JPH0353484A - Heater disconnection alarm - Google Patents

Abstract

PURPOSE:To simplify and ensure the setting of the alarm operating point by forming an alarm so as to emrt an alarm when the ratio of the heater current and the heater voltage is less than the set value under the condition that that pulse duration is more than a certain value and pulse dration of the current and the voltage are the same. CONSTITUTION:After the heater voltage and the heater current took in as input with an analog switch 3 are converted to the direct current by a rectifying circuit 4, the input the certain cycle is converted to the digital signal by a VF converter 5 and a pulse counter 7, and the time that the input current exceeds the preset threshold level is measured by a comparator 6 and a pulse duration measuring circuit 8. The pulse duration (input time) of the heater current and the heater voltage taken in as input are checked, and when the ratio of the heater current and the heater voltage is less than the set value under the condition that the pulse duration data is more than a certain value and the pulse duration of the current and the voltage are the same, alarm is generated. Setting of the alarm operating point can be thus simplified and ensured.

Description

[Detailed description of the invention] <Use for industrial waste> Masaaki Ki monitors the operating status of heaters built into 9 electric furnaces and drying furnaces for secondary industrial use, and issues an alarm in the event of a failure such as a disconnection. This is related to the heater cut-off alarm (12'4l).

Kujoto technology> Conventional heater disconnection alarms of this type are
-1513 As seen in the July bulletin, it was constructed with an analog circuit and the II alarm operating point was set using a volume resistor, so there were problems with delicate adjustment and individual differences, and especially when the heater turned on and off. There was a problem in which the operation became unstable when the on/off cycle was controlled by a type temperature controller that was fast.

Problems to be Solved by the Invention> The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to easily set the alarm operating point regardless of individual differences. It is an object of the present invention to provide a heater disconnection alarm that can operate reliably and quickly and reliably regardless of whether the temperature control method of the heater is an on-off type or a phase control type.

<Means for Solving the Problem> The heater disconnection alarm device of the present invention which achieves the purpose of refusing the warning is configured to alternately take in heater voltage and heater current as input, and to synchronize the timing of taking in with the cycle of the input AC frequency. A VF converter and pulse counter that digitally convert the input during a certain cycle, a comparator and 11 pulse width measurements that measure the time when the input voltage exceeds a preset threshold level. It is composed of a circuit, and when the pulse width data taken is above a certain value and the pulse widths of current and voltage are the same, an alarm is issued when the ratio of heater current to heater voltage is less than the set value. It is characterized by the following.

<Example> Embodiments of the present invention will be described below based on the drawings.

The heater is controlled by its control circuit (temperature regulator) A, and the control method may be an A-on/A-f control method or a phase control method.

An analog switch 3 is connected to this heater A via an instrument transformer 1 and an instrument transformer 2.

The analog switch 3 is for alternately inputting the heater voltage and heater current, and the one-zip microcomputer B synchronizes the input timing of the heater voltage and heater current with the cycle of the input AC frequency. control.

Note that the input waveform shown in FIG. 2 is for a case where the temperature control method of the heater is a phase control method. The heater voltage and heater current taken in as input by the analog switch 3 are converted from alternating current to direct current by the rectifier circuit 4, and then applied to the VF converter 5 and comparator 6. This rectifier circuit 4 is a circuit using an operational amplifier, and its output 1 is as shown in FIG.

And VF converter 5 and Vanoreska f converter 7
Accordingly, the input for a certain number of cycles from the bottom 1/2 recycle to a digital signal 0 is converted into a digital signal 0. As shown in Figure 2, the output of the VF converter 5 is a pulse train with a frequency proportional to the input voltage, so by counting one cycle with the pulse counter 7, the average value of the input voltage can be obtained and converted into a digital signal. The input value (input 1 pressure) is synchronized with the input cycle, so the chain is proportional to the average value. On the other hand, at the same time as the input is taken in, the comparator 6 and the pulse width measuring circuit 8 measure the time when the input voltage exceeds a predetermined threshold level.

Therefore, the heater current and heater'' taken as input
Check the pressure pulse 11] (input time), and if the value is below [ ] or a certain time, and the heater 1i
If the pulses 11] of i%t and the heater voltage are different from each other, no alarm processing is performed until new data is received, and the pulse width data is greater than a certain m and the pulse widths of the heater current and heater voltage are different from each other. In the same case, alarm processing is performed.

The II alarm process calculates the ratio of the heater current taken in as input, the heater current, and the heater voltage, and when the value is less than a set value, a heater disconnection lit alarm is issued. That is, when the heater current during normal operation is 1!8, the heater voltage is VQ, the heater current during measurement is lx, the heater voltage is VX, and the set value (current reduction rate) is A6, the following formula I 6 A 8≦1x・
・・・・・・■Vs vx Vs Vx Calculation is performed, and if the above ■ is normal, the above ■
In this case, it is determined that there is an abnormality and an alarm is output immediately indicating that the line is disconnected.

Note that the calculation of the ratio of the heater current and heater voltage should originally be done using the effective value, but since the waveforms of the heater current and heater voltage taken as input are the same, the average obtained by the pulse counter 7 should be used. You will understand that even if you calculate based on values, it will not actually work.

In addition, processing of various scales, etc. is carried out by the one-chip microcomputer B program, and the settings of each scale are controlled by the operation switch 9 and display 10 connected to the one-chip microcomputer B, and the data is recorded seven times. .

Effects of the Invention> Since the heater disconnection alarm according to the present invention is constructed in this manner, the load setting (normal load current value) and alarm operating point can be set using the operation switch (9) and the display (io). Digital settings can be made while monitoring data with "c", and therefore various values can be set easily and accurately without individual differences.

What's more, a converter was used to take in the regulator current and heater current as input and convert them into digital signals, so basically the average value could be converted into digital signals.
In addition, even with sequential input input equipped with a pulse width measuring circuit, there is no possibility of malfunction. Therefore, whether the heater temperature control method is the A-off method or the phase control method, it is possible to quickly and accurately control the temperature. It will start working. In other words, to convert the heater current and heater voltage into digital signals,
When using a so-called AD converter, it is necessary to create a circuit and input the average value in the analog section, or input the instantaneous value with a high-speed AD converter and calculate it into an average value (or effective value) through arithmetic processing. However, if the temperature control method of the heater is an on-off control type, the operation becomes unstable, and the latter is expensive, resulting in high costs. Since digital conversion is performed using a pulse counter and a pulse counter, it is possible to perform digital conversion of the average value at low cost.Furthermore, since the heater current and heater voltage are taken in alternately (sequentially), the temperature control method of the heater is particularly effective. In the case of a phase control type, there may be a mismatch in waveforms, which may cause malfunction, but the comparator output can be pulsed (11) by measuring the heater current input time and heater voltage input time in the measurement path, and make sure that both are the same. If the input waveforms are the same, an alarm process is performed; if they are different, it is assumed that the waveforms do not match, and no alarm process is performed. This eliminates the habit of malfunctioning even when sequential inputs are taken in.

Therefore, whether the temperature control method of the heater is an on-off type or a phase control type, the heater can operate reliably.

Furthermore, heater current and heater voltage are measured and heater disconnection is detected based on changes in the ratio.
Even in books, it is possible to detect lgilil or short-circuit failures.

Therefore, the intended purpose can be achieved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram. In the diagram

Claims (1)

[Claims] An analog switch that alternately inputs the heater voltage and heater current and controls the timing of the input so that it is synchronized with the cycle of the input AC frequency, a VF converter and a pulse counter that converts the input between fixed cycles into digital, Consists of a comparator and a pulse width measurement circuit that measure the time when the input voltage exceeds a preset threshold level, and the pulse width data acquired is above a certain value and the current and voltage pulse widths are the same. A heater disconnection alarm is characterized in that it issues an alarm when the ratio of heater current to heater voltage is less than a set value.