JPH08124653A - Electric heater - Google Patents

Abstract

PURPOSE: To provide a highly reliable and safe electric heater by constantly measuring electric resistance value between terminals of a heater wire and determining electricity application to the heater after judging the reliability of the heater based on the increasing ratio of the resistance. CONSTITUTION: An electric resistance measuring apparatus 1 is installed between terminals of a heater wire of a heater 2 utilized to heat an object to be heated. The measured electric resistance value is sent as an input signal to an electric resistance increasing ratio measuring apparatus 4 and the electric resistance increasing ratio at the time of application of prescribed electric power is measured. Based on the measured signal, the reliability of the heater is judged by a means 5 to judge reliability of the heater. Based on the judgement, if necessary, a control signal is sent to a means 6 to stop electricity application to the heater and then electricity application to the heater is stopped or an abnormal state is make known outside by alarming.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to household electric appliances and household equipment used in ordinary households, which use electric heaters, sheath heaters, ceramic heaters, and the like.

[0002]

2. Description of the Related Art In conventional household electric appliances and household appliances used in general households, electric heaters, sheathed heaters, and ceramic heaters include nichrome wire, iron chrome wire, copper nickel wire, tungsten wire, which have high electric resistance. Although molybdenum wire, silver alloy, etc. are used, if an abnormality such as a break in the heater wire or insulation failure occurs, the heater was replaced at that time.

Further, as a patent for improving the safety of the electric heater, Japanese Patent Publication No. 2-94383, "Control Device for Electric Heater" is disclosed.

[0004]

However, the conventional structure as described above has the following drawbacks.

That is, the conventional heater wire having a large electric resistance cannot be used because the wire is suddenly broken after the equipment has been used for a certain period of time. There is a high possibility that the resistance value of the heater wire will suddenly increase immediately before the wire breaks, causing local heating and causing a fire, and it is necessary to prevent it in advance.However, there is a means to predict an abnormality before the wire breaks. There wasn't. With conventional electric heaters, the user often finds an abnormality after disconnection and asks the equipment seller or repair technician to inspect and replace the heater, but the electric heater cannot be used from disconnection to repair. Yes It will interfere with daily life.

In addition, since a device seller, a device manufacturer, or the like may be liable for product liability in the event of a fire caused by an abnormality in the electric heater, there is always an abnormality such as disconnection. There was a request to understand the state of the equipment so that inspection and replacement can be performed quickly before an abnormality occurs.

The present invention solves the above problems, and an object thereof is to provide an electric heater having high reliability and safety.

[0008]

In order to achieve the above object, the electric heater of the present invention has the following constitution.

That is, a heater for heating an object to be heated,
An electric resistance measuring device between terminals of the heater wire, an electric resistance increasing rate measuring means for measuring an electric resistance increasing rate when a predetermined electric power is applied by using an electric resistance value measured by the electric resistance measuring apparatus as an input signal, and the electric resistance. Heater reliability determination means for determining the reliability of the heater based on the measurement signal from the increase rate measurement means, and heater energization determination for determining the energization of the heater thereafter based on the reliability of the heater determined by the heater reliability determination means. And a heater energization stopping means for stopping energization of the heater according to a control signal from the heater energization determining means.

Further, a heater for heating an object to be heated, an electric resistance measuring device between terminals of a heater wire, and an electric resistance increasing rate when a predetermined electric power is applied by using an electric resistance value measured by the electric resistance measuring device as an input signal. Electrical resistance increase rate measuring means, heater reliability determining means for determining the reliability of the heater based on the measurement signal from the electrical resistance increasing rate measuring means, and heater reliability determined by the heater reliability determining means. Based on the characteristics, a warning lamp and an abnormality warning notifying means for generating a warning sound are provided while the heater is energized thereafter.

Further, the heater for heating the object to be heated, the electric resistance measuring device between the terminals of the heater wire, and the electric resistance increasing rate when a predetermined electric power is applied with the electric resistance value measured by the electric resistance measuring device as an input signal. Electric resistance increase rate measuring means, a heater reliability determining means for determining a reliability limit of the heater based on a measurement signal from the electric resistance increasing rate measuring means, and a heater determined by the heater reliability determining means. Based on the reliability limit of
The configuration is provided with an abnormality warning notifying unit for generating a warning sound and a heater abnormality notifying unit for notifying the outside by a communication device based on the reliability of the heater determined by the heater reliability determining unit.

Further, the heater for heating the object to be heated, the electric resistance measuring device between the terminals of the heater wire, and the electric resistance increasing rate at the time of applying a predetermined electric power with the electric resistance value measured by the electric resistance measuring device as an input signal. An electric resistance increase rate measuring means for measuring the electric resistance and a heater abnormality notifying means for notifying a measurement signal from the electric resistance increase rate measuring means to the outside by a communication device are provided.

Further, an energization time measuring device for measuring the time from the start of energization of the electric heater to the stop of energization, and the heater of the heater when the measurement time measured by the energization time measuring device has passed a predetermined energization time. The heater reliability determining means for determining the reliability limit and the heater energization stopping means for stopping the energization of the heater in response to the control signal from the heater reliability determining means are provided.

Further, the energization time measuring device for measuring the time from the start of energization of the electric heater to the stop of the energization, and reliability of the heater when the measurement time measured by the energization time measuring device exceeds a predetermined energization time And a warning light and an abnormality warning notifying means for generating a warning sound during subsequent energization of the heater based on the reliability of the heater determined by the heater reliability determination means. It has a different configuration.

Also, the energization time measuring device for measuring the time from the start of energization of the electric heater to the stop of the energization, and reliability of the heater when the measured time measured by the energization time measuring device has passed a predetermined energization time. Heater reliability determining means for determining the limit of the reliability, a warning light and an abnormality warning notifying means for generating a warning sound during energization of the heater thereafter based on the reliability of the heater determined by the heater reliability determining means, and The heater reliability determining means is provided with a heater abnormality notifying means for notifying the outside by a communication device based on the reliability of the heater determined by the heater reliability determining means.

Further, an energization time measuring device for measuring the time from the start of energization of the electric heater to the stop of energization, and the time when the measurement time measured by the energization time measuring device exceeds a predetermined energization time as an input signal. It is configured to include a heater usage status reporting means for reporting to the outside by a communication device.

Further, a temperature increase electric resistance value measuring step for measuring an electric resistance value of the electric heater energized with a constant power application amount until the electric temperature rises from the first predetermined temperature to the second predetermined temperature, and the temperature increase. A first comparison in which the electric resistance value measured in the electric resistance value measuring step is compared with a first predetermined electric resistance value, and when the measured electric resistance value is smaller than the first predetermined electric resistance value, it is determined that the electric heater is abnormal. When the measured electric resistance value is larger than the first predetermined electric resistance value, the measured electric resistance value and the second predetermined electric resistance value larger than the first predetermined electric resistance value are compared, and the measured electric resistance value is second. A second comparison step of determining that the electric heater is normal when the electric resistance value is smaller than the predetermined electric resistance value, and determining that the electric heater is abnormal when the measured electric resistance value is larger than the second predetermined electric resistance value. did.

Further, the first comparison step or the second comparison step
If it is determined that the electric heater is abnormal in the comparison process,
The heater energization stopping means for stopping the energization of the heater is provided.

Further, the first comparison step or the second comparison step
When it is determined that the electric heater is abnormal in the comparison process, a warning lamp and an abnormality warning notifying means for generating a warning sound are provided during energization of the heater thereafter.

Further, when it is determined that the electric heater is abnormal in the first comparison step or the second comparison step, while the heater is energized thereafter, a warning light, an abnormality warning notifying means for generating a warning sound, and a communication device are provided to the outside. The heater abnormality reporting means for reporting is provided.

The content of Japanese Patent Publication No. 2-94383 "Electric heater control device" is to detect an abnormality in the power supply voltage and warn the user of a wrong connection or a failure of the internal switch to stop the equipment. The means used for solving the problems are obviously different, such as detecting an abnormality in the electric resistance value of the heater or determining the life based on the total energization time, stopping the equipment, and issuing a warning or notification to the user, the seller or the manufacturer.

[0022]

The present invention has the following functions due to the above-mentioned constitution.

That is, the electric heater of the present invention can judge the abnormality of the heater by the magnitude of the change in the increase rate of the electric resistance when the electric heater is energized.
The sheath heater, the heater wire of the ceramic heater is any material such as nichrome wire, iron chrome wire, copper nickel wire, tungsten wire, molybdenum wire, silver alloy, etc. having high electric resistance, and specific examples of the characteristics of the material are as follows. Oxides are generated on the surface of the heater wire with the passage of current, and the generated oxide may fall off and carbide may be precipitated at the grain boundaries, which may cause a rapid increase in electrical resistance. The coil winding part of is in contact with the adjacent wire. The surface heater wire made of tungsten and silver causes migration. This is based on the fact that when abnormal conduction occurs due to contact with a conductive foreign substance, the electric resistance value sharply decreases.

By having a function of periodically reporting the electric resistance value at the time of use in each home, the device seller, the device manufacturer, etc. can always grasp whether there is a problem in quality.

By integrating the total energization time with the energization time measuring device of the electric heater, it is possible to determine the life of the heater at the time when the safe use limit set according to the heater wire material is reached.

Further, when the abnormality of the heater is determined by the abnormality determining means, the electric heater is stopped to prevent the abnormal operation of the heater from continuing. Alternatively, it is possible to warn the user of the abnormality of the heater and to notify the outside by using a communication line.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

As shown in the figure, the electric resistance value between the terminals of the heater 2 when a predetermined electric power is applied is measured by the electric resistance measuring device 1. The electric resistance increase rate calculated by the electric resistance increase rate measuring device 4 is input to the heater reliability determination means 5 by using the measured value as an input signal, and the heater reliability determination means 5 stores the data. The rate of increase in electric resistance obtained in this way shows a substantially constant value from the start of use to the end of the life of the heater. In the heater reliability determination means 5, the accumulated electric resistance increase rate is compared with the electric resistance increase rate measured every time the heater is used, and when a substantially constant increase rate is determined, it is determined as "normal", and the increase rate is determined. When an abnormal change occurs in the, it is determined that "the life has been reached". On the basis of this determination result, the electric heater continues to be energized when it is "normal", but when it is "life", a control signal is input to the heater energization stopping means 6 to stop the heater energization.

It is an object of the present invention to work on the safety side such as stopping energization at the same time when a heater abnormality occurs. Hereinafter, description will be made based on specific examples.

(Embodiment 1) In this embodiment, a nichrome wire heater for a table stove of household electric appliances was used to conduct an energization test at 135V, which was higher than the normal voltage of 100V. When using this Nichrome wire heater and energizing 500, 70
The electric resistance value between the two terminals of the heater after 0, 800, and 900 hours was measured by the electric resistance measuring device 1. The electric resistance increase rate calculated by the electric resistance increase rate measuring device 4 is input to the heater reliability determination means 5 by using the measured value as an input signal, and the heater reliability determination means 5 stores the data. The rate of increase in electrical resistance thus obtained showed a substantially constant value from the beginning of use to 800 hours, but after 800 hours, the rate of increase increased to the right and was judged to be "life". Input to the heater energization stopping means 7 to stop energization of the heater. When this Nichrome wire heater was further energized, 98
It was disconnected at 0 hours. It is considered that this is because the resistance of the heater wire increased due to the formation of the oxide film on the heater surface, resulting in disconnection. From the above results, the safety of the heater is improved from the viewpoint of preventing fire accidents.

(Embodiment 2) In this embodiment having the structure shown in FIG. 2, an energization test was conducted under the same conditions as in Embodiment 1. The rate of increase in electrical resistance thus obtained showed a substantially constant value from the beginning of use to 800 hours, but after 800 hours, the rate of increase increased to the right and was judged to be "life". The alarm warning signal is input to the abnormality warning notification device 7, and the user is prompted to stop using the warning light or the warning sound. As a result of observing the cross section of the nichrome wire rod after the test with an optical microscope, it was found that the oxide film was locally generated violently and that the wire was about to break. From the above results, the safety of the heater is improved from the viewpoint of preventing fire accidents.

(Embodiment 3) In this embodiment having the structure shown in FIG. 3, a nichrome wire heater for a table stove of household electric appliances was used to conduct an energization test at 135V higher than the normal voltage of 100V. The electric resistance value between the two terminals of the heater at the start of use of this nichrome wire heater and after 500 hours of energization was measured by an electric resistance measuring device. The electric resistance increase rate calculated by the electric resistance increase rate measuring device 4 is input to the heater reliability determination means 5 by using the measured value as an input signal, and the heater reliability determination means 5 stores the data. The electrical resistance increase rate thus obtained showed a substantially constant value from the start of use to 700 hours. When the conductive cooking residue was brought into contact with the surface of the nichrome wire heater that continued to be energized for 750 hours,
At the same time as the cooking residue was carbonized in a few minutes, the electric resistance value of the heater decreased and it was judged as "life". The heater abnormality notification means 8 notifies the sales company or the manufacturer 10 through the domestic FAX or the telephone line 9. When the nichrome wire heater was further energized, the wire was broken several hours later. From the above results, the safety of the heater is improved from the viewpoint of preventing fire accidents.

(Embodiment 4) In the present embodiment having the configuration shown in FIG. 4, an energization test was carried out at 135 V, which is higher than the normal voltage of 100 V, by using a water heater for heating water of an electric water heater of housing equipment. As test water quality, total hardness 300pp
m, chlorine ion was adjusted to 100 ppm. The electrical resistance value between the two terminals of the heater was continuously measured with an electrical resistance measuring device at the start of use of this sheathed heater, at the time of energization for 500, 750, and 1000 hours, and after 1000 hours had elapsed. The electric resistance increase rate calculated by the electric resistance increase rate measuring device 4 is input to the heater abnormality notifying means 8 by using the measured value as an input signal, and is sent to the equipment seller or the equipment manufacturer 10 through the home FAX or the telephone line 9 at any time. Send data. The electric resistance value thus obtained is 1 from the beginning of use.
The value was almost constant up to 000 hours, but started to decrease gradually, and decreased sharply after 1150 hours. The cause of the decrease is that the scale, which is the hardness component, adheres to the heater surface, local corrosion occurs, and the heat conductivity decreases in the vicinity of the scale and the sheathed heater pipe is pierced due to an abnormally high temperature locally, It was analyzed that water entered the pipe. The sales company or the manufacturer 10 can promptly perform inspection, replacement, and the like as needed when the electric resistance value starts to gradually decrease. based on the above results,
The safety of the heater is improved from the viewpoint of preventing fire accidents.

(Embodiment 5) In this embodiment having the configuration shown in FIG. 5, an energization test was conducted under the same conditions as in Embodiment 4. As test water quality, total hardness 300ppm, chlorine ion 100pp
Adjusted to m. This sheath heater energization time measuring device 1
The time from the start of energization to the stop of energization is measured by 1 and the accumulated use time is stored. It has been previously confirmed in the durability test that this sheathed heater is normally energized for up to 1000 hours under the above-mentioned test conditions. Therefore, the heater reliability determination means 5 determines that the heater reliability limit is reached after 1000 hours. The control signal was input to the heater energization stopping means 6 to stop energization of the heater. After 1000 hours had passed, the power was further applied, and as a result, the wire was broken at 1150 hours. From the above results, the safety of the heater is improved from the viewpoint of preventing fire accidents.

(Embodiment 6) In the present embodiment having the configuration shown in FIG. 6, an energization test was conducted under the same conditions as in Embodiment 4. As test water quality, total hardness 300ppm, chlorine ion 100pp
Adjusted to m. This sheath heater energization time measuring device 1
The time from the start of energization to the stop of energization is measured by 1 and the accumulated use time is stored. It has been previously confirmed in the durability test that this sheathed heater is normally energized for up to 1100 hours under the above-mentioned test conditions. Therefore, the heater reliability determination means 5 determines that the heater reliability has reached the limit when 1100 hours have elapsed. The control signal is input to the abnormality warning notification device 7, and the user is prompted to stop using the warning light or warning sound. After 1100 hours, the current was further applied continuously, and as a result, the wire was broken at 1200 hours. From the above results, the safety of the heater is improved from the viewpoint of preventing fire accidents.

(Embodiment 7) In the present embodiment having the structure shown in FIG. 7, an energization test was carried out under the same conditions as in Embodiment 4. As test water quality, total hardness 300ppm, chlorine ion 100pp
Adjusted to m. This sheath heater energization time measuring device 1
The time from the start of energization to the stop of energization is measured by 1 and the accumulated use time is stored. It has been previously confirmed in the durability test that this sheathed heater is normally energized for up to 1000 hours under the above-mentioned test conditions. Therefore, the heater reliability determination means 5 determines that the heater reliability limit is reached after 1000 hours. , A control signal is input to the abnormality warning notifying device 7, a warning light or a warning sound is used to call the user to stop the use, and the heater abnormality notifying means 8 is used by the sales company or the manufacturer 10 through the home FAX or the telephone line 9. Call. After 1000 hours,
As a result of continuous energization, the wire was broken at 1150 hours. From the above results, the safety of the heater is improved from the viewpoint of preventing fire accidents.

(Embodiment 8) In the present embodiment having the structure shown in FIG. 8, a nichrome wire heater of a table stove for household electric appliances was used to conduct an energization test at 135V higher than the normal voltage of 100V. In the step of measuring the temperature rise electric resistance value of the nichrome wire heater at the start of the test, the electric resistance value at the time of rising from room temperature to 230 ° C. was measured. After turning on the power for one hour, when the power is turned off and the temperature returns to room temperature, the power is turned on again for one hour and then stopped. When this is repeated 500 times, the electrical resistance value is measured, and the measured value is compared with the electrical resistance value measured immediately after the start of the test as the first comparison step, and when it is less than 70% or greater than 140% of the value. Is determined as "life",
Stop energizing the heater. When it is within the range of 70 to 140% of that value, it is determined as "normal" and normal energization is performed.
The electric resistance value of the nichrome wire heater used in the test increased abnormally after 840 times, and this was determined to be "life". When the power was further applied continuously, the wire was broken 930 times. From the above results, the safety of the heater is improved from the viewpoint of preventing fire accidents.

[0038]

According to the electric heater of the present invention, the following effects can be obtained.

(1) When the rate of increase in the electric resistance of the heater changes rapidly, local abnormal heating occurs, causing a local high temperature, which may cause a fire due to combustion of flammable parts in the vicinity. , The electric heater is turned off or the power supply is stopped to improve safety.

(2) Since the user is warned at the same time when the heater abnormality is determined, an accident can be prevented.

(3) At the same time when the heater abnormality is judged,
In order to notify the equipment seller or equipment manufacturer,
Since prompt measures such as repairs are taken, the company can be held responsible from the perspective of CS.

(4) The equipment seller and the equipment manufacturer can always know whether there is a quality problem in the electric heater in the market through the communication equipment line, and can inspect and replace it promptly if necessary. Therefore, an accident due to a heater abnormality can be prevented, and an electric heater with high reliability and safety can be supplied without a period in which the heater cannot be used due to a break in the heater.

(5) By inputting the life time of the heater confirmed in advance by a durability test and stopping the safe side when the energization total time, which is the limit of reliability, is reached, the safety is ensured. A high electric heater can be supplied.

(6) Since the environment and purpose of use of the equipment are wide, various equipment failures may occur. For example, the coil winding portion of the heater wire comes into contact with the adjacent wire. The surface heater wire made of tungsten and silver causes migration. When, how, and for what reason occurs in individual devices used in each home, such as conduction due to contact with conductive foreign matter, wire diameter of the electric heater decreases due to local formation of oxide film, etc. can not predict. However, in the present invention, the abnormality is detected before the serious problem due to the rapid change of the increase rate of the electric resistance value, and the operation is stopped on the safe side.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an electric heater according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an electric heater showing another embodiment of the present invention.

FIG. 3 is the same configuration diagram

[Fig. 4] The same configuration diagram

[Fig. 5] The same configuration diagram

FIG. 6 is the same configuration diagram

[Fig. 7] The same configuration diagram

FIG. 8 is a flowchart of determination of an electric heater according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric resistance measuring device 2 Heater 4 Electric resistance increasing rate measuring device 5 Heater reliability judging means 6 Heater energization stopping device 7 Abnormality alarm reporting device 8 Heater abnormality reporting means 11 Energization time measuring device

Claims (12)

[Claims] 1. A heater for heating an object to be heated, an electric resistance measuring device between terminals of a heater wire, and an electric resistance increasing rate when a predetermined electric power is applied with an electric resistance value measured by the electric resistance measuring device as an input signal. Electrical resistance increase rate measuring means for measuring
A heater reliability determining means for determining the reliability of the heater based on the measurement signal from the electric resistance increase rate measuring means, and a subsequent energization of the heater based on the reliability of the heater determined by the heater reliability determining means. An electric heater comprising: heater energization determining means; and heater energization stopping means for stopping energization of the heater according to a control signal from the heater energization determining means. 2. A heater for heating an object to be heated, an electric resistance measuring device between terminals of a heater wire, and an electric resistance increasing rate when a predetermined electric power is applied with an electric resistance value measured by the electric resistance measuring device as an input signal. Electrical resistance increase rate measuring means for measuring
A heater reliability determination means for determining the reliability of the heater based on the measurement signal from the electric resistance increase rate measurement means, and a warning during the energization of the heater thereafter based on the reliability of the heater determined by the heater reliability determination means. An electric heater comprising: a lamp; and an abnormality warning notifying means for generating a warning sound. 3. A heater for heating an object to be heated, an electric resistance measuring device between terminals of a heater wire, and an electric resistance increasing rate when a predetermined electric power is applied with an electric resistance value measured by the electric resistance measuring device as an input signal. Electrical resistance increase rate measuring means for measuring
A heater reliability determination unit that determines the reliability limit of the heater based on the measurement signal from the electric resistance increase rate measurement unit, and a heater reliability determination unit that determines the reliability of the heater determined by the heater reliability determination unit It is equipped with a warning light, an alarm warning means for generating a warning sound during energization, and a heater abnormality notification means for notifying the outside by a communication device based on the reliability of the heater determined by the heater reliability determination means. And an electric heater. 4. A heater for heating an object to be heated, an electric resistance measuring device between terminals of a heater wire, and an electric resistance increasing rate when a predetermined electric power is applied with an electric resistance value measured by the electric resistance measuring device as an input signal. Electrical resistance increase rate measuring means for measuring
An electric heater comprising: a heater abnormality notifying means for notifying a measurement signal from the electric resistance increase rate measuring means to the outside by a communication device. 5. An energization time measuring device for measuring a time from the start of energization of an electric heater to a stop of energization, and a heater of a heater when a measurement time measured by the energization time measuring device exceeds a predetermined energization time. An electric heater comprising: a heater reliability determining means for determining a limit of reliability; and a heater energization stopping means for stopping energization of the heater according to a control signal from the heater reliability determining means. 6. An energization time measuring device for measuring a time from the start of energization of an electric heater to a stop of energization, and reliability of a heater when a measurement time measured by the energization time measuring device exceeds a predetermined energization time. And a warning light and an abnormality warning notifying means for generating a warning sound during subsequent energization of the heater based on the reliability of the heater determined by the heater reliability determination means. An electric heater characterized by that. 7. An energization time measuring device for measuring a time from the start of energization of an electric heater to a stop of energization, and reliability of a heater when a measurement time measured by the energization time measuring device exceeds a predetermined energization time. Heater reliability determining means for determining the limit of the reliability, a warning light and an abnormality warning notifying means for generating a warning sound during energization of the heater thereafter based on the reliability of the heater determined by the heater reliability determining means, and An electric heater comprising: a heater abnormality notifying means for notifying the outside by a communication device based on the reliability of the heater judged by the heater reliability judging means. 8. An energization time measuring device for measuring a time from the start of energization of an electric heater to a stop of energization, and an input signal at a time when a measurement time measured by the energization time measuring device exceeds a predetermined energization time. An electric heater comprising: a heater usage status reporting means for reporting to the outside by a communication device. 9. A temperature rise electric resistance value measuring step of measuring an electric resistance value of an electric heater, which is energized with a constant electric power application amount, until the electric heater rises from a first predetermined temperature to a second predetermined temperature, and the temperature increase. A first comparison in which the electric resistance value measured in the electric resistance value measuring step is compared with a first predetermined electric resistance value, and when the measured electric resistance value is smaller than the first predetermined electric resistance value, it is determined that the electric heater is abnormal. When the measured electric resistance value is larger than the first predetermined electric resistance value, the measured electric resistance value and the second predetermined electric resistance value larger than the first predetermined electric resistance value are compared, and the measured electric resistance value is second. A second comparison step of determining that the electric heater is normal when the electric resistance value is smaller than the predetermined electric resistance value, and determining that the electric heater is abnormal when the measured electric resistance value is larger than the second predetermined electric resistance value. Characteristic electric heater. 10. The electric heater according to claim 9, further comprising heater energization stopping means for stopping energization of the heater when it is determined that the electric heater is abnormal. 11. The electric heater according to claim 9, further comprising a warning lamp and an abnormality warning notifying means for generating a warning sound during energization of the heater when it is determined that the electric heater is abnormal. 12. An electric heater provided with a warning light, an abnormality warning notifying means for generating a warning sound and a heater abnormality notifying means for notifying the outside by a communication device while the heater is energized when it is determined that the electric heater is abnormal. The electric heater according to claim 9.