JP2017116278A - Circuit for determining resistance values of multiple loads - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine using a common constant-current circuit and comparator whether or not the resistance value of each of multiple types of water level electrodes P1, P2 differing in resistance value determination threshold exceeds each resistance value determination threshold.SOLUTION: The magnitude of a constant current outputted by a constant-current circuit 1 is made controllable by a control unit 2, and the magnitude of the constant current is varied in accordance with the type of water level electrodes P1, P2 that supply the constant current, with the fluctuation range of voltages occurring in the water level electrodes P1, P2 being thereby overlapped, whereby determination is made using a common comparison circuit 4 as to whether or not the resistance value of each water level electrode P1, P2 exceeds the respective resistance value determination threshold, that is, whether or not each water level electrode P1, P2 is detecting water.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multiple load resistance value determination circuit that determines whether or not a resistance value of a load such as a plurality of types of water level electrodes used in a water heater or the like exceeds a threshold value.

  The applicant of the present application includes, for example, the following Patent Document 1 including a multiplexer that selects a water level detection signal input from a plurality of water level electrodes according to a selection control signal output from the control unit and outputs the signal to the control unit. A water level detection signal detection device is disclosed.

  The water level electrode (load) of this conventional detection device outputs, as a water level detection signal, a voltage generated when a constant current (for example, 10 μA) is passed between the water level electrode and ground or ground using water as a conductor (water resistance). Therefore, a plurality of water level electrodes are provided for each location where water level detection is required. As a result, when each water level electrode is immersed in water, the resistance value decreases and the voltage of the water level detection signal also drops, so the comparator determines whether the voltage of the water level detection signal has fallen below a predetermined threshold. By outputting the determination result to the control unit, the control unit can determine whether each water level electrode is immersed in water and its resistance value is smaller than the resistance value determination threshold based on the determination result.

JP 2014-109437 A

  By the way, resistance value detection objects such as antifreezing liquid that serves as a heat medium for heating, drain water that is neutralized by a neutralizer, and hot water for hot water supply often have different resistance values. The voltage generated when a current is passed changes.

  For example, the first water level electrode has a resistance value of 300 kΩ when there is water (when the electrode is immersed in water), and 500 kΩ when there is no water (when the electrode is not immersed in water). Assuming that the water level electrode has a resistance value of 600 kΩ when there is water and 1 MΩ when there is no water, the voltage generated at the first level electrode is 3 V when there is water and no water when the constant current is 10 μA. On the other hand, the voltage generated at the second water level electrode is 6V when there is water and 10V when there is no water.

  Therefore, the determination threshold value of the voltage generated at the first water level electrode is 4 V (400 kΩ as the resistance value determination threshold value), for example, and the determination threshold value of the voltage generated at the second water level electrode is 7.5 V (750 kΩ as the resistance value determination threshold value). Or the constant current supplied to the first water level electrode is 10 μA, and the constant current supplied to the second water level electrode is 5 μA. It was necessary to provide a current circuit and a comparator for voltage determination.

  However, if a circuit is configured individually for each electrode, the number of parts increases, resulting in an increase in cost.

  Therefore, the present invention makes it possible to determine the resistance value of each of a plurality of types of loads having different resistance value determination thresholds using a common constant current circuit and a comparator, thereby reducing the number of parts and, consequently, cost. The purpose is to reduce.

  To achieve the above object, a constant current circuit, a plurality of loads, a control unit that outputs a selection control signal for selecting any one of the plurality of loads, and a selection by the selection control signal A switching circuit for supplying a constant current output from the constant current circuit to the one load to be applied, and whether a voltage level generated in the one load to which the constant current is supplied exceeds a predetermined threshold value In a multiple load resistance value determination circuit including a comparison circuit for determining whether or not, the present invention takes the following technical means.

  That is, in the resistance value determination circuit for a plurality of loads according to the present invention, the plurality of loads to which a constant current is supplied via the switching circuit includes a plurality of types of loads having different resistance value determination thresholds, and the constant current circuit Is configured such that the magnitude of the constant current can be adjusted and controlled by the control unit in accordance with the type of the load (claim 1).

  According to the multiple load resistance value determining circuit of the present invention, the constant current circuit is configured such that the magnitude of the constant current is controlled by the control unit in accordance with the type of the load supplying the constant current. Therefore, even if the resistance value determination threshold value of each load is different, the voltage generated when the resistance value of each load is assumed to match the resistance value determination threshold value is the same depending on the type of load. By adjusting the magnitude of the constant current, it is possible to determine whether or not the resistance value of different types of loads exceeds the respective resistance value determination thresholds using a common comparison circuit. By using the same equipment, the number of parts can be reduced, and the cost can be reduced.

  In the resistance value determination circuit for a plurality of loads according to the present invention, the constant current circuit adjusts the magnitude of the constant current based on a constant current control signal output from the control unit separately from the selection control signal. The control unit may be configured to output a constant current control signal corresponding to the type of load selected by the selection control signal. Preferably, the constant current circuit is based on the selection control signal. It may be configured such that the magnitude of the constant current is adjusted (Claim 2). According to this, there is no need to output a constant current control signal for controlling the magnitude of the constant current separately from the selection control signal, the configuration of the control unit can be simplified, and the present invention is not adopted. The control unit can be shared with other products, thereby further reducing the cost.

  Furthermore, the load further includes a fixed resistor as the type of the plurality of loads, and the control unit supplies the constant current larger than (the predetermined threshold value / the resistance value of the fixed resistor) to the fixed resistor. The comparison between the case where the constant current circuit is controlled and the case where the constant current circuit is controlled to supply a constant current smaller than (predetermined threshold value / resistance value of the fixed resistor) to the fixed resistor. It may be configured to determine whether or not a circuit failure is based on whether or not the determination results of the circuits are different (claim 3). According to this, when the circuit is normal, the determination result of the comparison circuit when the magnitude of the constant current supplied to the fixed resistor is changed should be different. It is possible to accurately determine that the current circuit or related circuit has failed, and when such a failure is determined, the failure location is notified by notifying that the failure is related to the constant current circuit. become able to.

  As described above, according to the resistance value determination circuit for a plurality of loads of the present invention, the respective resistance values of a plurality of types of loads having different resistance value determination threshold values can be obtained by using a common constant current circuit and a comparator. It is possible to determine whether or not each resistance value determination threshold value is exceeded, and it is possible to reduce the number of parts, and thus cost.

It is a circuit diagram of a resistance value determination circuit for a plurality of loads according to an embodiment of the present invention. FIG. 5 is a circuit diagram of a resistance determination circuit for multiple loads according to another embodiment of the present invention. FIG. 3 is a circuit diagram showing a first application example of the circuit shown in FIG. 2. FIG. 3 is a circuit diagram showing a second application example of the circuit shown in FIG. 2. FIG. 6 is a circuit diagram showing a third application example of the circuit shown in FIG. 2. FIG. 6 is a circuit diagram showing a fourth application example of the circuit shown in FIG. 2. FIG. 10 is a circuit diagram showing a fifth application example of the circuit shown in FIG. 2. FIG. 10 is a circuit diagram illustrating a sixth application example of the circuit illustrated in FIG. 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a resistance determination circuit for a plurality of loads according to an embodiment of the present invention, and the resistance values of various water level electrodes (loads) in a hot water supply apparatus similar to that disclosed in Patent Document 1 above are shown. It is preferably used for determining whether or not the resistance value determination threshold is exceeded, that is, whether each water level electrode is immersed in water (with water) or not (without water).

  In the illustrated example, three first water level electrodes P1 and one second water level electrode P2 are shown, and the first water level electrode P1 (for example, the level of drain water stored in the neutralizer is monitored). The water level electrode or the like) has a resistance value of 300 kΩ when there is water (when immersed in water) and 500 kΩ when there is no water (when not immersed in water), and the second level electrode P2 (for example, heating) The water level electrode for monitoring the water level in the expansion tank for water) shows a resistance value of 600 kΩ when there is water and 1 MΩ when there is no water, and the resistance value judgment threshold value of the first water level electrode P1 is 400 kΩ, The resistance value determination threshold value of the second water level electrode P2 is 750 kΩ. In addition to the water level electrodes P1 and P2, a fixed resistor Ra is connected as a dummy load to an empty port of the multiplexer 3 described later. The above resistance values are merely examples for understanding the present invention, and can be designed as appropriate resistance values.

  The resistance value determination circuit of the present embodiment includes a constant current circuit 1 and a microprocessor 2 as a control unit that outputs a selection control signal for selecting any one of the plurality of loads P1, P2, and Ra. A multiplexer 3 (switching circuit) for supplying a constant current output from the constant current circuit 1 to the one load selected by the selection control signal, and the one load to which the constant current is supplied And a comparison circuit 4 for determining whether or not the voltage level generated in the circuit exceeds a predetermined threshold value and outputting the determination result signal to the microprocessor 2.

  The constant current circuit 1 is configured such that the magnitude of the constant current can be adjusted and controlled by the microprocessor 2 in accordance with the type of load to which the constant current is supplied. In the illustrated example, the constant current output from the microprocessor 2 is configured. The control signal can be switched and controlled in two states, a state in which a constant current of 10 μA is output and a state in which a constant current of 5 μA is output.

  More specifically, the constant current circuit 1 includes an operational amplifier 11, a pnp transistor 12 having a base connected to the output of the operational amplifier 11, and an output connected between the emitter of the transistor 12 and a power supply (15V). The negative load circuit is configured by connecting the emitter of the transistor 12 to the inverting input terminal (−) of the operational amplifier 11. Further, a predetermined output current control voltage output from the voltage dividing circuit 14 is input to the non-inverting input terminal (+) of the operational amplifier 11, and the voltage of the inverting input terminal (−) is caused by a virtual short circuit of the operational amplifier 11. And the voltage at the non-inverting input terminal (+) become the same potential, whereby the voltage across the output load resistor 13 is determined, the current flowing through the resistor 13 and the transistor 12 is determined, and the constant current is obtained from the collector output of the transistor 12. It is output.

  Further, the voltage dividing circuit 14 of the constant current circuit 1 includes three resistors R1, R2, and R3 connected in series, and an npn transistor Q1 as a switching element that bypasses the resistor R3 when turned on. When the transistor Q1 is turned on, a voltage obtained by dividing the power supply voltage (15V) by the two resistors R1 and R2 is input to the non-inverting input terminal (+) of the operational amplifier 11, for example, 10 μA The constant current is output. On the other hand, when the transistor Q1 is off, a voltage divided by the resistor R1 and the combined resistance of the two resistors R2 and R3 is input to the non-inverting input terminal (+) of the operational amplifier 11, for example, 5 μA. The constant current is output.

  The microprocessor 2 is also responsible for various types of hot water supply operation control, heating operation control, and reheating operation control of the hot water supply device. FIG. 1 shows only the input / output ports related to the present invention. In the present embodiment, the selection control signal is constituted by a 3-bit logic signal output from three output ports (A output port, B output port, and C output port) of the microprocessor 2, and the selection control signal The signals are respectively input to the corresponding three control signal input ports (A, B, C) of the multiplexer 3.

  The multiplexer 3 may be an analog switch type that is commercially available in the form of a one-chip LSI, or may be configured on a substrate using a general-purpose logic gate circuit. The multiplexer 3 according to the present embodiment includes eight input / output ports (0 to 7) and one common port COM. According to the selection control signal input to the control signal input ports A, B, and C. Among the eight input / output ports, one input / output port shown in the table shown in FIG. 1 is connected to the common port COM, and the other input / output ports are insulated from the common port COM. The three first water level electrodes P1 are connected to the 0-2 input / output ports of the multiplexer 3, and the second water level electrode P2 is connected to the 4th input / output port. A fixed resistor Ra is connected to the seventh input / output port. The input / output port connecting the second water level electrode P2 may be an appropriate port. The load connected to the input / output port selected by the selection control signal (also referred to as “the load selected by the selection control signal” in this specification) has a constant current output from the constant current circuit 1. Is supplied via the multiplexer 3, and a detection voltage corresponding to the resistance value of each load is generated at the input / output port to which the load is connected, and the detection voltage is output from the common port COM.

  The comparison circuit 4 includes a comparator 41 and a voltage dividing circuit 42 that outputs a predetermined reference voltage (threshold value) for determination to the negative input terminal of the comparator 41, and is output from the common port COM. The detected voltage is input to the positive input terminal of the comparator 41. For example, the reference voltage (threshold value) can be set to 4 V, and if the detection voltage output from the common port COM exceeds the reference voltage, the determination signal output from the comparator 41 is a high signal, and is output from the common port COM. If the output detection voltage does not exceed the reference voltage, the determination signal output from the comparator 41 is a Low signal. The determination signal output from the comparator 41 is input to the scan input port of the microprocessor 2.

  The microprocessor 2 switches the contents of the selection control signal at predetermined time intervals (for example, several milliseconds to several tens of milliseconds) so as to repeatedly select the input / output ports 0 to 7 sequentially and scans at each time point. The determination signal input from the input port is stored in the storage means for each input / output port, and the determination signal is used as a parameter for various operation controls.

  In this embodiment, the microprocessor 2 outputs a selection control signal (A: 1, B: 0, C: 0) for selecting the fourth input / output port to which the second water level electrode P2 is connected. In some cases, the Low current signal is output from the constant current control port to turn off the transistor Q1, thereby controlling the constant current circuit 1 to output a constant current of 5 μA. On the other hand, when outputting other selection control signals, the transistor Q1 is turned on by outputting a High signal from the constant current control port, thereby controlling the constant current circuit to output a constant current of 10 μA. ing.

  Therefore, a constant current of 10 μA is supplied to the water level electrode P1, and a voltage of 300 kΩ × 10 μA = 3 V is output from the common port COM when there is water and 500 kΩ × 10 μA = 5 V when there is no water. Further, a constant current of 5 μA is supplied to the water level electrode P2, and a voltage of 600 kΩ × 5 μA = 3 V is output from the common port COM when there is water and 1 MΩ × 5 μA = 5 V when there is no water. Thus, according to the present embodiment, by changing the magnitude of the constant current output from the constant current circuit according to which type of water level electrode (load) is selected, The threshold of the voltage level for resistance value judgment can be made common, for example, 4V, etc., so that the comparison circuit 4 can also be shared, simplifying the circuit configuration, reducing the number of parts, and thus reducing the cost. Can be planned.

  Further, in the present embodiment, by connecting the fixed resistor Ra to the input / output port of the multiplexer 3 not connected to the water level electrode, the port scan control by the microprocessor 2 is controlled to be performed for all the input / output ports. The scan control software of the microprocessor 2 can be shared with other products.

  In addition, the fixed resistor Ra may be used to detect an abnormality in the constant current circuit 1 and related circuits (such as floating of the constant current control port of the microprocessor 2 and defective connection wiring) by the control method described below. it can. The abnormality detection control will be described in detail. When the resistance value of the fixed resistor Ra is, for example, 560 kΩ, the constant current circuit 1 outputs a constant current of 10 μA and any input to which the fixed resistor Ra is connected. When the output port is selected, the output voltage from the common port COM is 5.6 V, which is higher than 4 V, which is the reference voltage (voltage level threshold) of the comparison circuit 4, so that the comparison circuit 4 becomes High output. . On the other hand, when the constant current circuit 1 outputs a constant current of 5 μA and any one of the input / output ports to which the fixed resistor Ra is connected is selected, the output voltage from the common port COM is 2.8V, Since it is smaller than 4V which is the reference voltage of the comparison circuit 4, the comparison circuit 4 becomes a Low output.

  However, when an abnormality such as an open failure of components or wirings constituting the constant current circuit 1 occurs, for example, when the switching element Q1 is open, the output current of the constant current circuit 1 is 5 μA regardless of the content of the constant current control signal. Therefore, even if a High signal is output to the constant current circuit 1 as a constant current control signal in order to output a constant current of 10 μA, the output of the comparison circuit 4 when the fixed resistor Ra is selected is constantly low. Output.

  Therefore, when the constant current circuit 1 is controlled to supply 10 μA to the fixed resistor Ra (the reference voltage 4 V of the comparison circuit 4 / the constant current larger than 560 kΩ≈7 μA of the fixed resistor Ra) and the fixed resistor Ra On the basis of whether or not the determination result (output signal) of the comparison circuit 4 is different from when the constant current circuit 1 is controlled to supply 5 μA (constant current smaller than 7 μA) to By configuring the microprocessor 2 so as to determine whether or not a circuit failure has occurred, it is possible to accurately detect a circuit failure in the constant current circuit 1 or the like.

  When the switching element Q1 is short-circuited, the constant current output from the constant current circuit 1 is fixed at 10 μA. In this case, the determination result of the comparison circuit 4 is constant regardless of the constant current control signal. Thus, it can be determined that a circuit failure has occurred.

  When a plurality of fixed resistors Ra are attached, a constant current of 10 μA is supplied when scanning any one of the fixed resistors Ra, while a constant current of 5 μA is supplied when scanning another fixed resistor Ra. The failure determination can be performed based on whether the determination result of the comparison circuit 4 in each case is different. Moreover, the magnitude of the constant current can be changed at each scan timing for one fixed resistor Ra, and the failure determination can be performed depending on whether the determination result is different. In addition, when one scan time for one fixed resistor Ra is sufficiently long, the failure determination may be performed by changing the magnitude of the constant current supplied to the fixed resistor Ra during the one scan. Is possible.

  FIG. 2 shows a resistance determination circuit for a plurality of loads according to another embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, detailed description thereof is omitted, and different configurations are provided. The effect will be described.

  In the resistance value determination circuit of the present embodiment, each bit of the selection control signal output from the microprocessor 2 is inverted and input to the control signal input ports A to C of the multiplexer 3, respectively. The relationship between the output signal of the processor 2 and the selected input / output port is as shown in the table of FIG.

  In this embodiment, the constant current switching element Q1 of the constant current circuit 1 (in this embodiment) is selected only when the fourth input / output port is selected based on the selection control signal output from the microprocessor 2. FET) is turned off and the constant current output from the constant current circuit 1 is 5 μA. When other input / output ports are selected, the switching element Q1 is turned on and the constant current output from the constant current circuit 1 is 10 μA. The circuit configuration is as follows.

  That is, the control signal input terminal (gate) of the switching element Q1 is connected to the control power supply (5V) via the pull-up resistor R4 and is connected to the ground via the switching element Q3 (FET in the illustrated example). When the switching element Q3 is off, the gate of the switching element Q1 is pulled up and the switching element Q1 is turned on. When the switching element Q3 is on, the gate of the switching element Q1 is grounded and the switching element Q1 is Turn off.

  The control signal input terminal (gate) of the switching element Q3 is connected to the control power supply (5V) via the pull-up resistor R5, and the switching element Q2 (npn type transistor in the illustrated example, preferably a digital transistor). When the switching element Q2 is off, the gate of the switching element Q3 is pulled up to turn on the switching element Q3. When the switching element Q2 is on, the gate of the switching element Q3 is grounded. The switching element Q3 is turned off.

  The gate of the switching element Q3 is connected to the A output port of the selection control signal through the back electromotive voltage prevention diode D1 and the load resistor R6, and is selected through the back electromotive voltage prevention diode D2 and the load resistor R7. It is connected to the B output port of the control signal. As a result, if either the A output port or the B output port is Low output, the gate of the switching element Q3 is grounded through the output port so that the switching element Q3 is turned off and the switching element Q1 is turned on. It has become. Further, the control signal input terminal (base) of the switching element Q2 is connected to the C output port, and is on / off controlled by a signal output from the C output port.

  With this circuit configuration, the switching element Q1 is turned off only when the A output port is High output, the B output port is High output, and the C output port is Low output, that is, only when the fourth input / output port is selected. Then, a constant current of 5 μA is supplied to the second water level electrode P2, and in other cases, the switching element Q1 is turned on and a constant current of 10 μA is supplied to the first water level electrode P1 or the fixed resistor Ra. ing.

  According to the present embodiment, when the selection control signal selects a predetermined load (second water level electrode), the magnitude of the constant current output from the constant current circuit is adjusted based on the selection control signal itself. Therefore, the control configuration of the microprocessor 2 can be simplified, and the constant current value can be adjusted only by adding the logic circuit by using the existing microprocessor 2 as it is. There is no need to change software or add output ports.

  Further, according to the above circuit configuration, the switching element Q1 is turned on when which input / output port is selected depending on whether the switching elements Q2, Q3, the resistor R6, etc. are mounted on the substrate or not. You can change the variation.

  For example, as shown in FIG. 3, when neither of the load resistors R6 and R7 is mounted, the switching element Q1 is turned on / off depending only on the on / off of the switching element Q2, so that the C output port has a high output. When the switching element Q1 is ON, the switching element Q1 is turned OFF, and when the C output port is LOW output, the switching element Q1 is OFF. Therefore, in the example shown in FIG. 3, the first water level electrode P1 can be connected to the 0-3rd input / output port, and the second water level electrode P2 can be connected to the 4th-7th input / output port.

  As shown in FIG. 4, when only the load resistor R7 is not mounted, the first water level electrode P1 can be connected to the 0th, third, fifth and seventh input / output ports, and the fourth and sixth input / output ports. To the second water level electrode P2.

  Further, as shown in FIG. 5, when the switching element Q2 and the load resistor R6 are not mounted, the first water level electrode P1 can be connected to the second, third, sixth and seventh input / output ports. The second water level electrode P2 can be connected to the 4th and 5th input / output ports.

  Further, as shown in FIG. 6, when only the load resistor R6 is not mounted, the first water level electrode P1 can be connected to the 0th, 3rd, 6th, and 7th input / output ports, and the 4th, 5th input / output ports. To the second water level electrode P2.

  Further, as shown in FIG. 7, when only the switching element Q2 is not mounted, the first water level electrode P1 can be connected to the 1st, 3rd, 5th and 7th input / output ports, and the 0th and 4th input / output ports. To the second water level electrode P2.

  In addition, as shown in FIG. 8, when the switching element Q2 and the load resistor R7 are not mounted, the first water level electrode P1 can be connected to the first, third, fifth and seventh input / output ports. The second water level electrode P2 can be connected to the 4th and 6th input / output ports.

  Instead of mounting each resistor R6, R7 or switching element Q2 on the substrate, a circuit configuration substantially similar to the above is provided depending on whether or not each jumper wire is cut by providing jumper wires at appropriate locations. It is also possible.

  The present invention is not limited to the above-described embodiments, and the design can be changed as appropriate. For example, the resistance value determination circuit for a plurality of loads according to the above-described embodiment can be suitably applied to other appropriate hot water heaters, hot water heaters, and the like in addition to the hot water heater similar to that disclosed in Patent Document 1.

  In the above-described embodiment, the multiplexer 3 is one that can be switched to one of eight input / output ports by a 3-bit selection control signal. However, two or more input / output ports can be switched by an appropriate selection control signal. Anything is acceptable.

  Moreover, although the constant current circuit 1 showed what can switch an output to either one of two types of constant currents of 5 μA and 10 μA, if there are three or more types of loads, any of the three or more types of constant currents may be used. The crab output may be configured to be switchable.

1 constant current circuit 2 control unit 3 switching circuit (multiplexer)
4 Comparison circuit P1 Load (first water level electrode)
P2 load (second water level electrode)
Ra load (fixed resistance)

Claims (3)

A constant current circuit, a plurality of loads, a control unit that outputs a selection control signal for selecting any one of the plurality of loads, and the one load selected by the selection control signal A switching circuit for supplying a constant current output from the constant current circuit, and a comparison circuit for determining whether or not a voltage level generated in the one load to which the constant current is supplied exceeds a predetermined threshold value. In the multiple load resistance determination circuit provided,
The plurality of loads to which a constant current is supplied via the switching circuit includes a plurality of types of loads having different resistance value determination thresholds,
The constant current circuit is configured to be capable of adjusting and controlling the magnitude of the constant current according to the type of the load by the control unit.   The multiple load resistance value determining circuit according to claim 1, wherein the constant current circuit is configured such that a magnitude of the constant current is adjusted based on the selection control signal. Resistance value determination circuit.   The resistance determination circuit for a plurality of loads according to claim 1 or 2, further comprising a fixed resistor as the type of the plurality of loads, wherein the control unit is configured to (the predetermined threshold value / the fixed value) with respect to the fixed resistor. A constant current smaller than (predetermined threshold value / resistance value of the fixed resistance) is supplied to the fixed resistance. A plurality of loads configured to determine whether or not a circuit failure occurs based on whether or not the determination result of the comparison circuit differs between when the constant current circuit is controlled to Resistance value determination circuit.

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