Patent Application
20110259872
Heating pads and electric blankets are devices used to keep an object warmer than a surrounding temperature. For instance, they may be used to keep a person warm in a bed, or to warm a limb (e.g., an electric mitten), an animal (e.g., an electric pet blanket), an object (e.g., a pipe heater to thaw a pipe or prevent a pipe from freezing), etc. Heating pads and electric blankets in general will be referred herein as “heating pads,” unless the circumstances clearly indicate otherwise. Additional layers of insulation may be used with a heating pad, such as an outer layer of insulation to lessen heat loss, or an inner partially-insulative layer to lessen a risk from a hot spot in the heating pad excessively heating an adjacent portion of the object. The additional layers of insulation may be included with the heating pad, or may be external to the heating pad (e.g., an ordinary bed blanket, comforter, or the like), spread over at least a portion of the heating pad.
Electric heating pads and blankets have heating cables that include electrical conductor(s) or wire(s) as a heating element. A conventional heating cable has one heating conductor or wire. More advanced heating cables could have more conductors which could be used as heating wires or signal sensing wires. The electrical conductors commonly are wound in a helical shape along the length of the heating cable, in order to increase the length of the conductors per unit length of the heating cable, and to provide more even heating circumferentially around the heating cable. However, other configurations of one or more of the electrical conductors may be used.
For a cable with multiple helical wound conductors, the conductors are disposed substantially coaxially along the length of the heating cable. The inner conductor can be wound around a dielectric core which may also be used to produce a desired amount of stiffness or flexibility to the cable. A sheath of a resistive material used as a separation layer is disposed around the inner conductor, and the outer conductor is wound around the separation layer. A thermally conductive outer sheath is disposed around the outer conductor to protect the heating cable while permitting heat to pass to other portions of the heating pad. For cables that use one or multiple conductors for signal sensing, the outer conductor is normally used as a heating element, but the disclosure is not limited in this regard. Electricity passes through the heating element, and the inner conductor is used as a sensing wire.
The power dissipated in the electrical conductor varies with the resistance of the electrical conductor, as well as the current (or voltage) through the electrical conductor. The electrical conductors are commonly made from a material that has a positive temperature coefficient (“PTC”) characteristic, in which the resistance of the wire increases with an increasing temperature over a temperature range of interest.
The heat produced by the electrical conductors also will increase the temperature of the resistive material, producing a change in resistance of the separation layer with a change in its temperature. The separation layer may exhibit a negative temperature coefficient (“NTC”) characteristic in which the resistance of the separation layer decreases as its temperature increases over a temperature range of interest.
Temperature control methods known in the art for heating pads and electric blankets include using a conductor or wire that provides a feedback signal to a control for monitoring temperature and detecting local hot spots. A conductor is coupled to a control circuit, and the circuit is designed to provide a phase change (i.e., a phase shift) with a change in the temperature of the wire. This phase shift is used as an indicator of the temperature of the wire. Another control method known in the art provides hot spot detection by using an NTC resistive material. Limited control can be accomplished by detection of a low-resistance path at a hot spot between heating and sensing wires. When the resistance is lower than a pre-set threshold, the circuit will shut down power to prevent over heating.
A drawback of the conventional approaches is that the precision of the temperature control is limited by the sensitivity of the temperature-sensing material or the method of processing feedback provided from the temperature-sensing material. The sensitivity may be low, and furthermore the sensitivity may vary over at least a portion of the temperature range of interest. Over at least a portion of the temperature range of interest, the sensitivity may not be adequate to provide a desired accuracy of temperature control. Furthermore, known control algorithms may be susceptible to degraded accuracy under a variety of conditions, such as the heating pad being partially covered, uncovered, folded over, etc.
Embodiments of the invention disclosed herein use feedback from an NTC signal, or from both PTC and NTC signals, in order to provide positive control of the temperature of the heating pad. These embodiments of the invention provide alternative methods to control heating pad temperature, under a variety of conditions such as covered, uncovered, folded over, etc The more precise, positive control of heat generation at or near an over-heated condition of the heating pad allows for incorporation of additional safety controls, and can allow for the shut down of power to the heating pad before the heating pad becomes over heated.
One or more embodiments of the invention is usable as a controllable heating pad, the controllable heating pad including a heating conductor embedded in the heating pad, a sensing conductor embedded in the heating pad, a resistive material providing a distributed electrical path between the heating conductor and the sensing conductor, a first current sensor to sense a current in the heating conductor, and a second current sensor to sense a current in the sensing conductor.
One or more embodiments of the invention is usable as a controllable heating pad system, the controllable heating pad system including: a heating conductor embedded in the heating pad, the heating conductor formed from a positive temperature coefficient (PTC) material; a sensing conductor embedded in the heating pad; a resistive material separating the heating conductor and the sensing conductor, the resistive material providing a distributed electrical path from the heating conductor to the sensing conductor, the resistive material formed from a negative temperature coefficient (NTC) material; a first current sensor in series with the heating conductor; a second current sensor in series with the sensing conductor; and a controller to control a current in the heating conductor based on an input from the first current sensor and an input from the second current sensor, wherein the heating conductor, the sensing conductor, and the resistive material are at least partially enclosed within a heat-transmissive sheath.
One or more embodiments of the invention is usable as a method of controlling a temperature of a heating pad, the heating pad having an embedded heating conductor, an embedded sensing conductor, an embedded resistive material that separates the heating conductor and the sensing conductor, and wherein a controllable switch is in series with the embedded heating conductor, the method including the steps of warming the heating pad to at least a first predetermined temperature by use of an adjustable on/off signal to the controllable switch, measuring currents through a PTC material and an NTC material, in order to determine a temperature of the heating pad, and maintaining a temperature of the heating pad to within a predetermined temperature range by use of the adjustable on/off signal to the controllable switch.
One or more embodiments of the invention is usable as a circuit to monitor a controllable heating pad, the heating pad having an embedded heating conductor connecting a source voltage to a reference potential, an embedded sensing conductor connected to the reference potential, an embedded resistive material that provides a distributed electrical path between the heating conductor and the sensing conductor, and a controllable switch in series with the embedded heating conductor, the circuit including: a first current sensor in series with the embedded heating conductor, the first current sensor connected to the embedded heating conductor at an end of the embedded heating conductor; and a second current sensor in series with the embedded sensing conductor, the second current sensor connected to the embedded sensing conductor at an end of the embedded sensing conductor, wherein a current sensed by the first current sensor is a predetermined function of the temperature of the embedded heating conductor, and a current sensed by the second current sensor is a predetermined function of the temperature of the embedded sensing conductor.
One or more embodiments of the invention is usable as a circuit to monitor a controllable heating pad, the heating pad having an embedded heating conductor connecting a source voltage to a reference potential, an embedded sensing conductor, an embedded resistive material that provides a distributed electrical path between the heating conductor and the sensing conductor, and wherein a controllable switch is in series with the embedded heating conductor, the circuit including: a first current sensor in series with the embedded heating conductor, the first current sensor having a first port connected to the embedded heating conductor at an end of the embedded heating conductor, and a second port connected to the reference potential; a first resistor having a first port connected to a supply voltage, and a second port connected to a first end of the embedded resistive material; an electrical connection from a second end of the embedded sensing conductor to the first port of the first current sensor, the second end of the embedded sensing conductor at an opposite end from the first end of the embedded sensing conductor; a second current sensor having a first port connected to the first end of the embedded resistive material, and a second port connected to the reference potential.
Advantages of embodiments of the invention further include use of a simple control method, thereby allowing for a low-cost design. The control method may achieve a similar or slightly faster warm-up time than is generally known in the art. The control method can be implemented using conventional, lower-cost wiring, thereby providing for a low-cost design. The control method may also detect fault conditions in the heating pad more quickly than the conventional art, by the detection of an anomalous pattern of NTC resistance, or an anomalous combination of NTC and PTC resistances, thereby permitting the heating pad to be shut down before the fault conditions can cause overheating.
Without intending limitation unless explicitly stated, the term “heating pad” is used herein to refer to any kind of powered covering or electric blanket which is used to provide warmth.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.
Referring now to
The inner conductor 104 may be a PTC conductor normally used as a sensing wire, and the outer conductor 105 is a PTC heating conductor. Without limitation in this sense, the disclosure herein will refer to the inner conductor 104 as a sensing wire, and the outer conductor 105 as a heating wire.
The helical shape of the conductors 104, 105 along the length of the heating pad cable 100 increases the length of the electrical conductors 104, 105 per unit length of the heating pad cable 100 and provides more uniform heating circumferentially around the heating pad cable 100. However, other configurations of one or both of the electrical conductors 104, 105 may be used, for instance a braided conductor. An electrical path from the conductor 105 to the conductor 104 passes through the NTC resistive material 102 along a substantial length of the heating cable 100, preferably over the entire length of the heating cable 100. Respective proximal ends 106, 107 of the inner and outer conductors 104, 105 are electrically connected to a control unit which includes the control electronics, a user interface, and an interface to a power source. The distal end (not shown) of the heating wire outer electrical conductor 105 returns to the control unit and/or power source after looping through the heating pad.
Electrical resistance of the electrical conductor 105 causes electric current from an external power source to be converted into heat. The heat is transferred by conduction to other portions of the heating pad. When the external power source is disconnected, the heating pad cools toward equilibrium with the ambient temperature. Conductor 105 (the heating wire) may be configured to promote generation of heat, for instance by use of a wire having less resistance per unit length, e.g., a larger gauge wire.
Referring now to
One or more embodiments of the present invention provide a method of control of the current in a heating pad cable, such that a temperature of the heating pad at one or more predetermined locations is controlled to within a desired temperature tolerance. The outer spiral wire 105 is made from a PTC material, and is used to produce heat by resistive dissipation of energy. Resistive material 102 is made from an NTC material. As current flows through outer electrical conductor 105 to produce heat, the temperatures of electrical conductors 104, 105 and resistive material 102 rise. The resistance of electrical conductor 105, which is made from a PTC material, rises. The resistance of resistive material 102, which is made from an NTC material, decreases. One or more embodiments of the present invention convert the resistance of the NTC material, or the combination of NTC and PTC materials, into electrical signals for use as feedback to a controller. The controller will use the feedback to control the temperature of the heating pad, by controlling the voltage and/or current delivered to the electrical conductor 105. Non-limiting examples of the control may be control of the duty cycle of the power source connected to electrical conductor 105, pulse width modulation (PWM), or an on/off control of power delivered to electrical conductor 105, the on/off control being long in cycle compared to a PWM signal, etc. The signal from the NTC or the combination of NTC/PTC will be used to control heating pad temperature.
Referring now to
Referring now to
An electrical path through resistive material 102 to return electrical conductor 312 is represented by a single lumped resistor 303, but it should be understood that the resistance of the resistive material 102 is distributed along substantially the full length of the resistive material 102, forming a distributed electrical connection between the conductors 311, 312, along at least a portion of the length of the resistive material 102. The resistance of the resistive material 102 at any predetermined location is dependent upon the temperature of resistive material 102 at that location. Similarly, the resistance of the return electrical conductor 312 is represented in
A current limiting resistor 306 is placed in series with the lumped resistor 302. The output of the current limiting resistor 306 is provided as an input to a second (NTC) current sensing resistor 307. A sensing point 310 is used to measure the voltage across the second current sensing resistor 307. The first and second current sensing resistors 308, 307 are connected to electrical ground.
In the embodiment of
For the purpose of analyzing circuit performance, REQV represents the equivalent resistance from point 313 to ground, through parallel circuit legs RPTC2+R2 and RNTC+RGND1+R1+R3. The distributed resistance of conductor 312 is represented as equivalent lumped resistances 302a, 302b. The voltages VPTC at sensing point 309 and VNTC at sensing point 310 when switch 304 is closed are determined in accordance with equations (1) and (2). When the switch 304 is closed, the PTC voltage at sensing point 309 will be:
VPTC≈VL*R2/(RPTC1+RPTC2+R2) (1)
When the switch 304 is open, the NTC voltage at sensing point 310 will be:
V
NTC
=V
L*(REQV/(REQV+RPTC1))*R3/(R1+R3+RNTC+RGND1)
Because RPTC1<<RNTC and RGND1<<RNTC, this relationship for VNTC can be simplified to:
V
NTC
=V
L
*R3/(RPTC1+RNTC+RGND1+R1+R3).
So: VNTC≈VL*R3/(RNTC+R1+R3). (2)
When switch 304 is open, power is cut off to heating wire or conductor 311, and the temperature of the heating wire begins to fall. In this situation, voltages VPTC and VNTC at sensing points 309, 310 respectively are determined in accordance with equations (3) and (4):
V
PTC=0(ground voltage) (3)
V
NTC
=V
L
*R
3/(R1+R3+RNTC+RGND1+RPTC1) (4)
It is seen from equations (1)-(4) that the voltage at sensing points 309, 310 will change based on the temperature of the heating wire. Therefore, the voltages at sensing points 309, 310 can be detected and used by a controller to control the temperature of the heating pad.
Referring now to
V
PTC
=V
L
*R
3/(R3+RPTC1+RPTC2) (5)
When switch 404 is in an open position, power source 405 no longer supplies power directly to electrical conductor or heating wire 411. Conductor 411 begins to cool toward room temperature, causing the lumped resistances 401a, 401b through conductor 411 to decrease. Resistive material 102 also cools, causing lumped resistance 403 to increase. The NTC voltage at sensing point 410 is determined in accordance with equation (6), wherein “∥” represents the equivalent resistance of two parallel resistors:
V
NTC
=V
L*(R3+RRET1+RPTC2+((RRET2+R2+RPTC1)∥RNTc))/(R1+R3+RRET1+RPTC2+((RRET2+R2+RPTC1)∥RNTC)) (6)
Since RNTC is much larger than any of RRET1 or RRET2 or RPTC1 or RPTC2, this relationship for VNTC can be approximated by equation (7):
VNTC≈VL*(RNTC∥R2)/(R1+(RNTC∥R2)); (7)
Referring now to
Referring now to
Referring now to
Referring now to
Embodiments of the invention include a method of controlling switch 304 or 404, by use of voltages sensed at sensing points 309, 310 or 409, 410, in order to set and to maintain the temperature of the heating pad to a predetermined temperature. The method is implemented on a processor which collects voltage measurements at sensing points 309, 310 or 409, 410. The processor then uses those measurements as data inputs to a control method stored in a memory used by the processor. The memory storage of the control method may be implemented in any kind of digital storage used by processors for storage purposes. The memory storage of data used by the method or produced by the method may be implemented in any kind of dynamic or rewritable digital storage used by processors for storage purposes. The control method causes the processor to command switch 304 or 404 on and off in order to control the heating pad temperature. The control method includes at least a heating mode to warm up the heating pad from an ambient temperature, a temperature maintenance mode to keep the heating pad within a predetermined tolerance of a desired temperature, a safety mode to monitor for safe operating conditions, and a shut-down mode to turn off the heating pad in a controlled manner.
Referring now to
The control algorithm of Heating Mode 800 next passes to decision block 804, to check whether the temperature TN of the NTC material is greater than a predetermined threshold. For instance,
The loop to apply an on/off modulated signal to the heating cable begins with decision block 806, in which TP and TN are tested to determine if they are below a predetermined threshold. In one embodiment the predetermined threshold is 60° C. for both TP and TN. In other words, the control method should not change power mode if TP and TN both do not indicate that the temperature has reached the predetermined threshold. Other embodiments with other threshold temperatures may be possible, including unequal thresholds for TP and TN, so the invention is not limited in this regard. If the result of decision block 806 is affirmative (i.e., the heating pad is not above the predetermined threshold temperature), then a modulated signal having a relatively long “on” portion is provided by block 807 to control switch 304 or 404. The relatively long “on” portion will facilitate a more rapid heating of the cable. If the result of decision block 806 is negative (i.e., the heating pad is close to the target temperature), then a modulated signal having a relatively short “on” portion is provided by block 808 to control switch 304 or 404. The relatively short “on” portion will facilitate a more gradual heating of the cable. In one embodiment, the modulated signal having a relatively long “on” portion may comprise a signal that is on for 59 seconds and off for 1 second. The modulated signal having a relatively short “on” portion may comprise a signal that is on for 9 seconds and off for 1 second. It should be understood that different ratios of on/off times, or additional ratios that are dependent upon how much TP or TN differ from the predetermined temperature threshold, may be used to provide different or additional control over the rate of heating.
At the conclusion of block 807 or block 808, a test is made in decision block 809 to determine if the elapsed time has reached the time limit set by the user in block 803. If the result of decision block 809 is positive, then control passes to block 900, the Keep Temp mode. If the result of decision block 809 is negative, control passes to decision block 810. Decision block 810 checks whether TP or TN are greater than a predetermined threshold (e.g., 5° C.) of the target temperature established in block 803, and if one or both are greater than the predetermined threshold then control is transferred to the Keep Temp Mode 900. If both TP and TN are less than the predetermined threshold, then control loops back to decision block 806 for additional heating. A more precise ability to monitor the temperature of the heating pad allows for the heating pad to be rapidly warmed more closely to the desired temperature setting, with little risk of overheating, compared to the rate of warming associated with a same risk of overheating when a less precise monitoring ability is used.
Referring now to
Upon the conclusion of wait state 903, the temperature TN of the NTC material is measured, and decision block 904 determines whether temperature TN of the NTC material has cooled to a temperature less than the target temperature limit (“Temp”) associated with the user's selected heat setting, as set in block 803 of
Once temperature TN of the NTC material has cooled below the user's selected heat setting, control exits decision block 904 and continues to a heating block 905, in which the switch 304 or 404 is turned on for a relatively shorter duty cycle than blocks 807 and 808 of Heating Mode 800. For instance, heating block 905 may provide a cycle of 8 seconds ON and 2 seconds OFF. The relatively shorter duty cycle of heating block 905 provides for a cool-down compared to the relatively longer duty cycles of heating blocks 807 and 808 that produce heating. Upon the conclusion of one cycle of heating block 905, the temperature TN of the NTC material and the temperature TP of the PTC material are both tested at decision block 906 to determine if both TN and TP have fallen to at least 5° C. below the target temperature limit. If the result of decision block 906 yields a negative result, control passes back to heating block 905. If the result of decision block 906 yields a positive result, control passes to heating block 907.
Heating block 907 provides a relatively longer duty cycle than heating block 905, for instance a cycle of 9 seconds ON and 1 second OFF. The cycle of heating block 907 is sufficient to gradually raise the temperature of the heating blanket. Upon the conclusion of one cycle of heating block 907, the temperature TN of the NTC material and the temperature TP of the PTC material are both tested at decision block 908 to determine if at least one of TN and TP have risen to become greater than the target temperature limit. If the result of decision block 908 is negative, then control passes to heating block 907 for further warming. If the result of decision block 908 is positive, then control passes back to block 902 to disable heat and perform another iteration of the Keep Temp Mode 900. Keep Temp Mode 900 may be exited upon an auto-shutoff initiated by a watchdog timer or similar, causing transition to the ShutOFF mode 1100 described below.
Referring now to
The control algorithm enters Safety Mode 1000 at Start block 1001. Control first passes to the first decision block 1002, which checks whether power is turned on to the heating pad. If the response to decision block 1002 is affirmative, then control transfers to a first plurality 1050 of decision blocks. If the response to decision block 1002 is negative, then control transfers to a second plurality 1051 of decision blocks. Within the first and second pluralities 1050, 1051 of decision blocks, individual tests for anomalous conditions may be performed in any order.
In one embodiment, first plurality 1050 of decision blocks includes decision block 1003, which checks whether the auto-shutoff timer has expired. The auto-shutoff timer is a safety feature that prevents the heating pad from being turned on for more than a predetermined amount of time, thereby lessening the risk of overheating. If the response to decision block 1003 is affirmative, control passes to ShutOFF mode 1100, which is described in further detail below in connection with
In one embodiment, second plurality 1051 of decision blocks includes decision block 1008, which checks whether TN is greater than a predetermined threshold, wherein TN refers to the temperature of the NTC material, calculated from scaling the voltage sensed at NTC sensing points 310 or 410. The predetermined threshold used in decision block 1008 may be approximately 100° C., but other approximate values may be used that are greater than the maximum user-selected heat setting, and which are substantially the same as the predetermined threshold used in decision block 1004. If the response to decision block 1008 is positive, then control passes to optional block 1010 which may provide an NTC over-temperature indication to a user, and from there control passes to ShutOFF mode 1100. If the response to decision block 1008 is negative, then control passes to decision block 1009, which checks whether the NTC resistive material 102 is presenting an open circuit. If the response to decision block 1009 is positive, then control passes to optional block 1011 which may provide an NTC open indication to the user, and from there control passes to ShutOFF mode 1100. If the response to decision block 1009 is negative, then control passes to step 1012 which returns to the operating mode which called the Safety Mode 1000.
It should be noted that the decision blocks within each of first and second pluralities 1050 and 1051 may be performed in a different order from the order described in
Referring now to
The control algorithm enters ShutOFF Mode 1100 at block 1101. Control passes to a plurality 1151 of blocks that perform shutdown functions. Within the plurality 1151 of blocks, individual shutdown functions may be performed in any order. In the embodiment of
Referring now to
Measurements 1401-1404 represent temperatures of a heating pad in accordance with an embodiment of the present invention, measured at four different points in the heating pad. Prior to the time indicated by marker 1408, each measurement 1401-1404 has a relatively small periodic fluctuation around a respective mean value, thereby indicating that each measurement 1401-1404 of the heating pad is in a steady-state condition. Typically, a temperature spread of the mean values is approximately 10° C., depending on the locations of the heating wire and temperature sensors. Measurement 1405 is the ambient temperature of approximately 28° C.
Measurement 1406 is the NTC signal used to control the power on and off to the blanket. Note that the peaks and troughs of measurement 1406 are substantially synchronous in time with the peaks and troughs of temperature measurements 1401-1404, respectively. The synchronicity indicates that while the NTC signal of measurement 1406 is increasing, indicating that the current flow through the NTC material is increasing, the heating pad temperature is also increasing. A hotter heating pad decreases the resistance of the NTC material and produces a greater electrical current through the NTC material, as would be expected by its negative temperature coefficient.
Measurement 1407 is the power input, which has a power of approximately 40 watts peak. Input powers of approximately 40-75 watts peak (not illustrated) generally are usable for a heating pad used to warm a bed. Note that measurement 1407 illustrates alternating cycles of on, followed by off The “on” cycles are substantially synchronous in time with periods when the NTC current signal is increasing, as indicated by measurement 1406, and periods when the heating pad is heating up as indicated by measurements 1401-1404. Likewise, the “off” cycles of measurement 1407 are substantially synchronous in time with periods when the NTC current signal is decreasing, and periods when the heating pad is cooling down. Optionally, a power limit may be provided in the heater control, such that the “on” time of measurement 1407 is limited to no more than a predetermined length of time or a predetermined duty cycle.
At the time indicated by marker 1408, the heating pad was reconfigured from a full-blanket configuration into a half-blanket configuration, in which a significant portion of the heating pad (approximately half) was uncovered by the blanket.
Note that the NTC signal of measurement 1406 take a relatively long time to recover in the half-blanket configuration. This is because when approximately half of the pad is exposed, heat dissipation is much faster than if the whole heating pad were under a blanket in the full-blanket configuration. It will take more time for the heating pad to reach a desired temperature. Therefore the NTC signal associated with measurement 1407 recovers to a desired temperature much more slowly after marker 1408.
Referring now to
Measurement 1506 is the NTC signal used to control the power on and off to the blanket. As in the full blanket configuration, the peaks and troughs of measurement 1506 in the half blanket configuration are substantially synchronous in time with the peaks and troughs of temperature measurements 1501-1505, respectively. The synchronicity indicates that while the NTC signal of measurement 1506 is increasing, indicating that the current flow through the NTC material is increasing, the heating pad temperature is also increasing. A hotter heating pad decreases the resistance of the NTC material and produces a greater electrical current through the NTC material, as would be expected by its negative temperature coefficient. Measurement 1506 recovers more slowly during “on” periods of measurement 1507, compared to the recovery time of measurement 1406 during “on” periods of measurement 1407, because of greater heat loss from uncovered portions of the heating pad.
Measurement 1507 is the power input, having a peak power of approximately 40 watts. Note that measurement 1507 illustrates alternating cycles of approximately two minutes on, followed by one minute off. The “on” cycles are substantially synchronous in time with periods when the NTC current signal is increasing, as indicated by measurement 1506, and periods when the heating pad is heating up as indicated by measurements 1501-1505. As with the full blanket configuration of
It should be noted that, as illustrated by
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and/or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
