JP2011112474A - Input module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an input module capable of easily detecting a short circuit between channels. <P>SOLUTION: The input module has a plurality of channels for making a current flow to a resistance for input measurement connected to input terminals, measuring voltage values of voltages generated at both ends of the resistance for input measurement by a voltage measuring circuit, and incorporating the measured voltage value as an input value. The input module further includes: variable current sources provided at each channel of a plurality of channels and capable of varying a current value of the current flowing to the resistance for input measurement; and a control circuit for varying the current value of the current passing from the variable current source to the resistance for input measurement at each channel of the plurality of channels, measuring the voltage values of the voltages generated at both the ends of the resistance for input measurement by the voltage measuring circuit at each channel of the plurality of channels, comparing the voltage values measured before and after the change of the current, and when the change in voltage value is not proportional to a change in current value, that a short circuit is determined to be generated between the channels. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a channel for measuring the voltage value of the voltage generated at both ends of the input measurement resistor by flowing a current through the input measurement resistor connected to the input terminal, and taking the measured voltage value as an input value. More specifically, the present invention relates to an input module that can easily detect a short circuit between channels.

  Safety is one of the important items in the field of process industries, particularly in plant control devices. In recent years, IEC (International Electrotechnical Commission) established IEC61508 (functional safety of electrical / electronic / programmable electronic safety related systems) for functional safety, and it is widely applied to plant control devices. .

FIG. 5 is a configuration diagram showing an example of a conventional input module.
In FIG. 5, the input module M1 has a voltage measurement circuit IC1, a voltage measurement circuit IC2, a constant current source I1, a constant current source I2, an input terminal CN1, an input terminal CN2, an input terminal CN3, an input terminal CN4, and a control circuit CT1. is doing.

  The voltage measurement circuit IC1 and the voltage measurement circuit IC2 are circuits that measure voltage, and are mainly configured by an A / D converter (Analog to Digital Converter) or the like. The constant current source I1 and the constant current source I2 are current sources that flow a predetermined constant current value. The input terminals CN1 to CN4 are input terminals for signals to the input module M1. The control circuit CT1 takes in the voltage values measured by the voltage measurement circuit IC1 and the voltage measurement circuit IC2 as input values. The input measurement resistor R1 and the input measurement resistor R2 are resistors whose resistance values change depending on the ambient temperature, and are, for example, a resistance temperature detector.

  One end of the input terminal CN1 is connected to the output terminal of the constant current source I1 and the input terminal of the voltage measurement circuit IC1, and the output terminal of the voltage measurement circuit IC1 is connected to the input terminal V1 of the control circuit CT1. A power supply voltage is applied to the input terminal of the constant current source I1, and one end of the input terminal CN2 is connected to a common potential. The other end of the input terminal CN1 is connected to one end of the input measurement resistor R1, and the other end of the input measurement resistor R1 is connected to the other end of the input terminal CN2. The voltage measurement circuit IC1, the constant current source I1, and the input terminals CN1 and CN2 constitute a channel 1.

  One end of the input terminal CN3 is connected to the output terminal of the constant current source I2 and the input terminal of the voltage measurement circuit IC2, and the output terminal of the voltage measurement circuit IC2 is connected to the input terminal V2 of the control circuit CT1. A power supply voltage is applied to the input terminal of the constant current source I2, and one end of the input terminal CN4 is connected to a common potential. The other end of the input terminal CN3 is connected to one end of the input measurement resistor R2, and the other end of the input measurement resistor R2 is connected to the other end of the input terminal CN4. The voltage measuring circuit IC2, the constant current source I2, and the input terminals CN3 and CN4 constitute a channel 2.

The operation of such an input module will be described.
In the case of channel 1, a current having a current value i1 flows from the constant current source I1 to the input measurement resistor R1 via the input terminal CN1. As a result, a voltage v1 is generated at both ends of the input measurement resistor R1, and the voltage v1 is measured by the voltage measurement circuit IC1. The control circuit CT1 reads the voltage v1 measured by the voltage measurement circuit IC1.

Then, the control circuit CT1 calculates the resistance value r1 of the input measurement resistor R1 from the voltage value v1 and the current value i1 by the equation (1).
r1 = v1 / i1 (1)

  When calculating the resistance value r1 of the input measurement resistor R1, the control circuit CT1 calculates the ambient temperature of the input measurement resistor R1 from the resistance value r1. At this time, it is assumed that the relationship between the resistance value of the input measurement resistor R1 and the ambient temperature is known, and the control circuit CT1 also knows the relationship between the resistance value of the input measurement resistor R1 and the ambient temperature.

  Similarly, in the case of channel 2, a current whose current value is i2 flows from the constant current source I2 to the input measurement resistor R2 via the input terminal CN3. As a result, a voltage v2 is generated at both ends of the input measurement resistor R2, and this voltage v2 is measured by the voltage measurement circuit IC2. The control circuit CT1 reads the voltage v2 measured by the voltage measurement circuit IC2.

Then, the control circuit CT1 calculates the resistance value r2 of the input measurement resistor R2 from the voltage value v2 and the current value i2 by the equation (2).
r2 = v2 / i2 (2)

  When calculating the resistance value r2 of the input measurement resistor R2, the control circuit CT1 calculates the ambient temperature of the input measurement resistor R2 from the resistance value r2. At this time, it is assumed that the relationship between the resistance value of the input measurement resistor R2 and the ambient temperature is known, and the control circuit CT1 also knows the relationship between the resistance value of the input measurement resistor R2 and the ambient temperature.

  In this way, the current i1 is supplied from the constant current source I1 to the input measurement resistor R1, and the voltage v1 generated at both ends of the input measurement resistor R1 is measured. Then, the control circuit CT1 calculates the resistance value r1 of the input measurement resistor R1 from the voltage value v1 and the current value i1, and the input measurement resistor R1 from the known relationship between the resistance value of the input measurement resistor R1 and the ambient temperature. The temperature can be accurately measured by obtaining the ambient temperature. Further, the temperature of channel 2 can be measured in the same manner.

JP 2006-209470 A

  However, in the conventional example shown in FIG. 5, even if an unintended current flows through the input measurement resistor R1 or the input measurement resistor R2 when a short circuit accident occurs in the wiring between the channels, the input measurement resistor R1 or the input If the voltage generated at both ends of the measuring resistor R2 is in a measurable range, it can be measured, and therefore there is a problem that a short circuit between channels cannot be detected.

  Therefore, an object of the present invention is to realize an input module that can easily detect a short circuit between channels.

The invention described in claim 1
An input having a plurality of channels for supplying a current to an input measurement resistor connected to an input terminal, measuring a voltage value of a voltage generated at both ends of the input measurement resistor with a voltage measurement circuit, and taking the measurement voltage value as an input value In the module
A variable current source provided for each of the plurality of channels and capable of varying a current value of a current flowing through the input measurement resistor;
The current value of the current flowing from the variable current source to the input measurement resistor is changed for each of the plurality of channels, and the voltage value of the voltage generated at both ends of the input measurement resistor is measured for the plurality of channels. When the voltage value measured by the circuit is compared before and after the change of the current and the change of the voltage value is not proportional to the change of the current value, a short circuit has occurred between the channels And a control circuit for judging that.
The invention according to claim 2
An input having a plurality of channels for supplying a current to an input measurement resistor connected to an input terminal, measuring a voltage value of a voltage generated at both ends of the input measurement resistor with a voltage measurement circuit, and taking the measurement voltage value as an input value In the module
A variable current source provided for each of the plurality of channels and capable of varying a current value of a current flowing through the input measurement resistor;
A reference resistor provided for each of the plurality of channels, through which current flows from the variable current source via the input measurement resistor;
A voltage measuring circuit for measuring the voltage value of the voltage generated at both ends of the reference resistor;
The current value of the current flowing from the variable current source to the input measurement resistor is changed for each of the plurality of channels, and the voltage value of the voltage generated at both ends of the reference resistor is changed by the voltage measurement circuit for each of the plurality of channels. Measure and calculate the current value of the current flowing through the reference resistor. If the current value set in the variable current source and the current value flowing through the reference resistor are not equal, it is determined that a short circuit has occurred between the channels. And a control circuit.
The invention according to claim 3 is the invention according to claim 1 or 2,
The input measurement resistor is:
It is a resistance temperature detector.

The present invention has the following effects.
According to the first aspect, the control circuit changes the current value of the current flowing from the variable current source to the resistor connected to the input terminal for each channel, and sets the voltage value of the voltage generated at both ends of the input measurement resistor to the channel. Each time, the voltage is measured by the voltage measuring circuit, and the measured voltage values are compared before and after the current change. When the change in voltage value is not proportional to the change in current value, it is determined that a short circuit has occurred between the channels. As a result, when there is no short circuit between channels, the change in voltage value is proportional to the change in current value, so the presence or absence of a short circuit between channels can be distinguished, and a short circuit between channels can be easily detected. can do.

  According to claim 2, the control circuit changes the current value of the current flowing from the variable current source to the input measurement resistor connected to the input terminal for each channel, and the voltage generated at both ends of the reference resistor. The value is measured for each channel by the voltage measurement circuit, and the current value of the current flowing through the reference resistor is calculated. If the current value set for the variable current source and the current value flowing through the reference resistor are not equal, it is determined that a short circuit has occurred between the channels. As a result, when there is no short circuit between the channels, the current value set in the variable current source and the current value flowing through the reference resistor are equal, so the presence or absence of a short circuit between the channels can be distinguished and the channel can be easily connected. Can be detected.

It is the block diagram which showed the 1st Example of the input module of this invention. 1 is an equivalent circuit in a state in which channel 1 and channel 2 are short-circuited between channels in the embodiment of FIG. It is the block diagram which showed the 2nd Example of the input module of this invention. FIG. 4 is a configuration diagram in a state where channel 1 and channel 2 are short-circuited between channels in the embodiment of FIG. 3. It is the block diagram which showed an example of the conventional input module.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
FIG. 1 is a block diagram showing a first embodiment of the input module of the present invention. Here, the same components as those shown in FIG. 1 differs from the configuration shown in FIG. 5 in that a variable current source I3 is provided instead of the constant current source I1, and a variable current source I4 is provided instead of the constant current source I2. A control circuit CT2 is provided instead of the control circuit CT1.

  In FIG. 1, the input module M2 includes a voltage measurement circuit IC1, a voltage measurement circuit IC2, a variable current source I3, a variable current source I4, an input terminal CN1, an input terminal CN2, an input terminal CN3, an input terminal CN4, and a control circuit CT2. is doing.

  The voltage measurement circuit IC1, the variable current source I3, and the input terminals CN1 and CN2 constitute a channel 1. Similarly, the voltage measurement circuit IC2, the variable current source I4, and the input terminals CN3 and CN4 constitute a channel 2.

  The variable current source I3 and the variable current source I4 are current sources that can vary the current flowing through the input measurement resistor R1 or R2. The control circuit CT2 changes the current value of the current flowing from the variable current source I3 or I4 to the input measurement resistor R1 or R2 for each channel, and the voltage generated at both ends of the input measurement resistor R1 or R2 for each channel. A short circuit between the channels is detected by measuring the measurement circuit IC1 or IC2 and comparing the measured voltages before and after the change in current.

  In channel 1, a current is passed through the input measurement resistor R1 connected to the input terminals CN1 and CN2, and the voltage value of the voltage generated at both ends of the input measurement resistor R1 is measured by the voltage measurement circuit IC1, and the measured voltage value is measured. Capture as input value. Similarly, the channel 2 measures the voltage value of the voltage generated at both ends of the input measurement resistor R2 by passing a current through the input measurement resistor R2 connected to the input terminals CN3 and CN4, and measures the voltage. Takes a voltage value as an input value. The input module M2 has a channel 1 and a channel 2.

  One end of the input terminal CN1 is connected to the output terminal of the variable current source I3 and the input terminal of the voltage measurement circuit IC1, and the output terminal of the voltage measurement circuit IC1 is connected to the input terminal V3 of the control circuit CT2. A power supply voltage is applied to the input terminal of the variable current source I3, and one end of the input terminal CN2 is connected to a common potential. The other end of the input terminal CN1 is connected to one end of the input measurement resistor R1, and the other end of the input measurement resistor R1 is connected to the other end of the input terminal CN2. The output terminal I3_CTL of the control circuit CT2 is connected to the control terminal of the variable current source I3.

  One end of the input terminal CN3 is connected to the output terminal of the variable current source I4 and the input terminal of the voltage measurement circuit IC2, and the output terminal of the voltage measurement circuit IC2 is connected to the input terminal V4 of the control circuit CT2. A power supply voltage is applied to the input terminal of the variable current source I4, and one end of the input terminal CN4 is connected to a common potential. The other end of the input terminal CN3 is connected to one end of the input measurement resistor R2, and the other end of the input measurement resistor R2 is connected to the other end of the input terminal CN4. The output terminal I4_CTL of the control circuit CT2 is connected to the control terminal of the variable current source I4.

The operation of such an input module will be described.
The control circuit CT2 sets the current value i3 of the variable current source I3 through the output terminal I3_CTL, and sets the current value i4 of the variable current source I4 through the output terminal I4_CTL. A current having a current value i3 flows from the variable current source I3 to the input measuring resistor R1 via the input terminal CN1, and a current having a current value i4 flows from the variable current source I4 to the input measuring resistor R2 via the input terminal CN3. As a result, a voltage v3 is generated at both ends of the input measurement resistor R1, and a voltage v4 is generated at both ends of the input measurement resistor R2.

The control circuit CT2 reads the voltage v3 measured by the voltage measurement circuit IC1 and the voltage v4 measured by the voltage measurement circuit IC2. Then, the control circuit CT2 calculates the resistance value r1 of the input measurement resistor R1 from the voltage value v3 and the current value i3 by the equation (3), and the resistance value of the input measurement resistor R2 from the voltage value v4 and the current value i4. r2 is calculated by equation (4).
r1 = v3 / i3 (3)
r2 = v4 / i4 (4)

  Next, the control circuit CT2 changes either the current value i3 of the variable current source I3 or the current value i4 of the variable current source I4, and performs the same measurement.

  The control circuit CT2 includes the voltage v3 generated at both ends of the input measurement resistor R1 before changing the current value i3 of the variable current source I3 and the input measurement resistor R1 after changing the current value i3 of the variable current source I3. Are compared with each other. If the change in voltage v3 is proportional to the change in current value i3 of variable current source I3, it is determined that there is no short circuit between channels.

  The control circuit CT2 compares the voltage v4 generated at both ends of the input measurement resistor R2 before changing the current value i4 of the variable current source I4 and the current value i4 of the variable current source I4. The voltage v4 generated across the input measurement resistor R2 may be compared.

  When it is determined that there is no short circuit between the channels, the control circuit CT2 calculates the resistance value r1 of the input measurement resistor R1, and then calculates the ambient temperature of the input measurement resistor R1 from the resistance value r1. Similarly, after calculating the resistance value r2 of the input measurement resistor R2, the control circuit CT2 calculates the ambient temperature of the input measurement resistor R2 from the resistance value r2. At this time, the relationship between the resistance value of the input measurement resistor R1 or the input measurement resistor R2 and the ambient temperature is known, and the control circuit CT2 also relates the relationship between the resistance value of the input measurement resistor R1 or the input measurement resistor R2 and the ambient temperature. Assume that

  On the other hand, if the change in the voltage v3 is not proportional to the change in the current value i3 of the variable current source I3, it is determined that a short circuit has occurred between the channels, and the user of the input module has determined that an abnormality has occurred. To tell.

  As an example, a case where the wiring is normal will be specifically described. For example, the measurement when the resistance value r1 of the input measurement resistor R1 and the resistance value r2 of the input measurement resistor R2 are 100Ω will be described. Although the ambient temperature of the input measurement resistor R1 and the input measurement resistor R2 changes, a sudden change in ambient temperature occurs during measurement while changing the current value of the variable current source I3 or the variable current source I4. That is, description will be made assuming that there is no change in the resistance value.

The control circuit CT2 sets the current values of the variable current source I3 and the variable current source I4 to 1 mA, respectively. A current having a current value of 1 mA flows from the variable current source I3 to the input measurement resistor R1, and a current having a current value of 1 mA flows from the variable current source I4 to the input measurement resistor R2. At this time, the voltage v3 generated at both ends of the input measurement resistor R1 and the voltage v4 generated at both ends of the input measurement resistor R2 are expressed by equations (5) and (6).
v3 = r1 * i3 = 100Ω * 1 mA = 100 mV (5)
v4 = r2 * i4 = 100Ω * 1 mA = 100 mV (6)

The control circuit CT2 reads the voltage value of 100 mV from the voltage measurement circuit IC1 and the voltage measurement circuit IC2, respectively, and calculates the resistance value r1 of the input measurement resistor R1 and the resistance value r2 of the input measurement resistor R2 by equation (3). .
r1 = r2 = 100 mV / 1 mA = 100Ω (7)

Following the above measurement, the control circuit CT2 sets the current value of the variable current source I3 to 0.5 mA and sets the current value of the variable current source I4 to 1 mA. A current with a current value of 0.5 mA flows from the variable current source I3 to the input measurement resistor R1, and a current with a current value of 1 mA flows from the variable current source I4 to the input measurement resistor R2. At this time, the voltage v3 generated at both ends of the input measurement resistor R1 and the voltage v4 generated at both ends of the input measurement resistor R2 are expressed by equations (8) and (9).
v3 = r1 * i3 = 100Ω * 0.5 mA = 50 mV (8)
v4 = r2 * i4 = 100Ω * 1 mA = 100 mV (9)

The control circuit CT2 reads a voltage value of 50 mV from the voltage measurement circuit IC1 and a voltage value of 100 mV from the voltage measurement circuit IC2, and calculates the resistance value r1 of the input measurement resistor R1 and the resistance value r2 of the input measurement resistor R2 by equation (3). Is calculated.
r1 = 100Ω = 50 mV / 0.5 mA (10)
r2 = 100Ω = 100 mV / 1 mA (11)

  When the current value of the current passed through the input measurement resistor R1 or the input measurement resistor R2 changes from the measurement before the change of the current value of the variable current source I3 and the measurement after the change, the input measurement resistor R1 or Since the voltage generated at both ends of the input measurement resistor R2 is proportional to the change in the current value, it can be confirmed that the wiring is normal.

  Then, the control circuit CT2 determines the ambient temperature when the resistance values of the input measurement resistor R1 and the input measurement resistor R2 are 100Ω from the relationship between the resistance value of the input measurement resistor R1 and the input measurement resistor R2 and the ambient temperature. calculate.

  Next, the case where the wiring is abnormal, that is, the case where a short circuit is caused between the channels will be specifically described. FIG. 2 is an equivalent circuit in which the channel 1 and the channel 2 are short-circuited between the channels in the embodiment of FIG. In FIG. 2, an input measurement resistor R3 is a combined resistor in which an input measurement resistor R1 and an input measurement resistor R2 are connected in parallel.

As in the normal case, the measurement when the resistance value r1 of the input measurement resistor R1 and the resistance value r2 of the input measurement resistor R2 are 100Ω will be described. At this time, the resistance value r3 of the input measurement resistor R3 is expressed by the equation (12).
r3 = r1 * r2 / (r1 + r2) = 50Ω (12)

The control circuit CT2 sets the current values of the variable current source I3 and the variable current source I4 to 1 mA, respectively. A current obtained by adding the current of 1 mA from the variable current source I4 to the current of 1 mA from the variable current source I3 flows through the input measurement resistor R3. At this time, the voltage v3 or the voltage v4 generated at both ends of the input measurement resistor R3 is expressed by equation (13).
v3 = v4 = r3 * (i3 + i4) = 50Ω * 2 mA = 100 mV (13)

The control circuit CT2 reads the voltage value of 100 mV from the voltage measurement circuit IC1 and the voltage measurement circuit IC2, respectively, and calculates the resistance value r1 of the input measurement resistor R1 and the resistance value r2 of the input measurement resistor R2 by equation (3). .
r1 = r2 = 100 mV / 1 mA = 100Ω (14)

Following the above measurement, the control circuit CT2 sets the current value of the variable current source I3 to 0.5 mA and sets the current value of the variable current source I4 to 1 mA. A current obtained by adding the current of 1 mA from the variable current source I4 to the current of 0.5 mA from the variable current source I3 flows through the input measurement resistor R3. At this time, the voltage v3 or the voltage v4 generated at both ends of the input measurement resistor R3 is expressed by equation (15).
v3 = v4 = r3 * (i3 + i4) = 50Ω * 1.5 mA = 75 mV (15)

  In this case, even if the control circuit CT2 sets the current value of the variable current source I3 to 1 mA and the current value of the variable current source I4 to 0.5 mA, the voltage v3 generated at both ends of the input measurement resistor R3. Or the voltage v4 becomes 75 mV similarly from the equation (15).

The control circuit CT2 reads the voltage value of 75 mV from the voltage measurement circuit IC1 and the voltage measurement circuit IC2, respectively, and calculates the resistance value r1 of the input measurement resistor R1 and the resistance value r2 of the input measurement resistor R2 by equation (3). .
r1 = 75 mV / 0.5 mA = 150Ω (16)
r2 = 75 mV / 1 mA = 75Ω (17)

  The control circuit CT2 includes the voltage v3 generated at both ends of the input measurement resistor R1 before changing the current value i3 of the variable current source I3 and the input measurement resistor R1 after changing the current value i3 of the variable current source I3. Are compared with each other. A short circuit between the channels is detected because the change in the voltage v3 is not proportional to the change in the current value i3 of the variable current source I3.

  Specifically, when the current value i3 of the variable current source I3 is 1 mA (before change), the voltage v3 generated across the input measurement resistor R1 is 100 mV, whereas the current value i3 of the variable current source I3 is 0. At .5 mA (after change), the voltage v3 generated across the input measurement resistor R1 is 75 mV. That is, while the current value i3 of the variable current source I3 is 1/2, the voltage v3 generated across the input measurement resistor R1 is 3/4, which is not proportional. In this case, the control circuit CT2 informs the user of the input module that an abnormality has occurred.

  On the other hand, when the wiring is normal, when the current value i3 of the variable current source I3 is 1 mA (before change), the voltage v3 generated at both ends of the input measurement resistor R1 is 100 mV, while the variable current source I3 When the current value i3 is 0.5 mA (after change), the voltage v3 generated across the input measurement resistor R1 is 50 mV. That is, when the current value i3 of the variable current source I3 becomes 1/2, the voltage v3 generated across the input measurement resistor R1 also becomes 1/2, which is in a proportional relationship.

  In this way, the control circuit CT2 is generated at both ends of the input measurement resistor R1 and the input measurement resistor R2 before and after changing the current value of either the variable current source I3 or the variable current source I4. The voltage measurement circuit IC1 and the voltage measurement circuit IC2 respectively measure the voltage to be measured and compare the voltage value measured before changing the current value with the voltage value measured after changing the current value, thereby changing the current value. Therefore, it is possible to easily detect a short circuit between the channels.

[Second Embodiment]
FIG. 3 is a block diagram showing a second embodiment of the input module of the present invention. Here, the same components as those in FIG. 3 is different from the configuration shown in FIG. 1 in that a reference resistor Rref1, a reference resistor Rref2, a voltage measurement circuit IC3, and a voltage measurement circuit IC4 are newly provided, and a control circuit CT3 is provided instead of the control circuit CT2. It is a point provided.

  In FIG. 3, the input module M3 includes a voltage measurement circuit IC1, a voltage measurement circuit IC2, a voltage measurement circuit IC3, a voltage measurement circuit IC4, a variable current source I3, a variable current source I4, an input terminal CN1, an input terminal CN2, and an input terminal CN3. , An input terminal CN4, a reference resistor Rref1, a reference resistor Rref2, and a control circuit CT3.

  The voltage measurement circuit IC1, the voltage measurement circuit IC3, the variable current source I3, the reference resistor Rref1, and the input terminals CN1 and CN2 constitute a channel 1. Similarly, the voltage measurement circuit IC2, the voltage measurement circuit IC4, the variable current source I4, the reference resistor Rref2, and the input terminals CN3 and CN4 constitute a channel 2.

  The reference resistor Rref1 and the reference resistor Rref2 are highly accurate resistors with known errors and a small error. Similarly to the voltage measurement circuit IC1 and the voltage measurement circuit IC2, the voltage measurement circuit IC3 and the voltage measurement circuit IC4 are circuits for measuring voltage, and are mainly configured by an A / D converter or the like.

  The control circuit CT3 changes the current value of the current flowing from the variable current source I3 or I4 to the input measurement resistor R1 or R2 for each channel, and the voltage generated at both ends of the reference resistor Rref1 or Rref2 for each channel. A short circuit between channels is detected by measuring with IC3 or IC4.

  In channel 1, a current is passed through the input measurement resistor R1 connected to the input terminals CN1 and CN2, and the voltage value of the voltage generated at both ends of the input measurement resistor R1 is measured by the voltage measurement circuit IC1, and the measured voltage value is measured. Capture as input value. Similarly, the channel 2 measures the voltage value of the voltage generated at both ends of the input measurement resistor R2 by passing a current through the input measurement resistor R2 connected to the input terminals CN3 and CN4, and measures the voltage. Takes a voltage value as an input value. The input module M3 has a channel 1 and a channel 2.

  One end of the input terminal CN1 is connected to the output terminal of the variable current source I3 and the input terminal of the voltage measurement circuit IC1, and the output terminal of the voltage measurement circuit IC1 is connected to the input terminal V11 of the control circuit CT3. A power supply voltage is applied to the input terminal of the variable current source I3, and one end of the input terminal CN2 is connected to one end of the reference resistor Rref1 and the input terminal of the voltage measurement circuit IC3. The other end of the reference resistor Rref1 is connected to the common potential, and the output terminal of the voltage measurement circuit IC3 is connected to the input terminal V12 of the control circuit CT3.

  The other end of the input terminal CN1 is connected to one end of the input measurement resistor R1, and the other end of the input measurement resistor R1 is connected to the other end of the input terminal CN2. The output terminal I3_CTL of the control circuit CT3 is connected to the control terminal of the variable current source I3.

  One end of the input terminal CN3 is connected to the output terminal of the variable current source I4 and the input terminal of the voltage measurement circuit IC2, and the output terminal of the voltage measurement circuit IC2 is connected to the input terminal V21 of the control circuit CT3. A power supply voltage is applied to the input terminal of the variable current source I4, and one end of the input terminal CN4 is connected to one end of the reference resistor Rref2 and the input terminal of the voltage measurement circuit IC4. The other end of the reference resistor Rref2 is connected to the common potential, and the output terminal of the voltage measurement circuit IC4 is connected to the input terminal V22 of the control circuit CT3.

  The other end of the input terminal CN3 is connected to one end of the input measurement resistor R1, and the other end of the input measurement resistor R1 is connected to the other end of the input terminal CN4. The output terminal I4_CTL of the control circuit CT3 is connected to the control terminal of the variable current source I4.

The operation of such an input module will be described.
FIG. 4 is a configuration diagram in a state where the channel 1 and the channel 2 are short-circuited between the channels in the embodiment of FIG. As shown in FIG. 4, there are patterns (A) to (C) in the short circuit between channels.

  The control circuit CT3 sets the current value i3 of the variable current source I3 through the output terminal I3_CTL, and sets the current value i4 of the variable current source I4 through the output terminal I4_CTL. A current having a current value i3 flows from the variable current source I3 to the input measuring resistor R1 via the input terminal CN1, and a current having a current value i4 flows from the variable current source I4 to the input measuring resistor R2 via the input terminal CN3.

  The current flowing through the input measurement resistor R1 flows to the reference resistor Rref1 via the input terminal CN2, and the current flowing through the input measurement resistor R2 flows to the reference resistor Rref2 via the input terminal CN4. As a result, a voltage v3 is generated at both ends of the input measurement resistor R1, and a voltage v12 is generated at both ends of the reference resistor Rref1. Similarly, a voltage v4 is generated at both ends of the input measurement resistor R2, and a voltage v22 is generated at both ends of the reference resistor Rref2.

The control circuit CT3 reads the voltage v12 measured by the voltage measurement circuit IC3 and the voltage v22 measured by the voltage measurement circuit IC4. Then, the control circuit CT3 calculates a current value ir1 flowing in the reference resistor Rref1 from the voltage value v12 and the resistance value rr1 of the reference resistor Rref1 by the equation (18), and from the voltage value v22 and the resistance value rr2 of the reference resistor Rref2 The current value ir2 flowing through the reference resistor Rref2 is calculated by the equation (19).
ir1 = v12 / rr1 (18)
ir2 = v22 / rr2 (19)

  The control circuit CT3 determines whether or not the calculated current value ir1 is equal to the current value i3 set in the variable current source I3 in order to detect whether a short circuit has occurred between the channels. If there is no short circuit between the channels, the current i3 output from the variable current source I3 flows through the input measurement resistor R1 and then flows into the common potential via the reference resistor Rref1. Therefore, the reference resistor Rref1 Current of the current value i3 flows. On the other hand, if a short circuit between the channels has occurred, the current i3 output from the variable current source I3 branches or merges at the short circuit location, and therefore the reference resistor Rref1 has a current value different from the current value i3. Current flows.

If the calculated current value ir1 is equal to the current value i3 set in the variable current source I3, the control circuit CT3 determines that there is no short circuit between the channels, and sets the resistance value r1 of the input measurement resistor R1. It calculates with (20) Formula. The voltage value v11 is a voltage measured by the control circuit CT3 with the voltage measurement circuit IC1.
r1 = (v11−v12) / i3 (20)

  Then, after calculating the resistance value r1 of the input measurement resistor R1, the control circuit CT3 calculates the ambient temperature of the input measurement resistor R1 from the resistance value r1. At this time, it is assumed that the relationship between the resistance value of the input measurement resistor R1 and the ambient temperature is known, and the control circuit CT3 also knows the relationship between the resistance value of the input measurement resistor R1 and the ambient temperature.

  On the other hand, if the calculated current value ir1 is not equal to the current value i3 set in the variable current source I3, the control circuit CT3 determines that a short circuit between the channels has occurred and an abnormality has occurred. To the user of the input module.

Similarly, the control circuit CT3 determines whether or not the calculated current value ir2 is equal to the current value i4 set in the variable current source I4. If the calculated current value ir2 is equal to the current value i4 set in the variable current source I4, the control circuit CT3 determines that there is no short circuit between the channels, and determines the resistance value r2 of the input measurement resistor R2. It calculates with (21) Formula. The voltage value v21 is a voltage measured by the control circuit CT3 with the voltage measurement circuit IC2.
r2 = (v21−v22) / i4 (21)

  The control circuit CT3 calculates the resistance value r2 of the input measurement resistor R2, and then calculates the ambient temperature of the input measurement resistor R2 from the resistance value r2. At this time, it is assumed that the relationship between the resistance value of the input measurement resistor R2 and the ambient temperature is known, and the control circuit CT3 also knows the relationship between the resistance value of the input measurement resistor R2 and the ambient temperature.

  On the other hand, if the calculated current value ir2 is not equal to the current value i4 set in the variable current source I4, the control circuit CT3 determines that a short circuit between the channels has occurred and an abnormality has occurred. To the user of the input module.

  In this way, the control circuit CT3 calculates the current flowing through the reference resistor Rref1, and determines whether or not the calculated current value is equal to the current value i3 set in the variable current source I3. Therefore, it is possible to easily detect the short circuit between the channels.

The present invention is not limited to this, and may be as shown below.
In the embodiment shown in FIGS. 1 and 3, the measurement module M2 or the measurement module M3 is configured to have two channels, that is, the channel 1 and the channel 2, but the measurement module M2 or the measurement module M3 includes three or more channels. You may have a channel.

CT2, CT3 Control circuit I3, I4 Variable current source IC1-4 Voltage measurement circuit Rref1, Rref2 Reference resistance R1, R2 Input measurement resistance

Claims (3)

An input having a plurality of channels for supplying a current to an input measurement resistor connected to an input terminal, measuring a voltage value of a voltage generated at both ends of the input measurement resistor with a voltage measurement circuit, and taking the measurement voltage value as an input value In the module
A variable current source provided for each of the plurality of channels and capable of varying a current value of a current flowing through the input measurement resistor;
The current value of the current flowing from the variable current source to the input measurement resistor is changed for each of the plurality of channels, and the voltage value of the voltage generated at both ends of the input measurement resistor is measured for the plurality of channels. When the voltage value measured by the circuit is compared before and after the change of the current and the change of the voltage value is not proportional to the change of the current value, a short circuit has occurred between the channels And an input module. An input having a plurality of channels for supplying a current to an input measurement resistor connected to an input terminal, measuring a voltage value of a voltage generated at both ends of the input measurement resistor with a voltage measurement circuit, and taking the measurement voltage value as an input value In the module
A variable current source provided for each of the plurality of channels and capable of varying a current value of a current flowing through the input measurement resistor;
A reference resistor provided for each of the plurality of channels, through which current flows from the variable current source via the input measurement resistor;
A voltage measuring circuit for measuring the voltage value of the voltage generated at both ends of the reference resistor;
The current value of the current flowing from the variable current source to the input measurement resistor is changed for each of the plurality of channels, and the voltage value of the voltage generated at both ends of the reference resistor is changed by the voltage measurement circuit for each of the plurality of channels. Measure and calculate the current value of the current flowing through the reference resistor. If the current value set in the variable current source and the current value flowing through the reference resistor are not equal, it is determined that a short circuit has occurred between the channels. And an input module. The input measurement resistor is:
The input module according to claim 1, wherein the input module is a resistance temperature detector.

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