JPS613073A - Disconnection detecting system for analog measuring system - Google Patents

Abstract

PURPOSE:To enable accurate detection of disconnection of an input signal line without causing errors in the analog measurement, by turning on a switch provided at the input of an amplifier only when detecting disconnection to apply a high voltage while the gain thereof is lowered. CONSTITUTION:A switch 13 is OFF in the measuring of an input. Then, in an input signal line 1, a measuring end 1A is connected to an input terminal 2 and an input signal is inputted into an amplifier 3 via an RC filter 8 and a multiplexer 9A. Here, the multiplexer 9A is connected to the amplifier 3 as only a switch circuit is selected being controlled with a CPU10. An amplification signal of the amplifier 3 is converted into a digital value via an A/D converter 14 to be inputted into the CPU10. On the other hand, when detecting disconnection, the switch 13 is turned ON to apply a DC voltage VCC via a high resistance 5 while the gain of the amplifier 3 is lowered. Then, the signal of the amplifier 3 is converted into a digital value via the A/D converter 14 and inputted into the CPU10.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a detection method when an input signal line is disconnected in an analog measurement system, and in particular, to eliminate the possibility of causing an error in the measurement system when detecting a disconnection. The present invention relates to a disconnection detection method in a measurement system.

When performing remote measurement using an analog measurement system, fi11 determination is often performed by detection at the measurement end (leading the signal to the analog measurement circuit via the input signal line), and in such cases, manual labor is required. (Since a disconnection in the signal I#i makes measurement impossible, a disconnection detection function is generally provided, but it is not preferable that the disconnection detection causes an error in the 1jllll constant system.) The present invention also proposes a disconnection detection method suitable for various cases.

[Conventional technology]

As an analog measuring method having a disconnection detection function, there is a conventionally well-known analog measuring method as shown in FIG.

In FIG. 4, an input signal line 1 connects a detection signal at a measurement end IA, such as a thermocouple G, to an input terminal 2.

This input signal is input to the amplifier 3 and subjected to the required amplification, and the amplified signal is applied to the measuring device 4 to obtain an analog measurement value (power).

At this time, in order to detect a disconnection in the input signal line 1, a DC voltage Vcc which is considerably larger than the full range of the input signal is applied to the input side of the amplifier 3 via a high resistance 5 (resistance value Ra). If the input signal line 1 is not disconnected now, the input side of the amplifier 3 is short-circuited by the impedance 6 (resistance value Rs) of the input signal line 1, and the error voltage becomes the true input voltage e. will be added. Therefore, the amplifier input voltage e~ at this time is e=e; +e.

becomes.

On the other hand, when the input signal line 1 is disconnected, the input impedance 7 (resistance value R1) of the amplifier 3 is very high, so the input voltage e4 rises to a value close to the DC voltage VCC. By doing so, it can be determined that the wire is disconnected.

FIG. 5 shows the relationship between input and output values in the conventional system shown in FIG. As is clear from Fig. 5, in order to keep the measurement error due to the error voltage e within the allowable range when the input signal line is not disconnected, the value of the high resistance 5 is made very large, and RS<<REI, and the error It is necessary to set the value of the voltage e.

However, such high resistors are generally large in size and often expensive. Further, even if such a high resistance can be used, the value of the error voltage e will not become completely zero. Furthermore, the value Rs of impedance 6 of input signal line 1
is proportional to the length of the input signal line, so it is necessary to limit the length of the input signal line in order to keep the error within an allowable range.

On the other hand, in this system, when the input signal line is disconnected, the amplifier input voltage rises to near the DC voltage VCC as shown in FIG. In this case, the measurable range of the measuring device 5 is exceeded, so it is difficult to determine from the measured value whether the problem is due to a disconnection of the input signal line or an excessive input that exceeds the measurable range. Have difficulty.

Furthermore, as shown in FIG. 6, this type of analog measurement system generally has a large number of measurement circuits as shown in FIG. Although the system is often configured, if you try to insert an RC filter (not shown in 8) into the input signal line 1 to prevent noise, the resistance value R of the filter will be added to the impedance 6 of the input signal line 1. Therefore, the error voltage e becomes thicker.

FIG. 7 shows the relationship between input and output values in the case of the multi-input system shown in FIG. 6. When the resistance value R of the filter is added, the error voltage e is The error is even larger than in the case shown in Figure 4.

[Problem that the invention seeks to solve]

The present invention aims to provide a method that can reliably detect disconnection of an input signal line without causing an error in analog measurement in an analog measurement system that measures voltage at a measurement end via an input signal line. be.

[Means for solving problems]

In the method of the present invention, a switch is provided to turn on and off the DC voltage Vcc applied to the amplifier input via a high resistance in order to detect a disconnection.When measuring input, this switch is turned off, and when a disconnection is detected, this switch is turned on. In addition to applying a DC voltage Vcc to the amplifier, the amplifier gain is reduced when a disconnection is detected.

[For production]

In the method of the present invention, since the DC voltage Vcc for disconnection detection is not applied during input measurement, there is no error in input measurement, and when disconnection is detected, DC voltage ■cc is applied, making it possible to detect disconnection, and the amplifier Since the gain is lowered, it is possible to reliably discriminate between a disconnection state and an excessive input.

〔Example〕

FIG. 1 shows the configuration of an embodiment of a disconnection detection method in an analog measurement system of the present invention. In this figure, the same parts as in FIGS. 4 and 6 are indicated by the same numbers, and 9A is a multiplexer, 10 is a central processing unit (hereinafter abbreviated as CPU), and 11 is CPU 1.
0, 12 is a disconnection detection circuit, 13 is a switch for applying DC voltage, and 14 is an analog/digital (A/
D) is a converter.

In FIG. 1, the switch I3 is in an off state during input measurement. Human power signal line l (impedance R
s) connects the measuring end IA to the input terminal 2; The input signal is input to the amplifier 3 via the RC filter 8 and multiplexer 9A. At this time, the multiplexer 9A
Only one switch circuit is selected under the control of Ul0, and the measurement circuit connected to this switch circuit, including, for example, the measurement terminal IA, is connected to the amplifier 3. Also, amplifier 3 is C
By controlling PU10, it has a predetermined high gain during input measurement. The amplified signal of the amplifier 3 is converted into a digital value via the A/D converter 14 and input to the CPU10.

Further, when a disconnection is detected, the switch 13 is turned on,
A DC voltage Vcc is applied through a high resistance 5 (the resistance value is RQ, which does not need to be large in the conventional system), and at the same time the gain of the amplifier 3 is set to a low value. In this state, the amplified signal of the amplifier 3 is converted into a digital value via the A/D converter 14 and input to the CPU 1O.

FIG. 2 shows the relationship between input and output values in the case of the system shown in FIG. If input signal line 1 is currently disconnected,
Since a DC voltage Vcc with a large value is applied to the input, the output digital value of A/D converter 4 is within the measurable range, but is quite large, even though the gain of amplifier 3 is low. become. On the other hand, if the input signal line 1 is not disconnected, -Rs knee Vcc (R≦10Rs) is added to the input voltage as an error voltage, but this does not produce a very large output digital value. Furthermore, since the gain of amplifier 3 is lowered, the measured value due to excessive input (usually sufficiently lower than the DC voltage Vcc) is within the measurable range and is smaller than the value obtained when the wire is disconnected. can be distinguished.

FIG. 3 is a flowchart showing the process of disconnection detection and input measurement according to the method of the present invention. As shown in the figure, the CPU 10 controls the multiplexer 9A to designate the input channel to be measured (Step S1), and then turns on the switch 13 according to the disconnection detection command, causing the gain of the amplifier 3 to be disconnected. Step S2). As a result, the value converted by the A/D converter 14 is input to the CPU10 (step S3),
PLJIO determines whether or not there is a disconnection state based on this value (step S4), and if it is a disconnection state, cancels the subsequent free determination. When the wire is not disconnected, the input measurement command turns off the switch 13 and specifies the gain of the amplifier 3 to a predetermined value in accordance with the measurement range (step S5).
). As a result, the value converted by the A/D converter 14 is input to the CP LJ 10 (step S6),
The required measurements are taken.

〔Effect of the invention〕

As explained above, according to the method of the present invention, in an analog measurement system that inputs a detection signal to an amplifier via an input signal line and measures the amplified signal value, the switch provided at the amplifier input is turned on only when a disconnection is detected. Since a high voltage is applied to the amplifier input via a high resistance and the amplifier gain is reduced, disconnection detection processing can be performed without causing errors in input measurement, and it is possible to detect disconnection and excessive input conditions. can be reliably distinguished.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the disconnection detection method in the analog measurement system of the present invention, FIG. 2 is a diagram showing the relationship between input and output values in the case of the method shown in FIG. 1, and FIG. The figure is a flowchart showing the process of wire breakage detection and input measurement in the method of the present invention, FIG. 4 is a diagram showing a conventional analog measurement method having a wire breakage detection function, and FIG. FIG. 6 is a diagram showing the configuration of a multi-input system, and FIG. 7 is a diagram showing the relationship between input and output values in the multi-input system shown in FIG. 6. 1-human power signal line, IA measurement end, 2 input terminal, 3-amplifier, 4-measuring device, 5-high resistance, 6 impedance of human power signal line 1, 7 input impedance of amplifier 3, 8
-RC filter, 9-selector switch, 9A-multiplexer, 10-central processing unit (CPU), 11 control signal, 12-disconnection detection circuit, 13 DC voltage application switch, j4-analog digital (A/D>conversion) Device patent applicant Fuji Facom Control Co., Ltd. Agent Patent attorney Gobe Tamamushi (2 others) 12 Disconnection detection circuit Figure 2 (VCC) Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In an analog measurement system, the detection signal at the measuring end is input to the amplifier via the input signal line to measure the amplified signal value, and a high voltage is applied to the amplifier input side via a high resistance to detect the presence or absence of a break in the input signal line. , a switch for applying a high voltage to the amplifier input and a means for changing the amplifier gain are provided, and when a disconnection is detected, the switch is turned on and the amplifier gain is reduced, and when an input is measured, the switch is turned off and the amplifier gain is changed. A disconnection detection method in an analog measurement system that is characterized by bringing the voltage to a high level.