KR102700289B1 - analog signal input device - Google Patents

Abstract

An analog signal input device (1) comprises a first pulse transformer (3) for insulating an analog signal (W1) input from the outside, a first switching element (5) connected to the primary side of the first pulse transformer (3), a reset circuit (6) connected in parallel with the first pulse transformer (3) on the secondary side of the first pulse transformer (3) and having a resistance element (61) and a second switching element (62) connected in series with each other, and a control circuit (11) for outputting a drive signal (W2) for ON/OFF control of the first switching element (5) to the first switching element (5) and for outputting a reset signal (W4) for ON/OFF control of the second switching element (62) to the second switching element (62), and when the first switching element (5) is turned OFF, the control circuit (11) turns ON the second switching element (62).

Description

analog signal input device

The present disclosure relates to an analog signal input device.

Analog signal input devices are often used in industrial control and monitoring equipment. These analog signal input devices input analog signals output from devices such as temperature sensors with high precision into an AD converter. At this time, in order to convert analog signals to AD, insulation is necessary. In analog signal input devices, it is generally assumed that they will be used in a strict installation environment, and in order to avoid failures caused by ground loops through the ground, etc., insulation measures are taken between the input section and the internal circuit.

Therefore, when receiving an analog signal, it is proposed to adopt an insulation method using a transformer element as an insulation means in an analog signal input device. Patent document 1 discloses an analog signal input device that adopts an insulation method.

Patent Document 1: Japanese Patent Publication No. 2013-145509

The analog signal input device disclosed in Patent Document 1 has a waveform shaping circuit on the secondary side of a pulse transformer. This waveform shaping circuit demagnetizes the magnetic core of the pulse transformer. However, since the waveform shaping circuit is always electrically connected when outputting an analog signal to an AD converter, distortion easily occurs in the waveform of the analog signal output from the waveform shaping circuit. In this way, if distortion occurs in the waveform of the analog signal, there is a concern that the sensing precision of the analog signal by the AD converter may deteriorate.

The present disclosure was made to solve the above problems, and has as its purpose the provision of an analog signal input device capable of suppressing distortion of an analog signal.

An analog signal input device according to the present disclosure is an analog signal input device that inputs an analog signal input from the outside to an AD converter through insulation, the device comprising: a pulse transformer that insulates the analog signal; a first switching element from which an analog signal is input at one end and the other end is connected to the primary side of the pulse transformer; a reset circuit that is connected in parallel with the pulse transformer on the secondary side of the pulse transformer and has a resistance element and a second switching element that are connected in series with each other; and a control circuit that outputs a drive signal for controlling ON/OFF of the first switching element to the first switching element and a reset signal for controlling ON/OFF of the second switching element to the second switching element, wherein the control circuit turns ON the second switching element when the first switching element is turned OFF, thereby causing a reset current generated on the secondary side of the pulse transformer to flow to the resistance element, and the second switching element is conductive other than at a timing when the analog signal is input to the AD converter.

According to the present disclosure, distortion of an analog signal can be suppressed. As a result, the analog signal input device according to the present disclosure can sense an analog signal with high precision.

Fig. 1 is a circuit diagram showing the configuration of an analog signal input device according to embodiment 1.
Fig. 2 is a timing chart showing the operation waveforms of each part in the analog signal input device according to embodiment 1.
Fig. 3(a) is a circuit configuration diagram showing the driving state of the first pulse transformer. Fig. 3(b) is a timing chart showing the operating waveforms of each part in the driving state of the first pulse transformer.
Fig. 4(a) is a circuit diagram showing the reset state of the first pulse transformer. Fig. 4(b) is a timing chart showing the operation waveforms of each part in the reset state of the first pulse transformer.
Fig. 5 is a circuit diagram showing the configuration of an analog signal input device according to embodiment 2.
Figure 6 is a circuit diagram showing a conventional analog signal input device.
Figure 7 is a circuit diagram showing a conventional reset circuit.

Hereinafter, in order to explain the present disclosure in more detail, a form for implementing the present disclosure will be described according to the attached drawings.

Implementation form 1.

An analog signal input device (1) according to embodiment 1 will be described using FIGS. 1 to 4, FIG. 6, and FIG. 7.

First, an overview of the operation of an analog signal input device using a transformer insulation method will be explained using the technology disclosed in Patent Document 1 as an example.

The analog signal output from the sensor element is finally transmitted to the AD converter through the switching element and the pulse transformer. The sensor element is assumed to be, for example, a temperature sensor. At this time, if the analog signal output from the sensor element is a very low-frequency signal (substantially a DC signal), insulation transmission via the transformer is not possible if the analog signal remains a low-frequency signal, or the pulse transformer needs to be made extremely large. Therefore, in the technology disclosed in Patent Document 1, insulation transmission of the analog signal is performed using a small pulse transformer by forming (modulating) the analog signal into a transient pulse waveform.

Fig. 1 is a circuit diagram showing the configuration of an analog signal input device (1) according to Embodiment 1. This analog signal input device (1) has input terminals (1a, 1b). One or more sensor elements (2) are connected to the input terminals (1a, 1b) via a cable or the like.

An analog signal input device (1) comprises a first pulse transformer (3), a second pulse transformer (4), a first switch element (5), a reset circuit (6), an amplifier element (7), a multiplexer (8), a buffer element (9a, 9b), an AD converter (10), and a control circuit (11). This analog signal input device (1) adopts a transformer insulation method.

An analog signal input device (1) of this type is a device that precisely inputs an analog signal (sensor element signal) W1 output from a sensor element (2) to an AD converter (10) through insulation. In addition, the analog signal input device (1) has a number of circuits according to the number of input channels (the number of analog channels). Fig. 1 shows an example in which the number of input channels is 8 (Ch1 to Ch8).

The first pulse transformer (3) is to insulate the analog signal W1 input from the sensor element (2). In addition, the first pulse transformer (3) constitutes a pulse transformer.

The second pulse transformer (4) controls the first switching element (5) described later.

The first switching element (5) is connected to the primary side (insulation side) of the first pulse transformer (3). The first switching element (5) applies an analog signal W1 to the first pulse transformer (3). In addition, the first switching element (5) can receive a drive signal W2 from the second pulse transformer (4). The drive signal W2 is a signal for controlling the ON/OFF (opening and closing) of the first switching element (5).

The reset circuit (6) is connected in parallel with the first pulse transformer (3) on the secondary side (internal circuit side) of the first pulse transformer (3). This reset circuit (6) demagnetizes the magnetic core constituting the first pulse transformer (3). In other words, the reset circuit (6) resets the excitation current W6 (see Fig. 3) flowing in the first pulse transformer (3).

In addition, the reset circuit (6) has a resistance element (61) and a second switch element (62) that are connected in series with each other. Specifically, the resistance element (61) and the second switch element (62) are connected in series with respect to a signal line from the first pulse transformer (3). Then, a reset signal W4 can be input to the second switch element (62). The reset signal W4 is a signal for controlling ON/OFF (opening/closing) of the second switch element (62).

The amplifier element (7) is connected to the rear end of the reset circuit (6). This amplifier element (7) amplifies the analog signal W1 output from the first pulse transformer (3).

A multiplexer (8) selects one channel among multiple input channels. This multiplexer (8) is controlled by a control circuit (11) described later.

The AD converter (10) is connected to the rear end of the multiplexer (8). This AD converter (10) converts the analog signal W1 output from the multiplexer (8) into a digital signal. In addition, the AD converter (10) outputs the converted digital signal to the control circuit (11). In addition, in Fig. 1, the analog signal W1 output from the multiplexer (8) is represented as an AD conversion input signal W3.

The control circuit (11) has a processing unit (111), a timing control unit (112), and a Ch selection unit (113).

The processing unit (111) processes the digital signal output from the AD converter (10). In addition, the processing unit (111) outputs the processing result to the timing control unit (112) and the Ch selection unit (113).

The timing control unit (112) outputs a sample signal W8, a drive signal W2, and a reset signal W4 based on the digital signal processed by the processing unit (111).

The sample signal W8 is a signal for the AD converter (10) to sample the AD conversion input signal W3. This sample signal W8 is output to the AD converter (10) by the timing control unit (112). The drive signal W2 is output to the first pulse transformer (3) by the timing control unit (112) through the buffer element (9a), the multiplexer (8), and the second pulse transformer (4). The reset signal W4 is output to the reset circuit (6) by the timing control unit (112) through the buffer element (9b) and the multiplexer (8).

Here, in order for the control circuit (11) to control the ON/OFF of the first switching element (5), it is necessary to insulate the drive signal W2. For this reason, the analog signal input device (1) is equipped with a second pulse transformer (4). As shown in Fig. 1, the primary sides of the first pulse transformer (3) and the second pulse transformer (4) in the analog signal input device (1) are composed only of the first switching element (5) using a transistor.

In comparison, Fig. 6 is a circuit configuration diagram showing a conventional analog signal input device (1B). The conventional analog signal input device (1B) shown in this Fig. 6 adopts a photocoupler insulation method. The conventional analog signal input device (1B) has an amplifier element (7), a multiplexer (8), a buffer element (9a, 9b), an AD converter (10), a control circuit (11), a photocoupler (12), and an insulated power circuit (13). On the primary side of the analog signal input device (1B), an AD converter (10) and an insulated power circuit (13) are arranged.

Therefore, as shown in FIG. 1 and FIG. 6, when comparing the circuit configuration of the analog signal input device (1) of the transformer insulation method and the circuit configuration of the analog signal input device (1B) of the photocoupler insulation method, the analog signal input device (1) is advantageous in terms of the number of parts and manufacturing cost compared to the analog signal input device (1B).

In addition, the control circuit (11) controls the second switch element (62) so that the reset circuit (6) functions only at the timing when the element of the magnetic core of the first pulse transformer (3) is required immediately after driving the first pulse transformer (3).

Next, the operation of the analog signal input device (1) will be explained using Fig. 2.

Fig. 2 is a timing chart showing the operation waveforms in each part of the analog signal input device (1) according to Embodiment 1. The vertical axis of Fig. 2 represents the analog signal W1 input to the input terminal (1a, 1b), the drive signal W2 output from the timing control unit (112), the AD conversion input signal W3 input to the AD converter (10), and the reset signal W4 output from the timing control unit (112). In addition, the horizontal axis of Fig. 2 represents the passage of time.

The analog signal W1 is an output signal from the sensor element (2) and changes gradually over time.

The drive signal W2 turns the first switch element (5) ON or OFF via the buffer element (9a), the multiplexer (8), and the second pulse transformer (4). That is, the period during which the drive signal W2 becomes high potential becomes a period during which the first pulse transformer (3) is driven. During that period, a voltage corresponding to the amplitude of the analog signal W1 is transmitted to the secondary side of the first pulse transformer (3). In addition, the period during which the drive signal W2 becomes low potential becomes a period during which the first pulse transformer (3) is reset.

The waveform of the AD conversion input signal W3 is observed on the secondary side of the first pulse transformer (3). The AD conversion input signal W3 becomes a value corresponding to the amplitude of the analog signal W1 during a period in which the drive signal W2 becomes high potential. At this time, the amplitude of the AD conversion input signal W3 is sampled by the AD converter (10). In addition, a backswing occurs in the AD conversion input signal W3 during the time in which the reset signal W4 becomes high potential. This backswing is caused by a reset current W7 (see Fig. 4) that is generated as a residual of the excitation current W6 (see Fig. 3) of the first pulse transformer (3). The reset circuit (6) is provided to suppress excessive amplitude and long-term vibration of the backswing.

The reset signal W4 turns the second switch element (62) of the reset circuit (6) ON or OFF via the buffer element (9b) and the multiplexer (8). That is, the period during which the reset signal W4 is at a high potential is the period during which the magnetic core of the first pulse transformer (3) is demagnetized (reset). The backswing is rapidly damped and contracted by power consumption by the resistance element (61) of the reset circuit (6) during the period during which the magnetic core of the first pulse transformer (3) is demagnetized.

Next, the operation of the first pulse transformer (3) will be described in detail using FIGS. 3 and 4.

Fig. 3(a) is a circuit configuration diagram showing the driving state of the first pulse transformer (3). Fig. 3(b) is a timing chart showing the operating waveforms of each part in the driving state (driving period) of the first pulse transformer (3). The vertical axis of Fig. 3(b) represents the analog signal W1, the drive signal W2, the AD conversion input signal W3, the sample signal W8, and the exciting current W6. The horizontal axis of Fig. 3(b) represents the passage of time.

As shown in Fig. 3, an analog signal W1 is input as a constant value to the first pulse transformer (3). In addition, during the driving period of the first pulse transformer (3), the first switch element (5) is in an ON state for conducting the drive signal W2. On the other hand, the second switch element (62) is in an OFF state for blocking the reset signal W4.

When the drive signal W2 is conducted to the first switching element (5), an exciting current W6 flows to the primary side of the first pulse transformer (3). During the driving period of the first pulse transformer (3) (the conducting period of the first switching element (5)), the exciting current W6 increases linearly according to Faraday's law (electromagnetic induction), and the sum of the exciting currents W6 becomes Idr.

In addition, during the driving period of the first pulse transformer (3), an AD conversion input signal W3 corresponding to the analog signal W1 is generated on the secondary side of the first pulse transformer (3). The potential of this AD conversion input signal W3 becomes constant at Vin. In addition, the sample period by the sample signal W8 is set within the conduction period of the AD conversion input signal W3.

Fig. 4(a) is a circuit configuration diagram showing the reset state of the first pulse transformer (3). Fig. 4(b) is a timing chart showing the operation waveforms of each part in the reset state (reset period) of the first pulse transformer (3). The vertical axis of Fig. 4(b) represents the analog signal W1, the reset signal W4, the AD conversion input signal W3, and the reset current W7. The horizontal axis of Fig. 4(b) represents the passage of time.

In order to prevent saturation or demagnetization of the magnetic core constituting the first pulse transformer (3), it is necessary to demagnetize the magnetic core during the reset period by the reset signal W4.

As shown in Fig. 4, an analog signal W1 is input as a constant value to the first pulse transformer (3). In addition, during the reset period of the first pulse transformer (3), the first switch element (5) is in an OFF state that blocks the drive signal W2. On the other hand, the second switch element (62) is in an ON state that conducts the reset signal W4.

When the reset signal W4 is conducted to the second switching element (62), a reset current W7 flows to the secondary side of the first pulse transformer (3). During the conduction period of the second switching element (62) in the reset period of the first pulse transformer (3), the sum of the reset currents W7 becomes Irst. At this time, power consumption occurs in the reset current W7 because the reset current W7 flows to the resistance element (61) of the reset circuit (6). For this reason, the backswing of the AD conversion input signal W3 converges quickly.

That is, the reset circuit (6) has a resistance element (61) and a second switch element (62), and the reset current W7 flows through the resistance element (61) only during the reset period. For this reason, the first pulse transformer (3) is not affected by power consumption by the resistance element (61) during the driving period of the first pulse transformer (3). As a result, when the AD converter (10) samples the AD conversion input signal W3, the AD converter (10) can suppress distortion of the waveform of the AD conversion input signal W3 and sense the AD conversion input signal W3 with high precision.

In addition, in the analog signal input device (1), since the reset circuit (6) is arranged on the secondary side of the first pulse transformer (3), there is no need to provide an insulating element for the reset circuit (6) that controls the second switch element (62).

Here, Fig. 7 is a circuit configuration diagram showing a conventional reset circuit (6B). This conventional reset circuit (6B) connects a resistance element (61) and a rectifying element (64) such as a diode in series with respect to a signal line from the first switch element (5). In contrast, since the reset circuit (6) does not have the rectifying element (64) that the conventional reset circuit (6B) has, even if the analog signal W1 has a microamplitude greater than the forward drop voltage of the diode, the reset function can be exerted.

Above, the analog signal input device (1) according to embodiment 1 comprises a first pulse transformer (3) for insulating an analog signal W1 input from the outside, a first switching element (5) connected to the primary side of the first pulse transformer (3), a reset circuit (6) connected in parallel with the first pulse transformer (3) on the secondary side of the first pulse transformer (3) and having a resistance element (61) and a second switching element (62) connected in series with each other, and a control circuit (11) for outputting a drive signal W2 for ON/OFF control of the first switching element (5) to the first switching element (5) and for outputting a reset signal W4 for ON/OFF control of the second switching element (62) to the second switching element (62), and the control circuit (11) turns the second switching element (62) ON when the first switching element (5) is turned OFF. For this reason, the analog signal input device (1) can suppress distortion of the analog signal W1 (AD conversion input signal W3). As a result, the analog signal input device (1) can sense the analog signal W1 with high precision.

Implementation form 2.

An analog signal input device (1A) according to Embodiment 2 will be described using Fig. 5. Fig. 5 is a circuit configuration diagram showing the configuration of an analog signal input device (1A) according to Embodiment 2. In addition, configurations having the same function as those described in the above-described embodiment are given the same reference numerals and their descriptions are omitted.

An analog signal input device (1A) according to embodiment 2 has a reset circuit (6A) instead of the reset circuit (6) of the analog signal input device (1) according to embodiment 1.

The reset circuit (6A) is arranged on the secondary side of the first pulse transformer (3). This reset circuit (6A) is configured to have a magnetic core constituting the first pulse transformer (3). In addition, the reset circuit (6A) has a resistance element (61), a second switch element (62), and an inverting buffer element (63). The resistance element (61), the second switch element (62), and the inverting buffer element (63) are connected in series to a signal line from the first pulse transformer (3).

The drive signal W2 output from the timing control unit (112) of the control circuit (11) is input to the first switch element (5) through the buffer element (9a), the multiplexer (8), and the second pulse transformer (4). In addition, the drive signal W2 is input to the second switch element (62) through the buffer element (9a), the multiplexer (8), and the inverting buffer element (63).

That is, the reset signal W4 for controlling the ON/OFF of the second switch element (62) is generated by inverting the polarity of the drive signal W2 using the inverting buffer element (63). For this reason, the timing control unit (112) does not need to have a circuit for generating the reset signal W4 and a circuit for adjusting the output timing of the reset signal W4. As a result, the analog signal input device (1A) can simplify the circuit configuration of the control circuit (11).

Above, in the analog signal input device (1A) according to embodiment 2, the reset circuit (6A) has an inversion buffer element (63) that generates a reset signal W4 by inverting the polarity of the drive signal W2. For this reason, the analog signal input device (1A) can simplify the circuit configuration of the control circuit (11).

In addition, the present disclosure allows for free combination of each embodiment, modification of any component of each embodiment, or omission of any component in each embodiment, within the scope of the disclosure.

(Industrial applicability)

An analog signal input device according to the present disclosure can suppress distortion of an analog signal by turning a second switch element, into which a reset signal is input, ON when a first switch element, into which a drive signal is input, is turned OFF, and is suitable for use in an analog signal input device, etc.

1, 1A, 1B: analog signal input device, 1a, 1b: input terminal, 2: sensor element, 3: first pulse transformer, 4: second pulse transformer, 5: first switch element, 6, 6A, 6B: reset circuit, 61: resistance element, 62: second switch element, 63: inverting buffer element, 64: rectifier element, 7: amplifier element, 8: multiplexer, 9a, 9b: buffer element, 10: AD converter, 11: control circuit, 111: processing unit, 112: timing control unit, 113: channel selection unit, 12: photocoupler, 13: isolated power circuit, W1: analog signal, W2: drive signal, W3: AD conversion input signal, W4: reset signal, W6: excitation current, W7: reset current, W8: sample signal

Claims (2)

An analog signal input device that inputs an analog signal input from the outside to an AD converter through insulation.
A pulse transformer that insulates the above analog signal,
A first switching element, from which the analog signal is input and the other end is connected to the primary side of the pulse transformer,
A reset circuit having a resistance element and a second switch element connected in parallel with the pulse transformer and connected in series with each other on the secondary side of the pulse transformer,
A control circuit that outputs a drive signal for controlling ON/OFF of the first switch element, and outputs a reset signal for controlling ON/OFF of the second switch element, for the first switch element.
Equipped with,
The above control circuit causes the reset current generated on the secondary side of the pulse transformer to flow to the resistance element by turning the second switch element ON when the first switch element is turned OFF.
The above second switching element is conductive other than the timing at which the analog signal is input to the AD converter.
An analog signal input device characterized by: In paragraph 1,
An analog signal input device characterized in that the reset circuit has an inverting buffer element that generates the reset signal by inverting the polarity of the drive signal.