JP2546005B2 - A / D converter - Google Patents

Description

The present invention relates to an abnormality detection circuit for an analog signal input circuit used in an electronic control device.

[Conventional technology]

FIG. 2 is a circuit diagram of a conventional A / D conversion circuit. In the figure, (1A) and (1B) are external analog signals, and (2A) and (2B).
Is an input resistance, (3A) (3B), (4A) (4B) are filter circuits with resistors and capacitors provided for noise prevention,
(5A) and (5B) are input signal selection switches for multi-point input, (6) is an amplifier circuit for converting the signal level,
(7) is an A / D that converts analog signals into digital signals
It is a converter. (8) is an arithmetic unit to which the digital signal output from the A / D converter (7) is input, and (10) is the above (1).
A) to (5A) consisting of only one circuit, or (1
B) to (5B) composed of another or more circuits, an amplifier circuit (6) and an A / D converter (7), an A / D conversion card, (11A) (11B) Is wiring for transmitting external analog signals (1A) (1B) to the A / B conversion card (10).

 Next, the operation will be described.

The external analog signal (1A) is terminated by the input resistance (2A) when the input signal selection switch (5A) is turned on, and the filter circuit is composed of the input resistance (2A), the resistance (3A) and the capacitor (4A). Switch for noise removal (5
It is connected to the amplifier circuit (6) via A). This signal is amplified by the amplifier circuit (6) to the input signal level of the A / D converter (7), converted from an analog signal to a digital signal by the A / D converter (7) and input to the arithmetic unit (8). It
If an abnormality occurs in this circuit, the digital signal value of the A / D converter (7) will be different from the normal signal value. For example, the wiring (11A) from the analog signal (1A) is broken, or the input signal selection switch (5A) is O
In the case of a failure condition that does not occur, the input signal of the amplifier circuit (6) becomes 0 [V], and the digital signal value of the A / D converter (7) is the value when the analog input signal (1) is O [V]. Will be the same as The same applies to the operation in which the analog signal (1B) is A / D converted by the A / D converter (7). Similarly, if the amplifier circuit (6) or the A / D converter (7) itself becomes abnormal, the A / D converter (7) outputs a digital signal different from the true data.

[Problems to be Solved by the Invention]

Since the conventional A / D converter is configured as described above, the digital signal value changes when there is an abnormality in the circuit, but the change is due to the actual change in the analog input signal or due to the circuit abnormality. There was a problem that could not be identified.

The present invention has been made to solve the above problems, and an object thereof is to obtain an A / D conversion device capable of detecting an abnormality in an analog input circuit.

[Means for solving the problem]

The analog converter according to the present invention includes an input resistor that terminates an external analog signal, and an R connected to the input resistor.
-C filter, an A / D converter that converts an analog signal into a digital signal, a first switch that determines whether to connect the A / D converter and the R-C filter, and the A / D converter.
An arithmetic unit to which the digital signal of the D converter is input, the input resistance, the capacitor of the RC filter or the A /
It is provided with a series circuit of a reference power source and a second switch which are connected in parallel to one of the input terminals of the D converter.

[Work]

In the series circuit of the reference source and the second switch according to the present invention, the reference power supply is connected to the A / D conversion circuit by the second switch, the reference power supply voltage is converted into a digital signal value, and the digital signal value is input to the leakage section. Whether the A / D converter is normal or not is determined by the arithmetic unit whether or not the digital value input to the arithmetic unit when the second switch is on is the digital value corresponding to the reference power supply voltage. Immediately after the judgment is made and the second switch is turned on and then the second switch is turned on, it is determined whether or not the digital value input to the arithmetic unit is a digital value corresponding to the reference power supply voltage. It is determined whether the first switch is normal or not, and the digital value input to the arithmetic unit after a lapse of a certain time after the second switch is switched from the on state to the off state is determined by the input resistance. And the R-C filter determine whether or not the external wiring is disconnected by determining whether or not the external wiring is a digital value corresponding to the attenuation value of the reference power supply voltage according to the constant.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, (1A) to (5A), (1B) to (5B) (6)
(7), (8), (10), (11A), and (11B) are exactly the same as the prior art. (21) and (22) are parts provided for realizing the present invention, (21) is a reference power source for generating a reference voltage, (22) is a reference power source (21) of an amplifier circuit (6). A switch for connecting to and disconnecting from the input section.

 Next, the operation will be described.

When the switch (22) of the reference power input circuit is off
The A / D conversion card (10) is a circuit exactly the same as the conventional A / D conversion circuit, and works as a circuit for converting the external analog signal (1A) or (1B) into a digital signal. A circuit related to the external analog signal (1A) will be described. Circuit abnormality detection is first performed with the switch (22) of the reference power input circuit turned on. Input signal selection switch (5A) and (5
Turn off B). At this time, the voltage of the reference power source (21) is applied to the input of the amplifier circuit (6) and is converted into a digital signal by the A / D converter (7). By the calculation unit (8),
The digital signal value at this time is compared with the theoretical value to determine whether the amplifier circuit (6) and the A / D converter (7) are normal. Next, when the input signal selection switch (5B) is turned off and the input signal selection switch (5A) is turned on, the capacitor (4A) is charged with the voltage of the reference power supply (21). In this state, the switch (22) is turned off to perform A / D conversion, and the digital signal value immediately after the switch (22) is turned off and the digital signal value after a certain time after the switch (22) is turned off are An abnormality of the input signal selection switch (5A) and a disconnection state of the external analog signal are detected by the judgment made by the calculation section (8). That is, when the A / D converted digital signal value immediately after the switch (22) is turned off is a value slightly lower than the reference power supply voltage equivalent value, the capacitor 4A is charged from the reference power supply via the switch 5A. It has become
It can be said that the switch 5A is normal, and if the value is much lower than the reference power supply voltage equivalent value, it can be said that the switch 5A is abnormal because the capacitor 4A is not charged.

In addition, after the switch (22) is turned off, the A / D converted digital signal value is the attenuation value of the reference power supply voltage according to the time constant of the circuit composed of resistor 2A, resistor 3A and capacitor 4A. If it is equivalent, it is determined that there is no influence of the external analog signal (1A), so it is determined that the wiring (1A) is broken, and if it is not the digital signal value equivalent to the attenuation value of the reference power supply voltage, the external analog signal Since it is determined that the influence of (1A) was exerted, the wiring (11A) is determined to be normal. The same applies to checking the circuit for the external analog signal (1B).

In the above embodiment, the input circuit composed of the input resistor, the filter circuit formed by the resistor and the capacitor, and the input signal selection switch is (2A) to (5A) and (2A).
Although the example of two circuits B) to (5B) is shown, the same function can be realized by one circuit or three or more circuits. Also, the reference power supply input circuits (21) (22) are provided in the input section of the amplifier circuit (6), but they are connected in parallel with the input resistors (1A) (1B) or the capacitors (4A) (4B), respectively. May be provided, or A /
When the performance of the D converter is sufficiently high and the amplifier circuit (6) is not required, the same function can be realized even if it is provided before the A / D converter (7).

Also, although the input signal selection switches (5A) (5B) and the switch (22) are shown to use mechanical switches, they may be semiconductor switches, and the reference power supply (21) may be any one that can set a voltage. The same effect can be obtained even with small objects. Needless to say, the abnormal part detected by the calculation unit (8) can be displayed on the display unit (not shown) to easily replace the abnormal part or the A / D conversion card.

〔The invention's effect〕

As described above, according to the present invention, an input resistor for terminating an external analog signal, an RC filter connected to the input resistor, and an A / D converter for converting an analog signal into a digital signal are provided in the A / D converter. Vessel, this A / D converter and the above RC
A first switch for determining whether or not to connect a filter, an arithmetic unit to which a digital signal of the A / D converter is input, the input resistance, the capacitor of the RC filter or the A / D conversion. Since it has a series circuit of a reference power source and a second switch connected in parallel to any of the input terminals of the
It has the effect of detecting A / D converter abnormality, input signal selection switch abnormality, or external wiring abnormality. Further, due to the effect of this abnormality detection, it is possible to easily replace the defective card.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an A / D conversion circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional A / D conversion circuit. (1A) (1B) are external analog signals, (2A) (2B) are resistors, (3A) (3B) are resistors, (4A) (4B) are capacitors,
(5A) and (5B) are input selection switches, (6) is an amplifier circuit, (7) is an A / D converter, and (21) is a reference power source (22). In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. An input resistor for terminating an external analog signal,
RC filter connected to this input resistor, A / D converter for converting analog signal to digital signal, and A / D converter
A first switch for determining whether to connect the converter and the R-C filter, an arithmetic unit to which a digital signal of the A / D converter is input, the first switch, and the A / D converter.
A series circuit including a reference power source connected in parallel to the capacitor of the RC filter and a second switch is provided between the D converter and the D switch, and the first switch is turned off and the second switch is turned on to turn the reference on. A / D convert the power supply voltage and judge whether the A / D converter is normal by the digital value, and after the lapse of a predetermined time after turning on the first switch with the second switch on. Turn off the second switch, and determine whether or not the first switch is normal based on whether the A / D converted value immediately after the second switch is turned off is a value slightly lower than the reference power supply voltage equivalent value. , And whether or not the A / D conversion value after a predetermined time has elapsed after the second switch was turned off is equivalent to the attenuation value of the reference power supply voltage according to the time constant of the circuit of the input resistance and the RC filter. Is characterized by determining whether or not an external analog signal is connected. A / D converter.