JPH0338960Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a control device for controlling the temperature of a heater such as a surface heater whose temperature distribution is not uniform.

[Prior art]

Since the responsiveness of liquid crystal display elements deteriorates when the operating temperature is low, assistance with a heater is required. A surface heater is generally used as the heater, and is turned on at low temperatures and turned off at temperatures above a certain level.

Therefore, as shown in FIG. 4, the surface heater 1 is connected to the power source 3 via the control section 2, and a temperature sensor (thermistor) 4 is attached to the surface heater 1, and the contacts of the control section 2 ( (relay contacts, etc.) are turned on and off.
In that case, the temperature distribution of the surface heater 1 is not uniform, and the temperature rises more rapidly at the center than at the edges.
The location of the temperature sensor is an issue. In the case of a surface heater, accurate control can be achieved by detecting the temperature in the center and controlling the temperature based on that, but since the center has an effect on the display, it is common to install a temperature sensor at the end. This makes accurate temperature control difficult. For example, when a temperature sensor is installed at an end, the temperature at that location and the temperature at the center increase as shown in FIGS. 5 and 6. Figure 5 shows the temperature rise from -30°C, and Figure 6 shows the temperature rise from -20°C, where the solid line shows the temperature at the center of the surface heater and the broken line shows the temperature at the sensor part.

In FIG. 5, when the temperature of the sensor part reaches the set temperature point c, the temperature in the central part has already exceeded the dangerous temperature and reached point d, and it cannot be said that normal control is achieved.

Also, in Figure 6, the temperature of the sensor section reaches the set temperature in a shorter time than the temperature rise curve from -30℃.
In order to reach point c', the temperature in the center is low and off, but it still exceeds the critical temperature and reaches point d'.

[Purpose of invention]

An object of the present invention is to provide a heater control device that can accurately control the temperature of a heating element without being restricted by the mounting position of a temperature sensor.

[Summary of the idea]

The present invention provides a heater control device in which a temperature sensor is attached to the end of the heater, and the temperature detected by the sensor is compared with a reference value to control the heater on and off. The present invention is characterized in that the reference value is automatically changed so that when the detected value of the ambient temperature rises, the heater control temperature is raised, and when the ambient temperature falls, the heater control temperature is lowered.

〔Example〕

1 and 2 show an embodiment of the present invention, in which 11 is a surface heater, 12 is a control section, and 13 is a power source. Connected. 14 is a temperature sensor (thermistor) attached to a part of the surface heater 11; 15 is a temperature sensor (thermistor) that detects the ambient temperature; these detection signals are given to the control section 12. The heater temperature sensor 14 is for detecting the heater temperature to be compared with a reference value, and the ambient temperature sensor 15 is for detecting the ambient temperature used for changing the reference value.

The control section 12 has a circuit configuration as shown in FIG. In Figure 2, CP ₁ to CP ₃ are comparators, Q ₁ to _{Q 3} are transistors, R ₁ to R ₃ are resistors, ZD ₁ is a Zener diode, RY is a relay,
RYa is the normally open contact of this relay RY, and comparator CP ₁ compares the detected temperature with the reference value.
The relay RY is energized or deenergized by the transistor _Q2 , which is turned on or off depending on the comparison result, and the surface heater 11 is energized when its contact RYa is closed.

Note that a temperature sensor 15 is incorporated in the part where the reference value is set. Further, a positive temperature coefficient thermistor PTC is connected in series with the surface heater 11 to prevent overcurrent.

Next, the operation will be described. If the ambient temperature and the temperature at the installation point of the sensor 14 are the same, the potential at point C of the reference voltage setting section and the potential at point B of the input section of comparator _CP1 will be approximately the same potential. The potential at the other point D of the input section is a value obtained by dividing the potential at point C by the resistors R ₁ and R ₂ (because the transistor Q ₁ is on and the resistor R ₃ is not included).

In this state, the comparator CP ₁ compares the potentials at points B and D, and when V _B > V _D , the output becomes L level, turning on transistor Q ₂ and turning on the relay.
RY is energized, and current flows through the surface heater 11 as the relay contact RYa closes.

When the heater temperature increases due to energization, the resistance value of the sensor 14 decreases, and the potential at point B decreases. Then, when V _B < V _D , the output of comparator CP ₁ becomes H level, and transistor Q ₂
is turned off and the heater power is turned off. By repeating this process, the heater temperature is controlled. This temperature rise curve is shown in Figure 3.

In that case, when the ambient temperature changes, sensor 1
The resistance value of 5 changes, and the reference value also changes. for example,
When the ambient temperature rises, the resistance value of the sensor 15 decreases, and the potential V _C at point C decreases. Therefore, the potential at point D, which is the reference value of the comparator CP ₁ , decreases, so the potential at which the comparator CP ₁ operates decreases, and the actual heater control temperature increases. When the ambient temperature drops, the opposite operation occurs and the heater control temperature becomes lower.

That is, when the ambient temperature Ta is -30°C, the heater 1 is turned off when the temperature of the sensor reaches point b in Figure 3.
1 is turned off, and the temperature of the central portion is controlled to the point a. Similarly, when the ambient temperature Ta is -20 DEG C., the heater 11 is turned off when the sensor section is at point b', and the temperature at the center becomes point a'.

Note that the comparators CP ₂ and CP ₃ are for temperature restriction and protection, and operate as follows.

The reference potential V _E (potential at point E) is input to the (-) input terminal of the comparator CP ₂ , and when V _E <V _B , the output becomes H level and the transistor Q ₃ is turned off. In this state, transistor _Q2 can be controlled by comparator _CP1 . however,
When V _E < V _B , the output of comparator CP ₂ becomes L level, transistor Q ₃ turns on, and
Control is disabled by the comparator _CP1 of the transistor _Q2 . That is, power supply to the heater 11 is forcibly blocked.

Comparator _P3 receives reference potential V _F (potential at point F) at its (-) input terminal, and when V _B < V _F , the output becomes L level, transistor Q ₃ is turned on, and transistor Q Comparator of ₂ CP ₁
This makes control impossible. As a result, sensor 1
If the resistance value becomes excessive or the lead wire is broken due to abnormality 4, the power supply to the heater 11 is stopped.

In addition, the heater 11 is equipped with a positive characteristic thermistor.
PTCs are connected in series, and if the power supply becomes uncontrollable, self-heating will increase the resistance value and automatically limit the current.

By the way, hysteresis operation is performed when controlling the heater on and off. That is, transistor
When Q ₂ turns off, transistor Q ₁ turns off, and V _D becomes Vc × (R ₂ + R ₃ / R ₁ + R ₂ + R ₃ ). At this time, the potential difference Vc×(R ₂ +R ₃ /R ₁ +R ₂ +R ₃ −R ₂ /R ₁ +R ₂ ) causes hysteresis operation.

〔effect〕

As described above, according to the present invention, the ambient temperature is measured in addition to the heater temperature, and the reference value is changed according to the ambient temperature, so even if the heating element has an uneven temperature distribution, the temperature Temperature control can be performed accurately regardless of the mounting position of the sensor.
Furthermore, by changing the circuit constants, the set temperature and hysteresis can be freely selected. Furthermore, since it has a thermistor disconnection detection circuit, overheating can be prevented even when the thermistor is disconnected, making it safe.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the heater control device according to the present invention, Fig. 2 is a circuit diagram of the control section in the same embodiment, Fig. 3 is a temperature rise characteristic diagram of the same embodiment, and Fig. 4 5 is a block diagram showing a conventional example.
6 and 6 are conventional temperature rise characteristic diagrams. 11...Surface heater, 12...Control unit, 13...
...Power supply, 14...Temperature sensor for detecting heater temperature, 15...Temperature sensor for detecting ambient temperature,
CP ₁ to _{CP 3} ... Comparator, Q ₁ to _{Q 3} ... Transistor, R ₁ to _{R 3} ... Resistor, RY ... Relay, RYa
...Relay contact.

Claims (1)

[Scope of utility model registration request] In a heater control device in which a temperature sensor is attached to the end of the heater and the detected temperature is compared with a reference value to control the heater on and off, a temperature sensor is installed to detect the ambient temperature, and the detected value is A heater control device characterized in that the reference value is automatically changed so that when the ambient temperature rises, the heater control temperature is raised and when the ambient temperature falls, the heater control temperature is lowered.