JPS6156764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam leak detection device that detects steam leaks in pipes or the like through which high-temperature steam passes based on changes in humidity or humidity and temperature.

Conventionally, when detecting steam leaks from piping or valves through which high-temperature steam passes, such as those used in power plants, it is necessary to place a mirror or a matted surface close to the area where steam is thought to be leaking, and to prevent condensation from condensing on the mirror surface. It was determined that steam was leaking. However, such visual judgment is not only time-consuming and inaccurate, but also fails to detect minute leaks.
In power plants and the like, it is extremely important to detect such leaks early and take countermeasures in order to facilitate equipment maintenance and prevent accidents.

The present invention has been made to meet such demands, and an object of the present invention is to provide a steam leak detection device that can easily and reliably detect steam leaks.

By the way, the inventors have discovered that when a steam leak occurs, there are two modes: a case where the vicinity of the leak part becomes high temperature and high humidity, and a case where the relative humidity increases intermittently. The former is mainly found in conditions where the atmosphere is stable, such as indoors, and the latter is mainly found outdoors in windy conditions. The present invention is configured so that steam leakage can be detected in any of these cases.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In this figure, the output end of the oscillator 1 is connected to a parallel connection of a humidity detection element R _H and a resistor R _P via a DC cutoff capacitor C1 and a resistor R1. The oscillator 1 outputs an oscillation signal having a period sufficiently shorter than the response speed of the humidity detection element R _H and having a constant amplitude value. The humidity detection element R _H is an element whose resistance value changes in response to changes in relative humidity, and for example, a ceramic humidity sensor is used which can prevent deterioration of performance by heating the sensor section. This ceramic humidity sensor is an element whose resistance value decreases as relative humidity increases. When a DC voltage is applied to the humidity detection element R _H , it is electrolyzed and its resistance and humidity resistance characteristics change, so only an AC component is applied. The parallel resistor R _P is a resistor for changing the detection sensitivity of humidity change with respect to relative humidity. One end of the humidity detection element R _H is connected to an input terminal of the impedance conversion circuit 2 and a smoothing capacitor C2 via a rectifying diode D. The impedance conversion circuit 2 is for impedance matching with the next stage signal processing section, and converts a high impedance input signal into a low impedance signal. The output of the impedance conversion circuit 2 is applied to a low-pass filter 3 having a cutoff frequency of, for example, several Hz. low pass filter 3
is made insensitive to rapid minute humidity changes to prevent sensitivity in detection. The output of low-pass filter 3 is a differentiator circuit consisting of capacitor C3 and resistor R2.
It is applied to one input terminal of the comparator 4 via DIF. The other input terminal of the comparator 4 is connected to a power supply voltage dividing circuit including resistors R3 and R4. Comparator 4 detects when the amount of change in humidity increase is greater than a predetermined value and
It outputs the level. The output of the low-pass filter 3 is also directly given as one input of the comparator 5, and the other input terminal is connected to a voltage dividing circuit consisting of resistors R5 and R6. The comparator 5 outputs an H level output when the humidity is above a predetermined value, and the output is output from the AND circuit 7.
given to. On the other hand, a temperature detecting element R _T such as a thermistor, together with a resistor R7, constitutes a voltage dividing circuit for the power supply voltage, and is applied to the comparator 6 together with the input of the voltage dividing circuit consisting of resistors R8 and R9. The comparator 6 outputs an H level output when the temperature is above a predetermined value, and the output is given to the AND circuit 7. The AND circuit 7 takes the AND of the comparators 5 and 6, and its output is the OR circuit 8.
given to. The OR circuit 8 calculates the logical sum of the AND circuit 7 and the comparator 4, and its output is given to the display device 9. The display device 9 includes, for example, a light emitting element and a sounding means, and displays the leakage of steam.

Here, the humidity detection element R _H and the temperature detection element R _T are provided at the tip of a small probe rod (not shown),
It is assumed that it is connected to the main body containing other circuits by a cord. This probe is brought close to valves, pipes, and other areas where high-temperature steam passes through to detect steam leaks.

Next, the operation of this embodiment will be explained with reference to FIGS. 2a and 2b. FIGS. 2a and 2b are graphs showing the operating range of the present steam leak detection device with respect to relative humidity and temperature or humidity change rate, respectively. The AC output of the oscillator 1 is applied to the humidity detection element R _H and the resistor R _P via the capacitor C1 and the resistor R1. As a result, an alternating current voltage V1 corresponding to the relative humidity is obtained at both ends thereof. AC voltage V1 is diode D and capacitor
It is rectified by C2, and a DC voltage V2 of a magnitude corresponding to the relative humidity is obtained across the capacitor C2. This DC voltage V2 is passed through the above-mentioned impedance converter 2 and low-pass filter 3 to the differential circuit.
Differentiated by DIF. This differential output V3 is given to the comparator 4, and the other input of the comparator 4 is the voltage dividing circuit output V4 by the resistors R3 and R4.
compared to Therefore, if the relative temperature detected by the humidity detection element R _H changes at a rate higher than a predetermined rate, the output V3 of the differentiating circuit DIF changes to the voltage dividing circuit output V4.
becomes smaller, and the comparator 4 outputs an H level signal. Note that when the relative humidity is high, the resistance value of the relative humidity detection element R _H is small, so the combined resistance value of the resistance R _P and the relative humidity detection element R _H is almost determined by the resistance value of the relative humidity detection element R _H. It changes greatly depending on humidity changes. Conversely, when the relative humidity is low, the resistance value of the relative humidity detection element R _H is large,
The combined resistance value is almost determined by the parallel resistance R _P and does not change significantly even with changes in relative humidity. Therefore, the output of comparator 4 is as shown in Fig. 2b.
As shown in , if the relative humidity is low, it will not work unless the rate of change in humidity is large. Also, when the relative humidity increases, the output of the low-pass filter 3 given to the comparator 5 becomes the output of a voltage divider circuit consisting of resistors R5 and R6.
When the voltage is below V5, the comparator 5 outputs an H level. The values of resistors R5 and R6 are determined in advance so that the critical relative humidity for performing this operation is, for example, 65%. Next, the temperature rises, and the voltage divider circuit output V6 consisting of resistor R7 and temperature detection element R _T becomes a resistor.
When the voltage becomes smaller than the output V7 of the voltage dividing circuit composed of R8 and R9, the comparator 6 outputs an H level. The values of resistors R8 and R9 are determined in advance so that the critical temperature for performing this operation is, for example, 55°C. Then, if both the temperature and relative humidity are above the critical values as shown in FIG. 2a, the AND circuit 7 becomes H level. The OR circuit 8 gives an output to the display device 9 when the comparator 4 or the AND circuit 7 is at H level, and the display device 9 displays the leakage of steam.

As described above, according to the present invention, steam leakage can be detected both when the vicinity of the leakage part becomes high temperature and high humidity, and when the relative humidity increases intermittently. In addition, steam leak detection is easier and more reliable than conventional visual inspection methods, and is highly effective in preventive maintenance of equipment and accident prevention. Furthermore, when the humidity is low in detection based on the rate of change in relative humidity, Figure 2b
As shown in Figure 2, it has low sensitivity, so it will not malfunction due to the presence of a small amount of water droplets or the observer's breath. When the humidity is high, there are few external influences, so even slight changes in humidity can be detected as steam leaks, making it possible to prevent malfunctions.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2a is a graph showing relative humidity relative to temperature, and Fig. 2b is a graph showing the operating range of the steam leak detection device relative to relative humidity relative to humidity change rate. be. 1... Oscillator, 2... Impedance converter,
3...Low pass filter, 4,5,6...Comparator, R _H ...Humidity detection element, R _T ...Temperature detection element, DIF... Differential circuit, R _P ... Parallel resistance.

Claims (1)

[Scope of Claims] 1. A humidity detection circuit that includes a humidity detection element and converts relative humidity into an electrical quantity; a differentiation circuit that differentiates the output of the humidity detection circuit; and a predetermined first reference for the output of the differentiation circuit. a second comparator that compares the output of the humidity detection circuit with a predetermined second reference value; and a temperature detection circuit that includes a temperature detection element and converts temperature into an electrical quantity. and a third comparator that compares the output of the temperature detection circuit with a predetermined third reference value, the output of the first comparator, and the AND output of the second and third comparators. A steam leak detection device comprising: a logic circuit that takes a logical sum; and an output device that outputs a steam leak output based on an output of the logic circuit. 2. The steam leak detection device according to claim 1, wherein the humidity detection element is a ceramic humidity sensor. 3. Claim 1 or 3, wherein the humidity detection circuit includes an oscillation circuit that applies an alternating voltage to the humidity detection element, and a rectification circuit that rectifies the voltage across the humidity detection element. Steam leak detection device according to item 2. 4. The steam leak detection device according to claim 1, wherein the output device comprises visual or auditory display means. 5. The steam leak detection device according to claim 2, wherein the humidity detection circuit includes a resistor connected in parallel to the humidity detection element.