Input Module Of Industrial Control Apparatus

1. An input module of an industrial control apparatus comprising: an input circuit to which a digital signal from an external source is input, the input circuit outputting a binary signal as an internal signal; and a determination unit determining a level of the digital signal based on the internal signal output from the input circuit, and the determination unit outputting a determination result of the digital signal to an external device, wherein the input circuit includes: an OR AND circuit receiving the digital signal and a clock signal, the OR AND circuit outputting a logical sum product signal indicating a logical sum product of the digital signal and the clock signal, the clock signal having a binary level switching at a predetermined cycle; and a signal output unit including a switching element, a first main terminal of the switching element being connected with a first supply line that supplies a first voltage corresponding to a high level of the internal signal, a second main terminal of the switching element being connected with a second supply line that supplies a second voltage corresponding to a low level of the internal signal, the switching element is in an on state during a high level of the logical sum product signal and is in an off state during a low level of the logical sum product signal, the signal output unit outputting a signal obtained at the second main terminal of the switching element as the internal signal, and the determination unit: determines that the digital signal has a low level when the low level of the internal signal continues for a certain time period; determines that the digital signal has a high level when the internal signal switches from the low level to the high level and then switches to the low level again; and determines an occurrence of a fixing failure when the internal signal switches from the low level to the high level and then fails to switch to the low level again; and wherein the external device, which the determination result determined by the determination unit is output to, is provided by a central processing unit module; wherein the central processing unit module controls an operation of a control target and the control target is configured to stop an operation in response to an activation of an emergency stop switch of the control target; wherein the level of the digital signal switches in response to the activation of the emergency stop switch of the control target; wherein, when a level of the internal signal repeatedly switches within a period shorter than a half cycle of the clock signal, the determination unit executes an interpolation process and determines that no level switch occurs in the internal signal; wherein, when the determination unit continuously executes the interpolation process for a set time period, the determination unit stops a determination of the level of the digital signal and outputs, to the central processing unit module, a determination result that is the same as a result in a case of the activation of the emergency stop switch.

2. The input module according to claim 1, wherein the determination unit determines that the digital signal has the high level when (i) the internal signal switches from the low level to the high level and continues the high level for a first time period, and then (ii) the internal signal switches from the high level to the low level and continues the low level for a second time period, the first time period corresponds to a period in which the clock signal has a high level, and the second time period corresponds to a period in which the clock signal has a low level.

3. The input module according to claim 1, wherein the determination unit determines that the digital signal has the high level when the internal signal switches from the high level to the low level and then switches to the high level again.

4. The input module according to claim 3, wherein the determination unit determines that the digital signal has the high level when (i) the internal signal switches from the high level to the low level and continues the low level for a second time period, and then (ii) the internal signal switches from the low level to the high level and continues the high level for a first time period, the first time period corresponds to a period in which the clock signal has a high level, and the second time period corresponds to a period in which the clock signal has a low level.

5. The input module according to claim 1, wherein, when a level of the internal signal repeatedly switches within a period shorter than a half cycle of the clock signal, the determination unit executes an interpolation process and determines that no level switch occurs in the internal signal.

6. The input module according to claim 5, wherein the external device, which the determination result determined by the determination unit is output to, is provided by a central processing unit module, the central processing unit module controls an operation of a control target and the control target is configured to stop an operation in response to an activation of an emergency stop switch of the control target, the level of the digital signal switches in response to the activation of the emergency stop switch of the control target, and, when the determination unit continuously executes the interpolation process for a set time period, the determination unit stops a determination of the level of the digital signal and outputs, to the central processing unit module, a determination result same as a result in a case of the activation of the emergency stop switch.

7. The input module according to claim 6 1, wherein the set time period is obtained by subtracting at least a necessary time period from a predetermined time period, the predetermined time period is preliminarily set as an upper limit of a time period from the activation of the emergency stop switch to an actual operation stop of the control target, and the necessary time period is a time period required for the central processing unit module to execute a process for emergently stopping the control target.

8. An input module of an industrial control apparatus comprising: an input circuit to which a digital signal from an external source is input, the input circuit outputting a binary signal as an internal signal; and a microcomputer determining a level of the digital signal based on the internal signal output from the input circuit, and the microcomputer outputting a determination result of the digital signal to an external device, wherein the input circuit includes: an OR AND circuit receiving the digital signal and a clock signal, the OR AND circuit outputting a logical sum product signal indicating a logical sum product of the digital signal and the clock signal, the clock signal having a binary level switching at a predetermined cycle; and a photo coupler including a switching element, a first main terminal of the switching element being connected with a first supply line that supplies a first voltage corresponding to a high level of the internal signal, a second main terminal of the switching element being connected with a second supply line that supplies a second voltage corresponding to a low level of the internal signal, the switching element is in an on state during a high level of the logical sum product signal and is in an off state during a low level of the logical sum product signal, the photo coupler outputting a signal obtained at the second main terminal of the switching element as the internal signal, and the microcomputer: determines that the digital signal has a low level when the low level of the internal signal continues for a certain time period; determines that the digital signal has a high level when the internal signal switches from the low level to the high level and then switches to the low level again; and determines an occurrence of a fixing failure when the internal signal switches from the low level to the high level and then fails to switch to the low level again; and wherein the external device, which the determination result determined by the microcomputer is output to, is provided by a central processing unit module; wherein the central processing unit module controls an operation of a control target and the control target is configured to stop an operation in response to an activation of an emergency stop switch of the control target; wherein the level of the digital signal switches in response to the activation of the emergency stop switch of the control target; wherein, when a level of the internal signal repeatedly switches within a period shorter than a half cycle of the clock signal, the microcomputer executes an interpolation process and determines that no level switch occurs in the internal signal; wherein, when the microcomputer continuously executes the interpolation process for a set time period, the microcomputer stops a determination of the level of the digital signal and outputs, to the central processing unit module, a determination result that is the same as a result in a case of the activation of the emergency stop switch.