JPS6050306B2 - Analog input device diagnostic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diagnostic device for an analog input device, and more particularly to a diagnostic device for an analog input device that actively utilizes an analog input signal holding circuit of the analog input device for diagnosis.

Diagnosis of analog input devices for processes that is commonly performed involves disconnecting the analog input signal source, supplying a known voltage signal, etc. from another signal source, and determining whether or not a specified output signal is obtained. I was investigating the condition.

A parts-out circuit is also provided for diagnosis on the analog signal source side. For example, a part-out circuit may be provided that directs the thermocouple as an analog signal source in a safe direction and displays an alarm when a disconnection accident occurs. The present invention does not require separation of the analog input signal source and also has a parts-out function, and its main purpose is to provide a diagnostic device that can perform diagnosis with an extremely simple configuration.

Still another object is to provide a diagnostic device which is particularly suitable for use in diagnosing each channel of a point input switching device which processes signals from analog signal sources at each point. In order to achieve this object, the present invention actively uses a capacitor provided to hold signals from an analog input source for diagnostic purposes, and detects failures of the analog input device based on the discharge characteristics of this capacitor. It is designed to diagnose the presence or absence and the nature of the failure. This will be explained in detail below using the drawings.

FIG. 1 is a connection diagram showing an embodiment in which the diagnostic device of the present invention is applied to a direct-coupled analog input device.

In the figure, a signal from an analog input signal source 1 is applied via a pair of relatively long conductive wires 1, , 12 to an analog signal holding circuit 2 which also functions as a filter. The output of the analog signal circuit 2 is the sampling switch S.
It is applied to the input circuit 3 via WI, and the corresponding output is obtained at the output terminal OUT. The reference voltage source 4 is connected in parallel to the analog signal holding circuit 2 via the diagnostic charging switch SW2. And the above switch SW
1 and SW2 are on/off controlled by a switch control circuit 5. Note that the analog input signal source 1 is an analog signal voltage Es internal resistance R. The analog signal holding circuit 2 is representatively shown as having a resistor R1 and a capacitor C1, and the reference voltage source 4 is representatively shown as having a reference voltage ERl and an internal resistance R2. Next, the operation of the apparatus shown in FIG. 1 will be explained in detail using the waveform diagram shown in FIG.

Now, the sampling switch SWl is connected to the switch control circuit 5.
When the circuit is turned on for a period of time as shown in FIG. 2a, the analog signal holding circuit 2 provides an output corresponding to the analog signal voltage Es to the input circuit 3 (FIG. 2d).

Next, for diagnosis, while the sampling switch SWl is off, the switch SW2 is turned on by the switch control circuit 5 as shown in FIG. 2b.

Then, the capacitor C1 is charged from the reference voltage source 4, and its terminal voltage EO rises as shown in FIG. 2C. When the switch SW2 is turned off, charging from the reference voltage source 4 stops and the capacitor C1 starts discharging. Therefore switch S
After W2 is turned off, when the sampling switch SWl is turned on at a predetermined timing (T2, t3), a predetermined voltage (EA, EB) appears at the output terminal 0UT of the input circuit 3 in relation to the discharge characteristics. . The above switch SW
The period from 2 on until the charging due to this on is canceled and at least the steady state is restored is given as a diagnostic stage. When the analog input device is normal, in the diagnosis stage, the output obtained from the analog signal holding circuit 3 through the sampling switch SWl after the start of discharge to the read output terminal 0UT is in the discharge state as shown by the solid lines EA and EB in Figure 2d. In the first reference signal reading stage for checking, it is greater than some predetermined value, and in the next verification reading stage, it is less than some other predetermined value. However, when the analog input device is abnormal, the size at the reference signal reading stage or the confirmation reading stage in FIG. Or, in the latter stage, it appears larger than the predetermined value.

In this way, the presence or absence of a failure in the analog input device can be easily determined from the change in the output appearing at the output terminal of the input circuit in the diagnostic stage.

Looking at this quantitatively, for convenience of explanation, switches SWl, S
Assuming that the offset voltage and on-resistance of W2 are zero and there is no leakage current, the steady-state voltage ER5 of the charging voltage of the capacitor C1 by the reference voltage source 4 is as follows.

The value of R is generally in the relationship R1≧10R0, R1≧100R2, so now, RO=100Ω, R1=1KΩ,
If R2 = 10Ω, then when the span of the analog input voltage E, is smaller than 10 times the reference voltage ER, the influence of the analog input voltage Es on the steady voltage ER'' is 1.
0% or less, ER? In the case of E, it is less than 1%.

On the other hand, the time constant τ during discharging is given by τ=C1(RO+R1), and if the end point of the reference signal reading period T2 is set at the start of discharging, that is, when 0.1τ has elapsed since the switch SW2 is turned off, by the end of T2 The terminal voltage of capacitor C1 drops by about 10%. Next, if the start point of the confirmation reading period is set at the start of discharge, that is, when 3τ has elapsed since the switch SW2 was turned off, the terminal voltage of the capacitor C1 becomes 5% or less. The above is the result when the analog input device is operating normally, but if this is not the case, that is, (a) if a voltage higher than the predetermined voltage cannot be obtained at the reference signal reading stage, (1) capacitor C1 Possible causes include loss of capacitance and short-circuit failure (2) defective sampling switch SW1 (3) defective switch control circuit (4) short-circuit failure of resistor R1 (5) failure of the input circuit.

On the other hand, (b) If a voltage lower than the predetermined voltage is not obtained in the confirmation reading stage, (1) a disconnection failure in the resistor R1, (2) a disconnection in the connecting conductor, (3) a disconnection failure in the analog input signal source, etc. This is thought to be the cause.

In addition, if normal results are not obtained due to a failure in the circuit added for diagnosis, such as a defect in switch SW2, the prescribed results may not be obtained in the stages (a) and (b) above. .

As can be seen from the above description, according to the present invention, the operating state can be reliably diagnosed including the function of the circuit added for diagnosis.

Furthermore, as is clear from the above explanation, in the event of a failure such as a disconnection of the analog input signal source, for example, a disconnection of a thermocouple, the terminal voltage of capacitor C1 maintains its charged value even after the diagnostic stage, so it exhibits a burnout function. However, in order to point in a safe direction, it is only necessary to select the polarity of the reference voltage.

FIG. 3 shows another embodiment of the diagnostic device of the present invention, and is a connection diagram when applied to an isolation type analog input device, in which parts corresponding to those in FIG. 1 are given the same reference numerals.

The difference from FIG. 1 is that a pulse transformer T is provided between the sampling switch SWl and the input circuit 3 in FIG. 1, and the primary winding of the transformer T is connected in parallel to the capacitor C1 via the sampling switch SWll. The next winding is connected to the input circuit 3 through another sampling switch SWl2 that operates on and off in synchronization with the switch SWll.
connected to. Further, the reference voltage source 4 is connected in parallel to the secondary winding of the transformer T via a switch SW2. The operation will be explained using FIG. 4.

The differences from the device in Figure 1 at the diagnostic stage are as follows:
Charging of the capacitor C1 from the reference voltage source 4 is not performed by turning on the switch SW2 once, but is performed N times depending on the characteristics of the capacitor C1 and the transformer T.

These operations are shown in FIGS. 4a-d. Although it is possible to charge the capacitor C1 and use it for a desired diagnosis by turning on the switch once, it is not practical. The other operations are the same as those shown in FIG. 1, and will therefore be omitted. FIG. 5 is a connection diagram of an embodiment of the diagnostic apparatus of the present invention applied to a multi-point input device, and parts corresponding to those in FIG. 3 are denoted by the same or similar symbols.

The only difference is the switch operation for charging the capacitor CIi in the diagnostic stage of each channel CHi, and the other operations are the same as in FIG. 3. The difference is that the switch SW2 is kept on during the charging period, and the sampling switches SWlh and SW1 are synchronously turned on and off N times to give the required amount of charge to the capacitor CIi.
Note that the on/off operations of the switches SW2 and SWl2 may be reversed. FIG. 6 is a connection diagram of a direct-coupled analog input device according to yet another embodiment when applied to the multi-point input device of the diagnostic device of the present invention. Indicated with a code.

The operation can be easily understood from the explanations in FIGS. 1 and 5, so a redundant explanation will be omitted. In the figure, the capacitor of each analog signal holding circuit is charged from the reference voltage source 4 via the sampling switch, but the switch SW2
Of course, it is also possible to provide the same number of channels as the number of channels and charge the batteries directly as shown in FIG. 1, and the same can be said for the embodiment shown in FIG. A diagnostic stage is provided in this way, and a known voltage is stored in the capacitor using the reference voltage ER and the required number of pulses N. After that, the discharge state is checked via the sampling switch in the reference signal reading stage and the confirmation reading stage, and a predetermined value is set at the output. The presence or absence of the above-mentioned abnormality and the details of the failure are detected based on whether or not the error is obtained.

As explained above, according to the present invention, diagnosis of an analog input device can be realized by simply adding a slight means to an analog input device having an analog signal holding circuit.

Furthermore, since the operation of the analog input device can be inspected without disconnecting the analog input signal source, automation of diagnosis can be easily realized by providing a diagnostic stage during the operation of the device. Also,
Except for the diagnostic stage, during the operating period of the analog input device, the analog signal holding circuit has no superimposition from anything other than the analog signal source, so accuracy is not impaired. Furthermore, it has the advantage of not requiring a burnout circuit and also having a burnout function.

[Brief explanation of the drawing]

Fig. 1 is a connection diagram of an embodiment of the diagnostic device of the present invention applied to a direct-connection type analog input device, Fig. 2 is an explanatory diagram of the operation of the device in Fig. 1, and Fig. 3 is an isolation type analog input device. A connection diagram of an embodiment of the diagnostic device of the present invention applied to an input device, FIG. 4 is an explanatory diagram of its operation, and FIGS. 5 and 6 are connection diagrams showing other embodiments. 1... Analog input signal source, 2... Analog signal holding circuit, 3... Input circuit, 4...
...Reference voltage source, 5...Switch control circuit,
R...Resistance, C...Capacitor, SW...
...Switch, T...Transformer.

Claims (1)

[Claims] 1. A signal from an analog signal source is stored in an analog signal holding circuit including a capacitor, and the stored signal is supplied to an input circuit via a sampling switch controlled on and off by a switch control circuit, and the analog signal is processed. A diagnostic device for an analog input device, wherein the analog signal holding circuit is provided with a reference voltage source for charging via a charging switch, and in the diagnostic stage, the capacitor of the analog signal holding circuit is charged from the reference voltage source. A diagnostic device for an analog input device, which charges the capacitor until it reaches a predetermined value, reads out the state of discharge of the capacitor after stopping charging, and checks the operating state of the analog input device.