambient temperature is above the second temperature.
The first temperature can be not more than zero °C. The first temperature can be not more than -5°C, preferably -10°C.
The second electrical power can be at least 10% greater than the first electrical power, preferably at least 20% greater, more preferably at least 30% greater and can be 50% greater.
The heating ccmtroller can further comprise a temperature sensor for mcasuring an ambient temperature of an environment in which the controller or the heating cable is located.
The controller can further be configured to determine the current ambient temperature and decrease the electrical power output to the heating element when the ambient tcmperature exceeds a first temperature.
The controller can further be configured to control the source of electrical power to deliver the second electrical power to more than one heating clement. The second elcctrical power can be delivered to two heating elements, at least two heating elements or more.
The cable heating controller can further comprise an input by which a user can select one of a plurality of different output power settings. The input can be in the form of a plurality of switches, such as DIP switches. The controller can have at least two or at least three, or more, different output power settings.
The controller can further comprise circuitry including at least one resistor with a known resistance. The circuitry can include a junction at which the calibration wire can be electrically connected to form a voltage divider. The voltage divider can be used to determine the resistance of the calibration wire. The controller can be configured to apply a known voltage to the resistor. The circuitry can be arranged to measure the voltage at the junction.
The circuitry can further include a low pass filter and/or an amplificr The low pass filter and amplifier can be connected in series to the junction. The amplifier can have a programmable gain. The circuitry can further comprise a filter to remove or reduce mains frequency interference, for example at about 50Hz or fi0llz.
Said circuitry can further comprise an analog to digital converter. The analog to digital converter can be in communication with an output of the amplifier.
Said circuitry can further comprise a microprocessor.
A second aspect of the invention provides heating cable for a cable heating, system, comprising: at least one heating element; and a calibration wire, wherein the calibration wire and heating element have substantially the same length and the calibration wire has a substantially temperature independent resistance.
The heating cable can comprise a plurality of heating elements. The calibration wire can be substantially the same length as each or all of the heating elements.
A third aspect of the invention provides a cable heating system comprising: a cable heating controller according to the first or fourth aspect of the invention, and any preferred features thereof; and a heating cable according to the second aspect of the invention, and any preferred features thereof.
A fourth aspect of the invention provides a cable heating controller for a cable heating system, comprising: a source of electrical power for outputting electrical power to a heating cable, the heating cable including at least one heating clement; and a controller, wherein the controller is configured to: detennine an ambient temperature; determine a first electrical power to output to the heating element at a temperature above a first temperature and a second electrical power to output to the heating element at a temperature below the first temperature, wherein the second electrical power is -eater than the first electrical power; and control the source of electrical power to deliver the second electrical power to the heating element while the ambient temperature is below the first temperature and to deliver the first electrical power to the heating element if the ambient temperature is above the first temperature.
By determining the length of the heating element, the controller can accurately determine what electrical power to supply and so in many instances it will be possible to increase the electrical power supplied to the heating element when desired, for example if the ambient temperature is less than a threshold temperature. Hence, it is possible to apply more electrical power at lower temperatures so as to reduce the time otherwise needed to heat up an entity to which the heating cable is applied.
The controller can further be configured to determine a first duty cycle corresponding to the first electrical powcr arid a second duty cycle corresponding, to the second electrical power and to control the source of electrical power using, the appropriate duty cycle. The second duty cycle can be at least 10%, 20%, 30%, 40% or 50% greater than the first duty cycle.
The controller can further be configured to control the source of electrical power to deliver the second electrical power to a plurality of heating elements while the ambient temperature is below the first temperature.
The controller can further be configured to control the source of electrical power to deliver the first electrical power to fewer than the plurality of heating elements if the ambient temperature is above the first temperature.
The controller can further be configured to control thc source of electrical power to deliver the first electrical power to a single heating element if the ambient temperature is above the first temperature.
Preferred features of the first aspect of the invention can also be preferred features of the fourth aspect of the invention.
A fifth aspect of the invention provides a method fix controlling a heating cable, wherein the heating cable includes at least one heating element and a calibration wire, the calibration wire and heating element having substantially the same length and the calibration wire having a substantially temperature independent resistance, the method comprising: detennining the resistance of the calibration wire; calculating the length of the heating element from the determined resistance; determining the electrical power to output to the heating element using the calculated length; and controlling a source of electrical power to deliver the determined electrical power to the healing element.
Counter part method features to the preferred features of the first aspect of the invention can also be preferred features of the fifth aspect of the invention.
A sixth aspect of the invention provides a method for controlling a heating cable, wherein the heating cable including at least one heating element having a length, the method comprising: determining the length of the heating element; determining, using the determined length, a first electrical power to output to the heating element at a temperature above a first temperatire; determining a second electrical power to output to the heating element at a temperature below the first temperature, wherein the second electrical power is greater than the first electrical power; detenrii*ning an ambient temperature; and controlling a source of electrical power to deliver the second electrical power to the heating element while the ambient temperature is below the first temperature and to deliver the first electrical power to the heating element if the ambient temperature is above the first temperature.
Counter part method features to the preferred features of the fourth aspect of the invention can also be preferred features of the sixth aspect of the invention.
An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a schematic diagram of a cable heating system according to the invention, including a cable hcating controller according to the invention and a heating cable according to the invention; Figure 2 shows a perspective view of a section through the heating cable of the invention; and Figure 3 shows a process flow chart illustrating a method of controlling a cable heating system according to the invcntion.
Like items in different Figures share common reference signs unless indicated otherwise.
Figure 1 shows a schematic circuit diagram of a cable heating system 100 according to an aspect o-f the invention and including a controller 102 also according to an aspect of the invention and a heating cable 104 further according to an aspect of the invention.
S
The cable healing controller 102 comprises a power supply controller 110 and a microprocessor 112 in communication with the power supply controller 110. The power supply controller 110 includes a transformerless power supply 114 which also includes a system voltage regulator which provides various signals at different voltages used by other parts of the overall controller 102. The power supply controller 110 also includes a bank of DIP switches 116 by which a user can selcct one of a plurality of different power outputs to be supplied by the controller 102. For example, the controller 102 can supply three different power outputs, 10W/rn, 15W/rn or 20W/rn.
The controller 102 includes an input for a mains power supply 118. A connector is also provided for a lead 120 for a temperature sensor 122 which can be used to sense the ambient temperature Tamb in the environment of the heating system 100 and in particular the environment of the heating cable. A suitable temperature sensor 122 would be an NTC thermistor temperature probe such as an AT-I 1 thermistor as provided by ATC Semitec Ltd of Northwich, Cheshire, the United Kingdom. The ambient temperature sensor provides a signal indicative of the sensed temperature as an input to the microprocessor 112. The controller 102 is generally earthcd 124 using any suitable approach.
The controller 102 includes circuitry 126 used to determine the length of the hcating cable 1 04 attached to thc controller 102. The circuitry generally provides a voltage divider including a reference or standard resistor (Rs) 128 and a temperature independent resistance (Rt) 130 provided by a length of electrically conducting wire 158 within cable 104. A calibration voltage Vi of about SV (+/-2.5%) can be applied by the system voltage regulator to the reference or standard resistor 128 which has a resistance of about SOOkOhrn. At a junction 132 a voltage Vo is measured and supplied to a low-pass filter 134 having a cut-off frequency of approximately 250Hz. The output of the low-pass filter 134 is fed to a programmable gain amplifier 136 with its gain set to thirty two. The amplifier provides no buffering and its output follows the input signal quickly.
The output of the amplifier 136 is provided as an input to an analog to digital converter (A/D) 138 which also receives a reference voltage signal (Vrcf') 140 from the system voltage regulator. Vrcf can be set at about 5V, but if Yref is set at 4.09EV, and if a 12-bit A/D is used, then the A/D 138 output fed to the microprocessor is lmV per bit which helps to simplify the microprocessor software. The low-pass filter 134 and amplifier 136 help to improve the accuracy of cable 104 length measurement by the AID. A digital 5-tap finite impulse response filter (not shown) tuned to reject noise at mains frequency (e.g. 50}-Iz in the United Kingdom and other countries or 60Hz in the United States and other countries) can also be included in order to help remove any mains interference signals.
Figure 2 shows a perspective view of the construction of the heating cable 104 and an equivalent schematic circuit diagram of the heating cable 104 is shown in Figure 1. The heating cable 104 includes a first 150 and a second 152 heating element each in the form of a plurality of wires with an insulating coating. The cable 104 also includes an earth wire 154. The cable 104 also includes a calibration wire 156. The calibration wire 156 has a central conductor 158 made from an electrically conducting material which has a substantially temperature independent resistance over the typical operating temperature range of the cable heating system 100. The calibration wire 156 has an insulating outer 160. The temperature independent resistance wire 158 can he made from an alloy of 80% nickel and 20% chromium. The resistance per meter of a wire made of such a material can be approximately 40 ohms/rn. This material has a tcmpcrature coefficient of resistance (TCR) of approximately 0.01% per 0(1 However, other materials arc also suitable, such as alloys of nickel/chromium/iron and nickel/copper. For example a 44% nickel 56% copper alloy can be used, but it has a less good resistance range and is more expensive and therefore maybe less suitable for sonic applications. Any material with a TCR of less than about 0.1% per °C can be suitable.
In order to provide the required heat output, the resistance per meter of the wire of the heating elements requires certain alloys to be used, such as copper alloys. However, such alloys have a reasonably high temperature coefficient of resistance, e.g approximately 3.9% per 10°C. Hence, the resistance of the heating elements cannot be used to rejiably detemñne the length of the cable as it will vary considerably depending on the ambient temperature of the environment in which the cable has been installed.
Finally, heating cable 104 also includes a foil earth cover 162 and an outer protective coating 164 made of an ultra-tough polymer. A heating cable 104 so constructed can have an outer diameter of approximately 6.4mm, a power range of approximately 100W to 3000W (at the three heating power settings of 10W/rn, 15W/rn and 20W/rn) and an operating ambient temperature range of approximately -40 °C to +105°C.
The heating cable 104 can be provided in a plurality of different lengths (as illustrated by the dashed line segments in Figure 1) so as to heat different length entities. For example, Table I below lists eight different standard lengths of heating cable 104, the range of length over which each cable can be used and the resistivity per meter of the heating elements 150, 152 for each length.
Cable No. Length Range/rn Resistance Ohms/rn lOtol8 17.7 2 18to30 6.4 3 30to50 2.3 4 50to85 0.8 85to120 0.3 6 l2Oto 184 0.17 7 184 to 240 0.099 8 240 to 300 0.064
Table I
As illustrated in Figure 1, after a heating cable has been cut to length, each of the two heating cores 150, 152 is connected at each end to tenninals of the power supply controller 114, the earth cable 154 is earthed to the controller 102. One end of the calibration resistance wire 158 is connected to a neutral terminal of the AC supply which is used as the DV potential in the transformerless power supply 114 and the other end is connected to junction 132. As the calibration wire is built into the heating cable 104 with the two heating elements 150, 152, when the heating cable 104 is cut to length, the calibration wire 158 will automatically be cut to substantially the same length as the heating elements 150, 152. The calibration wire then presents a substantially temperature independent resistance, Rt, which can he used by the controller to determine the length to which the cable has been cut. irrespective of the environment in which the cable heating system has been installed, and hence the resistance of the heating elements for that length and hence the power to be output to the heating elements can be determined.
Figure 3 shows a process flow chart illustrating a method 300 of operation of the cable heating controller 102 which includes determining the length of the heating cable 104.
Microprocessor 112 includcs non-volatile memory storing instructions in the form of a suitable computer program which can be executed to implement the logic illustrated in Figure 3. The microprocessor can also access pcrsistcntly stored data relating to various properties of the different heating cables 104 that can be attached to the heating controller 102, such as their range of operating lengths, resistance per unit length and any other data required by the microprocessor in order to carry out the method. The microprocessor may also receive data needed to carry out its operations from various electrical signals supplied to it by other parts of the controller 102, such as the output of AID 138. The microprocessor 112 may also output various electrical signals as control or data signals to other parts of the controller 102, such as the power supply controller 114 in order to set or vary the duty cycle of the power supply controller.
At stcp 302 the resistance Rt of the calibration wire 158 is determined by the microprocessor. As mentioned above, the standard rcsistor 128 and the resistance of the calibration wire 158 form a voltage dividcr to which a known voltage Vi is applied. The voltage Vo at junction 132 is given by: Vo = Vi x (Rt/(Rt+Rs)). Hence, by measuring Vo, the microprocessor can determine Rt from: Rt (Vo x Rs)/(Vi -Vo). Values of Rs and Vi are stored in non-volatile memory in the microprocessor. Flence, to calculate Rt only Vo needs to be found. The output of the analog to digital converted A/Dout is representative of Vo: A/flout = Vo x G x (no. of AID bits)/Vref, where G is the gain of amplifier 136 and "no. of A/D bits" refers to the resolution of the analog to digital converter 138. For example, if the AID 138 is a ten bit device then no. of A/D bits = 2A10 = 1024. Hence, the microprocessor rcccives A/Dout and can calculate Vo using Vo = (AIDout x Vref)/(G x no. of A/D bits). Hence, the microprocessor 112 can determine Rt for thc attached cable. As the calibration wire is made from a material with a substantially temperature independent resistance, the determined value of Rt can reliably be used to accurately determine the length of the heating cable attached irrespective of the environment in which the cable heating system 100 is installed.
-Once Rt is determined at step 302, the microprocessor 112 then determines 304 the length of the overall heating cable 104 that is attached to the heating controllerl 02. The microprocessor has. access to a persistently stored value of the resistance per metre of the material of the calibration wire and hence the length of the calibration wire 158, and therefore of the heating cable 104, is simply given by Rt divided by resistance pcr mctcr.
At step 306, the microprocessor determines the power setting of the cable heating controller 102 by reading a signal from the DIP switch unit 116 which indicates the power setting specified by a user, e.g. lOW/rn. Then at step 308, the microprocessor detennines which of the plurality of different length heating, cables has been attached to the controller 102. This is carried out by a simple look up of the heating cable data illustrated in Table I. Hence, if a length of 15m has been determined at step 304, then heating cable no. 1 will have been attached whereas if a length of 11 Om was determined, then heating cable no. S will have been attached. At step 310, the resistance per meter of the heating cable determined to be attached at step 308 is obtained from the data of Table 1, for example using a data structure which stores the data shown in Table I in persistent memory accessible by the microprocessor 112.
Then at step 31 2 the duty cycle required in order to provide the desired heating power output is determined. For example, if a 10W/rn power setting has bccn sciected, and the heating cable length has been determined to be I Sm, then an output power of 150W is required. The power supply controller can supply 240V AC from the mains power supply to thc hcating elements. The total resistance of a one of the heating elements is calculated from the determined length, 1 Sm, and the resistance per meter for the heating cable no., as provided by the data shown in Table I (in this case 17.7 ohm/rn). Hence, the total resistance of a one of the heating elements is 265.5 ohm and hence the maximum possible output power at 240V is given by V2/R which is approximately 217W. Hence, the duty cycle required to deliver the needed 150W is approximately 69%.
At step 314, the microprocessor determines the ambient temperature using a signal from the ambient temperature probe 122. The controller can operate using a normal duty cycle at normal operating temperatures or using an increased duty cycle at lower than normal temperatures, in order to reduce the time needed to heat an entity up to a desired temperature. In the described embodiment an enhanced duty cycle is used for ambient temperatures below -I 0°C and a normal duty cycle is used for ambient temperatures between -10°C and 5°C. These temperatures are particularly suitable for the application of heating water pipes in buildings to prevent them from bursting owing to the formation of ice,
S
At step 316, it is determined whether the measure ambient temperature is less than -10°C, and if so then processing proceeds to step 318 at which the normal duty cycle determined at step 312 (in this example 69%) is increased by 35% (in this example to approximately 93%) to an enhanced or increased duty cycle. Then processing proceeds to step 322 at which the microprocessor 112 controls the power supply controller 114 using a duty cycle of 93% to supply electrical power 322 to a one of the two heating elements 150 or 152. In many circumstances the nonnal duty cycle will he such that only a singe one of the heating elements needs to be used to supply the enhanced duty cycle also. Generally, two heating elements are supplied so that if one of the heating elements breaks (as indicated by presenting an infinite resistance) then the controller can supply power to the other of the heating elements. However, in circumstances in which the enhanced duty cycle would require weater than the maximum power that can be delivered to a single heating element, then the power supply controller can supply po7cr to both of the heating clements at the same time so as to deliver the power requirement corresponding to the enhanced duty cycle.
At stcp 324 it is determined whether any signal has been received to indicate that the controller should stop operating, for example a power down siai or some other interrupt signal. If not, then processing returns to step 3 14 at which the ambient temperature is determined again. The microprocessor is synchronised to the mains AC cycle and so the ambient temperature is measured every 2Oms (for 50Hz) or every 16.óms (for 60Hz).
Processing then proceeds as described above. If at step 316 it is determined that the ambient temperature is eater than -10°C, either because of the enhanced heating or because the ambient temperature was not initially less than -10°C, then processing proceeds to step 320 at which it is determined whether the ambient temperature is less than 5°C. If so, then processing proceeds to step 322 and the microprocessor 112 controls the power supply controller 114 using the normal duty cycle of 69% to supply electrical power 322 to one of the two heating elements. Otherwise, if it is determined at step 320 that the ambient temperature is greater than 5°C, then the microprocessor 112 controls the power supply controller 114 not to supply electrical power to the heating element as the temperature is now sufficiently high, e.g. to avoid ice damage to a water pipe.
Hence, a single cable heating controller 102 can be used with a plurality (8 in the described embodiment) of different heating cables and one of a plurality of different power output settings (three in the described embodiment of 10, 15 or 20W per linear metre of cable) can be selected by a user, e.g. dining installation of the cable heating. system 100.
A single controller 102 can be installed in any environment and attached to any desired length of cable I 04. A prior known temperature environment is almost impossible to guarantee since such systems can be installed in a huge range of environments. Therefore, within each of the heater cables, a resistance wire of a known resistance per metre, which is temperature independent, is provided and can be measured by the controller to determine the length of the cable and hence calculate the correct electrical power to deliver to the cable. The resistance wire has substantially no change in resistance with ternpcrature.
Therefore over all temperature ranges in which the cable heating system will be installed the resistance of this wire as measured by the controller will always and only relate to the length of the heating cable The controller, having been pre-programmed with the resistance per metre of this calibration wire, can reliably calculate the length of the cable and use this value to supply the appropriate power to the heating cable. This also allows different controller power settings to be selectable by a user without having to increase the number of cables to he provided (eight compared with twenty four (one for each of three different power scttings)) Another feature of the invention is the enhanced duty cycle in which the cable heating controller 102 increases the power output to the heating cable 104 automatically if the ambient teinpcrature drops below a predetermined threshold (in the described embodiment -10°C) to prevent frcczing of the pipes. This allows the heating cable to be set at a lower power output, thereby conserving energy, for most conditions while still remaining effective if environmental conditions are extreme for brief periods. This feature is possible due to the duty cycle in most situations being less than 100% for a given power output, e.g. I OW/rn. The controller can therefore increase the duty cycle in extreme conditions since excess power is available. Additionally, in embodiments in which multiple heating elements are provided in the cable, other heating elements can be used to supply extra heating power if the power required is greater than that which a single heating, clement can supply.
Claims (15)
- <claim-text>CLAIMS: 1. A cable heating controller for a cable heating system, comprising: a source of electrical power for outputting electrical power to a heating cable, the heating, cable including at least one heating element and a calibration wire, wherein the calibration wire and heating element have substantially the same length and the calibration wirc has a substantially temperature independent resistance; and a controller, wherein the controller is configured to: determine the resistance of the calibration wire; calculate the length of the heating element from the determined resistance; determine the electrical power to output to the heating clement using the calculated length; and control the source of electrical power to deliver the determined electrical power to the heating element.</claim-text> <claim-text>
- 2. A cable heating coiitroller as claimed in claim 1, wherein the controller is further configured to: detennine a resistance per unit length associated with thc calculated length; and calculate the resistance of the heating element using the determined resistance per unit length.</claim-text> <claim-text>
- 3. A cable heating controller as claimed in any preceding claim, wherein the controller is further configured to determine a duty cycle corresponding to the determined electrical power to output to the heating clement and wherein the duty cycle is used to control the source of electrical power.</claim-text> <claim-text>
- 4. A cable heating controller as claimed in any preceding claim, wherein the controller is further configured to determine a first electrical power to output to the heating element at a temperature above a first temperature and a second electrical power, greater than the first electrical power, to output to the heating element at a temperature below the first temperature.</claim-text> <claim-text>
- 5. A cable heating controller as claimed in claim 4, and further comprising a temperature sensor for measuring an ambient temperature of an environment in which the controller is located.</claim-text> <claim-text>
- 6. A cable healing controller a claimed in claim 4 or 5, wherein the controller is further configmed to: control the source of electrical power to deliver the second electrical power to more than one heating elcment.</claim-text> <claim-text>
- 7. A cable heating controller as claimed in any preceding claim, and further comprising an input by which a user can.select one of a plurality of different output power settings.</claim-text> <claim-text>
- 8. A cable heating controller as claimed in claim 1, wherein the controller further comprises circuitry including at least one known rcsistance and including a junction at which the calibration wire can be electrically connected to form a voltage divider.</claim-text> <claim-text>9. A cable heating contro]ler as claimed in claim 8, wherein said circuitry further includes a low pass flltcr and an amplifier connected in series to the junction.</claim-text> <claim-text>10. A cable heating controller as claimed in claim 9. wherein said circuitry further comprises an analog to digital convertcr which is in communication with an output of the amplifier.</claim-text> <claim-text>11. A cable heating controller as claimed in any preceding claim whcrcin said circuitry further comprises a microprocessor.</claim-text> <claim-text>12. A heating cable for a cable heating system, comprising: at least one heating element; and a calibration wire, wherein the calibration wire and heating element have substantially the same length and the calibration wire has a substantially temperature independent rcsistanee.IS</claim-text> <claim-text>13. A heating cable as claimed in claim 12, wherein the heating cable comprises a plurality of heating elements and wherein the calibration wire is substantially the same length as each of the heating elements.</claim-text> <claim-text>14. A cable heating system comprising: a cable heating controller as claimed in any of claims I to 11; and a heating cable as claimed in any of claims 12 to 13.</claim-text> <claim-text>15. A cable heating controller for a cable heating system, comprising: a source of electrical power for outputting electrical power to a heating cable, the heating cable including at least one heating element having, a length; and a controller, wherein the controller is configured to: determine the length of the heating element; determine, using the detennined length, a first electrical power to output to the heating clement at a temperature above a first temperature; determinc a second electrical power to output to the heating element at a temperature below the first temperature, wherein the second electrical power is greater than the first electrical power; determine an ambient tcmpcrature; and control the source of electrical power to deliver the second electrical power to the hcating element while the ambient temperature is below the first temperature and to (leliver the first electrical power to the heating element if the ambient temperature is above the first temperature.</claim-text> <claim-text>16. A cable heating controller as claimed in claim 15, wherein the controller is further configured to determine a first duty cycle corresponding to the first electrical power and a second duty cycle corresponding to the second electrical power and to control the source of electrical power using the appropriate duty cycle.</claim-text> <claim-text>17. A cable heating controller as claimed in claim 15 or 16, wherein the controller is further configured to control the source of electrical power to deliver the second electrical power to a piurality of heating elements while the ambient temperature is below the first temperature.</claim-text> <claim-text>18. A cable heating controller as claimed in claim 17, wherein the controller is thither configured to control the source of electricalpower to deliver the first electrical power to fewer than the plurality of heating elements if the ambient temperature is above the first temperature.S</claim-text> <claim-text>19. A cable heating controller as claimed in claim 18, wherein the controller is thither configured to control the source of electrical power to deliver the first electrical power to a single heating element if the ambient temperature is above the first temperature.</claim-text> <claim-text>20. A method for controlling a heating cable, wherein the heating cable includes at least one heating element and a calibration wire, the calibration wire and heating element having substantially the same length and the calibration wire having a substantially temperature independent resistance, the method comprising: determining the resistance of the calibration wire; calculating the length of the heating element from the determined resistance; determining the electrical power to output to the heating element using the calculated length; and controlling a source of electrical power to deliver the determined electrical power to the heating element.</claim-text> <claim-text>21. A method for controlling a heating cable, wherein the heating cable including at least one heating element having a length, the method comprising: determining the length of the heating element; determining, using the determined length, a first electrical power to output to the heating element at a temperature above a first temperature; determining a second electrical power to output to the heating element at a temperature below the first temperature, wherein the second electrical power is greater than the first electrical power; determining an ambient temperature; and controlling a source of electrical power to deliver the second electrical power to the heating element while the ambient temperature is below the first temperature and to deliver the first electrical power to the heating element if the ambient temperature is above the first temperature.Amendments to the claims have been filed as follows CLAiMS: 1. A cable heating controller for a cable beating system, comprising: a source of electrical power for outputting electrical power to a heating cable, the heating cable including at least one beating element and a calibration wire, wherein the calibration wire and heating element have substantially the same length and the calibration wire has a substantially temperature independent resistance; and a controller, wherein the controller is configured to: determine the resistance of the calibration wire; calculate the length of the heating element front the determined resistance; determine the electrical power to output to the heating element using the calculated length; and control the source of electrical power to deliver the determined electrical power to the heating element.* 2. A cable heating controller as claimed in claim I, wherein the controller is thrtber configured to: * * determine a resistance per unit length of the heating element_associated with the calculated length; and "". 20 calculate the resistance of the heating element using the determined resistance per ** *** * unit length.3. A cable heating controller as claimed in any preceding claim, wherein the controller is f\irther configured to determine a duty cycle corresponding to the determined electrical power to output to the heating clement and wherein the duty cycle is used to control the source of electrical power.4. A cable heating controller as claimed in any preceding claim, wherein the controller is thither configured to determine a first electrical power to output to the heating element [atjif an ambient temperature of an environment in which the controller or heating element is located is above a first temperature and a second electrical power, greater than the first electrical power, to output to the heating element if said ambient temperature is below the first temperature.5. A cable heating controller as claimed in claim 4, and further comprising a temperature sensor for measuring the ambient temperature of an environment in which the controller or heating element is located.6. A cable heating controller as claimed in claim 4 or 5, wherein the controller is further configured to: control the source of electrical power to deliver the second electrical power to more than one heating element.7. A cable heating controller as claimed in any preceding claim, and further comprising an input by which a user can select one of a plurality of different output power settings.* 8. A cable heating controller as claimed in claim 1, wherein the controller further * :flt 15 comprises circuitry including at least one known resistance and including a junction at which the calibration wire can be electrically connected to form a voltage divider.* S * S * .
- 9. A cable heating controller as claimed in claim 8, wherein said circuitry further : *. includes a low pass filter and an amplifier connected in series to the junction. * 20*
- 10. A cable heating controller as claimed in claim 9, wherein said circuitry further comprises an analog to digital converter which is in communication with an output of the amplifier.
- 11. A cable heating controller as claimed in any preceding claim wherein said circuitry further comprises a microprocessor.
- 12. A heating cable for a cable heating system, comprising: at least one heating element; and a calibration wire, wherein the calibration wire and heating element have substantially the same length and the calibration wire has a substantially temperature independent resistance.
- 13. A heating cable as claimed in claim 12, wherein the heating cable comprises a plurality of beating elements and wherein the calibration wire is substantially the same length as each of the heating elements.
- 14. A cable heating system comprising: a cable heating controller as claimed in any of claims ito 11; and a heating cable as claimed in any of claims 12 to 13.
- 15. A method for controlling a heating cable, wherein the heating cable includes at least one heating element and a calibration wire, the calibration wire and heating element having substantially the same length and the calibration wire having a substantially temperature independent resistance, the method comprising: -determining the resistance of the calibration wire; *: * calculating the length of the heating element from the determined resistance; *..: 15 determining the electrical power to output to the heating element using the calculated length; and * controlling a source of electrical power to deliver the determined electrical power to the heating element. * ** * * * *.**S.. *S* S *</claim-text>
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1203998.8A GB2495349A (en) | 2012-03-07 | 2012-03-07 | Heating cable having a calibration wire |
| EP13158168.8A EP2637473B1 (en) | 2012-03-07 | 2013-03-07 | Cable heating |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1203998.8A GB2495349A (en) | 2012-03-07 | 2012-03-07 | Heating cable having a calibration wire |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB201203998D0 GB201203998D0 (en) | 2012-04-18 |
| GB2495349A true GB2495349A (en) | 2013-04-10 |
Family
ID=46003256
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1203998.8A Withdrawn GB2495349A (en) | 2012-03-07 | 2012-03-07 | Heating cable having a calibration wire |
Country Status (2)
| Country | Link |
|---|---|
| EP (1) | EP2637473B1 (en) |
| GB (1) | GB2495349A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105845212A (en) * | 2016-05-20 | 2016-08-10 | 广西南慧电缆有限公司 | Multifunctional farm cable |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9733201B2 (en) | 2013-11-15 | 2017-08-15 | Pentair Thermal Management Llc | Thermal age tracking system and method |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006072765A1 (en) * | 2005-01-08 | 2006-07-13 | Thermocable (Flexible Elements) Limited | A controller for a heating cable |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4314145A (en) * | 1978-01-30 | 1982-02-02 | Raychem Corporation | Electrical devices containing PTC elements |
| US6288372B1 (en) * | 1999-11-03 | 2001-09-11 | Tyco Electronics Corporation | Electric cable having braidless polymeric ground plane providing fault detection |
| US6703593B2 (en) * | 2000-12-18 | 2004-03-09 | Asuk Technologies Llc | Low and high voltage electrical heating devices |
-
2012
- 2012-03-07 GB GB1203998.8A patent/GB2495349A/en not_active Withdrawn
-
2013
- 2013-03-07 EP EP13158168.8A patent/EP2637473B1/en active Active
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006072765A1 (en) * | 2005-01-08 | 2006-07-13 | Thermocable (Flexible Elements) Limited | A controller for a heating cable |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105845212A (en) * | 2016-05-20 | 2016-08-10 | 广西南慧电缆有限公司 | Multifunctional farm cable |
Also Published As
| Publication number | Publication date |
|---|---|
| EP2637473A1 (en) | 2013-09-11 |
| EP2637473B1 (en) | 2014-05-21 |
| GB201203998D0 (en) | 2012-04-18 |
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