JP2900793B2 - Water level detection method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode type water level for detecting whether or not a specified water level has been reached by utilizing the conductivity of water when detecting the water level, for example, detecting the water level in a boiler can. The present invention relates to an improvement in a detection method and an apparatus therefor.

[0002]

2. Description of the Related Art In general, the detection of the water level in a boiler or the like can be performed by:
A water level detection rod is inserted into the can via an electrode holder, and a voltage is applied between the water level detection rod and the can, and the electric conduction before and after the water level in the can reaches the water level detection rod. The water level is detected by comparing the degrees. The voltage applied between the can and the electrode is generally an AC voltage. By applying the AC voltage in this manner, if the water surface has not reached the electrode, the AC voltage is detected as it is, and if the water surface has reached the electrode, the AC voltage drops due to the electric resistance of the water. If the electrode is detected and the electrode and the can are short-circuited or a failure occurs in the detection circuit, various states are detected by detecting no voltage fluctuation.

Referring to a specific example, as shown in FIG. 4, a water level detection vessel (1) is connected to a boiler (B) via a gas phase communication pipe (1a) and a liquid phase communication pipe (1b). ), And water level detecting electrodes (2 in the illustrated example) (2) and (2 ') are arranged in an insulated state with respect to the water level detecting vessel (1). A voltage is applied between the detection electrodes (2) and (2 '). And, in a state where the water level has not reached the water level detection electrodes (2) and (2 ′), the applied voltage is directly detected, and the water level has reached the water level detection electrodes (2) and (2 ′). In the state, the above-described applied voltage is detected in a state where the voltage drops due to the resistance of the canned water, thereby detecting that the water level has reached a predetermined position.

The water level detection device (3) is incorporated in a control system (4) for the entire boiler, and the output of the water level detection device (3) is a water supply control device in the control system (4). As one of the control signals when the water pump (6) is started / stopped by the device (5), and the combustion control device (7) in the control system (4) is used to start and stop the combustion device (8). As one of the control signals at the time of stopping, in particular, the combustion device (8)
Is used as a control signal for performing interlock when the water level has not reached at the time of starting.

[0005]

In the water level detecting device (3) having the above structure, the detected value of the applied voltage is compared with a predetermined threshold value V, and the magnitude relation between the threshold value and the predetermined value is compared. Only to detect whether or not the water level has reached, and the comparison circuit for that only outputs a true or false logical value. In this case, the insulation of the water level detection electrode (2) is poor. And water level detector
Due to the failure of (3), the logical value (generally, expressed as a predetermined voltage width) may fluctuate. Specific examples include a water level detection container (1) and a water level detection electrode (2),
(2 ') to the insulating member (not shown) that retains the electrical insulation, water droplets in the water level detection container (1) adhere, or the insulating member deteriorates (due to cracks, etc.). However, if the insulation property is impaired, the water level detection container (1) and the water level detection electrodes (2), (2 ′) are brought into conduction even though the water level has not reached the detection end.

[0006] When the water level is detected by mistake,
In particular, when it is determined that the actual water level has reached the set water level even though it is lower than the set water level, the boiler is in a so-called empty-fired state, which causes heating of the can body and other problems. In particular, in recent years, boilers have been fail-safe, such as reviewing safety standards, and therefore, there has been an increasing demand for a water level detection device that can avoid abstention even when the above-described inconvenience occurs. I have. Accordingly, the present invention has been made in view of the above-described problems, and the present invention provides an electrode-type water level detection method that realizes a fail-safe operation that can prevent an accident by preventing erroneous determination due to electrode insulation failure or circuit failure. It is an object of the present invention to provide a achieved water level detection method and apparatus.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. First, in the detection method, a water level detection terminal is provided at a set water level in the water level detection container. Position, and attached a water level detection electrode in an electrically insulated state, to detect whether the water level in the water level detection container has reached the water level detection end using the conductivity of water, An AC voltage is applied to the water level detection electrode, and two thresholds V1 and V2 are set between the value of the detection signal for reaching the water level and the value of the detection signal for not reaching the water level. After making a logical decision to make the case within the range true, smoothing the output signal of this logical decision, comparing the smoothed output signal with a predetermined threshold V3, and generating a pulse signal when exceeding the threshold V3 And this pulse signal It is characterized by detecting the water level, and in the detection device, with respect to the water level detection container, the water level detection end is located at a set water level in the water level detection container, and electrically insulated In a state where a water level detection electrode is attached in a state and the water level in the water level detection container detects whether or not the water level has reached the water level detection end by using the conductivity of water, an AC voltage is applied to the water level detection electrode. A power supply and a water level detection signal from the water level detection electrode are input, and two threshold values V set between a value of the detection signal of reaching the water level and a value of the detection signal of not reaching the water level.
1, a first comparison circuit for making a logical judgment that the case where the water level detection signal falls within the range of V2, a smoothing circuit for smoothing an output signal from the first comparison circuit, and an output of the smoothing circuit. A second comparison circuit for receiving a signal, comparing the smoothed output signal with a predetermined threshold value V3 and generating a pulse signal when the signal exceeds the threshold value V3, and determining a water level based on the output from the second comparison circuit. It is characterized by including a determination circuit for detecting.

[0008]

According to the water level detection method of the present invention, an AC voltage is applied to the water level detection electrode (2), and two values are set between the value of the detection signal indicating that the water level has reached and the value of the detection signal indicating that the water level has not yet reached. Threshold values V1 and V2 are set, a logical decision is made to make the case where the detection signal is within the range of the threshold values V1 and V2, and an output signal of the logical decision is smoothed. Compared with V3, a pulse signal is generated when the threshold value V3 is exceeded. When the water level has reached the water level detection end (2a) of the water level detection electrode (2), this pulse signal becomes a pulse signal, and the water level is the water level detection end (2a).
If the signal does not reach the threshold, or if there is a defect such as poor insulation of the detection circuit or the water level detection electrode (2), the signal becomes a pulse-free signal with a certain value, and the water level is detected based on the difference in the characteristics of this signal. .

Further, according to the water level detection device of the present invention, an AC voltage is applied to the water level detection electrode (2) by the AC power supply (10), and the water level detection terminal of the water level detection electrode (2) is applied. The case where the water level has reached (2a) and the case where the water level has not yet reached are detected as changes in the amplitude of the AC voltage. This detection signal has two threshold values V1 and V2 between the amplitude width of the detection signal when the water level is reached and the amplitude width of the detection signal when the water level is not reached.
Is set in the first comparison circuit (20) in which is set, and the first comparison circuit (20) makes a logical judgment that the case where the water level detection signal falls within the range of the two threshold values V1 and V2 is true. The output signal from the first comparison circuit (20) is
After being smoothed by (30), it is input to the second comparison circuit (40). The second comparison circuit (40) compares the output signal from the smoothing circuit (30) with a predetermined threshold V3, and generates a pulse signal when the smoothed output signal exceeds the threshold V3. The water level is detected by the determination circuit (50) based on the pulse signal. The output from the second comparison circuit (40) is
When the water level has reached the water level detection end (2a) of the water level detection electrode (2), a pulse signal is generated, and the water level has not reached the water level detection end (2a), or the detection circuit or the water level detection In the case of a defect such as poor insulation of the electrode (2), a signal having a constant value and no pulse is detected, and the water level is detected based on a difference in characteristics of the signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment in which the present invention is applied to the boiler water level detecting device shown in FIG. 4 will be described below. The water level detection method and apparatus according to the present invention are characterized by the configuration after the water level detection electrode, and the details of the configuration and the operation of each circuit are shown in FIG. 1 and FIG. One example is shown in FIG.
This will be described below.

First, in FIG. 3, a water level detecting container (1)
Is communicated with the gas phase communication pipe (1a) and the liquid phase communication pipe (1b) from the boiler (B), as described above, so that the water level in the water level detection vessel (1) and the boiler (B) The water level in the can is configured to be linked. This water level detection container
In (1), two water level detection electrodes (2) and (2 ′) are arranged in an electrically insulated state. These water level detection electrodes (2),
(2 ′), one of the water level detection ends (2a) is above the water level detection end (2a ′) of the other, and therefore, the configuration shown in the drawing is configured to detect two water levels. . That is, the upper level of the water level is detected by the upper water level detection end (2a), and the lower level of the water level is detected by the lower water level detection end (2a '). In this water level detection container (1), in addition to the water level detection electrodes (2) and (2 '), it is necessary to apply an AC voltage for signal detection to these water level detection electrodes (2) and (2'). There is a water level detection container as a counter electrode
(1) is used. This is because a metal material is frequently used as a material in a pressure vessel such as a boiler, and the pressure vessel is generally configured to be grounded to a can body. The water level detection container (1) itself may be used as a counter electrode, or an electrode may be separately provided. In this example,
Since two water level detection electrodes are used, two sets of water level detection devices are used correspondingly, and therefore, each water level detection electrode (2),
(2 ') is connected to each water level detection device (60), (60'), and the water level detection container (1) is connected to both water level detection devices (60), (60 '). The outputs of the water level detection devices (60) and (60 ') are input to the water supply control device (5) and the combustion control device (7) of the boiler control system (4), and the water supply pump (6) and the combustion apparatus
It is configured to perform water supply control such as start / stop of (8) and combustion control.

Hereinafter, the specific configuration of the water level detection device (60) and the operation of each circuit will be described with reference to FIGS. 1 and 2, but one of the water level detection devices will be described. In the water level detection device (60) shown in FIG. 1, input terminals (61) and (61) for connecting a water level detection container (1) and a water level detection electrode (2), a water supply control device (5) and a combustion control device ( 7) and the like, and an output terminal (62) to a control device. An AC power supply (10) is connected between the input terminals (61) and (61) via a first resistor (R1).
The AC power supply (10) may be any power supply that generates a predetermined AC voltage necessary for detection. For example, a power supply (not shown) for driving a circuit can be used directly or by dividing the power supply. The first resistor (R1) is connected to the AC power supply.
This is for dividing the AC voltage applied by (10). Both ends of the series-connected AC power supply (10) and the first resistor (R1) are connected to a first comparison circuit (20).

The first comparison circuit (20) comprises a second resistor (R2) for adjusting the input voltage and third to fifth resistors (R3) to (R3) to (R3) for setting the two thresholds V1 and V2. R5) and each threshold V1,
By calculating the logical product of the signals from the two comparators (I1) and (I2) for performing the determination for each V2 and the two comparators (I1) and (I2),
An AND circuit (I3) for determining whether or not the detection signal is within the range between the two thresholds V1 and V2. still,
Since the voltage change between the water level detection container (1) and the water level detection electrode (2) is an alternating current, this threshold value is shown in FIG. 2 (A)-(A), (B)-
As shown in (a) and (C)-(a), both positive and negative values are obtained. In the first comparison circuit (20), the third to fifth resistors (R
3) to (R5) are connected in series, and the AC voltage of the AC power supply (10) is applied to both ends thereof. Depending on the value of each resistor (R3) (R4) (R5), the threshold V1, V2 is set. That is,
The voltages across the fourth resistor (R4) are the thresholds V1 and V2,
For each of the comparators (I1) and (I2), the signal line of the threshold value and the detection signal line are connected in reverse to each other. Then, each comparator (I
1) (I2) compares the detection signal value input via the second resistor (R2), and at this time, each of the comparators (I1) and (I2) is connected to one of the thresholds V1 and V2, respectively. The magnitude of the value of the signal input to the comparator is determined, and the threshold values V1,
By comparing with V2, a true or false signal is output. The true / false signal from each of the comparators (I1) and (I2) is A
The detection signal is input to the ND circuit (I3) and the detection signals
2, (A)-(b), (B)-(b),
The true value is output as the pulse signal as shown in (C)-(b).

Therefore, in the first comparison circuit (20), the width (that is, the time width) of the output pulse signal changes according to the signal value of the water level detection signal input to the first comparison circuit (20). This is a circuit configuration that changes the so-called duty ratio. As such a first comparison circuit (20), for example, a window comparator is used. The signal from the first comparison circuit (20) is, in the illustrated embodiment,
The signal is input to the smoothing circuit (30) via the NOT circuit (I4).

In the smoothing circuit (30), the first comparison circuit
A smoothed output signal according to the duty ratio of the pulse signal from (20) (see (A)-(C), (B)-(C), (C)-(C) in FIG. 2) is output. The smoothing circuit (30) in this embodiment includes a sixth resistor
Although a simple CR type smoothing circuit formed by combining (R6) and a capacitor (C) is used, other well-known types of smoothing circuits can be used.

Further, the output signal of the smoothing circuit (30)
The second comparison circuit (40) outputs a predetermined pulse signal when the output signal is equal to or higher than a predetermined threshold value V3. That is, the output from the second comparison circuit (40) is
When the water level reaches the water level detection end (2a) of the water level detection electrode (2), a pulse signal as shown in (B)-(d) of FIG. 2 is obtained, and the water level is detected by the water level detection. In the case of failure to reach the end (2a) or insufficiency such as poor insulation of the detection circuit or the water level detection electrode (2), see (A)-(D) and (C)-(D) in FIG. It is a signal without a pulse having a constant value as described above. The second comparison circuit (40) in this embodiment uses a photocoupler,
With this configuration, in addition to the output of the signal as described above, the AC power supply (10) and the circuits such as the determination circuit (50) after the second comparison circuit (40) are electrically cut off, and the determination circuit (50) This prevents excessive voltage from being applied to the side. The second comparison circuit (40) is not limited to such a photocoupler, but may be any comparison circuit that generates a pulse when the input signal is equal to or more than a predetermined value. Then, the output signal from the second comparison circuit (40) is input to the determination circuit (50).

The determination circuit (50) sets a reference voltage by dividing a DC voltage from a DC power supply (51) by seventh and eighth resistors (R7) and (R8). Is compared with a preset reference voltage (threshold value V3) to determine whether the input signal is a pulse-like signal or a signal without a pulse having a constant value. If the water level has reached the water level detection end (2a) of the detection electrode (2), the water level has not reached the water level detection end (2a), or there is a defect such as poor insulation of the detection circuit or the water level detection electrode (2). Judge whether or not. Then, in the boiler control system (4), for example, the determination result is obtained by starting or stopping the water supply pump (6) or the combustion device (8) by the water supply control device (5) or the combustion control device (7). This is used as a control signal when performing the interlock when the water level has not reached at the time of starting the combustion device (8).

Here, as described above, according to the water level detecting device according to the present invention, focusing on the shape of the signal input to the determination circuit (50), the water level is detected by the water level detecting electrode (2). When it reaches the end (2a), it becomes a pulse-like signal, and when the water level does not reach the water level detection end (2a), or when there is a defect such as poor insulation of the detection circuit or the water level detection electrode (2). Is a signal without a pulse having a constant value. Therefore, when the water level has reached the water level detection end (2a) of the water level detection electrode (2), the water level has not reached the water level detection end (2a), or the detection circuit has a defect or the water level detection electrode (2 ) Can be clearly distinguished from the case where insulation failure is detected.Especially, when the detection circuit is defective or the water level detection electrode (2) is defective, the water level reaches Is not detected. Therefore, in the water level detection device used in combination with the boiler water supply control device (5) and the combustion control device (7) as described above, when the water level does not reach the predetermined water level, there is a problem with the detection device and the water level. The water level is not detected by mistake due to the insulation failure of the detection electrode (2), but both are detected as not reaching the water level. Danger can be avoided, in other words, failsafe can be achieved.

In the above description, a specific embodiment in which the present invention is applied to a water level detecting device for a boiler has been described. However, the present invention is not limited to such a water level detecting device for a boiler. It can be applied to the detection of the water level of a water supply tank and the detection of the liquid level of a chemical liquid tank. Incidentally, boiler water is generally a good conductor of electricity because chemicals are introduced for water quality management, and such a water level detection method is particularly suitable, but other well water or tap water is used as a water source. When the present invention is applied to the detection of the water level of water, since the electric conductivity is not so high, it is necessary to make appropriate adjustments such as narrowing the interval between the threshold values V1 and V2.

[0020]

According to the present invention, when the water level has reached the water level detection end of the water level detection electrode, a pulse signal is generated, and the water level has not reached the water level detection end, or the detection circuit or In the case of a defect such as poor insulation of the water level detection electrode, a signal without a pulse having a certain value is obtained, and the water level is detected based on a difference in the characteristics of the signal. It is possible to clearly distinguish between the case where the water level has reached the water level detection end and the case where the water level has not reached the water level detection end, or a case where a failure of the detection device or insulation failure of the water level detection electrode has been detected. In the case of the above-mentioned problem or the insulation failure of the water level detecting electrode, it is no longer erroneously detected that the water level has reached as in the conventional case. Therefore, when reaching the predetermined water level is erroneously detected and causes a serious accident, for example, a water level detection device used in combination with the above-described boiler water supply control device or combustion control device, etc. By applying such a method, such danger can be effectively avoided, in other words, fail-safe operation can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an embodiment of the present invention.

2 (A), 2 (B), and 2 (C) are diagrams for explaining the operation of each circuit in the embodiment shown in FIG. 1; 2 (A), 2 (B), 2 (C), 2 (D), 2 (A), 2 (B), and 2 (B), respectively.
(C), the water level detection signal, the output signal of the first comparison circuit,
5 is a diagram illustrating an output signal of a smoothing circuit and an output signal of a second comparison circuit.

FIG. 3 is a drawing for explaining an example of a specific application form of the present invention.

FIG. 4 is a diagram illustrating a general method of detecting a water level in a boiler.

[Explanation of symbols]

 (1) Water level detection vessel (2) Water level detection electrode (2 ') Water level detection electrode (2a) Water level detection end (2a') Water level detection end (10) AC power supply (20) First comparison circuit (30) Smoothing circuit ( 40) Second comparison circuit (50) Judgment circuit (60) Water level detector (60 ') Water level detector

Claims (3)

(57) [Claims] A water level detection electrode is provided in a state in which a water level detection end (2a) is located at a set water level in the water level detection vessel (1) and is electrically insulated from the water level detection vessel (1).
Attach (2), to detect whether the water level in the water level detection container (1) has reached the water level detection end (2a) using the conductivity of water, wherein the water level detection electrode (2) AC voltage is applied to the sensor, and two thresholds V1 and V2 are set between the value of the detection signal for reaching the water level and the value of the detection signal for not reaching the water level, and the detection signal is within the range of the thresholds V1 and V2. Is true, and the output signal of the logical judgment is smoothed, and the smoothed output signal is compared with a predetermined threshold value V3. When the output signal exceeds the threshold value V3, a pulse signal is generated. A water level detection method, wherein a water level is detected based on a signal. 2. A water level detection electrode which is positioned relative to a water level detection vessel (1) at a set water level in the water level detection vessel (1) and is electrically insulated.
Attach (2), to detect whether the water level in the water level detection container (1) has reached the water level detection end (2a) using the conductivity of water, wherein the water level detection electrode (2) An AC power supply (10) that applies an AC voltage to the water level detection signal from the water level detection electrode (2) is input, and is set between the value of the detection signal of reaching the water level and the value of the detection signal of not reaching the water level. A first comparison circuit (20) for making a logical judgment that the case where the water level detection signal falls within the range of the two threshold values V1 and V2 is true;
A smoothing circuit (3) for smoothing the output signal from the comparison circuit (20)
0) and the output signal of the smoothing circuit (30), and compares the smoothed output signal with a predetermined threshold value V3 to generate a pulse signal when exceeding the threshold value V3.
And a determination circuit (50) for detecting a water level based on an output from the second comparison circuit (40). 3. The water level detecting device according to claim 2, wherein said first comparison circuit is a window comparator.