JP6382135B2 - Wireless sensor terminal and wireless transmission method - Google Patents

Description

  The present invention relates to a wireless sensor terminal and a wireless transmission method, and more particularly, to a wireless sensor terminal and a wireless transmission method having a sensor function for measuring a signal under measurement and a wireless transmission function for wirelessly transmitting a measurement result.

  In recent years, systems for managing power consumption in large power consumption facilities such as factories, research institutes, schools, hospitals, commercial facilities, offices, and public facilities have attracted attention for energy saving measures. Similarly, wireless sensor network systems for managing power consumption for each room or for each power consuming device are also drawing attention in general houses. In this wireless sensor network system, for example, currents flowing through a plurality of power lines connected to a switchboard that supplies power to each room in a house are separately measured by a plurality of wireless sensor terminals, and the measurement results are provided at predetermined positions. Wirelessly transmitted to the receiving device. The receiving device analyzes the received signal, and monitors and manages the power consumption for each room, monitors the operating status of the power consuming device, and the like.

  As a wireless sensor terminal used in this type of wireless sensor network system, a battery is installed as a power source, and the terminal's own identification information includes the digital value of the measured current amount and the digital value of the power consumption as it is. The transmission signal is generally wirelessly transmitted to the management center at predetermined time intervals. However, since the wireless sensor terminal is equipped with a battery as a power supply, it is necessary to replace the battery with a new one every time the battery deteriorates and the required power supply voltage cannot be obtained. It is.

  Therefore, in order to eliminate the need for battery replacement, a so-called non-powered wireless sensor terminal that is equipped with a self-supporting power source without a battery is known. According to a non-feed type wireless sensor terminal, for example, after being attached to a power line connected to a switchboard, detecting an electromagnetic induction current induced by an alternating current flowing through the power line, and rectifying the electromagnetic induction current into a direct voltage The stored DC voltage is used as the power supply voltage for each part of the terminal.

  However, to convert electromagnetic induction current, which is a minute level, into a high-voltage DC voltage and store it, and to use that stored DC voltage as a power supply voltage to reliably execute wireless transmission at predetermined time intervals It is desirable that power consumption during wireless transmission is low. However, since the power consumption during wireless transmission is proportional to the total amount of data (total amount of telegrams) of the transmission signal, a transmission signal in a format that directly includes the digital value of the measured current amount and the digital value of the power consumption The conventional wireless sensor terminal for transmission has a problem that power consumption is large because the total amount of data of the transmission signal is large.

  In such a non-feeding type wireless sensor terminal with high power consumption, in order to obtain a required power supply voltage, there is a problem that power must be stored for a long period of time, which is unpractical. Alternatively, because the total amount of data in the transmission signal is large, when the storage voltage is set as the power supply voltage, the power supply voltage drops below the voltage value required for transmission before completing the transmission of the entire data amount of the transmission signal. However, transmission may not be completed. Therefore, it is extremely difficult to store the electromagnetic induction current after being rectified to a DC voltage and use the stored DC voltage as a self-sustained power source for the wireless sensor terminal.

  Therefore, the present inventor does not include the current amount of the current detected by the transmitting current sensor in the transmission signal data, and changes the transmission interval of the transmission signal to convert the reception interval of the reception signal into a current value on the reception side. A non-feeding type wireless sensor terminal having a configuration has been proposed (for example, see Patent Document 1). According to this non-powered wireless sensor terminal, since the amount of detected current is not included in the data of the transmission signal, the amount of data of the transmission signal can be minimized, thereby reducing the power consumption of the wireless sensor terminal as much as possible. A non-feed type wireless sensor terminal using a DC voltage stored after rectification as a self-sustained power source can be practically used.

JP 2014-096017 A

  However, the non-feed-type wireless sensor terminal described in Patent Document 1 increases the transmission frequency, for example, once every 0.5 seconds when the current value of the power line to be measured increases. When there is another parasitic wireless sensor terminal using the wireless communication terminal, transmission signals frequently collide, and the wireless sensor network system does not hold. In the non-feed-type wireless sensor terminal described in Patent Document 1, if the time constant of transmission is increased by increasing the capacity of the capacitor that stores the DC voltage obtained by rectifying the electromagnetic induction current, the transmission frequency is reduced. Thus, the probability of collision of transmission signals can be reduced, but it is necessary to use an electrolytic capacitor having a large shape as a capacitor having a large capacity, which makes it difficult to reduce the size of the terminal.

  The present invention has been made in view of the above points, and provides a small non-feed-type wireless sensor terminal and wireless transmission method that does not increase the transmission frequency even when the current value of the current to be measured is large. Objective.

In order to achieve the above object, a wireless sensor terminal according to the present invention includes a current measuring unit, a DC voltage generating unit that generates a DC voltage corresponding to the current value of the current to be measured measured by the current measuring unit, and a DC voltage. A storage capacitor that is charged and held by the DC voltage generated by the generation means, a series circuit including a current limiting resistor and a threshold determination capacitor connected in parallel to the storage capacitor, and a current of the current to be measured A resistance voltage dividing circuit that resistance-divides the voltage at the connection point of the current limiting resistor and the threshold judgment capacitor according to the value, and whether or not the resistance divided voltage obtained by the resistance voltage dividing circuit is equal to or higher than the reference voltage Voltage comparison means for detecting the signal, wireless transmission means for wirelessly transmitting a transmission signal obtained by modulating a radio frequency pre-assigned with data including the terminal ID, and resistance voltage division by the voltage comparison means The voltage at the connection point is applied as the operating power supply voltage to the wireless transmission means for a predetermined period from the time when the pressure is detected to be higher than the reference voltage, and the operating power supply voltage is applied to the wireless transmission means after the predetermined period has elapsed. Power supply voltage applying means for stopping
Measure the transmission interval, which is the operation stop period of the wireless transmission means, from the operation stop time of the wireless transmission means when the predetermined period has elapsed until the time when the voltage comparison means detects that the resistance divided voltage is equal to or higher than the reference voltage. The transmission interval varies between the DC voltage generated by the DC voltage generating means and the voltage at the connection point at the time when the resistance divided voltage is detected to be equal to or higher than the reference voltage. A difference value of 1 and a ratio of the second difference value between the DC voltage and the voltage at the connection point at the operation stop time of the wireless transmission means at the time when the predetermined period has elapsed, and each value of the current limiting resistor and the threshold judging capacitor It sets based on a product, It is characterized by the above-mentioned.

In order to achieve the above object, the wireless sensor nodes of the present invention, the connection at the time it is detected that the DC voltage generated by the DC voltage generating means V _p, resistance divided voltage is equal to or higher than the reference voltage When the voltage at the point is V _th , the voltage at the connection point at the operation stop time of the wireless transmission means when a predetermined period has elapsed is V _min , and the product of each value of the current limiting resistor and the threshold judging capacitor is K, the transmission interval the _{K · log e {(V p} -V min) / (V p -V th)}
It is represented by.

In order to achieve the above object, the wireless transmission method of the present invention includes a DC voltage generating step for generating a DC voltage corresponding to the current value of the current to be measured measured by the current measuring means, and a DC voltage generating step. The charging current step for charging and holding the storage capacitor with the generated DC voltage, and the current to be measured at the connection point of the current limiting resistor and the threshold judgment capacitor constituting the series circuit connected in parallel to the storage capacitor A resistance voltage dividing step for dividing the voltage according to the current value by resistance, a voltage comparing step for detecting whether or not the resistance divided voltage obtained by the resistance voltage dividing step is equal to or higher than a reference voltage, and a voltage comparing step. Apply the voltage at the connection point as a power supply voltage for operation to the wireless transmission means for a predetermined period from the time when it is detected that the resistance divided voltage is equal to or higher than the reference voltage. The transmission signal modulated radio frequency data containing D is wirelessly transmitted, after a predetermined period of time includes a radio transmitting unit control step of stopping the application of the radio transmission unit of the voltage at the connection point,
Measure the transmission interval, which is the operation stop period of the wireless transmission means, from the operation stop time of the wireless transmission means when the predetermined period has elapsed until the time when the resistance comparison voltage is detected to be equal to or higher than the reference voltage by the voltage comparison step. The transmission interval varies between the DC voltage generated by the DC voltage generation step and the voltage at the connection point at the time when the resistance divided voltage is detected to be equal to or higher than the reference voltage. A difference value of 1 and a ratio of the second difference value between the DC voltage and the voltage at the connection point at the operation stop time of the wireless transmission means at the time when the predetermined period has elapsed, and each value of the current limiting resistor and the threshold judging capacitor It sets based on a product, It is characterized by the above-mentioned.

  According to the present invention, even if the current value of the current to be measured is large, it is possible to realize a small non-feed type wireless sensor terminal in which the transmission interval is not shortened and the transmission frequency is not high.

It is a circuit diagram of one embodiment of a wireless sensor terminal concerning the present invention. 5 is a flowchart of an embodiment of a wireless transmission method according to the present invention. 2 is a timing chart for explaining the operation of FIG. 1. It is a schematic diagram explaining the format and transmission interval of an example of the radio | wireless transmission signal in this invention.

Next, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a circuit diagram of an embodiment of a wireless sensor terminal according to the present invention. The wireless sensor terminal 10 of this embodiment includes a current transformer CT (Current Transformer), a current measurement / storage circuit unit 11, a power supply control unit 12, and a wireless transmission unit 13. The current measurement / storage circuit unit 11 is a circuit unit that generates a DC voltage corresponding to the value of the measured current obtained by measuring the current and stores it as a power supply voltage, and is connected to the secondary winding of the current converter CT. The load resistor R ₀ , the Cockcroft-Walton circuit 111, the Zener diode DZ ₀ , the storage capacitor C _p , the current limiting resistor R _lim, and the threshold determination capacitor C ₀ are included.

The current converter CT, which is a transformer, includes a clamp mechanism having a known structure on the primary winding side, for example, forms a ring-shaped core by clamping the power line of the switchboard with the clamp mechanism, and is wound around the core. An induced electromagnetic current having a value corresponding to the current flowing through the power line (current to be measured) is induced in the secondary winding. An alternating voltage is generated in the load resistor R ₀ connected to the secondary winding of the current converter CT by an electromagnetic induction current having a value corresponding to the current to be measured which is a current flowing through the power line.

The Cockcroft-Walton circuit 111 is a circuit in which capacitors and diodes are connected in multiple stages, and is a known booster and rectifier circuit with low power consumption that rectifies an input AC voltage into a high-voltage DC voltage. The Cockcroft-Walton circuit 111 boosts and rectifies a very low level input AC voltage to generate a high-voltage DC voltage V _p , and the DC voltage V _p is divided into two values on the positive side and the negative side of the Cockcroft-Walton circuit 111. A parallel circuit of a Zener diode DZ ₀ and a storage capacitor C _p connected between the output terminals, and a series circuit of a current limiting resistor R _lim and a threshold determination capacitor C ₀ connected in parallel to the parallel circuit; , Applied to the comparators U ₀ and U ₁ and the analog switch 121, respectively. The Zener diode DZ ₀ is for preventing element destruction. The storage capacitor C _p is charged by the output voltage V _p of the Cockcroft-Walton circuit 111 and holds (stores) the charged voltage. Therefore, the terminal voltage of the storage capacitor C _p is a voltage value V _p corresponding to the value of the AC voltage input to the Cockcroft-Walton circuit 111.

In the present embodiment, the storage capacitor in the wireless sensor terminal described in Patent Document 1 is divided into a storage capacitor C _p and a threshold determination capacitor C ₀ , and a current limiting resistor R _lim and a threshold determination capacitor C _0. Is characterized in that a series circuit consisting of is connected in parallel to the storage capacitor C _p and the inflow of power to the threshold judgment capacitor C ₀ is controlled by the current limiting resistor R _lim . Usually, since the output AC voltage from the current converter CT is saturated at a certain voltage value, the minimum transmission interval can be set from the saturation voltage value, the current limiting resistor R _lim and the threshold judging capacitor C ₀ .

Power supply control unit 12, an analog switch 121, a resistor divider by the parallel-connected resistors R ₁ and R ₂ to the threshold determination for the capacitor C _0, voltages V ₁ was divided by the resistor divider and the reference voltage V first comparator U for comparing the _{ref 0,} the timer circuit 122 for delaying the signal output from the first comparator U _0, the voltage V ₂ output from the timer circuit 122 and the reference voltage V _ref to the voltage comparator It consists of a second comparator U ₁ . The analog switch 121 is switching-controlled by the output signal of the comparator U ₁ , and the DC voltage V ₀ output from the connection point of the current limiting resistor R _lim and the threshold judging capacitor C ₀ is supplied to the wireless transmitter 13 during the ON period. The power supply voltage is applied, and the application of the DC voltage V _{0 to} the wireless transmission unit 13 is cut off during the off period.

Capacitor timer circuit 122 includes a diode D ₀ whose anode is connected to the output terminal of the comparator U _0, which is connected between the connection point and the GND the non-inverting input terminal of the cathode and the comparator U ₁ of the diode D ₀ consisting of C ₁ and a resistor R _3. The power supply voltage is applied to the comparators U ₀ and U ₁ from the Cockcroft-Walton circuit 111. Further, the resistance voltage dividing circuit using the resistors R ₁ and R _{2 divides the} DC voltage V ₀ output from the connection point of the current limiting resistor R _lim and the threshold value judging capacitor C ₀ , and the obtained resistance voltage dividing circuit. A voltage V ₁ is applied to the non-inverting input terminal of the comparator U ₀ .

The wireless transmission unit 13 includes a micro control unit (MCU) 131 and a radio IC (RFIC: radio frequency integrated circuit) 132, and a voltage V ₀ selected by the analog switch 121 is applied as an operation power supply voltage. Then, the operation is started, and a predetermined carrier frequency is modulated with a transmission signal of a predetermined format and transmitted. As will be described later, the timer circuit 122 is provided so that the analog switch 121 continues to selectively output the voltage V ₀ until the wireless transmission unit 13 completes the transmission operation.

Next, an outline of the operation of the wireless sensor terminal 10 of the present embodiment shown in FIG. 1 will be described with reference to the flowchart of FIG.
First, it is determined whether or not the current flowing through the power line is detected by the current converter CT (step S101). When the current is detected, an electromagnetic induction current having a value corresponding to the detected current to be measured is induced in the primary winding of the current converter CT, thereby generating a minute level AC voltage in the load resistor R _0. . The Cockcroft-Walton circuit 111 boosts and rectifies a minute level AC voltage from the load resistor R ₀ to generate a high-voltage DC voltage V _p (step S102), and uses the DC voltage V _P as a storage capacitor C _p. And charging according to a charging time constant determined by each value of C _p , C ₀ , and R _lim (step S103).

Subsequently, the voltage V ₁ obtained by dividing the voltage V ₀ at the connection point of the current limiting resistor R _lim and the threshold judging capacitor C ₀ by the resistor voltage dividing circuit using the resistors R ₁ and R ₂ is a predetermined reference. It is determined whether or not the voltage is equal to or higher than V _ref (step S104). When voltage V ₁ is equal to or greater than a predetermined reference voltage V _ref turns on the analog switch 121 (step S105). Accordingly, the voltage V ₀ is applied as a power supply voltage to the wireless transmission unit 13 through the analog switch 121, so that the wireless transmission unit 13 wirelessly transmits a transmission signal (step S106).

Since power is consumed by the wireless transmission operation of the radio transmission section 13, it starts to drop its power source voltage V _0. Further, when the voltages V ₁ output voltage V ₂ of the timer circuit 122 from the time becomes equal to or larger than a predetermined reference voltage V _ref is detected to have dropped to be started, to less than the reference voltage V _ref decreases (step S107) The analog switch 121 is turned off (step S108). Thereby, since the power supply voltage is not applied to the wireless transmission unit 13, the wireless transmission unit 13 stops the wireless transmission (step S109).

On the other hand, the Cockcroft-Walton circuit 111 continues to apply the generated DC voltage V _P to the storage capacitor C _p for charging (step S103). Thereafter, the operations in steps S104 to S109 are repeated. Here, the period during which the wireless transmission unit 13 continues the wireless transmission operation is determined by the timer time of the timer circuit 122, but the timer operation is not completed before the wireless transmission of the transmission signal is completed. It is set to such a value. Further, as will be described later, by providing the current limiting resistor R _lim and the threshold value determining capacitor C ₀ , the transmission interval from the wireless transmission operation stop time to the next wireless transmission operation start time is the same as the measured current value. Therefore, it is made to be much longer than before.

Next, the operation of the wireless sensor terminal 10 of this embodiment will be described in detail with reference to the timing chart of FIG.
For example, assuming that a current converter CT having a structure in which a coil is wound around a core is attached to a power line connected to a switchboard at time t ₀ shown in FIG. 3, the current flowing through the power line (current to be measured) An electromagnetic induction current having a predetermined _value flows in the secondary winding of the current converter CT, is further converted into a very low level AC voltage by the load resistance R ₀ , and is applied to the Cockcroft-Walton circuit 111. The Cockcroft-Walton circuit 111 boosts and rectifies a minute level AC voltage from the load resistor R ₀ , generates a high DC voltage, and applies it to the capacitor C _p , C _p , C ₀ , R _lim The battery is charged (accumulated) according to a charging time constant determined by each value. As a result, the terminal voltage of the capacitor C _p rises steeply from the time t ₀ toward the output DC voltage value of the Cockcroft-Walton circuit 111 as indicated by V _p in FIG. This terminal voltage V _p is a value corresponding to the current value of the current to be measured.

As the storage voltage V _p increases, the voltage V ₀ and the voltage V ₀ at the connection point of the current limiting resistor R _lim and the threshold determining capacitor C ₀ are divided by the resistor voltage dividing circuit using the resistors R ₁ and R _2. The voltage V ₁ obtained by pressing begins to rise from time t _{0 as} shown in FIG. These voltages V ₀ and V ₁ are also values according to the current value of the current to be measured. The comparator U ₀ constantly compares the voltage V ₁ and the reference voltage V _ref, and outputs a low level voltage (here, GND) when the voltage V ₁ is less than the reference voltage V _ref. high-level voltage (here, equal to V _p) at time t ₁ that V ₁ is equal to or larger than the reference voltage V _ref and outputs a. At time t ₁ , the voltage V ₀ reaches V _th as shown in FIG.

Comparator U ₁ is compared with the voltage V ₂ and the reference voltage V _ref from the timer circuit 122 at all times, the output voltage of the comparator U ₀ becomes high level, the timer circuit 122 of the comparator U ₁ at that time t ₁ Since the voltage V ₂ applied to the non-inverting input terminal is also at a high level higher than the reference voltage V _ref , a high level voltage is output to turn on the analog switch 121. As a result, the voltage V _{0 at} the connection point of the current limiting resistor R _lim and the threshold value determining capacitor C ₀ at time t ₁ is supplied to the MCU 131 and the wireless IC 132 constituting the wireless transmission unit 13 through the analog switch 121, respectively. To start these operations.

Since power is consumed by the operation of MCU131 and wireless IC132 from time t _1, the voltage V ₀ which connection point of the current limiting resistor R _lim and threshold value determining capacitor C _0, as shown in FIG. 3 (A) , It decreases with time from time t ₁ according to the discharge time constant of C ₀ . Accordingly, the resistance divided voltage V ₁ starts to decrease from time t ₁ , and as shown in FIG. 3A, immediately after time t ₁ , the voltage V ₁ becomes less than the reference voltage V _ref and the output voltage of the comparator U ₀ . Becomes a low level (here, GND). Therefore, as shown in FIG. 3B, the output voltage of the comparator U ₀ is at a high level only for a very short time from the time t ₁ , and the high level output period T _INS is not sufficient to complete the radio transmission. It is enough time.

Here, when the timer circuit 122 does not exist, the output voltage of the comparator U ₁ becomes low level immediately after the high-level output period T _INS of the comparator U ₀ elapses, and the analog switch 121 is switched to the OFF state. The supply of the operation power supply voltage to the wireless IC 132 is cut off, and the operation is stopped. There is a problem if the MCU 131 and the wireless IC 132 have not yet completed the wireless transmission operation of the transmission signal when the operation is stopped.

Therefore, in the present embodiment, the time until the output voltage of the comparator U ₁ becomes low level is delayed by the timer circuit 122, and sufficient time for the MCU 131 and the wireless IC 132 to complete the wireless transmission operation of the transmission signal can be secured. I am doing so. That is, since the diode D ₀ in the timer circuit 122 is forward-biased from the time t ₁ when the high level is output from the comparator U ₀ and the capacitor C ₁ starts to be charged by the forward current from the diode D ₀ , The terminal voltage V ₂ increases rapidly according to the charging time constant of C ₁ .

Here, the comparators U ₀ and U ₁ are of a type whose high-level output voltage is equal to the power supply voltage (so-called rail-to-rail comparator), and the high-potential side power supply voltage is the storage voltage V _p. Therefore, it is assumed that the low-potential-side power supply voltage is GND. In this case, as shown in FIG. 3A, the input voltage V ₁ of the comparator U ₀ starts to decrease from the time t ₁ as shown in FIG. 3A due to the start of the operation of the wireless transmission unit 13 immediately after time t ₁ . Thus, immediately after time t ₁ , the voltage V ₁ becomes less than the reference voltage V _ref, and the output voltage of the comparator U ₀ becomes low level.

Then, the terminal voltage of the capacitor C ₁ becomes higher than the anode potential of the diode D ₀ . For this reason, the diode D ₀ is reverse-biased, and the charge of the capacitor C ₁ starts to be discharged through the resistor R ₃ according to the discharge time constant determined by the capacitance value of C ₁ and the resistance value of R ₃ . As a result, the voltage V ₂ starts to gradually decrease with time as shown in FIG. 3A, and becomes lower than the reference voltage V _ref at time t ₂ . As a result, as shown in FIG. 3C, the output voltage of the comparator U ₁ becomes low level at time t ₂ , the analog switch 121 is turned off, and the operation power supply voltage V ₀ is applied to the MCU 131 and the wireless IC 132. Shut off. Here, the discharge time constant of C ₁ of the timer circuit 122 is such that the period from time t ₁ to time t ₂ is sufficient for the MCU 131 and the wireless IC 132 to complete the wireless transmission operation of the transmission signal. Is set to Thus, as shown in FIG. 3D, the analog switch 121 is turned on for a sufficient period from time t ₁ to time t ₂ , and outputs the operation power supply voltage V ₀ to the MCU 131 and the wireless IC 132. The transmission operation can be continued.

When the wireless transmission operation is started, as shown in FIG. 3A, the power supply voltage V ₀ for operation from the connection point of the current limiting resistor R _lim and the threshold judgment capacitor C ₀ starts to decrease due to power consumption. decreases in the time t ₂ to V _min. Since the analog switch 121 is turned off at time t ₂ as described above, the application of the operation power supply voltage V ₀ to the MCU 131 and the wireless IC 132 is cut off, and the wireless transmission operation is stopped. As a result, power consumption by the wireless transmission operation is stopped, the charging of the capacitor C ₀ of the power storage voltage V _P, begins to rise again above voltage V ₀ from V _min as shown in FIG. 3 (A), it Along with this, the resistance divided voltage V _{1 of} V ₀ also starts to rise.

Thereafter, at time t ₃ when the voltage V ₁ becomes equal to or higher than the reference voltage V _ref , a high level voltage is output from the comparator U _{0 as} shown in FIG. The comparator U ₁ is applied with a high-level voltage higher than the reference voltage V _ref from the comparator U ₀ through the timer circuit 122, and outputs a high-level voltage immediately after time t _{3 as} shown in FIG. The analog switch 121 is turned on. As a result, the voltage V _{0 at} the connection point of the current limiting resistor R _lim and the threshold judgment capacitor C ₀ is supplied to the MCU 131 and the RFIC 132 constituting the wireless transmission unit 13 through the analog switch 121 as operating power supply voltages at time t ₃ , respectively. Applied to start these operations again.

The voltage V ₂ becomes less than the reference voltage V _ref as shown in FIG. 3 (A) from the time t ₃ at time t ₄ after the setting time of the timer circuit 122. As a result, as shown in FIG. 3C, the output voltage of the comparator U ₁ becomes low level at time t ₄ , the analog switch 121 is turned off, and the operation power supply voltage V ₀ is applied to the MCU 131 and the wireless IC 132. And stop these operations again. Thereafter, the same operation as described above is repeated. A period P ₀ from the wireless transmission operation stop time t ₂ to the next wireless transmission operation start time t ₃ is a transmission interval. As described above, according to the wireless sensor terminal 10 of the present embodiment, as shown in FIG. 3D, the wireless transmission unit 13 is necessary for completing the operation using the voltage V ₀ and the ground potential GND as the operation power supply voltage. By applying a predetermined time (time t _{1 to} t ₃ , time t _{3 to} t ₄ ) that is longer than a predetermined time for operation, it is possible to realize a non-powered wireless sensor terminal having a self-sustained power supply.

  In the present embodiment, the wireless transmission signal is transmitted at a transmission interval corresponding to the measured value of the current to be measured. This will be described below with reference to FIG. For example, as schematically shown in FIG. 4A, the MCU 131 of the wireless transmission unit 13 transmits transmission data in a format including a fixed pattern preamble 21, transmission content data 22, and an error detection code 23 having a predetermined number of bits. Is generated. The radio IC 132 modulates the transmission data with a specific radio frequency assigned to the radio sensor terminal 10 using a predetermined modulation method as a carrier frequency, and transmits it as a radio transmission signal. Here, the data 22 is a terminal ID assigned to each wireless sensor terminal.

In addition, the wireless transmission unit 13 transmits a wireless transmission signal to the reception device as schematically illustrated in FIG. 4B at a transmission interval corresponding to the measured value of the current to be measured. 4B, a section T ₀ indicates a period during which the transmission signal having the format shown in FIG. 4A is wirelessly transmitted, and the operation period of the wireless transmission unit 13 (from time t ₁ to time t ₂ described above). Or equivalent to the period from time t ₃ to time t ₄ ), for example, 1 ms (constant). Further, sections T ₁ and T ₂ between two adjacent sections T ₀ indicate transmission intervals (corresponding to P ₀ in FIG. 3D) that are varied according to the measured current value, for example, 100 ms to 300 ms. It can be varied within the range. FIG. 4B is a diagram for explaining the difference between the section T ₀ and the sections T ₁ and T ₂ , and the relative relationship between the lengths of these sections is different from the actual for convenience of illustration. Show.

Here, when the measured value of the current to be measured changes, the output DC voltage V _p of the Cockcroft-Walton circuit 111 changes accordingly. Therefore, the voltage V ₀ at the connection point between R _lim and C ₀ determined by the values of the storage capacitor C _p , the current limiting resistor R _lim , and the threshold judgment capacitor C ₀ increases from the time immediately after the wireless transmission operation is stopped. The rising slope and the rising slope of the resistance divided voltage V ₁ change. For this reason, the time until the resistance divided voltage V ₁ reaches the reference voltage V _ref changes. This time is a transmission interval according to the measured value of the current to be measured.

Next, according to the wireless sensor terminal 10 of the present embodiment, it will be described that the transmission interval does not become short (the transmission frequency is high) even when the amount of current to be measured is large. Now, when the transmission interval and T _int, the transmission interval T _int of the wireless sensor nodes 10 of FIG. 1 is expressed by the following equation.
T _int = C ₀ · R _lim · log _e {(V _p −V _min ) / (V _p −V _th )} (1)
In the above equation, C ₀ is the capacitance value of the threshold judgment capacitor C ₀ , R _lim is the resistance value of the current limiting resistor R _lim , V _p is the output DC voltage of the Cockcroft-Walton circuit 111, and V _min is FIG. the value of the voltage V ₀ in the radio transmission operation stop time shown in (a), V _th is the value of the voltage V ₀ in the radio transmission operation starting time shown in Figure 3 (a).

As an example, when C ₀ is 100 μF, R _lim is 1 MΩ, and the current value of the current to be measured is 50 A, V _p is 7 V, V _min is 1 V, and V _th is 2 V. Substituting into the equation (1), the transmission interval T _int is 18 s. On the other hand, since C ₀ is conventionally 100 μF and R _lim is about 1Ω of the input resistance of the Cockcroft-Walton circuit 111, when the current value of the measured current is 50 A, V _p is 7 V and V _min is 1V and _Vth are 2V. Therefore, if these values are substituted into the equation (1), the transmission interval T _int is 18 μs, which is extremely short.

Thus, according to the wireless sensor terminal 10 of the present embodiment, even when the current value of the current to be measured is a large value such as 50 A, the transmission interval T _int can be significantly increased compared to the conventional case. . For this reason, even if another parasitic wireless sensor terminal using a transmission signal of the same carrier frequency exists nearby, the probability that the transmission signal collides can be greatly reduced. Further, according to the wireless sensor terminal 10 of the present embodiment, since the storage capacitor C _p having the same capacity as that of the conventional one can be used, a large-capacity large electrolytic capacitor is unnecessary, and the size of the capacitor is not as small as that of the conventional one. A power supply type wireless sensor terminal can be configured.

  Note that the wireless sensor terminal 10 of the present embodiment varies the transmission interval of the wireless transmission signal in accordance with the value of the measured current. Therefore, the receiving device side determines the current of the measured current from the reception interval of the received signal. Although a configuration for converting the value is required, it is not necessary to include information indicating the measured current value in the wireless transmission signal. Since the amount of information indicating the measured current value is relatively large, the wireless sensor terminal 10 of the present embodiment that does not include the information indicating the measured current value in the wireless transmission signal can minimize the data amount of the wireless transmission signal. And power consumption during transmission can be reduced. This is suitable for application to a wireless sensor terminal of an independent power source. Note that the receiving device applied to the wireless sensor terminal 10 of the present invention is the same as that of the prior art, and is not related to the gist of the present invention, so that the description thereof is omitted.

DESCRIPTION OF SYMBOLS 10 Wireless sensor terminal 11 Current measurement and electrical storage circuit part 12 Power supply control part 13 Wireless transmission part 111 Cockcroft-Walton circuit 121 Analog switch 122 Timer circuit 131 Micro control unit (MCU)
132 Wireless IC (RFIC)
CT current converter U ₀ , U ₁ comparator R ₀ load resistance C _p storage capacitor C ₀ threshold judgment capacitor R _lim current limiting resistor DZ ₀ Zener diode P ₀ , T ₁ , T ₂ transmission interval

Claims (4)

Current measuring means;
DC voltage generating means for generating a DC voltage corresponding to the current value of the current to be measured measured by the current measuring means;
A storage capacitor charged and held by the DC voltage generated by the DC voltage generating means; and
A series circuit composed of a current limiting resistor and a threshold judging capacitor connected in parallel to the storage capacitor;
A resistance voltage dividing circuit for resistively dividing the voltage at the connection point of the current limiting resistor and the threshold judging capacitor according to the current value of the current to be measured;
Voltage comparison means for detecting whether or not the resistance divided voltage obtained by the resistance voltage dividing circuit is equal to or higher than a reference voltage;
Wireless transmission means for wirelessly transmitting a transmission signal obtained by modulating a radio frequency previously assigned with data including a terminal ID;
The voltage at the connection point is applied as an operation power supply voltage to the wireless transmission unit for a predetermined period from the time when the voltage comparison unit detects that the resistance divided voltage is equal to or higher than the reference voltage, and the predetermined period has elapsed. The power supply voltage application means for stopping the application of the voltage of the connection point to the wireless transmission means after,
In the operation stop period of the wireless transmission means from the operation stop time of the wireless transmission means at the time when the predetermined period has elapsed to the time when the voltage comparison means detects that the resistance divided voltage has become equal to or higher than the reference voltage. The transmission interval is varied according to the current value of the current to be measured, and the DC voltage generated by the DC voltage generation means and the resistance divided voltage are equal to or higher than the reference voltage. And a second difference value between the DC voltage and the voltage at the connection point at the operation stop time of the wireless transmission means when the predetermined period has elapsed. The wireless sensor terminal is set based on the ratio of the current and the product of each value of the current limiting resistor and the threshold judging capacitor. The DC voltage generated by the DC voltage generating means is V _p , the voltage at the connection point at the time when the resistance divided voltage is detected to be equal to or higher than the reference voltage is V _th , and When the voltage at the connection point at the operation stop time of the wireless transmission means is V _min and the product of each value of the current limiting resistor and the threshold judging capacitor is K, the transmission interval is K · log _e {(V _p −V _min ) / (V _p −V _th )}
The wireless sensor terminal according to claim 1, wherein:   3. The wireless sensor terminal according to claim 1, wherein the power supply voltage application unit is set to a time length sufficient for the wireless transmission unit to complete a wireless transmission operation as the predetermined period. 4. A DC voltage generating step for generating a DC voltage corresponding to the current value of the current to be measured measured by the current measuring means;
A charging step of charging and holding the capacitor for storage by the DC voltage generated by the DC voltage generation step;
A resistance voltage dividing step of dividing a voltage corresponding to a current value of the current to be measured at a connection point of a current limiting resistor and a threshold judging capacitor constituting a series circuit connected in parallel to the storage capacitor;
A voltage comparison step for detecting whether or not the resistance divided voltage obtained by the resistance voltage division step is equal to or higher than a reference voltage;
Data including the terminal ID by applying the voltage at the connection point as a power supply voltage for operation to the wireless transmission means for a predetermined period from the time when the resistance comparison voltage is detected to be equal to or higher than the reference voltage in the voltage comparison step. A wireless transmission means control step of wirelessly transmitting a transmission signal modulated with a radio frequency, and stopping application of the voltage at the connection point to the wireless transmission means after the predetermined period has elapsed,
In the operation stop period of the wireless transmission means from the operation stop time of the wireless transmission means at the time when the predetermined period has elapsed to the time when the voltage comparison step detects that the resistance divided voltage has become equal to or higher than the reference voltage. The transmission interval is varied according to the current value of the current to be measured, and the transmission interval is set such that the DC voltage generated by the DC voltage generation step and the resistance divided voltage are equal to or higher than the reference voltage. And a second difference value between the DC voltage and the voltage at the connection point at the operation stop time of the wireless transmission means when the predetermined period has elapsed. And a product of each value of the current limiting resistor and the threshold judging capacitor.

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