Analog input device

Abstract

An analog input device (1) comprises input terminals (11, 12), a resistance voltage dividing circuit (13) composed of input resistors (131, 132) and power supply resistors (133, 134), a capacitor (14), a semiconductor switch (15) that converts a signal divided by the resistance voltage dividing circuit (13) to a pulse signal, an input transformer (16), a sample-and-hold circuit (21), an AD converter (22), a rectifying and smoothing circuit (18) that generates a power supply voltage (Vtest), a power supply transformer (19) that causes the rectifying and smoothing circuit (18) to generate the power supply voltage (Vtest), and a power supply pulse signal generation unit (233). Not only the voltage (Vin) of the input signal but also the power supply voltage (Vtest) are divided by the resistance voltage dividing circuit (13) and transmitted to the AD converter (22).

Description

Analog Input Device

[0001] The presently disclosed technology relates to an analog input device.

[0002] In an analog input device, when detecting the voltage value or current value of an input signal output from an input signal source, or when detecting disconnection of the input signal source, insulation between the input side and an internal circuit is required. For example, Patent Document 1 describes an analog input device that multiplexes and collects a plurality of analog signals from sensors or the like. This device includes an analog signal transformer, a drive transformer, an inhibit generation circuit, a continuous pulse generation circuit, an AND gate, and a rectifying / smoothing circuit.

[0003] The analog signal transformer receives an analog signal at a primary winding via a first semiconductor switch, and generates, on a secondary winding, a pulse having an amplitude corresponding to the analog signal by driving the first semiconductor switch to turn on and off. The drive transformer receives a drive pulse at a primary winding via a second semiconductor switch, and generates, on a secondary winding, a pulse for driving the first semiconductor switch to turn on and off.

[0004] The inhibit generation circuit generates an inhibit pulse having a pulse width wider than that of the drive pulse. The continuous pulse generation circuit generates continuous pulses each having a pulse width narrower than that of the drive pulse. The AND gate obtains a logical product of the inhibit pulse from the inhibit generation circuit and the continuous pulse from the continuous pulse generation circuit, and drives a primary winding of a power transformer.

[0005] The rectifying / smoothing circuit is connected to a secondary winding of the power transformer, obtains a DC voltage corresponding to a power pulse train, and applies the DC voltage to the primary winding of the analog signal transformer via a high-resistance path. This rectifying / smoothing circuit is connected to both ends of an analog signal input via high resistors. When the analog signal input is disconnected, power supply voltage is supplied from the rectifying / smoothing circuit via the high resistors, and a voltage higher than that of an analog signal is applied, so that disconnection of the input signal source can be detected.

[0006] International Publication No. 2008 / 133081

[0007] The semiconductor switches in analog input devices receive a drive pulse signal and rapidly switch on and off, converting a DC analog signal into a pulse signal that rapidly alternates between high and low. Because semiconductor switches operate at high speed, unlike other elements, they are more likely to fail than other elements when the device is operated for a long period of time. However, the conventional technology described in Patent Document 1 has the problem that while it can detect a break in the input signal source, it cannot detect a failure in the semiconductor switch present in the detection circuit.

[0008] The disclosed technology solves the above-mentioned problems and aims to provide an analog input device that can detect not only disconnections in the input signal source but also failures in semiconductor switches.

[0009] The analog input device according to the disclosed technology comprises an input terminal for inputting an analog input signal from an input signal source, an input resistor connected to the input terminal, a power resistor connected to the input resistor, a capacitor connected to the input resistor and holding charge, a resistive voltage divider circuit consisting of the input resistor and the power resistor, a semiconductor switch connected to the input resistor and the capacitor and converting the signal divided by the resistive voltage divider circuit into a pulse signal, an input transformer that transmits the input signal to the next stage, a sample-and-hold circuit that converts the pulse signal transmitted via the input transformer back into a DC signal, an AD converter that converts the DC signal into a digital signal, a rectifier-smoothing circuit connected to the input resistor via the power resistor and used to detect failures in the semiconductor switch and open circuits in the input signal source, a power transformer that generates a DC voltage in the rectifier-smoothing circuit using a power pulse signal, and a power pulse signal generation unit that generates a power pulse signal, wherein not only the voltage of the input signal but also the DC voltage is divided by the resistive voltage divider circuit and transmitted to the AD converter.

[0010] According to the analog input device of the disclosed technology, the resistive voltage divider circuit divides not only the input signal but also the DC voltage used to detect semiconductor switch failures and open circuits in the input signal source, and transmits it to the AD converter. As a result, the analog input device of the disclosed technology can detect semiconductor switch failures in addition to open circuits in the input signal source, based on whether or not the divided DC voltage is observed by the AD converter.

[0011] Figure 1 is a circuit diagram showing an example configuration of an analog input device according to Embodiment 1. Figure 2 is a circuit diagram showing an example configuration of an analog input device according to Embodiment 2.

[0012] Embodiment 1. The analog input device according to Embodiment 1 receives an analog signal from an input signal source, converts the input signal into a pulse signal using a semiconductor switch, transmits the pulse signal to a subsequent stage via an input transformer, and converts the pulse signal into a digital signal for signal processing. In particular, the analog input device according to Embodiment 1 includes a rectifier and smoothing circuit that generates a DC voltage used to detect semiconductor switch failures and open circuits in the input signal source, and a resistive voltage divider circuit that divides not only the input signal but also the DC voltage and transmits it to a subsequent stage. In the analog input device according to Embodiment 1, in addition to detecting open circuits in the input signal source, a semiconductor switch failure can be detected based on whether or not the divided DC voltage is observed in a subsequent stage.

[0013] (Basic Configuration of Analog Input Device) Figure 1 is a circuit diagram showing an example configuration of an analog input device 1 according to Embodiment 1. In Figure 1, the analog input device 1 is a device that observes the input signal voltage Vin from the input signal source 10 and outputs the observation result. For example, the analog input device 1 is required to have not only a fast response speed for input and output of signals, but also to minimize the linearity or error of the input and output characteristics. As shown in Figure 1, the analog input device 1 includes an input signal source 10, input terminals 11 and 12, a resistor voltage divider circuit 13, a capacitor 14, a semiconductor switch 15, an input transformer 16, a drive transformer 17, a rectifier and smoothing circuit 18, a power transformer 19, an amplifier 20, a sample-and-hold circuit 21, an AD converter 22, and a control unit 23.

[0014] (Input Signal Source) The input signal source 10 outputs an analog input signal. The input signal source 10 is a circuit that supplies electrical signals such as voltage or current, and has positive and negative polarity. Examples include a DC power supply, an AC power supply, or a battery. In a DC power supply, the direction of the voltage is constant, and the positive and negative terminals are clearly distinguished. Similarly, in the case of a battery, electrons flow from the positive terminal to the negative terminal. On the other hand, in an AC power supply, the positive and negative terminals switch at a constant period, and the polarity of the voltage changes.

[0015] (Input Terminals) Input terminals 11 and 12 are input terminals for receiving analog input signals from the input signal source 10. Input terminal 11 is connected to the positive side (high potential side) of the input signal source 10. Input terminal 12 is connected to the negative side (low potential side) of the input signal source 10. As shown in Figure 1, an input signal voltage Vin is applied to input terminals 11 and 12.

[0016] (Resistor Voltage Divider Circuit) The resistor voltage divider circuit 13 consists of an input resistor 131, an input resistor 132, a power supply resistor 133, and a power supply resistor 134. In particular, the resistor voltage divider circuit 13 divides not only the input signal voltage Vin, but also the DC voltage Vtest generated by the rectifier-smoothing circuit 18, which will be described later. The signal divided by the resistor voltage divider circuit 13 is transmitted to the AD converter 22. The input resistors 131 and 132, together with the capacitor 14, function as an RC-connected low-pass filter, smoothing out sharp changes in the input signal input via input terminals 11 and 12.

[0017] Input resistor 131 has one end connected to input terminal 11 and the other end connected to one end of the primary winding of input transformer 16. Input resistor 132 has one end connected to input terminal 12 and the other end connected to the drain terminal of the field-effect transistor (hereinafter referred to as "FET") that constitutes the semiconductor switch 15.

[0018] Power resistor 133 is connected to input resistor 131, and power resistor 134 is connected to input resistor 132. Specifically, one end of power resistor 133 is connected to the connection path between input resistor 131 and capacitor 14, and the other end is connected to one output terminal of rectifier / smoothing circuit 18. One end of power resistor 134 is connected to the connection path between input resistor 132 and the drain terminal of the FET constituting the semiconductor switch 15, and the other end is connected to the other output terminal of rectifier / smoothing circuit 18.

[0019] In the analog input device 1 shown in Figure 1, the resistance value of input resistor 131 is R1, the resistance value of input resistor 132 is R2, the resistance value of power supply resistor 133 is Rp, and the resistance value of power supply resistor 134 is Rn. In the resistive voltage divider circuit 13, although power supply resistors 133 and 134 are high resistances, their resistance values ​​Rp and Rn are set to approximately the same order (order of magnitude) as the resistance values ​​R1 and R2. As a result, a single resistive voltage divider circuit 13 can divide not only the input signal voltage Vin but also the DC voltage Vtest. Since only one resistive voltage divider circuit 13 is required, the number of resistive elements required for resistive voltage division is also reduced. In the example in Figure 1, for the sake of simplicity of explanation, R1 = R2 and Rp = Rn are assumed, and signal amplification by the input transformer 16 and amplifier 20 is not performed.

[0020] (Capacitor) Capacitor 14 is connected to input resistors 131 and 132 and is a capacitor that holds charge. Specifically, one end of capacitor 14 is connected to the connection path between input resistor 131 and one end of the primary winding of input transformer 16, and the other end is connected to the connection path between input resistor 132 and the drain terminal of the FET that constitutes semiconductor switch 15. As described above, capacitor 14 functions together with input resistors 131 and 132 as an RC-connected low-pass filter, smoothing out sharp changes in the input signal input through input terminals 11 and 12.

[0021] (Semiconductor Switch) The semiconductor switch 15 is connected to the input resistor 132 and converts the signal divided by the resistor voltage divider circuit 13 into a pulse signal. For example, the semiconductor switch 15 may be a C-MOS. C-MOS has a semiconductor circuit structure that combines two different transistor technologies, pMOSFET and nMOSFET. Specifically, the source terminals of the pMOSFET and nMOSFET are connected to one terminal of the primary winding of the drive transformer 17, and the gate terminals of both FETs are connected to the other terminal of the primary winding of the drive transformer 17. With the divided input signal voltage Vin input as a continuous voltage signal to the drain terminal, the input signal is converted into a pulse signal such as a square wave by applying a drive pulse signal to the gate terminals of the nMOSFET and pMOSFET and switching them on and off alternately.

[0022] (Input Transformer) The input transformer 16 transmits the pulse signal converted from the input signal by the semiconductor switch 15 to the subsequent amplifier 20. As shown in Figure 1, one end of the primary winding of the input transformer 16 is connected to the input terminal 11 via the input resistor 131, and the other end of the primary winding is connected to the drain terminal of the FET that constitutes the semiconductor switch 15. In addition, the amplifier 20 is connected to one end of the secondary winding of the input transformer 16, and the other terminal of the secondary winding is at ground potential.

[0023] (Drive Transformer) The drive transformer 17 is a transformer that drives the semiconductor switch 15 on and off by transmitting a drive pulse signal W1 to the semiconductor switch 15. As shown in Figure 1, one end of the primary winding of the drive transformer 17 is connected to the gate terminals of the two FETs that make up the semiconductor switch 15, and the other end of the primary winding is connected to the source terminal common to the two FETs that make up the semiconductor switch 15. One terminal of the secondary winding of the drive transformer 17 is connected to the drive pulse signal generation unit 232, and the other end of the secondary winding is at ground potential.

[0024] (Rectifier and Smoothing Circuit) The rectifier and smoothing circuit 18 is connected to the input resistors 131 and 132 via power supply resistors 133 and 134, and generates a DC voltage Vtest. For example, the rectifier and smoothing circuit 18 rectifies and smooths the power supply pulse signal W2 transmitted via the power transformer 19 to generate a DC voltage Vtest. The rectifier and smoothing circuit 18 is composed of, for example, a diode for rectifying the pulse signal and a capacitor for smoothing the rectified DC signal. Note that the value of the DC voltage Vtest is resistively divided by the resistive voltage divider circuit 13, so it is not input to the semiconductor switch 15 at its original value.

[0025] (Power Transformer) The power transformer 19 generates a DC voltage Vtest in the rectifier and smoothing circuit 18 in response to the power pulse signal W2. As shown in Figure 1, the primary winding side of the power transformer 19 is connected to the rectifier and smoothing circuit 18, the power pulse signal generation unit 233 is connected to one end of the secondary winding of the power transformer 19, and the other end of the secondary winding is at ground potential. A current corresponding to the pulse signal flows through the secondary winding of the power transformer 19, and this current change generates an induced electromotive force in the primary winding. This induced electromotive force allows a pulse signal to be obtained in the primary winding of the power transformer 19 as well.

[0026] (Amplifier) ​​The amplifier 20 amplifies the signal input via the input transformer 16. The amplifier 20 amplifies the input signal to the required level and provides a signal suitable for subsequent processing. Note that if the signal transmitted to the secondary side via the input transformer 16 is not to be amplified, the analog input device 1 does not need to be equipped with the amplifier 20.

[0027] (Sample-and-Hold Circuit) The sample-and-hold circuit 21 is a circuit that converts the pulse signal transmitted through the input transformer 16 back into a DC signal. For example, the sample-and-hold circuit 21 has a charging capacitor inside, and when the input signal reaches a high level, the switch turns on and the voltage of the input signal is held in the capacitor. When the input signal changes to a low level, the switch turns off and the capacitor continues to hold the charge, and in this state, the held voltage is output for a certain period of time. In this way, the sample-and-hold circuit 21 can convert the pulse signal back into a DC signal.

[0028] (AD Converter) The AD converter 22 performs analog-to-digital conversion on the input signal via the sample-and-hold circuit 21 to generate a digital signal. The input signal converted to a digital signal by the AD converter 22 is output to the control unit 23. In the detection of a broken wire in the input signal source 10 or a fault in the semiconductor switch 15, if only the DC voltage Vtest divided by the resistor voltage divider circuit 13 is input to the AD converter 22, it is determined that the semiconductor switch 15 is operating normally, but the input signal source 10 is broken. Also, in the detection of a broken wire in the input signal source 10 or a fault in the semiconductor switch 15, if a value equivalent to 0V is input to the AD converter 22 and the DC voltage Vtest divided by the resistor voltage divider circuit 13 is not observed, it is determined that the semiconductor switch 15 is faulty.

[0029] (Control Unit) The control unit 23 processes the digital signal generated by the AD converter 22 and controls the switching operation of the semiconductor switch 15 and the generation of the DC voltage Vtest by the rectifier and smoothing circuit 18. As shown in Figure 1, the control unit 23 includes a signal processing unit 231, a drive pulse signal generation unit 232, and a power supply pulse signal generation unit 233. The control unit 23 may be implemented by a dedicated processing circuit, or it may be implemented by a processor executing a program to realize its functions.

[0030] (Signal Processing Unit) The signal processing unit 231 processes the input digital signal. For example, the signal processing unit 231 may detect a disconnection in the input signal source 10 or a fault in the semiconductor switch 15 based on the output value of the AD converter 22.

[0031] (Drive pulse signal generation unit) The drive pulse signal generation unit 232 generates a drive pulse signal W1 for driving the semiconductor switch 15 on and off. For example, in the normal operation of the analog input device 1, which does not perform fault detection, the drive pulse signal generation unit 232 generates a drive pulse signal W1 and outputs the drive pulse signal W1 to the secondary side of the drive transformer 17. The drive transformer 17 drives the semiconductor switch 15 on and off by transmitting the drive pulse signal W1 to the semiconductor switch 15.

[0032] (Power pulse signal generation unit) The power pulse signal generation unit 233 generates a power pulse signal W2 to generate a DC voltage Vtest in the rectifier and smoothing circuit 18. For example, the power pulse signal generation unit 233 generates a power pulse signal W2 when detecting a disconnection in the input signal source 10 or a fault in the semiconductor switch 15, rather than during the normal operation of the analog input device 1, and outputs the power pulse signal W2 to the secondary side of the power transformer 19. The power transformer 19 transmits the power pulse signal W2 to the rectifier and smoothing circuit 18, thereby generating a DC voltage Vtest in the rectifier and smoothing circuit 18.

[0033] Next, the operation of the analog input device 1 will be described. The input signal from the input signal source 10 is input via input terminals 11 and 12. Input resistors 131 and 132 and capacitor 14 function as an RC-connected low-pass filter, smoothing out sharp changes in the input signal, such as sharp pulse noise. Capacitor 14 also has the function of maintaining the potential of the input signal voltage Vin by storing charge.

[0034] In the conventional technology described in Patent Document 1, when the analog input signal source is not disconnected, the input signal voltage Vin is input as is without being affected by the DC voltage Vtest because the resistance of the analog input signal source is small. On the other hand, in the analog input device 1, when the input signal source 10 is disconnected, it becomes open, and the DC voltage Vtest from the rectifier and smoothing circuit 18 is transmitted to the semiconductor switch 15 via the power supply resistors 133 and 134. At this time, a pulse voltage value different from the input signal voltage Vin from the input signal source 10 appears on the secondary winding of the input transformer 16, so the disconnection of the input signal source 10 can be detected.

[0035] Furthermore, in the conventional technology described in Patent Document 1, a rectifier and smoothing circuit is connected to both ends of the analog signal input via an input resistor, and if the analog signal input is disconnected, the power supply voltage is supplied to the rectifier and smoothing circuit via a high resistor. As a result, a voltage higher than that of the analog signal is applied, making it possible to detect the disconnection. However, when the analog signal input is not disconnected, the amount of current flowing from the power supply side to the rectifier and smoothing circuit via the high resistor is considerably smaller than the amount of current flowing from the analog signal input to the rectifier and smoothing circuit via the input resistor, so the current from the power supply side is suppressed.

[0036] In contrast, the analog input device 1 sets the resistance values ​​Rp of the power supply resistor 133 and Rn of the power supply resistor 134 to approximately the same order as the resistance values ​​R1 of the input resistor 131 and R2 of the input resistor 132. As a result, the analog input device 1 can perform not only voltage division of the input signal voltage Vin but also voltage division of the DC voltage Vtest generated by the rectifier and smoothing circuit 18 using a single resistor voltage divider circuit 13. Since only one resistor voltage divider circuit 13 is required, the number of resistor elements required for resistor voltage division can be reduced.

[0037] The portion of Figure 1 including the rectifier-smoothing circuit 18, power transformer 19, and power pulse signal generation unit 233 can be described as a power supply circuit for generating a DC voltage Vtest. The power pulse signal W2 generated by the power pulse signal generation unit 233 is transmitted to the rectifier-smoothing circuit 18 via the power transformer 19, and the rectifier-smoothing circuit 18 rectifies and smooths the power pulse signal W2 to generate a DC voltage Vtest.

[0038] The DC voltage Vtest generated by the rectifier-smoothing circuit 18 is supplied to the input resistor 131 connected to the input terminal 11 and the input resistor 132 connected to the input terminal 12 via the power supply resistors 133 and 134. In the resistor voltage divider circuit 13, the DC voltage Vtest is divided by the voltage division function of the input resistor 131 and the power supply resistor 133, and by the voltage division function of the input resistor 132 and the power supply resistor 134. As a result, the analog input device 1 operates as follows.

[0039] (Normal Operation) In normal operation of the analog input device 1, when no disconnection detection of the input signal source 10 or fault detection of the semiconductor switch 15 is performed, the power pulse signal generation unit 233 does not operate. As a result, the rectifier and smoothing circuit 18 does not generate a DC voltage Vtest. If the input signal source 10 is not disconnected at this time, the input signal voltage Vin is divided by the resistor voltage divider circuit 13 and transmitted to the next stage as a value of Vin・Rp / (R1+Rp) or Vin・Rn / (R2+Rn). The AD converter 22 receives the above divided value. On the other hand, if the input signal source 10 is disconnected, no input signal voltage Vin is generated. As a result, the analog input device 1 can detect a disconnection of the input signal source 10. For example, the signal processing unit 231 detects a disconnection of the input signal source 10 by monitoring the voltage value input to the AD converter 22.

[0040] In normal operation, when the power pulse signal generation unit 233 is activated, if the input signal source 10 is disconnected, the input signal voltage Vin will not be generated. However, the DC voltage Vtest will be divided by the resistor voltage divider circuit 13 and transmitted to the next stage as a value of Vtest・Rp / (R1+Rp) or Vtest・Rn / (R2+Rn). Although this is not the value of the input signal voltage Vin, it may be recognized as an input signal in normal operation.

[0041] Furthermore, when the power pulse signal generation unit 233 is operated during normal operation, even if the input signal source 10 is not disconnected, the input signal voltage Vin becomes Vin・Rp / (R1+Rp) or Vin・Rn / (R2+Rn), and the DC voltage Vtest becomes Vtest・Rp / (R1+Rp) or Vtest・Rn / (R2+Rn). Therefore, the semiconductor switch 15 receives the difference voltage between Vin・Rp / (R1+Rp) and Vtest・Rp / (R1+Rp), or the difference voltage between Vin・Rn / (R2+Rn) and Vtest・Rn / (R2+Rn). In this case as well, it may be recognized as an input signal during normal operation. To avoid such misrecognition of input signals, the analog input device 1 does not operate the power pulse signal generation unit 233 during normal operation.

[0042] (Fault Detection Operation) When detecting a disconnection in the input signal source 10 or a fault in the semiconductor switch 15, the analog input device 1 operates the power pulse signal generation unit 233. At this time, if a voltage value corresponding to Vtest・Rp / (R1+Rp) or Vtest・Rn / (R2+Rn) is input to the AD converter 22, the divided voltage value of the input signal voltage Vin is not observed. Therefore, it is determined that the semiconductor switch 15 is operating normally, but the input signal source 10 is disconnected. For example, the signal processing unit 231 makes this determination by monitoring the above voltage value input to the AD converter 22 and outputs the result.

[0043] On the other hand, when a voltage corresponding to 0 V is input to the AD converter 22, it is determined that the semiconductor switch 15 is faulty. Since the primary winding side and the secondary winding side of the input transformer 16 are not connected to each other, only high-frequency signals are propagated from the primary winding side to the secondary winding side. Because the semiconductor switch 15 always operates at high speed, it has a higher probability of failure than other elements when the apparatus is operated for a long time. In contrast, the failure rate of the input transformer 16, which does not undergo high-load operation like the semiconductor switch 15, is orders of magnitude lower than that of the semiconductor switch 15. Therefore, when a voltage corresponding to 0 V is input to the AD converter 22, no pulse signal is transmitted from the primary side to the secondary side of the input transformer 16, and no pulse signal is generated by the semiconductor switch 15, that is, it is determined that the semiconductor switch 15 is faulty. At this time, whether the input signal source 10 is disconnected cannot be detected. Note that, similarly to the above, the signal processing unit 231 may perform the determination and output the result thereof.

[0044] As described above, even when the input signal source 10 is not disconnected, the analog input apparatus 1 can detect a state where the semiconductor switch 15 is not driven to turn on / off in accordance with the high level and low level of the drive pulse signal W1 as a failure of the semiconductor switch 15.

[0045] As described above, the analog input device 1 according to Embodiment 1 comprises input resistors 131 and 132 connected to input terminals 11 and 12, power resistors 133 and 134 connected to input resistors 131 and 132, a capacitor 14 connected to input resistors 131 and 132 to hold charge, a resistive voltage divider circuit 13 consisting of input resistors 131 and 132 and power resistors 133 and 134, a semiconductor switch 15 connected to input resistors 131 and 132 and capacitor 14 to convert the voltage divided by the resistive voltage divider circuit 13 into a pulse signal, and an input transformer 16 that transmits the pulse signal to the amplifier 20. The analog input device 1 includes a sample-and-hold circuit 21 that converts the pulse signal amplified by the amplifier 20 back into a DC signal, an AD converter 22 that converts the DC signal into a digital signal, a rectifier-smoothing circuit 18 connected to input resistors 131 and 132 via power resistors 133 and 134 that generates a DC voltage Vtest, a power transformer 19 that generates the DC voltage Vtest in the rectifier-smoothing circuit 18 using a power pulse signal, and a power pulse signal generation unit 233 that generates a power pulse signal. The resistor voltage divider circuit 13 divides not only the input signal voltage Vin but also the DC voltage Vtest and transmits it to the AD converter 22. As a result, the analog input device 1 can detect a break in the input signal source 10 as well as a failure in the semiconductor switch 15 based on whether or not the divided DC voltage Vtest is observed in the AD converter 22.

[0046] In the analog input device 1 according to Embodiment 1, the power pulse signal generation unit 233 outputs a power pulse signal to the power transformer 19 when it detects a break in the input signal source 10 or a failure in the semiconductor switch 15. When the DC voltage Vtest divided by the resistor voltage divider circuit 13 is observed by the AD converter 22, it is determined that the semiconductor switch 15 is operating normally, but the input signal source 10 is broken. If the DC voltage Vtest divided by the resistor voltage divider circuit 13 is not observed by the AD converter 22, it is determined that the semiconductor switch 15 is faulty. As a result, the analog input device 1 can detect a failure in the semiconductor switch 15 in addition to detecting a break in the input signal source 10.

[0047] Embodiment 2. In the analog input device according to Embodiment 1, the DC voltage Vtest generated by the rectifying and smoothing circuit is limited within the voltage range of the power supply pulse signal. In contrast, the analog input device according to Embodiment 2 allows the rectifying and smoothing circuit to generate the DC voltage Vtest without being limited to the voltage range of the power supply pulse signal.

[0048] FIG. 2 is a circuit diagram showing a configuration example of an analog input device 1A according to Embodiment 2. In FIG. 2, the analog input device 1A is a device that observes the input signal voltage Vin from the input signal source 10 and outputs an observation result, similarly to Embodiment 1. For example, the analog input device 1 is required to reduce the linearity or error of input / output characteristics in addition to the response speed of signal input / output. As shown in FIG. 2, the analog input device 1A includes an input signal source 10, an input terminal 11, an input terminal 12, a resistance voltage divider circuit 13, a capacitor 14, a semiconductor switch 15, an input transformer 16, a drive transformer 17, a rectifying and smoothing circuit 18, a power supply transformer 19, an amplifier 20, a sample-and-hold circuit 21, an AD converter 22, a control unit 23, a detection power supply 24, and a power semiconductor switch 25. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0049] (Detection Power Supply) The detection power supply 24 is a power supply connected to one end of the secondary winding of the power supply transformer 19 as shown in FIG. 2. For example, as shown in FIG. 2, the detection power supply 24 is connected to one end of the secondary winding of the power supply transformer 19 via a resistor for limiting the current flowing through the power supply transformer 19.

[0050] (Power Semiconductor Switch) The power semiconductor switch 25 is a switching element connected to the other end of the secondary winding of the power supply transformer 19 and driven to turn on and off based on the power supply pulse signal W2. For example, the power semiconductor switch 25 is constituted by an FET. In this case, the power semiconductor switch 25 has a drain terminal connected to the other end of the secondary winding of the power supply transformer 19, a gate terminal connected to the power pulse signal generation unit 233, and a source terminal set to the ground potential.

[0051] Next, the operation of the analog input device 1A will be described. Here, we will describe the generation of the DC voltage Vtest by the rectifier and smoothing circuit 18. When the power pulse signal generation unit 233 is activated during fault detection, the power pulse signal W2 is input to the gate terminal of the power supply semiconductor switch 25. The power pulse signal W2 alternates between high and low levels. The power supply semiconductor switch 25 turns on when the power pulse signal W2 is at a high level and turns off when it is at a low level.

[0052] When the power supply semiconductor switch 25 is ON, the resistance between the drain terminal and the source terminal decreases, and current from the detection power supply 24 flows to the secondary winding side of the power transformer 19. The change in current on the secondary winding side of the power transformer 19 affects the primary winding side, generating an induced electromotive force. Due to this induced electromotive force, the voltage on the primary winding side of the power transformer 19 becomes a voltage value corresponding to the voltage of the detection power supply 24. On the other hand, when the power supply semiconductor switch 25 is OFF, the resistance between the drain terminal and the source terminal is high, and no current flows to the secondary winding side of the power transformer 19, so no induced electromotive force is generated, and there is no change in the voltage on the primary winding side of the power transformer 19.

[0053] In this way, when the power pulse signal W2, which alternates between high and low levels, is input to the gate terminal of the power supply semiconductor switch 25, a pulse signal corresponding to the voltage of the detection power supply 24 is generated on the primary winding side of the power transformer 19. This signal is input to the rectifier and smoothing circuit 18. The rectifier and smoothing circuit 18 generates a DC voltage Vtest corresponding to the voltage of the detection power supply 24 by rectifying and smoothing the pulse signal transmitted from the power transformer 19.

[0054] As described above, the analog input device 1A according to Embodiment 2 is configured to include a detection power supply 24 connected to one end of the secondary winding of the power transformer 19, and a power supply semiconductor switch 25 connected to the other end of the secondary winding of the power transformer 19, which is driven on and off by a power pulse signal. The power transformer 19 generates a DC voltage Vtest in the rectifier and smoothing circuit 18 by a pulse signal corresponding to the voltage of the detection power supply 24 transmitted from the secondary winding side to the primary winding side of the power supply semiconductor switch 25 when it is turned on or off. In this way, the analog input device 1A generates a DC voltage Vtest by a pulse signal corresponding to the voltage of the detection power supply 24, thus improving the degree of freedom in setting the DC voltage Vtest.

[0055] Furthermore, it is possible to combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment.

[0056] The analog input device according to the disclosed technology can be used, for example, as an input function for analog signals measured by various sensors.

[0057] 1, 1A Analog input device, 10 Input signal source, 11, 12 Input terminals, 13 Resistor voltage divider circuit, 14 Capacitor, 15 Semiconductor switch, 16 Input transformer, 17 Drive transformer, 18 Rectifier and smoothing circuit, 19 Power transformer, 20 Amplifier, 21 Sample and hold circuit, 22 AD converter, 23 Control unit, 24 Detection power supply, 25 Power supply semiconductor switch, 131, 132 Input resistors, 133, 134 Power supply resistors, 231 Signal processing unit, 232 Drive pulse signal generation unit, 233 Power supply pulse signal generation unit.

Claims

1. An analog input device comprising: an input terminal for inputting an analog input signal from an input signal source; an input resistor connected to the input terminal; a power resistor connected to the input resistor; a capacitor connected to the input resistor and holding charge; a resistive voltage divider circuit consisting of the input resistor and the power resistor; a semiconductor switch connected to the input resistor and the capacitor and converting the signal divided by the resistive voltage divider circuit into a pulse signal; an input transformer that transmits the input signal to a subsequent stage; a sample-and-hold circuit that converts the pulse signal transmitted through the input transformer back into a DC signal; an AD converter that converts the DC signal into a digital signal; a rectifier-smoothing circuit connected to the input resistor via the power resistor and used to generate a DC voltage for detecting failures in the semiconductor switch and disconnections in the input signal source; a power transformer that generates the DC voltage in the rectifier-smoothing circuit using a power pulse signal; and a power pulse signal generation unit that generates the power pulse signal, wherein the resistive voltage divider circuit divides not only the voltage of the input signal but also the DC voltage and transmits it to the AD converter.

2. The analog input device according to claim 1, characterized in that the power pulse signal generation unit outputs the power pulse signal to the power transformer when it detects a break in the input signal source or a failure in the semiconductor switch, and when the DC voltage divided by the resistor voltage divider circuit is observed by the AD converter, it is determined that the semiconductor switch is operating normally but the input signal source is broken, and when the DC voltage divided by the resistor voltage divider circuit is not observed by the AD converter, it is determined that the semiconductor switch is faulty.

3. The analog input device according to claim 1 or 2, comprising: a detection power supply connected to one end of the secondary winding of the power transformer; and a power supply semiconductor switch connected to the other end of the secondary winding of the power transformer and driven on / off by the power pulse signal, wherein the power transformer generates the DC voltage in the rectifier and smoothing circuit by a pulse signal corresponding to the voltage of the detection power supply transmitted from the secondary winding side to the primary winding side of the power transformer by the on / off switching of the power supply semiconductor switch.

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