JP2006300525A - Water level detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a water level with high resistance to noise under wide environmental conditions. <P>SOLUTION: A water level detector comprises a first DC power supply 100 for supplying a current for a serial circuit of a thermistor 101 for detecting a water level and a resistor 102 serially connected to the thermistor 101; a second DC power supply 114 having a voltage lower than a voltage of the first DC power supply 100; and a first analog voltage detection circuit 111 for receiving both the supply of a current from the second DC power supply 114 and a voltage of the thermistor 101 via a first voltage conversion circuit 108. It is detected on the basis of a value of the first analog voltage detection circuit 111 whether a water level has reached the thermistor 101 or not. Since the first analog voltage detection circuit 111 can detect an analog voltage corresponding to a voltage of the thermistor 101, the first analog voltage detection circuit 111 has high resolution to enable fine adjustments of determination criteria corresponding to changes in environmental conditions when changed, the prevention of the occurrence of almost every error operation due to noise, and adaptation to wide environmental conditions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water level detection device used in washing machines, dishwashers, air conditioners and the like.

  Conventionally, this type of water level detection device detects a water level by providing a water level sensor configured using a self-heating type thermistor, an operating point resistance and an operating point switching resistor, and an operating point switching transistor ( For example, see Patent Document 1).

  FIG. 6 shows a circuit diagram of a conventional water level detection device described in Patent Document 1.

  As shown in FIG. 6, a series circuit of a water level sensor 1 and a water level detection resistor 01 constituted by a self-heating type thermistor is connected to a constant voltage power source 2 and provided with a comparator 4 for comparing the voltage of the operating point resistor 3. The water level of the water storage tank 7 is detected and a detection signal is sent to the control means (microcomputer) 10.

The operating point switching resistors 11, 12, 13, and 14 are turned on / off by a signal from the control means (microcomputer) 10, and the voltage dividing ratio with the operating point resistor 3 is changed by the operating point switching transistors 21, 22, 23, and 24. Therefore, the operating point voltage input to the comparator 4 is changed, and the control means (microcomputer) 10 has an optimum operating point according to the detection values by the water temperature thermistor 31 and the temperature thermistor 32. By switching on and off the operating point switching transistors 21, 22, 23, and 24 so that the voltage is maintained, a water level detecting device having a wide usable temperature range is realized.
JP 2001-159556 A

  However, in the case of this type of conventional water level detection device that detects whether or not the water level reaches the thermistor by the water level sensor 1 constituted by a self-heating thermistor, whether the thermistor is submerged in water or in the air The voltage of the thermistor when it is in the water or in the air is the same as that of the thermistor element itself. Although it varies depending on the temperature, the temperature of the thermistor element itself varies considerably depending on environmental conditions such as ambient temperature, the strength of the wind hitting the thermistor, the presence or absence of water flow, and the voltage of the thermistor also varies.

  For this reason, in the configuration of the conventional water level detection device, each operating point switching transistor is switched from the control means (microcomputer) to cope with the ambient temperature such as water temperature or air temperature which is one of the environmental conditions. Since the transistor has only two states of on / off, even if a large number of operating point switching transistors, such as four, is provided, the operating point voltage cannot be changed continuously, and therefore switching is performed. In the vicinity of the temperature condition, the difference between the voltage of the water level sensor 1 input to the comparator 4 and the operating point voltage is reduced, and there is a problem that malfunction due to noise is likely to occur.

  The present invention solves the above-described conventional problems, and provides a water level detection device that can set a comparative voltage with higher resolution, is less prone to malfunction due to noise, and can be used in a wide range of environmental conditions. The purpose is that.

  In order to solve the above-described conventional problems, a water level detection device according to the present invention supplies a current to a thermistor for detecting a water level, a resistor connected in series to the thermistor, and a series circuit of the thermistor and the resistor. A first DC power supply, a second DC power supply whose voltage is lower than the voltage of the first DC power supply, a current is supplied from the second DC power supply, and the voltage of the thermistor is converted into a first voltage. A first analog voltage detection circuit received via a circuit, receiving the value of the first analog voltage detection circuit, and detecting whether the water level has reached the thermistor, The power supply from the first DC power source having a high voltage enables the thermistor to self-heat firmly, so the ratio of the resistance value of whether the thermistor is underwater or in the air is large. As a result, the thermistor terminal voltage difference can be very large, and the detection performance of the thermistor itself is sharp. In addition, it is built into a microcomputer that works with the second DC power supply. Since the voltage can be read by the first analog voltage detection circuit such as an AD converter having a resolution of 1), the resolution can be considerably increased.

  Therefore, for the read voltage, for example, it is possible to slightly change the threshold value when determining whether the thermistor is in water or in the air according to the change in ambient temperature, and the characteristics of the original thermistor The operation can be performed while ensuring a noise margin that effectively utilizes the.

  Other environmental conditions other than ambient temperature also vary depending on changes in the operating mode of the equipment used as an application, for example, when wind is applied to the thermistor, or when water is flowing. If there is, there will be a need for fine adjustment of the comparison value, for example, due to the malfunction, but since this can also be read with the above-described high resolution, the threshold value is also reduced. A minute change is effective and can respond.

  Therefore, by changing the comparison value for the read voltage finely according to environmental conditions such as ambient temperature, it is possible to realize excellent characteristics that are unlikely to cause malfunction due to noise under a wide range of environmental conditions.

  Since the water level detection device of the present invention can read the voltage of the thermistor that generates heat with high resolution, it has a high ability to cope with changes in environmental conditions, is unlikely to malfunction due to noise, and has high stability.

  According to a first aspect of the present invention, there is provided a thermistor for detecting a water level, a resistor connected in series to the thermistor, a first DC power supply for supplying a current to a series circuit of the thermistor and the resistor, A second DC power supply that is lower than the voltage of the first DC power supply, and a first analog voltage detection circuit that receives current from the second DC power supply and receives the voltage of the thermistor via the first voltage conversion circuit. And receiving the value of the first analog voltage detection circuit to detect whether or not the water level has reached the thermistor, the power from the first DC power supply having a high voltage. The supply enables the thermistor to self-heat firmly, increasing the ratio of the resistance value of whether the thermistor is underwater or in the air, and the difference in the terminal voltage of the thermistor is also very large A large one can be obtained, and the thermistor itself has a sharp detection performance. In addition, the first analog such as an AD converter that has a considerable resolution is built in a microcomputer that operates with the second DC power source. Since the voltage can be read by the voltage detection circuit, the resolution can be considerably increased. Therefore, for the read voltage, for example, it is possible to slightly change the threshold value when determining whether the thermistor is in water or in the air according to the change in ambient temperature, and the characteristics of the original thermistor The operation can be performed while ensuring a noise margin that effectively utilizes the.

  Other environmental conditions other than ambient temperature also vary depending on changes in the operating mode of the equipment used as an application, for example, when wind is applied to the thermistor, or when water is flowing. If there is, there will be a need for fine adjustment of the comparison value, for example, due to the malfunction, but since this can also be read with the above-described high resolution, the threshold value is also reduced. A minute change is effective and can respond.

  Therefore, by changing the comparison value for the read voltage finely according to environmental conditions such as ambient temperature, it is possible to realize excellent characteristics that are unlikely to cause malfunction due to noise under a wide range of environmental conditions.

  In particular, the second invention is provided with opening / closing means connected in series to the thermistor and resistor of the first invention and supplied with current from the first DC power supply, and the first analog voltage detection circuit A voltage corresponding to the power supply voltage of the first DC power supply is received via the first voltage conversion circuit during the period when the means is off, and a malfunction due to noise in a wide range of environmental conditions with a relatively simple configuration. In addition, it is possible to prevent the erroneous detection of the voltage variations of the first DC power supply and the second DC power supply and to exhibit excellent response.

  In the third invention, in particular, the opening / closing means of the second invention is provided with an ON period and an OFF period alternately, and the first DC power supply and the second DC power supply are initially configured with a relatively simple configuration. In addition to the voltage variation, it is possible to effectively cope with the characteristic that the voltage value fluctuates with time, and an extremely high malfunction suppression function can be realized.

  According to a fourth aspect of the invention, in particular, the water level detection device of the first aspect of the invention is provided with a second voltage conversion circuit and a second analog voltage detection circuit that receives the first DC power supply via the second voltage conversion circuit. And receiving the outputs of both the first analog voltage detection circuit and the second analog voltage detection circuit to detect whether or not the water level has reached the thermistor. Responding to variations in the DC power supply and the second DC power supply and changes in the time axis, the water level can be detected continuously.

  In the fifth aspect of the invention, in particular, the water level detection device according to any one of the first to fourth aspects includes temperature detection means for detecting the temperature in the vicinity of the thermistor. For example, according to the output of the temperature detection means. Thus, if the threshold value at the time of detecting the water level is changed, it is possible to sufficiently take measures against a temperature condition which is one of environmental conditions and has a large influence degree.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 shows a circuit of a water level detection device according to a first embodiment of the present invention. The circuit includes a first DC power supply 100 that outputs a voltage of 12 volts, a thermistor 101, and a resistor 102 of 250 ohms. The thermistor 101 has a series circuit, and the thermistor 101 is self-heated when a current is supplied from the first DC power supply 100.

  The thermistor 101 is connected by a lead wire (not shown) from a 2-pin connector 103, and the terminal on the low potential side of the thermistor 101 has opening / closing means 104 composed of an NPN transistor, 101, resistor 102, and switching means 104 are connected in series, and when the switching means 104 is on, current is supplied from the first DC power supply 100, and the thermistor 101 causes self-heating. ing.

  If the thermistor 101 has a small amount of self-heating, the difference in internal element temperature between the case where the thermistor 101 is in water and the case where it is in the air is small, and the resistance ratio tends to be low. However, in this embodiment, since the first DC power supply 100 having a high voltage of 12V, which is higher than the 5V power supply often used for a normal microcomputer chip or the like, is used, it is about 100 mW. Since the self-heating power can be obtained, the temperature difference of the internal element between the case where the thermistor 101 is in the water and the case where it is in the air can be increased, and a large resistance ratio can be obtained. Sharp detection characteristics can be realized.

  By the way, when trying to self-heat the thermistor from the 5V power supply that is common with the microcomputer, a thermistor having a fairly low resistance value of about several tens of ohms is used. In addition, the inflow current from the 5V power supply becomes as large as a few hundred mA when in the air, and changes within the range of 0 to 5V are observed. In comparison, the absolute value of the voltage difference between the water and the air is also reduced accordingly, so that the noise is weak.

  The diode 105 is provided so as to release an induced voltage generated by an inductance component of the wiring and the like to prevent an overvoltage from being applied to the switching means 104 at the moment when the switching means 104 is turned off. is there.

  The voltage V1 at the terminal on the high potential side of the thermistor 101 is input to the first voltage conversion circuit 108 constituted by the resistors 106 and 107.

  In this embodiment, the series resistance value of the resistors 106 and 107 is set to about 10 kilohms, which is higher than that of the resistor 102. Therefore, the first resistance with respect to the divided output V1 by the thermistor 101 and the resistor 102 is set. The influence of the voltage conversion circuit 108 is small and almost negligible, and a voltage obtained by dividing V1 by the resistors 106 and 107 and attenuated to 37.5% is output.

  The voltage output from the first voltage conversion circuit 108 is input to the first analog voltage detection circuit 111 after passing through the resistor 109 and the capacitor 110 in order to further remove noise components.

  In the present embodiment, the first analog voltage detection circuit 111 is composed of an AD conversion (analog / digital conversion) circuit provided in the one-chip microcomputer 112, and is an 8-bit digital. A value is output to the processing circuit 113 of the microcomputer 112.

  Note that the microcomputer 112 operates by supplying power from the second DC power supply 114 having a voltage of 5 V lower than the voltage of the first DC power supply 111, and the first analog voltage detection circuit 111 is The value obtained by dividing the input analog voltage V1a by 5V supplied from the second DC power supply 114 is output to the processing circuit 113 as a maximum of 256.

  The diode 115 is clamped so that the output of the first voltage conversion circuit 108 does not become higher than the voltage of the second DC power supply 114 when the power is turned on, when the power is turned off, or when a surge occurs. It is provided to protect the computer 112. The Q terminal which is the output of the processing circuit 113 is connected to the base of the opening / closing means 104 and turns on / off the opening / closing means 104.

  In the present embodiment, the voltage 12V of the first DC power supply 100 is higher than the voltage 5V of the second DC power supply 114, and as a result, a generally used 5V power supply is used for the microcomputer 112. With the characteristic that the thermistor 101 performs high-accuracy water level detection, 12 V that can sufficiently perform the necessary self-heating is secured as the first DC power supply 100, The voltage range of 0 to 12 V that can be taken as the value of the voltage V 1 of the thermistor 101 is received by the first analog voltage detection circuit 111 via the first voltage conversion circuit 108, and is digital within the range of 0 to 5 V. It can be converted to a value.

  Further, in this embodiment, in order to detect the temperature in the vicinity of the thermistor 101, temperature detecting means 116 using the thermistor is also connected via the connector 117. The temperature detection unit 116 has a low potential side terminal connected to the ground (GND), and a high potential side terminal connected to the second DC power supply 114 of 5 V by a resistor 118. The voltage of the divided voltage generated at the high potential side terminal is further received by the third analog voltage detection circuit 121 as the V2 voltage after the influence of noise is suppressed by the resistor 119 and the capacitor 120.

  In the present embodiment, the third analog voltage detection circuit 121 is provided in the one-chip microcomputer 112 in the same manner as the first analog voltage detection circuit 111, and has a voltage of 0V to 5V. The voltage V2 within the range is input, converted into 256 levels, and output to the processing circuit 113. The processing circuit 113 is converted into temperature data of the temperature detection means 116 by an internal program.

  FIG. 2 is a layout diagram of the thermistor 101 and the temperature detection means 116 in the present embodiment.

  In FIG. 2, around the thermistor 101, a Teflon (registered trademark) tube 130 having an outer diameter of 3 mm, which is rich in insulation and heat resistance, and a filler 131 using a heat resistant resin injected from both upper and lower ends of the tube 130. The terminals 133 and 134 of the thermistor 101 are drawn from the lead wire 135 with insulation coating, but the terminals 133 and 134 are submerged in the water due to the rise in water level. Even if it becomes a state, it is the structure which can maintain the electrical insulation between water.

  Further, in the present embodiment, the thermistor 101 covered with the insulating layer 132 is provided in a tubular windproof body 136 made of a resin-made 9 mm diameter pipe.

  By providing the tube-shaped windbreak body 136 outside the insulating layer 132, the windbreak body 136 weakens the flow of air to the thermistor 101 when the water level is low and the thermistor 101 is in the air. Since the heat release due to self-heating of the thermistor 101 is reduced, the temperature of the thermistor 101 is higher and reaches about 140 degrees Celsius, and the thermistor 101 is submerged in water. In this case, water enters from the lower opening 136a of the windbreak body 136 so that the water level in the windbreak body 136 rises and air can freely escape from the upper opening 136b. It has become.

  Therefore, when the water level rises to L1, the difference in the escape of heat from the thermistor 101 can be made larger than when the water level is low, and the margin for erroneous detection due to noise or the like can be made larger. It is possible to take.

  Depending on the diameter and material of the windbreak body 136, the windbreak performance and how the heat escapes from the thermistor 101 when the water level rises change. Good characteristics were obtained.

  Since the upper and lower ends of the windbreak body 136 made of pipe are open, when the water level rises, the water passes through the lower opening 136a and there is water between the insulating layer 132 and the windbreaker 136. It is configured to allow the state to do.

  Accordingly, when the water reaches the height of the thermistor 101, the heat generated by the self-heating of the thermistor 101 escapes to the water through the insulating layer 132, and the thermistor 101 is cooled. It becomes everything.

  In the present embodiment, temperature detection means 116 is provided which is composed of another thermistor and detects the temperature in the vicinity of the thermistor 101 at substantially the same height L1 as the thermistor 101. The temperature detection means 116 is a resin insulating layer. 140 is arranged in the periphery thereof, so as to ensure electrical insulation between the terminals 142 and 143 drawn from the lead wire 141 with insulation coating and the surrounding water.

  Note that the temperature detecting means 116 is used at a current value at which self-heating is almost negligible, and therefore it is not necessary to use a resin material with particularly high heat resistance for the surrounding insulating layer 140.

  FIG. 3 is a graph showing the operational characteristics of the water level detection device according to the present embodiment. The vertical axis represents the analog voltage V1 and the horizontal axis represents the temperature, which corresponds to the temperature detection value by the temperature detection means 116. It is treated as something to do. The first analog voltage detection circuit 111 receives a voltage value V1a multiplied by a certain coefficient by dividing the voltage value of the voltage V1 by the first voltage conversion circuit 108, and converts it to a digital value. Will be.

  The alternate long and short dash line T is a threshold value for V1, and if it is higher than the threshold value, it is determined that the underwater, that is, the water level exceeds L1, and if it is lower than the threshold value, the air, that is, the water level is lower than L1. Is determined in the processing circuit 113.

  In the present embodiment, the threshold value at each temperature is set in increments of 1 ° C. according to the temperature value detected by the temperature detection means 116, so a substantially smooth curve is realized at any temperature. Compared to the conventional configuration where the water level detection is performed by switching the stepped threshold value, the margin for noise etc. is sufficiently large over the entire temperature range, and the stability is higher. It is possible.

  4A and 4B show operation waveforms of each part of the water level detection device according to the present embodiment. FIG. 4A shows a signal waveform of the Q output terminal of the processing circuit 113 of the microcomputer 112, and FIG. The voltage V1, (c) at the potential side terminal is the waveform of the input voltage V1a of the first analog voltage detection circuit 111.

  In the present embodiment, the period Ton when the Q signal is High and the opening / closing means 104 is ON is 2 minutes, and the period Toff when the Q signal is Low and the opening / closing means 104 is OFF is 100 ms. During the Ton period, a voltage of 12 V is applied from the first DC power supply 100 to the series circuit of the resistor 102 and the thermistor 101, so that the thermistor 101 self-heats and the voltage V1 of the high potential side terminal of the thermistor 101 is increased. The voltage is generated depending on the ambient temperature condition (temperature condition in the vicinity of the thermistor 101) shown in FIG. 3 and whether the thermistor 101 is in the water or in the air. When the Toff period starts, the thermistor 101 becomes low. Since the terminal on the potential side is disconnected from the ground and becomes open, V1 is pulled up by the first DC power supply 100 of 12 V by the resistor 102 of 250 ohms.

  Here, as described above, in this embodiment, the resistance value that is the sum of the resistors 106 and 107 of the first voltage conversion circuit 108 is set to a value that is considerably larger than that of the resistor 102. V1 becomes a value close to 12 V that is the output voltage of the first DC power supply 100 during the Toff period.

  Note that, during the Toff period, current supply to the thermistor 101 is not performed, so the temperature of the element of the thermistor 101 decreases. However, in this embodiment, the Toff time is as short as 100 ms. Therefore, the element temperature drop of the thermistor 101 during the Toff period is slight, and when it enters Ton next time, although the V1 voltage value rises due to the drop in the temperature of the thermistor 101, the short-time In the meantime, the temperature returns to the original temperature, and a sufficiently steady state is obtained after 2 minutes of Ton, and V1 also becomes a stable value.

  Thus, by setting Toff as short as 100 ms, thermistor 101 is advantageous in terms of the temperature cycle life when used in conditions where the temperature change of the thermistor 101 is small. In contrast, there is little thermal stress on the elements and caulking portions (not shown) of the thermistor 101, and there is an effect that the use with high reliability and high stability is possible. V1a shown in (c) is a voltage having a value obtained by multiplying V1 by 0.375 times by the first voltage conversion circuit.

  Thereby, the microcomputer 112 connected to the output of the second DC power supply 114 of 5V is effective and rational between 0V and 5V which is the voltage detection range of the built-in first analog voltage detection circuit 111. In order to ensure the degree of self-heating required for water level detection by the thermistor 101, a value of 12V, which is the voltage output value of the first DC power supply 100, which is necessary for the thermistor 101, is generally used. A circuit in which the voltage conversion (attenuation) operation by the action of the first voltage conversion circuit 108 is relatively simple while the value is sufficiently higher than that of the second DC power supply 114 that outputs the 5V voltage at which the microcomputer operates. Realized with a configuration, which ensures both excellent water level detection characteristics and the adoption of general microcomputer devices, which is cost-effective and reliable. It is possible to provide a water level sensing device excellent in stability.

  However, since the first DC power supply 100 and the second DC power supply 114 are configured by completely different systems here, mutual initial variations occur independently of each other. For the DC power supply 100, the voltage becomes 12.5V, which is higher, while for the second DC power supply 114, there is a possibility that the voltage will vary to a low value of 4.7V. Since the voltages V1 and V1a are high, and the first analog voltage detection circuit 111 is supplied with 4.7V as its own power supply, the full-scale voltage when converted to a digital value is 0.3V. Since there is a tendency to output a higher digital value to the processing circuit 113 by the amount of the decrease, the electric power of the thermistor 101 is significantly increased as a total digital value. So that would read the.

  Also, when a variation tendency opposite to the above occurs, even if the thermistor 101 is not changed, it is input to the processing circuit 113 as a considerably lower digital value. It will become something.

  Therefore, the water level detection device in the present embodiment detects the voltage value of the first DC power supply 100 from reading V1a during the Toff period, and thereby corrects the V1a value during the ON period of the switching means 104. It is operating.

  As a method of correction, the percentage of the V1a value of the actual off period with respect to 12 V, which is the standard as the voltage value of the first DC power supply 100, is calculated as a percentage, and the value is used as a correction value to determine the on period. The correction is applied to the stable value inside.

  However, other than such a method, for example, a method using a table or the like, or a method using a value obtained by dividing the V1a reading value in the on period and the V1a reading value in the off period may be used. There are various methods for applying correction based on the off-period reading corresponding to the power supply voltage value of the DC power supply 100, and any of them may be realized.

  The first voltage conversion circuit 108 constituted by the resistors 106 and 107 also has variations in the resistance value used, and the voltage division ratio (input / output voltage characteristics) generated for that reason is also natural. In this embodiment, since the V1 detection is performed from the V1a voltage using the same first voltage conversion circuit 108, the influence is also cancelled. For example, it is possible to use inexpensive resistors 106 and 107 with relatively low accuracy such as 5%, which is extremely effective in terms of cost.

  In addition to the initial variation of the parts, for example, if the operation of the water level detection device continues after the power is turned on, due to heat generation in the airframe, for example, the fluctuation of the output voltage of the first DC power supply 100, the first 2 may cause a change in the output voltage of the DC power supply 114 and a change in the resistance value due to the temperature characteristics of the resistance values of the resistors 106 and 107. In the present embodiment, such a change However, since correction is applied at intervals of 2 minutes, there is no problem. For example, even when a low-cost one having a slight fluctuation due to temperature characteristics is used, sufficiently stable water level detection characteristics can be obtained. This is also effective.

  As described above, in the water level detection device according to the present embodiment, the processing circuit 113 receives the value of the first analog voltage detection circuit 111 and detects whether or not the water level has reached the thermistor 101. In addition, the first analog voltage detection circuit 111 receives the voltage corresponding to the power supply voltage of the first DC power supply 100 through the first voltage conversion circuit 108 during the period when the switching means 104 is off, The first DC power supply 100 and the second DC power supply 114 act so as to absorb the characteristic variation due to the initial variation of the voltage value, and the opening / closing means 104 is provided with the ON period and the OFF period alternately. For example, when the respective output voltages fluctuate due to the temperature rise of the first DC power supply 100 and the second DC power supply 114 from the start of operation, the fluctuations are also absorbed. It can have excellent characteristics that are not easily affected by variations and temperature characteristics.

  In this embodiment, the temperature detection means 116 is provided in addition to the thermistor 101 having self-heating, and the ambient temperature of the thermistor 101 is detected. It is possible to switch the magnitude of the self-heating of the thermistor 101 by changing the magnitude of the current flowing through the thermistor 101, and the temperature rise of the thermistor 101 due to the self-heating is negligible. A configuration in which a temperature in the vicinity (ambient temperature) is detected in the period, a threshold value is determined based on the detected value, and a comparison with an analog voltage value in a state where self-heating occurs may be performed.

(Embodiment 2)
FIG. 5 shows a circuit diagram of a water level detection device according to the second embodiment of the present invention. Note that the same parts as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In this embodiment, as shown in FIG. 5, the microcomputer 150 includes a second analog voltage detection circuit having an equivalent configuration in addition to the first analog voltage detection circuit 111 described in the first embodiment. 151.

  Then, the second voltage conversion circuit 155 constituted by the resistor 153 and the resistor 154 is connected to the first DC power supply 100, and the signal voltage that is divided and attenuated by the ratio of the resistance value is used for noise removal. The obtained voltage V3a is input to the second analog voltage detection circuit 151 through the resistor 156 and the capacitor 157.

  Thus, the first DC power supply 100 is received via the second voltage conversion circuit 155, and the processing circuit 152 receives the output of the first analog voltage detection circuit 111 and the second analog voltage. In response to both the outputs of the detection circuit 151, and further receives a signal from the temperature detection means 116 that detects the temperature in the vicinity of the thermistor 101, it detects whether or not the water level has reached the thermistor 116. ing.

  The diode 158 prevents and protects a voltage exceeding the power supply voltage from being applied to the input terminal of the third analog voltage detection circuit 121 of the microcomputer 150 when the water level detection device is turned on or off. It is provided for this purpose.

  Other configurations are the same as those of the first embodiment.

  In the present embodiment, the output signal from the Q terminal of the processing circuit 152 is always high throughout the period during which the water level detection operation is required, and the opening / closing means 104 is kept on. Yes.

  In the present embodiment, self-heating is always applied to the thermistor 101. Therefore, for V1a, the voltage V1 of the thermistor 101 is always converted to a range of 0 to 5V by the first voltage conversion circuit 108. V1a is input to the first analog voltage detection circuit 111. The voltage value of the first DC power supply 100 is converted by the second voltage conversion circuit 155, and the second analog voltage is converted to V3a. It is read from the detection circuit 151 and converted into a digital value.

  Therefore, both the detection of the thermistor 101 voltage and the detection of the voltage of the first DC power supply 100 are performed without stopping the self-heating of the thermistor 101, and after the detection and sending to the processing circuit 152, the first As in the first embodiment, the first analog voltage detection circuit 111 is corrected by the detected voltage value from the first DC power supply 100, and the water level is set to L1 by the threshold value depending on the temperature in the vicinity of the thermistor 101. It is determined whether or not the vehicle has come.

  Therefore, it is advantageous particularly when quick response is required for the operation for detecting that the water level increases and the thermistor 101 is submerged. Further, when the first DC power supply 100 has a characteristic such that the output voltage varies greatly with respect to the load current, the switching means 104 is turned off and the thermistor 101 is self-heated as in the first embodiment. The first DC power supply 100 generally has a characteristic that the load current decreases and the output voltage tends to increase. However, such a characteristic is relatively large ( Even in the configuration in which the load regulation is inferior, the configuration according to the second embodiment can always be detected as the V3a value corresponding to the voltage value of the first DC power supply 100 under the raw load current condition. Even a simple power supply can be used.

  However, even in the configuration of the first embodiment, there may be a case where it can be considerably covered if correction is made using the characteristics of the load current and the output voltage of the first DC power supply 100, which are designed. It will be left to the person. Note that the opening / closing means 104 need not be provided as long as it is not turned off, and may be omitted. However, in this embodiment, when the period during which the water level detection is not required continues for a long time, the processing circuit It is assumed that Low is output from 152 to the Q terminal and is turned off, and unnecessary power necessary for self-heating is cut off.

  In particular, in the case of a normal operation state such as overflow detection, in the case of a water level detection device in which the thermistor 101 is in the air, when a self-heating current is supplied to the thermistor 101 for a long time, The temperature of the element of the thermistor 101 is considerably high, and the life of the surrounding insulator may be a problem. However, in this embodiment, it is advantageous because unnecessary heat generation can be eliminated.

  In the present embodiment, as in the first embodiment, the temperature detection means 116 for detecting the temperature in the vicinity of the thermistor 101 is provided. However, for example, in the operation sequence of the water level detection device, the temperature change When the waveform can be predicted, or when the temperature in the vicinity of the thermistor 101 can be substantially estimated based on the correlation with the temperature of another part that is not in the vicinity of the thermistor 101, the temperature at which the temperature in the vicinity of the thermistor 101 is measured. The detection means 116 may not be provided, and the threshold value may be changed by a table or a function by estimation or the like. Even in this case, the threshold value can be adjusted with a very high resolution as compared with the conventional stepwise method. High effects such as prevention of malfunction due to noise can be achieved.

  Further, in a water level detection device configured such that wind from a fan or the like hits the thermistor 101, or in a water level detection device configured such that there is a water flow in the water, the strength of the wind or the strength of the water flow is determined in advance. It is often known, and by appropriately changing the threshold value accordingly, it becomes possible to detect the water level in accordance with various environmental conditions, which also works effectively.

  For example, in the configuration of the first and second embodiments, an apparatus in which the water level detection device is used is in a certain operation mode, for example, a washing / drying machine, and enters a drying mode. Is a condition where the thermistor 101 hits the thermistor 101, the relationship between the thermistor voltage V1 in the air and the ambient temperature is slightly higher than the solid line A in the no-air condition, as shown by the broken line A1 in FIG. Become.

  This is because the thermistor 101, which is self-heating, receives a cooling effect due to the wind, and the temperature of the element portion decreases, so that the resistance value increases and the thermistor 101 moves upward in the graph of FIG.

  Here, when the water level detection device is operated with the threshold value indicated by the alternate long and short dash line T, the distance from the characteristic curve W in water does not change, but the amount of increase in the characteristic in air from A to A1 Although it becomes narrower, especially when it is in the air at high temperatures, there is a high possibility that it will be erroneously detected as “water present” with a little noise.

  In that case, the processing circuit 113 or the processing circuit 152 recognizes that the wind is applied to the thermistor 101 by its own control software or from another control microcomputer via communication means or the like, and calculates the threshold curve. By moving slightly upward from T to T1, the threshold value T1 can be present at a level approximately halfway between W on the underwater side and A1 in the air. Can be used in an almost equally divided state on the underwater side and in the air side, and it is possible to cope with the influence of wind, which is one of the environmental conditions.

  In each of the above embodiments, the threshold is changed according to the ambient temperature of the thermistor 101 for detecting the water level, thereby obtaining good detection characteristics for a wide range of temperatures. It is not absolutely necessary. For example, a correction value corresponding to the output value of the temperature detection means 116 is derived from a mathematical formula or a table, and this correction value is added to, subtracted from, or multiplied by, the first analog voltage conversion circuit 111. In the above, a comparison with a certain threshold value may be performed, and it may be detected whether the water level has reached the thermistor 101 based on the magnitude relationship with the threshold value. As long as it functions as a function of water level detection, the same effect can be obtained in any circuit configuration and program algorithm configuration. .

  As described above, the water level detection device according to the present invention is capable of accurately detecting the water level under a wide range of environmental conditions, such as a washing machine, a dryer, a washing / drying machine, a dishwasher, and an air conditioner. It can be widely used in various devices and devices that handle liquids.

Circuit diagram of water level detection device in Embodiment 1 of the present invention (A) Cross-sectional view of the thermistor mounting portion of the water level detection device (b) Cross-sectional view of temperature detection means of the water level detection device Characteristic graph of ambient temperature and thermistor voltage V1 of the water level detector (A)-(C) Operation waveform diagram of each part of the water level detector Circuit diagram of water level detection device in embodiment 2 of the present invention Circuit diagram of conventional water level detector

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 1st DC power supply 101 Thermistor 102 Resistor 104 Opening and closing means 108 1st voltage conversion circuit 111 1st analog voltage detection circuit 114 2nd DC power supply 116 Temperature detection means 121 3rd analog voltage detection circuit 151 2nd Analog voltage detection circuit 155 Second voltage conversion circuit

Claims (5)

A thermistor for detecting a water level; a resistor connected in series to the thermistor; a first DC power supply for supplying current to a series circuit of the thermistor and the resistor; and a voltage of the first DC power supply. A lower second DC power supply, and a first analog voltage detection circuit that receives current from the second DC power supply and receives the voltage of the thermistor through a first voltage conversion circuit, A water level detection device that receives the value of the first analog voltage detection circuit and detects whether or not the water level has reached the thermistor. Opening / closing means connected in series to the thermistor and the resistor and supplied with current from the first DC power supply is provided, and the first analog voltage detection circuit is configured to switch the first DC power supply during the OFF period of the opening / closing means. The water level detection device according to claim 1, wherein a voltage corresponding to the power supply voltage is received through the first voltage conversion circuit. The water level detection device according to claim 2, wherein the opening / closing means is provided with an on period and an off period alternately. A second voltage conversion circuit; and a second analog voltage detection circuit that receives the first DC power supply via the second voltage conversion circuit. The first analog voltage detection circuit and the second analog voltage The water level detection device according to claim 1, wherein the output of both of the detection circuits is received to detect whether or not the water level has reached the thermistor. The water level detection apparatus of any one of Claims 1-4 provided with the temperature detection means which detects the temperature of the vicinity of a thermistor.