JPH02270280A - Protective device of electric heater - Google Patents

Abstract

PURPOSE:To prevent any breakdown of the heater in the title due to the attachment of dust, dirt, oil, etc., by detecting an abnormal decrease in a current flowing through a positive thermistor with the aid of a current detector, and then actuating a switching mechanism for shutting off a current fed to the positive temperature coefficient thermistor. CONSTITUTION:When an overcurrent flows through an electric heater 8 due to some abnormality or other therein, or when the quantity of air is abnormally decreased as a result of blinding a filter 6 and attaching dust, dirt, oil, etc., onto the surface of each of radiating fins in the electric heater 8, and a switching element 22 is turned ON to melt down a current fuse 20, that is, a current fed to the electric heater is shut off. When the quantities of dust, dirt, oil, etc., attached to the electric heater 8 are increased for decreasing the quantity of air passing through the electric heater can be accordingly shut off. Thus, any short circuit accident in the electric heater due to the attachment of dust, dirt, oil, etc., thereto can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a protection device for an electric heater using a positive temperature coefficient thermistor that maintains the temperature of a heat generating part at a substantially constant temperature. It is.

(b) Conventional technology In general, as a conventional protection device for electric heaters,
There was one such as that shown in Publication No. 9-28822. The device described in this bulletin is a protection device for an indoor auxiliary heater used when heating an air conditioner, and includes a temperature fuse that blows when the temperature of the indoor auxiliary heater exceeds a predetermined temperature, and a protection device for the indoor auxiliary heater. A temperature relay that opens the contact piece at a temperature lower than the temperature at which the temperature fuse melts is installed in the current-carrying path of the heater.

As a result, the contact piece of the temperature relay opens in response to a temporary temperature rise, and in the event of an abnormality such as a sudden rise in heater temperature, the temperature fuse blows, preventing abnormal heating of the indoor auxiliary heater. Met.

(c) Problems to be Solved by the Invention All of the conventional devices described above were intended to prevent abnormal overheating of the heater. When such a device is applied to an electric heater that uses heat generated by a positive temperature coefficient thermistor (PTC heater, ceramic heater, etc.), it is possible to protect the heater from abnormal heat generation. However, if a positive temperature coefficient thermistor is exposed to an increased amount of dirt, dust, oil, etc., this dust or oil may cause short circuit damage to the positive temperature coefficient thermistor.In this case, the positive temperature coefficient thermistor may cause abnormal heat generation due to its characteristics This did not occur and resulted in destruction, and could not be protected by temperature fuses or temperature relays.

In order to solve these problems, the present invention provides a protection device that can prevent damage to an electric heater using a positive temperature coefficient thermistor due to dirt, dust, oil, etc.

(d) Means for Solving the Problems The present invention provides a protection device for an electric heater that uses heat generated when a positive temperature coefficient thermistor is energized. A switch mechanism that cuts off energization to the PTC thermistor when the value falls below a predetermined value, a return means that returns the switch mechanism, and prevents operation of the switch mechanism for a predetermined period of time from the start of energization of the PTC thermistor. It is equipped with a blocking mechanism that

(*) Effect By using a protective device configured in this way,
A current detector detects an abnormal drop in the current flowing through the PTC thermistor, and operates a switch mechanism to cut off the current flow to the PTC thermistor.

(F) Example Hereinafter, an example in which the protection device of the present invention is applied to an air conditioner will be described based on the drawings. FIG. 1 is a sectional view of an installed ceiling-embedded air conditioner. In the figure, 1 is the ceiling of a room to be conditioned, 2 and 3 are the casings of the air conditioner, 4 is a circular fan, and 5 is an electric motor for this fan. As the electric motor 5 rotates, the air in the conditioned room is circulated sideways in the direction of the solid arrow. That is, the air in the conditioned room passes through the air filter 6, the wire mesh 7 for protecting the heater, the electric heater 8, the fan 4, and the indoor heat exchanger 9 in this order.

The electric heater 9 uses the heat generated by a positive temperature coefficient thermistor.
It is called a TC heater or a ceramic heater, and automatically adjusts the amount of electricity so that the heat generation temperature is always constant. FIG. 2 is an explanatory diagram showing current characteristics (time-current) at the start of energization of a general electric heater used in this embodiment. H, M, and L are values obtained when the air flow rate (rotational speed of the electric motor 5) is changed to high, medium, and slightly less than 9, respectively. The current stabilizes 12 seconds (about 10 seconds) after the start of current flow, and the stable values are I M (A), I M (A), and I M (A), respectively.
I L (A), and this value varies depending on the heat generation temperature of the electric heater 8 used (designed heat generation temperature depending on the shape of the radiation fin), that is, the temperature of the air after passing through the electric heater 8.

Fig. 3 is an explanatory diagram showing the current characteristics (airflow amount - current) of the electric heater.
MISL is the current value when the air flow amount is F9H+FSMIFSL.

FIG. 4 is an electric circuit diagram for controlling energization of the electric heater. In the figure, reference numeral 10 denotes a connection section of the electric heater, in which three electric heaters 8 are connected in a triangle shape. These electric heaters are connected to the R phase, S phase, and T phase of a three-phase power supply via normally open contacts 11, 12, and 13, respectively. 14,15
．． 16 is an i-current detector (current transformer, etc.);
This detects the current applied to each electric heater. 17 is a rectifying and smoothing section, and a current detector 14゜15.1
The voltage detected by the microprocessor 18 is rectified and smoothed, then converted to a DC voltage potential and sent to the analog input terminal of the microprocessor 18 (
(Terminal with internal analog/digital conversion function) A/
Output to DR, A/DS, and A/DT. That is, the DC voltage corresponding to the current value detected by the current detector 14゜15.16 is applied to the terminals A/DR and A of the microprocessor 18.
/DS, output to A/DT. microprocessor 18
is converted to digital data and then stored as current value data.

19 is a relay which opens and closes the normally open contacts 11, 12, and 13; that is, the relay 19 is energized and the normally open contacts 1
1, 12, and 13 are closed, the electric heater is energized. One end of this relay 19 is connected to a DC power supply (4B (V)) via a current fuse 20 (a current breaker that resets by operating a manual switch may be used), and the other end is connected to a DC power supply (4B (V)) via a switching element 21. Grounded.

This switching element 21 turns on when the terminal OH of the microprocessor 18 reaches an H level potential (outputting an ON signal).Similar to the switching element 21, the switching element 21 becomes ON when the terminal OE of the microprocessor 18 reaches an H level potential. When the switching element 22 is in the ON state, there is no load on the switching element 22, so that the DC power supply of 48 V> is short-circuited to earth via the current fuse 20 and the switching element 22. Therefore, the current fuse 20 is blown. As a recovery means to recover from this state, the current fuse is replaced. Reference numeral 23 is a light emitting element, which lights up in conjunction with the ON of the switching element 22. Note that the terminal 0 of the microprocessor 1B is connected to the air conditioner. Outputs control signals for other equipment, such as signals for setting the 0N10FF or operating capacity of the compressor, the rotation speed of the electric motor 5, etc.
Terminal I is a terminal for inputting various data such as room temperature, outside temperature, and room temperature set value.

Reference numeral 5150 is an explanatory diagram showing the main operations of the microprocessor 18 shown in FIG. First, in step SL, the air conditioner is started up by turning on the power, and the operation of the equipment that makes up the air conditioner, such as the compressor and electric motor, is controlled.Then, the process proceeds to step S, and as a result of step S, the electric heater is turned on. It is determined whether the signal is being outputted, and if the ON signal of the electric heater is being outputted, the process proceeds to step S4. In step S4, the switching element 21 is currently set to OFF.
It is determined whether or not the FF is set, that is, whether or not the electric heater is currently energized. If the electric heater is not energized, the timer starts counting in step S, and then the process proceeds to step S. At step S, the switching element 21 is turned on and this state is held. That is, it energizes the electric heater. After this,
In step S, it is determined whether or not the timer's time has reached time UP (TP time measurement), and if the time has not reached time UPL, step S! Return to When time UP is determined in step S1, the process advances to step S, where the current detectors 14, 1
If the detected current value I in any of 5.16 is “■≧I, +
It is determined whether or not the electric heater is Step S then determines whether or not an overcurrent has flowed through.

Proceed to the step and the air flow rate of the motor is strong (H), medium (M), and less than 9 (L).
511 * S Im
Proceed to.

In this step S16+SII*SII, the current value I detected by any of the current detectors 14, 15, and 16 is I≦1□'', 'I≦IBM'', and ``I≦Is'', respectively.
In other words, the air flow actually passing through the electric heater is determined to be equal to the amount of air blown F shown in Fig. 3.
so+ FSMI This is to judge whether or not it has become below FSL. Step S I y S II + S
11 +S11 is satisfied, step S1. Then, the switching element 22 is turned on. That is, the current fuse 20 shown in FIG. 4 is blown out.

In the electric heater protection device configured as described above, when an overcurrent flows in the electric heater due to some abnormality, the filter 6 is clogged, or dirt, dust, oil, etc. adhere to the surface of the electric heater's heat radiation fin. When the air volume is abnormally reduced, the switching element 22 is turned on to blow the current fuse 20. In other words, the current supply to the electric heater is cut off.

(G) Effects of the Invention The present invention provides a protection device for an electric heater that uses heat generated when a positive temperature coefficient thermistor is energized, and includes a current detector that detects the current flowing through the positive coefficient thermistor, and a detection value of the current detector that is set to a predetermined value. a switch mechanism that cuts off the energization to the positive temperature coefficient thermistor when the value falls below a value, a return means that restores the switch mechanism, and a blocking mechanism that prevents the switch mechanism from operating for a predetermined period of time after the start of energization of the positive temperature coefficient thermistor. With this, when the current flowing through the electric heater becomes less than a predetermined value, the switch mechanism shuts off the electricity to the electric heater. That is, when the amount of dirt, dust, oil, etc. adhering to the electric heater increases, the amount of air passing through the electric heater decreases, and the current decreases, the electric current to the electric heater can be cut off. Therefore, it is possible to prevent short-circuit accidents of the electric heater caused by dirt, dust, oil, etc., which occur when the amount of dirt, dust, oil, etc. attached increases. Also,
Since the switch mechanism is reset by operating the return means, chattering operation due to automatic return can be prevented.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a ceiling-embedded air conditioner installed, Figure 2 is an explanatory diagram showing the time-current characteristics of the electric heater, and Figure 3 is the air flow-current characteristic of the electric heater. FIG. 4 is an electric circuit diagram for controlling energization of the electric heater, and FIG. 5 is an explanatory diagram showing the main operations of the microprocessor shown in FIG. 4. 8... Electric heater, 14-16... Current detector, 18... Microprocessor, 20... Current fuse, 21.22... Switching element.

Claims (2)

[Claims] (1) A protection device for an electric heater, which uses heat generated when a positive temperature coefficient thermistor is energized, and performs a protective operation when the current applied to the positive temperature coefficient thermistor is equal to or less than a predetermined value. (2) In a protection device for an electric heater that uses the heat generated when a positive temperature coefficient thermistor is energized, there is a current detector that detects the current flowing through the positive temperature coefficient thermistor, and a current detector that detects the current flowing through the positive temperature coefficient thermistor, and when the detected value of this current detector becomes less than a predetermined value, the The present invention is characterized by comprising a switch mechanism that cuts off energization to the characteristic thermistor, a return means that restores the switch mechanism, and a blocking mechanism that prevents the switch mechanism from operating for a predetermined period of time after the start of energization of the positive characteristic thermistor. Protective device for electric heaters.