JPH0749533Y2 - Heater burnout detection circuit for temperature controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a heater burnout detection circuit for a temperature controller.

(Prior Art) A heater is installed in a furnace in this type of temperature controller, and the heat generated by the energization of the heater heats the inside of the furnace, while a temperature sensor is provided at an appropriate location in the furnace. There is one that detects the temperature in the furnace and controls energization to the heater to adjust and control the temperature in the furnace.

In such a temperature controller, if the heater is disconnected, normal temperature control cannot be performed. Therefore, conventionally, the disconnection of the heater can be detected and the required treatment can be performed.

FIG. 3 is a circuit diagram of a conventional example of such a heater disconnection detection circuit for a temperature controller.

The heater burnout detection circuit shown in FIG. 3 is composed of a current transformer (CT) 2 for detecting the heater current S0 and a smoothing circuit 4 for smoothing and outputting the output of the current transformer 2 and corresponding to the heater current value. A detection circuit 6 that outputs a detection output S1 of a detection level, and a volume as a setting unit that outputs a setting output S2 of a setting level determined corresponding to the detection level of the detection output S1 output from the detection circuit 6 when the heater is burnt out. 8 and a comparison circuit 10 which outputs a heater disconnection detection signal S3 based on a comparison between the detection level of the detection output S1 given from the detection circuit 6 and the setting level of the setting output S2 given from the volume 8. .

(Problems to be Solved by the Invention) In the heater disconnection detection circuit having the above configuration, it is necessary to set the setting output S2 by the volume 8 based on the detection output S1 output from the detection circuit 6 at the time of heater disconnection. With such settings, even if the setting is performed once, when replacing the heater due to heater burnout or aging, the detection output S1 at heater burnout also fluctuates, so adjust the volume again. It is troublesome because it is necessary to perform the setting work.

Also, the steady-state heater current value may change due to changes or changes in the power supply voltage of the load, or due to other factors.If such a change occurs, the detection output S1 at the time of heater disconnection also changes. Therefore, even in such a case, it is necessary to perform the above setting by adjusting the volume and change the set value correspondingly, which is also troublesome.

The present invention has been made in view of the above problems, and the setting for detection of disconnection is automatically performed even when there is a factor such as a change of the heater or a fluctuation of the heater current in a steady state. In this way, the purpose is to be able to release the troublesome setting work.

(Means for Solving the Problem) In order to achieve such an object, the heater burnout detection circuit for a temperature controller of the present invention detects a heater current and responds to this heater current value based on this detection. Detecting means for outputting the detected output of the detected level, setting means for outputting the set output of the set level determined corresponding to the detected level of the detected output output from the detecting means when the heater is disconnected, and the detecting means. A detection circuit for outputting a heater disconnection detection signal based on a comparison between the detection level of the detection output given from the setting means and the setting level of the setting output given from the setting means. A peak value holding means for holding a given detection output by a peak value, and a hold output given from the peak value holding means. Attenuator means for attenuating to a predetermined value as the heater disconnection detection level and outputting it as the set output to the comparison circuit.

(Function) The peak value holding means in the above configuration holds the peak value of the detection output given from the heater current detecting means and outputs it to the attenuator means. The attenuator means attenuates the hold output given from the peak value holding means to a predetermined value as the heater disconnection detection level and outputs it as a set output to the comparison circuit.

As described above, even if the steady-state value of the heater current fluctuates or is changed, the setting output following the heater current is given without any setting operation of the setting means.

When the wire breakage occurs and the detection output level is equal to or lower than the heater wire breakage detection level, a heater wire breakage detection signal is output from the comparison circuit.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram of a heater burnout detection circuit for a temperature controller according to an embodiment of the present invention. Parts corresponding to those in the conventional example of FIG. 3 are designated by the same reference numerals and are designated by the same reference numerals. Only the names of the parts are listed, and the detailed description thereof is omitted.

In FIG. 1, 6 is a detection circuit including a current transformer 2 and a smoothing circuit 4, and 10 is a comparison circuit.

The heater disconnection detection circuit of this embodiment has the following configuration different from the conventional example.

That is, in the present embodiment, the setting means 12 is used to set the peak value hold circuit 14 for holding the detection output S1 supplied from the detection circuit 6 in the peak value, and the hold output supplied from the peak value hold circuit 14 to, for example, 1 / N. And an attenuator circuit 16 which outputs the set output to the comparison circuit 10.

FIG. 2 is a specific circuit diagram of the heater burnout detection circuit of FIG. As shown in FIG. 2, the peak value holding circuit 14 which is a feature of this embodiment is composed of a parallel circuit of a capacitor C and a resistor R1, and the detection output from the detection circuit 6 via a backflow prevention diode D. S1 is to be given. The attenuator circuit 16 is composed of resistors R2 and R3 connected in series with each other with a resistance ratio of 1 / N, and the connection point of both resistors R2 and R3 is connected to the comparison circuit 10. And this attenuator circuit 16 is a buffer
It is connected to the peak value hold circuit 14 via 18.

The operation of the setting means 12, which is the main part of this embodiment, will be described.

The peak value hold circuit 14 holds the peak value of the detection output S1 given from the heater current detection circuit 6 and outputs it to the attenuator circuit 16. The attenuator circuit 16 outputs 1 / N of the hold output given from the peak value hold circuit 14.
It is attenuated to and output to the comparison circuit 10 as the set output S2.

Here, the resistance ratio of the resistors R2 and R3 is given from the detection circuit 6 to the comparison circuit 10 in consideration of heater disconnection detection when, for example, two heaters are connected in parallel and one of them is disconnected. When the detection level of the detected detection output S1 is 1/2 or less of the steady value, the value of the disconnection detection level (resistance ratio) is set to 1/2 of the steady value hold output.

Therefore, even if the steady-state value of the heater current fluctuates or is changed, the setting circuit 12 does not perform any setting operation, and the comparison circuit 10 always follows the setting output of 1 / N of the steady-state heater current. Since S2 is given, the comparison circuit 10
Since the required setting output S2 is always given to, the setting work like the above-mentioned conventional example becomes unnecessary.

Here, there is a heater burnout and the heater current is 1 / N of the steady state.
In the following, the comparison circuit 10 outputs the heater disconnection detection output S3 based on the comparison between the detection output S1 given from the detection circuit 6 and the setting output S2 from the setting means 12.

(Effect of the Invention) As is apparent from the above description, according to the present invention,
Even when the heater is replaced or when the steady-state value of the heater current fluctuates or is changed, the steady-state heater current of the predetermined value is always set in the comparison circuit without any setting operation of the setting means. Since the setting output for detecting the disconnection, which is attenuated to the value, is provided, the troublesome setting work as in the above-described conventional example is eliminated.

[Brief description of drawings]

1 and 2 relate to an embodiment of the present invention. FIG. 1 is a block circuit diagram of the embodiment, and FIG. 2 is a specific circuit diagram of the embodiment. FIG. 3 is a circuit diagram of a conventional example. 6 ... Detection circuit, 10 ... Comparison circuit, 12 ... Setting circuit, 14
...... Peak value hold circuit, 16 …… Attenuator circuit.

Claims (1)

[Scope of utility model registration request] 1. A detection means for detecting a heater current and outputting a detection output of a detection level corresponding to the heater current value based on the detection, and a detection output of the detection output from the detection means when the heater is disconnected. A setting means for outputting a setting output of a setting level determined corresponding to the detection level; and a heater based on a comparison between the detection level of the detection output given by the detecting means and the setting level of the setting output given by the setting means. A heater disconnection detection circuit for a temperature controller, comprising: a comparator circuit for outputting a disconnection detection signal, wherein the setting means comprises a peak value holding means for holding a peak value of a detection output given from the detection means, and a peak value holding means. The applied hold output is attenuated to a predetermined value as the heater disconnection detection level, and then the set output is used as the output. Temperature regulating dexterity heater disconnection detection circuit, characterized in that is constituted by the attenuator means for outputting the 較回 path.