JPH02226029A - Disconnection detecting apparatus for voltage signal generating circuit - Google Patents

Abstract

PURPOSE:To detect a disconnection of a voltage signal generating circuit by providing a power source for detecting a disconnection with a function to generate a plurality of detecting voltages different from each other, periodically selecting said detecting voltages and outputting said selected voltage through an A/D converter. CONSTITUTION:Every time an output from a voltage signal generating circuit 1 is A/D converted, switches SW1 and SW2 are sequentially driven by a CPU 4 thereby to switch a power source 5 for detecting a disconnection. A switching frequency of this power source, namely, a period of the A/D conversion of the power source is set shorter than a changing time of the output signal of the voltage signal generating circuit 1, namely, a changing time T of an input signal from an A/D converter 3 which signal is taken into the CPU 4. In other words, the switching frequency is set to be (t). Accordingly, when the voltage signal generating circuit 1 is not disconnected, approximately constant data corresponding to the output signal of the circuit 1 is taken into the CPU 4.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides a voltage signal generation circuit for temperature control, for example, a combustion device! This invention relates to a device for detecting disconnection of wiring such as a thermocouple in a TIK or a unified signal of 1 to 5V.

[Prior art]

Conventionally, this type of disconnection detection device has a voltage signal generation circuit, for example, a thermocouple, which is connected to a disconnection detection power source 5 via a limiting resistor R to detect the disconnection of the thermocouple, as shown in FIG. A current i for detection is connected through the limiting resistor R.
is washed away. Since the wiring resistance of this electric current R1 and the thermocouple causes an error when measuring the thermoelectromotive force, the value of the resistance R is generally set so that the detected current i is sufficiently small. Then, the value of the product of the detection chamber fii and the resistance R is input to the operational amplifier 2.

Of course, the output end of the thermocouple is connected to the input end of the operational amplifier 20.

In FIG. 6, when the thermocouple, that is, the voltage signal generating circuit is not disconnected, the circuits become as shown in FIG. 7. In this circuit diagram, the output voltage Vo+ of the operational amplifier 2 is given by the following equation.

``Zen + rf ■o, = E ...... (1) r・ Here, E is the thermoelectromotive force of the thermocouple.In addition, in this equation, the effect of the current for detecting disconnection of the thermocouple is ignored. There is.

In addition, if the thermocouple in FIG. 6 is disconnected, both circuits become as shown in FIG. 8. The output voltage VO! of the operational amplifier 2 in this circuit becomes as follows.

■(1,=　’・+rfV 1 win Here, V is the voltage of the disconnection detection power supply 5.

Generally, the thermoelectromotive force E of a thermocouple is in the unit of millivolts, so if the detection voltage V is set in the unit of volts, for example, a normal state and a disconnection state can be easily distinguished.

[Problems to be solved by the present invention] In the method shown in FIG. It is necessary to set a value, for example, 15VK, that is sufficient to distinguish it from the range of 5 signals from O to IOV. This is because it is impossible to determine whether the voltage of the disconnection detection power supply 5 is due to a disconnection in the voltage signal generation circuit 1 or whether the input signal from this circuit has become excessive. Furthermore, it is not preferable from an economic point of view to design a large difference between the voltage of the disconnection detection power supply 5 and the range of the input signal voltage.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of these conventional problems, it is an object of the present invention to provide a disconnection detection device that does not require setting the voltage of a power supply for disconnection detection to a potential that is extremely different from the electromotive force of the voltage signal generation circuit.

[Summary of the invention]

In order to achieve the object, the present invention provides a disconnection detection power supply with a function of generating a plurality of different detection voltages, periodically selects these detection voltages, and uses the A/D
Disconnection of the voltage signal generation circuit is detected by outputting the signal through a converter, and the voltage of the disconnection detection power source may be at the same level as the electromotive force of the voltage signal generation device.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

That is, in FIG. 1, reference numeral 1 denotes a voltage signal generating circuit, which is composed of, for example, a thermocouple circuit. Output terminals a and b of this voltage signal generation circuit are connected to the input terminal of an operational amplifier 2. The resistor ri+rf determines the gain of the operational amplifier 2. Also, the output terminal of this operational amplifier has an A/D
A converter 3 is connected. Furthermore, the output end of this A/D converter is connected to the CPU 4. One of the output terminals of the voltage signal generation circuit 1, that is, the positive input of the operational amplifier 2 1) 1i
A disconnection detection power source 5 is connected to the disconnection detection power source 5 through a relatively high resistance R, for example, 20 (MΩ).The disconnection detection power source 5 has a plurality of different voltages V, , V.

and is selectively switched by switches SWI and SW2. Note that this switch is controlled by the CPU 4. More specifically, the CPU 4 switches to a predetermined algorithm.

In the above configuration, the output signal of the voltage signal generating circuit 1 may be, for example, the temperature inside the furnace as shown in FIG.

When the voltage signal generation circuit 1 is operating normally, that is, in a non-disconnection state, the output of this circuit (Fig. 2) is input to the A/D converter 3 through the operational amplifier 2, and at this time, the analog signal is converted into a digital signal. The signal (FIG. 3) is further input into CPo 4.

Therefore, every time the output of the voltage signal generation circuit 1 is A/D converted, the switches SWI and SW2 are sequentially driven by the CPO 4 to switch the disconnection detection power supply 5. The switching cycle of this power supply, that is, the A/D conversion cycle of the power supply, is compared to the change time T of the output signal of the voltage signal generation circuit 1, that is, the change time T of the input signal from the A/D converter 3, which is taken into the CPU 4. When the voltage signal generation circuit 1 is set to C, substantially constant data (FIG. 4) corresponding to its output signal (FIG. 2) is taken into the CPU 4 when the voltage signal generation circuit 1 is not disconnected. This is because the temperature change in the furnace is much slower than the operating time of the A/D converter 3. For example, if the furnace temperature change is a minute value, the operating time of the A/D converter 3 is j17 seconds. Set to the unit value.

FIG. 5 is a flowchart showing the operating procedure. First, at the start, the controlled object, for example, the voltage signal generating circuit 1 in the furnace is in the on state lIK, and its output signal E is output from the operational amplifier 2 and The signal is taken in by the CPU 4 through the A/D converter 3 as a converted value corresponding to the signal.

Therefore, in the flowchart of FIG. 5, steps to be taken when an abnormality occurs in the voltage signal generating circuit 1 will be explained first. In other words, the CPU 4 selects the changeover switch SW.
Switch I and SW2 sequentially. First, select switch SWI.
, and open switch SW2 (step 1).

Next, wait for the A/D conversion value to stabilize (step 2).

When the A/D conversion value becomes stable, the value is taken into the CPU 4 (step 3).

Here, the input signal E of the voltage signal generation circuit 1 is equal to the voltage 1 of the disconnection detection power supply 5, that is, E = V,
If so, CPU 4 determines that there is a suspicion of a disconnection and selects YES.
becomes. Therefore, this time, the CPU 4 opens the selector switch SWI and closes SW2 instead (step 6).

Then, wait until the conversion value of the A/D converter 3 becomes stable (step 7).

When the converted value becomes stable, the value is taken in by CPO4 (step 8).

Here, when the output signal E of the voltage signal generation circuit 1 and the output voltage Vt of the disconnection detection power supply 5 are equal, that is, E = V
, it becomes YES. If the determination by the CPU 4 is YES in step 4 and the determination by the CPU 4 is YES in step 9, it is assumed that a disconnection has occurred in the voltage signal generation circuit 1, and the process moves to disconnection detection processing (step 11).

Further, close the changeover switch SWI and open the changeover switch SW2 to take in the A/D conversion value again. After confirming that a conversion value corresponding to the voltage V of the disconnection detection power supply 5 is obtained, it is determined that the disconnection has occurred. That judgment becomes even more certain.

Next, a case where there is no abnormality in the voltage signal generation circuit 1 will be described.

That is, in step 4, the input signal E from the voltage signal generation circuit 1 is the voltage (2) of the disconnection detection power supply 5.

If it is different from , the CPU 4 determines that there is no disconnection, and the result is No. As a result, the process proceeds to normal processing (step 5).

Further, in step 9, when the output signal E of the voltage signal generation circuit 1 and the output voltage Vt of the disconnection detection power supply 5 are different,
That is, if the actual input voltage is E=V and there is no disconnection, the result is KNO and the process moves to normal processing (step 10).

Further, even if the determination in step 4 is YES, that is, even if there is a suspicion that the voltage signal generation circuit 1 is disconnected, if the determination is NO in step 9, it is assumed that there is no disconnection and normal processing (step 10
).

Note that when comparing the A/D conversion value and the output voltage of the disconnection detection power supply 5, ■ or ■, consider circuit errors, etc., and do not judge based on the A/D conversion value =■, but rather V, -t. ≦A/D conversion value≦V, +t is used as an actual judgment. This is the blur tolerance.

〔Effect of the invention〕

As described above, in this invention, the disconnection detection power supply 5 has the function of outputting a plurality of different detection voltages, and the output voltage of the voltage signal generation circuit l and the output voltage of the disconnection detection power supply 5 are
Input to the Dffi converter 3 and power supply 5 for disconnection detection
The output state of the A/D converter 3 is compared by switching the output state of the A/D converter 3, and a disconnection of the voltage signal generation circuit 1 is detected thereby. As long as the detected voltage of the power supply 5 does not vibrate at exactly the same frequency as the operation of the changeover switches SWI and SW2 that match the A/D conversion cycle, there is no chance of misjudging the disconnection state (and the A/D conversion cycle is The time constant is in seconds, and if it is sufficiently small compared to the time constant of the actual voltage signal generation circuit, it will not be mistakenly determined to be a disconnection.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing one embodiment of a disconnection detection device for a voltage signal generating circuit according to the present invention, FIG. 2 is a characteristic diagram showing the output voltage of the voltage signal generating circuit, and FIG. 3 is a diagram showing the output voltage of the voltage signal generating circuit. C through the A/D converter in a non-disconnected state
A characteristic diagram showing the data taken into the PU. Figure 4 is a characteristic diagram showing the data taken into the CPU via the KA/D converter when the voltage of the disconnection detection power supply is switched. Figure 5 is a characteristic diagram showing the data taken into the CPU through the KA/D converter.
6 is a circuit diagram showing a conventional device, FIG. 7 is an equivalent circuit diagram when the voltage signal generation circuit of FIG. 1 is in a non-disconnected state, and FIG. FIG. 3 is an equivalent circuit diagram when the same circuit is in a disconnected state. 1... Voltage signal generation circuit, 2... Operational amplifier, 3.
... A/D converter, 4... CPU, 5... Power supply for disconnection detection RL... Resistor, SWI, SW2... Changeover switch patent applicant: Yamatake Honeywell Co., Ltd. agent, patent attorney 1 ) Hiroshi Sawa (2 others)

Claims (2)

[Claims] (1) An operational amplifier (2) for amplifying the output of the voltage signal generation circuit (1) is connected to the output terminal of the voltage signal generation circuit (1),
Further, an A/D converter (3) for A/D converting the output signal from this amplifier is connected to the output terminal of this operational amplifier, and one of the output terminals of the voltage signal generation circuit (1) is connected to a relatively high A disconnection detection power source (5) having a plurality of different output voltages is connected through a resistor (RL) of a different value, and the disconnection detection power source (5) is connected between the disconnection detection power source and the resistor (RL). ) switch to selectively change the output voltage of (
SW1) (SW2) are provided, and the voltage signal generation circuit (1
) and the output voltage of the disconnection detection power supply (5) are simultaneously supplied to the operational amplifier (2), and these signals are outputted through the A/D converter (3) to obtain the voltage signal. A disconnection detection device for a voltage signal generation circuit, characterized in that it detects a disconnection state of the generation circuit (1). (2) The output terminal of the A/D converter (3) is connected to the CPU (4
) is connected, and the above A/D converter (3) is connected by this CPU.
) and the changeover switches (SW1) (SW2), and also input the output signal of the disconnection detection power supply (5) and the output of the voltage signal generation circuit (1) to the A/D converter (3). , and a disconnection state of the voltage signal generation circuit (1) is detected by processing the output of the A/D converter by the CPU (4) according to a certain determination algorithm. A disconnection detection device for a voltage signal generation circuit according to claim 1.