JPH06207961A - Analog input unit - Google Patents

Abstract

PURPOSE:To provide an analog input unit in which an operation equivalent to duplication can be realized when analog input circuits to be connected with sense elements are multiplexed. CONSTITUTION:A sense element S outputting its own measuring current is connected between the external connection terminals TA and TB of an analog input unit 1 which are connected in parallel with two analog input circuits A11, A12. In the analog input circuits A11, A12, switches SW11, SW12 and measuring resistances R11, R12 are connected in series with the external connecting terminals TA, TB. The measuring resistors R11, R12 have the other ends connected with a ground terminal TC and the terminal voltages of the measuring resistors R11, R12 are detected by means of operational amplifiers OP11, OP12 and monitored by means of disconnection detecting comparators CO11, CO12. Only one of the switches SW11, SW12 is then turned ON by a duplication control section MC thus realizing an operation equivalent to that where only one analog input circuit is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog input device in which a measured current from one sensing element suitable for use in a process control system or the like is input to a plurality of analog input circuits and multiplexed.

[0002]

2. Description of the Related Art In a conventional analog input device, when an analog input circuit is connected in parallel to a sensing element to form a dual structure, when the characteristics of the sensing element, that is, the sensing element itself generates a measurement current, Although it differs depending on when a measurement current is required, etc., the sneak of the input current in the analog input circuit
When the disconnection detection means is provided, it goes around to the disconnection detection route, and due to an increase in the measurement current supplied to the sensing element,
It may not be possible to perform the same measurement as a single analog input device.

That is, for example, a solar cell is irradiated.
The sensing element that outputs a current according to the amount of light
Configure the analog input device by duplicating the log input circuit
In this case, as shown in FIG.
Input terminal T_A,T_BIn the meantime, it may become a constant current source for solar cells, etc.
The intelligent element S is connected to these external input terminals T_A,T_BAnd contact
Ground (GND) terminal T_CTwo analog input circuits A each
₁₁And A₁₂Are connected in parallel. With these analog
Force circuit A_11,A₁₂Are output from the sensing element S.
External input terminal T for detecting measured current as voltage_A
And T_BMeasuring resistor R connected in series between_11,R
₁₂And this measuring resistor R_11,R₁₂The voltage between the terminals of
Operational amplifier OP_11,OP₁₂And one input side is DC
Power supply V_REFFor measuring R via_11,R₁₂One end of the other
One input side has a measuring resistor R_11,R ₁₂Connected to the other end of
Disconnection detection comparator CO_11,CO₁₂With and
Measuring resistance R_11,R₁₂And external input terminal T_BGrounded between
Terminal T_CIs connected to the operational amplifier OP_11,OP₁₂Output
The analog input voltage from the side_11,CO
₁₂With the configuration that the disconnection detection signal is output from each output side of
To do.

Further, as in the direct type of thermocouple, the measuring current
For sensing elements with temperature sensors that need to supply
Dual analog input circuit to configure an analog input device.
In case of forming the external connection terminal T, as shown in FIG._A,
T_CA thermocouple TC is connected between them, and an external connection terminal T
_B,T_CBetween the temperature sensor S_TExternal connection terminal T _A
~ T_CTwo analog input circuits A each_{twenty one,}A_{twenty two}Are parallel
It is connected to the. These analog input circuits A_{twenty one,}A_{twenty two}
Each of the input terminals has an external connection terminal T_AInto the other
Force side external connection terminal T_COperational amplifier O connected to
P_{twenty one,}OP_{twenty two}And one input side is DC power supply V_REFThrough
External connection terminal T_CThe other input side is directly the external input terminal
T_ADisconnection detection to detect disconnection of the thermocouple system connected to the
Comparator CO_{twenty one,}CO_{twenty two}And this comparator C
O_{twenty one,}CO_{twenty two}Input of the other side and DC power supply V_REFWith the negative side of
DC power supply VD inserted in series between_{twenty one,}VD_{twenty two}And pull
Up resistance R_{twenty one}, R_{twenty two}And DC power supply VD_{twenty one,}VD_{twenty two}Over
Resistance R_{twenty one,}R_{twenty two}Connection point and external input terminal T_BBetween
Temperature sensor S inserted_TMeasurement that supplies measurement current to the
Current source CS_{twenty one,}CS_{twenty two}And operational amplifier OP_{twenty one}，
OP_{twenty two}The analog input voltage from the output side of the
CS_{twenty one,}CS_{twenty two}And external connection terminal T_BFrom the temperature sensor
Input signal is comparator CO_{twenty one,}CO_{twenty two}From the output side of
The disconnection detection signal is output respectively.

In addition, a resistance temperature detector is used to pass this.
The voltage difference between the current route and the current route that does not pass through it
When measuring the force voltage, as shown in FIG.
One end of the resistance temperature detector Pt is connected to the external connection terminal T_AAnd T_BContact
And connect the other end to the external connection terminal T_CConnect to this
External connection terminal T_A~ T_C2 analog inputs each
Road A_31,A₃₂Are connected in parallel. These analogs
Input circuit A_31,A₃₂Each has an external input terminal T_AIn series
Disconnection detection resistor R connected to_31,R₃₂And this resistance R
_31,R₃₂DC power source V for disconnection detection at one end of_REFThrough one
One input side is connected and resistance R_31,R₃₂Directly on the other end of
Disconnection detection comparator CO connected to the other input side
_31,CO₃₂And the resistance R on the negative side_31,R₃₂And DC power supply V
_REFBetween the positive electrode side and the measuring current source CS_311,C
S₃₁₂; CS_321,CS₃₂₂Through the external connection terminal T_B,T
_CDC power supply VD connected to_31,VD₃₂And one input
Current source CS for measurement_311,CS₃₂₁And external input terminal T
_BConnected to the other input side of the measuring current source CS_312,
CS₃₂₂And external input terminal T_CA measurement channel connected between
Peamplifier OP_31,OP₃₂And an analog input circuit A
_31,A₃₂Disconnection detection resistor R _31,R₃₂And DC power supply V
D₃₁, VD₃₂Is connected to each other, and the operational amplifier OP
_{31 ,}OP₃₂The analog input voltage from the output side of the
Data CO_31,CO₃₂Disconnection detection signals are output from the output side of
It has a forceful configuration.

[0006]

However, in the case where the analog input device is configured by duplicating the analog input circuit as described above, in the case of the analog input device 1 of FIG. 4, there is an unsolved problem as described below. There are challenges. That is, in the operation in the single configuration having only one analog input circuit A ₁₁ , the current i _IN output from the sensing element S flows through the voltage measuring resistor R ₁₁ , so that both ends of the resistor R ₁₁ are An input voltage V ₁₁ represented by the equation (1) is generated.

V ₁₁ = i _IN · R ₁₁ (1) However, as shown in FIG. 4, when the two analog inputs A ₁₁ and A ₁₂ are duplicated, the current output from the sensing element S i _IN is the current i _A1 supplied to the analog input circuit A _11.
And the current i _A2 supplied to the analog input circuit A ₁₂ . Here, two analog input circuits A ₁₁ and A ₁₂
Are set to be equivalent, the following expressions (2) to (4) are established.

R ₁₁ = R ₁₂ (2) i _in = i _A1 + i _A2 (3) i _A1 = i _A2 (4) Therefore, the voltage of the analog input circuit A ₁₁ Measuring resistance R
_The voltage V ₁₁ generated across both ends of ₁₁ is expressed by the following equation (5).

[0009] _{V 11 = i A1 · R 1} = i IN · R 1/2 ............ (5) After all, two analog inputs equivalent to each other circuit A ₁₁ and A
_In the case of duplication by ₁₂ , the detection voltage V ₁₁ becomes half the value of the unification _{, the} analog input value output from the operational amplifiers OP _{11 and} OP ₁₂ becomes half, and the comparator CO
There is an unsolved problem that the reference voltage of ₁₁ and CO ₁₂ also needs to be halved, and an analog input circuit equivalent to that of the unification cannot be applied.

In the case of the analog input device 1 of FIG.
Also analog input circuit A_{twenty one}Operation in singlet with only
Is the measuring current source CS_{twenty one}Measured current i from_A1Is the temperature sensor
S _TThrough analog input circuit A_{twenty one}To be returned to
The temperature sensor S_TThe resistance value of R_SAnd when
Temperature sensor measurement voltage V expressed by equation (6)_{twenty one}Occurs
It

[0011] _{V 21 = i A1 · R S} ............ addition (6), the input voltage V _T1 of the analog input circuit A ₂₁ by the thermocouple TC, the input voltage error of the thermocouple due to the electromotive force and the wiring resistance R _L V _e and the input voltage error V _e is pulled up by the pull-up resistor R ₂₁ for detecting disconnection.
The current i _P1 passing through the pull-up resistor R ₂₁ passes through the thermocouple TC, which causes an error. This input voltage error V _e can be expressed as V _e = i _P1 · R _L (7)

On the other hand, as shown in FIG. 5, when the two analog input circuits A _21, A ₂₂ are duplicated, the temperature sensor S _T has a measurement current of the two analog input circuits A _21, A _22. The measuring currents i _A1 and i _A2 are supplied from the sources CS _{21 and} CS ₂₂ , and the two analog input circuits A _21, A
_{Since 22} is configured equivalently, the following expressions (8) to (10) are established.

R ₂₁ = R ₂₂ (8) i _A1 = i _A2 (9) i _P1 = i _P2 (10) Therefore, the temperature sensor measurement of the analog input circuit A ₁₁ The voltage V ₂₁ is V ₂₁ = (i _A1 + i _A2 ) _RS = 2i _A1 · R _S ............ (11), which is twice the value in the case of unification and the sensor input value is different. There are unresolved issues.

Further, the thermocouple TC has a disconnection detection current i _P1 from the analog input circuit A ₂₁ and an analog input circuit A _22.
Since the disconnection detection current i _p2 from is supplied, the input voltage error V _{e is, V e = (i P1 +} i P2) R L = 2i P1 · R L ............ (12) , and this Also in this case, the value becomes twice as large as that of the unification, and the measured voltage V _T1 also differs, so that the operational amplifier OP ₂₁
There is also an unsolved problem in that the analog input value output from is also different.

Further, in the case of the analog input device 1 of FIG.
Also analog input circuit A₃₁Unification movement consisting only of
Product is analog input circuit A₃₁Input voltage V₃₁But for measurement
Current source CS₃₁₂Measuring current i from_A12Is the resistance thermometer P
Analog input open A through t ₃₁The route to return to
Constant current source CS₃₁₂Measuring current i from_A11Is the resistance temperature
Expressed by the voltage difference due to the route of returning without flowing through the body Pt
Be done.

Assuming that the resistance value of the resistance temperature detector Pt is R _P and the wiring resistance between the analog input circuit A ₃₁ and the resistance temperature detector Pt is “0”, the input voltage V ₃₁ is It can be expressed by equation (13). V ₃₁ = i _A12 · R _P ...... (13) Further, due to the measuring currents i _A11, i _A12 from the measuring current sources CS _311, CS ₃₁₂ , both ends of the disconnection detecting resistor R ₃₁ are
The disconnection detection voltage V _D1 represented by the following equation (14) is generated.

V _D1 = (i _A11 + i _A12 ) R ₃₁ (14) On the other hand, as shown in FIG. 6, two analog input circuits A
_When duplexing with _31, A ₃₂ ,
Current source CS for measurement of two analog input circuits A _21, A _{22
Since the} measuring currents i _A12 and i _A22 are supplied from the _{312 and} CS ₃₂₂ , and the two analog input circuits A _{21 and} A ₂₂ are configured equivalently, the following formulas (15) to (16) are To establish.

[0018] _{R 31 = R 32 ............ (15} ) i A11 = i A12 = i A21 = i A22 ............ (16) Therefore, the input voltage V ₃₁ inputted to the analog input circuit A _31, the V ₃₁ = (i _A12 + i _A22 ) R ₃₁ = 2i _A12 · R ₃₁ (17), and the duplex connection doubles the input voltage V _{31 as} compared with the case of single connection. There is an unsolved problem that the analog input values output from the operational amplifier OP ₃₁ are different.

Therefore, the present invention has been made by paying attention to the above-mentioned unsolved problems of the prior art, and when the analog input circuit is multiplexed, the sneak route of the measurement current, the disconnection detection route and the measurement current route are measured. It is an object of the present invention to provide an analog input device capable of handling an analog input value or a wire breakage detection value in each route in the same manner as in the case of unifying.

[0020]

To achieve the above object, an analog input device according to a first aspect of the present invention is an analog input device in which a plurality of analog input circuits are connected in parallel to one sensing element and multiplexed. Each of the analog input circuits is characterized by being provided with a disconnection detecting means for detecting a disconnection of the measurement system and a switching means for interrupting a sneak route of a current generated in the multiplexing configuration.

The analog input device according to a second aspect of the present invention is an analog input device in which a plurality of analog input circuits are connected in parallel to one sensing element that outputs a measurement current, and the analog input circuits are multiplexed. A disconnection detecting means for detecting a disconnection of the provided measurement system and a switching element inserted in the route of the measurement current flowing from the sensing element, and the switching element of one selected analog input circuit are controlled to be in an ON state. It is characterized in that it is provided with a multiplexing control unit.

Further, in the analog input device according to a third aspect of the present invention, a plurality of analog input circuits each having a measuring current supply means for supplying a measuring current to the sensing element are connected in parallel to one sensing element. In the multiplexed analog input device, disconnection detection means for detecting disconnection of the measurement system provided in each of the analog input circuits and a switching element inserted in the disconnection detection current supply route of the disconnection detection means are selected. It is characterized in that it is provided with a multiplexing control section for controlling only the switching element of one analog input circuit to an ON state.

Furthermore, in the analog input device according to a fourth aspect of the present invention, a plurality of analog input circuits each having a measuring current supply means for supplying a measuring current to the sensing element are connected in parallel to one sensing element. In the connected and multiplexed analog input device, a disconnection detection means for detecting a disconnection of a measurement system provided in each of the analog input circuits, a switching element inserted in a measurement current supply route, and one selected analog input It is characterized by including a multiplexing control unit for controlling only the switching element of the circuit to be in an ON state.

[0024]

In the analog input device according to claim 1,
A current sneak route occurs due to the multiplexing of the analog input circuit, but this sneak route can be cut off by the switching means to realize an analog input equivalent to the unification and a disconnection detection function.

In the analog input device according to the second aspect, when a plurality of analog input circuits are connected in parallel to the sensing element which outputs the measuring current by itself, the route of the sneak current of the measuring current from the sensing element in each analog input circuit. That is, a switching element is inserted in series with a voltage measuring resistor that detects a current value as a voltage value, and among these switching elements, only the switching element corresponding to one preselected analog input circuit is turned on by the multiplexing control unit. Since the switching element of the other analog input circuit is kept in the off state, the voltage between the terminals of the voltage measurement resistor of the selected one analog input circuit is also measured by the other analog input circuit. , When multiple analog input circuits are connected in parallel to one sensing element that outputs the measured current by itself Can in each analog input circuit which is multiplexed to form the equivalent of the analog input signal and when connecting one of the analog input circuit to the sensing element.

In the analog input device according to the third aspect, a plurality of analog input circuits are connected in parallel to the sensing element,
When the measurement current is supplied from the measurement current supply means of each analog input circuit to the measurement element to obtain the measurement current, the switching element is connected to the disconnection detection current route from the disconnection detection means of each analog input circuit. Of the switching elements, only the switching element corresponding to one preselected analog input circuit is turned on by the multiplexing control unit, and the switching elements of the other analog input circuits are kept off. Therefore, the disconnection detection current is supplied to the sensing element only from the disconnection detection means in the selected one analog input circuit,
By measuring the voltage between the terminals of the sensing element due to this disconnection current also in other analog input circuits, the analog input signal equivalent to the case where one analog input circuit is connected to the sensing element in each multiplexed analog input circuit Can be formed.

In the analog input device according to the fourth aspect, a plurality of analog input circuits are connected in parallel to the sensing element,
When the measurement current is supplied from the measurement current supply means of each analog input circuit to obtain the measurement current, the switching element is provided in the measurement current supply route from the measurement current means of each analog input circuit. Of the switching elements, only the switching element corresponding to one preselected analog input circuit is turned on by the multiplexing control unit, and the switching elements of the other analog input circuits are kept off. Therefore, a plurality of measuring currents are supplied from the measuring current supply means in one selected analog input circuit to the sensing element, and the voltage difference between these measuring current routes is measured by each analog input circuit, thereby making it possible to perform multiplexing. In each analog circuit, the analog input signal equivalent to the case where one analog input circuit is connected to the sensing element is formed. It can be.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of the present invention, which has a circuit configuration corresponding to FIG. 4 described above. That is, the analog input device 1 is formed with external input terminals T _{A and} T _B for connecting a sensing element and one ground (GND) terminal T _C, and a solar cell is provided between the external input terminals T _{A and} T _B. As described above, the sensing element S that outputs a current according to the amount of light emitted is connected, and the ground terminal T _C is grounded.

The analog input device 1 has an external input terminal T _A,
2 connected in parallel to T _B and the ground (GND) terminal T _C
It has two analog input circuits A ₁₁ and A ₁₂ . These analog input circuits A _{11 and} A ₁₂ are connected in series between external input terminals T _A and T _B for detecting the measurement current output from the sensing element S as a voltage, and have the same resistance value. Resistances R _11, R ₁₂ and this measurement resistance R
_11, operational amplifier OP _11, to which the voltage across the terminals of R ₁₂ is input
OP ₁₂ and one of the input sides are connected to one end of the measuring resistors R _{11 and} R ₁₂ through the DC power supply V _REF , and the other input side is directly connected to the other ends of the measuring resistors R _{11 and} R ₁₂ for detecting the disconnection. and a comparator CO _11, CO _12, the ground terminal T _C between the measurement resistor R _11, R ₁₂ and the external input terminal T _B is connected, the analog input signal from the output side of the operational amplifier OP _11, OP ₁₂ Is input to a control device composed of a computer or the like via a processing circuit such as an A / D converter and the comparator CO _11,
The disconnection detection signal is directly input to the control device from the output side of CO ₁₂ .

Then, each analog input circuit A_11,A₁₂of
Measuring resistance R_11,R₁₂As a switching element in series with
Switch SW_11,SW₁₂These switches are inserted
SW _11,SW₁₂Each analog input circuit provided externally
A₁₁And A₁₂Multiplexing system in which disconnection detection signal from
Master / slave from redundant control unit MC as control unit
Depending on the signal, either one is on and the other is off
Controlled, analog input circuit A₁₁And A₁₂Switch
SW₁₁And SW₁₂So that both are not turned on
Controlled by.

Next, the operation of the first embodiment will be described.
Now, the redundant control unit MC causes the analog input circuit A ₁₁
It is assumed that the switch SW ₁₁ is supplied with a master signal and is controlled to be turned on, and the switch SW ₁₂ of the analog input circuit A ₁₂ is supplied with a slave signal and is controlled to be turned off.

In this state, for example, a sensing device composed of a solar cell is used.
Measured current i output from element S_INIs the external input terminal T
_B, Analog input circuit A₁₁Measuring resistance R₁₁,switch
SW ₁₁And external input terminal T_AReturn to the sensing element S via
And the analog input circuit A₁₂Then switch SW₁₂But
Due to being in the off state, the measuring resistance R₁₂Input containing
The sneak route of the current is cut off, and the measured current i_IN
Will not flow.

Therefore, the analog input circuit A₁₁Well then
If there is no line, the measuring resistance R₁₁Measured current at
i_INIs the input voltage V₁₁(= I
_IN・ R₁₁) As operational amplifier OP₁₁To be entered in
More, this operational amplifier OP₁₁From the measured current i_INAccording to
An analog input signal consisting of voltage is output, and this is the A / D
It is input to the control device via a converter, etc.
Output comparator CO ₁₁Comparison voltage of the input side voltage is broken
Reference voltage V that serves as a criterion for judgment_REFBecause it will be larger,
For example, the disconnection detection signal of the logical value "1" is transmitted to the control device and the duplex.
It is input to the conversion control unit MC.

Further, the analog input circuit A _12, assuming that there is no break, the measurement current i _IN does not flow, the input voltage V ₁₂ of the operational amplifier OP ₁₂ is an external input terminal T _A and T _B
Since the terminal voltage V ₁₁ of the measuring resistor R ₁₁ of the voltage or the analog input circuit A ₁₁ between analog analog input signal outputted from the operational amplifier OP ₁₂ is output from the operational amplifier OP ₁₁ of the analog input circuit A ₁₁ The value becomes equal to the input signal, and the disconnection detection signal output from the disconnection detection comparator CO ₁₂ also becomes the logical value "1".

On the other hand, the duplex control unit MC inputs an analog input signal.
Road A₁₁Instead of analog input circuit A _{twenty one}The master signal to
In case of supplying the voltage, contrary to the above, the analog input circuit A₁₂
Measuring resistance R₁₂Measured current i between terminals_INDepending on the terminal
Voltage V_{twenty one}Is generated, and this is the operational amplifier OP
₁₂To the analog input signal
It At this time, the measuring resistance R₁₂Resistance and the aforementioned analog
Input circuit A₁₁Measuring resistance R₁₁Have the same resistance
And the voltage between terminals V₁₂Is V₁₂= I_IN・ R₁₂= I_IN・ R₁₁= V₁₁ And both analog input circuits A₁₂And A₁₁From above
The same analog input signal as the
Line detection comparator CO₁₂And CO₁₁Entered in
The force voltage also has the same value.

Therefore, even when two analog input circuits A ₁₁ and A ₁₂ are connected to the sensing element S and multiplexed,
The input voltages V ₁₁ and V ₁₂ to the operational amplifiers OP ₁₁ and OP ₁₂ of the analog input circuits A ₁₁ and A ₁₂ are detected by the sensing element S.
It is possible to make the input voltage equal to the input voltage V ₁₁ expressed by the above-mentioned equation (1) in the case of the single connection in which one analog input circuit is connected to the input voltage of the disconnection detection comparators CO ₁₁ and CO ₁₂ . Can be set to the same input voltage as that of the singularization.

[0037] Incidentally, a duplexing control unit MC for example the switch SW ₁₁ of the analog input circuit A ₁₁ in a state that the on-state, the resulting disconnection input current route including the measuring resistor R ₁₁ in the analog input circuit A ₁₁ , Measuring resistor R ₁₁
Since the inter-terminal voltage V ₁₁ becomes zero, the disconnection detection signal output from the disconnection detection comparator CO ₁₁ becomes a logical value “0”, and this is input to the duplication control unit MC. in, in place of the analog input circuit a ₁₁ switch SW ₁₂ of the analog input circuit a ₁₂ is controlled to be turned on, between the corresponding terminals of the analog input circuit a ₁₂ measured current i _iN at the measuring resistor R ₁₂ legitimate It is possible to generate a voltage and continue to output a normal analog input signal. Further, when the disconnection detection signals output from the disconnection detection comparators CO ₁₁ and CO _{12 of the} analog input circuits A ₁₁ and A ₁₂ are both logical values “0”, they are connected between the external input terminals T _A and T _B. It can be determined that the external route including the detected sensing element S is broken.

Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment corresponds to the above-described analog input device of FIG. 5 for the sensing element which does not output the measurement current by itself and requires the supply of the measurement current. That is, as shown in FIG. 2, the analog input device 1 has external connection terminals T _{A and} T _B and an external connection terminal T _C common to them, and the external connection terminal T as a sensing element is provided.
_A thermocouple TC is connected between _{A and} T _{C ,} and a temperature sensor S _T for compensation is connected between the external connection terminals T _{B and} T _C.

The analog input device 1 has an external connection terminal T._A
~ T_CAnalog input circuits A connected in parallel to
_{twenty one,}A_{twenty two}Is equipped with. These analog input circuits A_{twenty one,}
A_{twenty two}Each of the input terminals has an external connection terminal T _ATo the other
Input side external connection terminal T_CMeasuring opera connected to
OP_{twenty one,}OP _{twenty two}And one input side is DC power supply V_REFTo
Through external connection terminal T_CThe other input side is directly external input
Terminal T_ADisconnection to detect disconnection of thermocouple system connected to
Detection comparator CO_{twenty one,}CO_{twenty two}And this comparison
CO_{twenty one,}CO_{twenty two}Input of the other side and DC power supply V_REFNegative side of
DC power supply VD inserted in series between_{twenty one,}VD_{twenty two}as well as
Resistor R for pull-up_{twenty one}, R_{twenty two}And DC power supply VD_{twenty one,}VD
_{twenty two}And resistance R_{twenty one,}R_{twenty two}Connection point and external input terminal T_BWith
Temperature sensor S interposed between_TSupply measurement current to
Measurement current source CS_{twenty one,}CS_{twenty two}And operational amplifier OP
_{twenty one}, OP_{twenty two}The analog input signal from the output side of the
Source CS_{twenty one,}CS_{twenty two}And external connection terminal T_BFrom the temperature
Sensor input signal through the processing circuit such as A / D converter
It is input to a control device composed of a computer etc.
Computer CO_{twenty one,}CO_{twenty two}Disconnection detection signal from the output side of
The configuration is such that it is directly input to the control device.

Then, each analog input circuit A_{twenty one}And A_{twenty two}
Is the measuring current source CS_{twenty one}And CS_{twenty two}Switch on the output side of
Switch SW as a switching element₂₁₁And SW₂₂₁Are in series
And is connected to the pull-up resistor R_{twenty one}And R
_{twenty two}Switch SW as a switching element in series with₂₁₂
And SW₂₂₂Are connected to these switches SW_211,SW
₂₁₂And SW_221,SW₂₂₂Each analog provided outside by
Input circuit A_{twenty one}And A _{twenty two}The disconnection detection signal from
Master from duplication controller MC as a multiplexing controller
/ Either analog input circuit depending on slave signal
Is turned on and the other is turned off, and the analog input
Force circuit A_{twenty one}And A_{twenty two}Is a switch SW₂₁₁~ SW₂₂₂Is all
So that both of them will not turn on and become masters together.
Controlled.

Next, the operation of the second embodiment will be described.
Now, the duplex control unit MC outputs a master signal to each of the switches SW _211, SW _{212 of the} analog input circuit A ₂₁ , controls both of these switches SW _211, SW ₂₁₂ to the ON state, and _A slave signal is output to each switch SW _221, SW _{22 2} of ₂₂ ,
It is assumed that the switches SW _221, SW ₂₂₂ are both controlled to be in the off state.

In this state, it is assumed that no wire breakage has occurred.
Then, the analog input circuit A_{twenty one}Current source CS for measurement only
_{twenty one}Measurement current i output from_A1And pull-up resistor
R_{twenty one}Disconnection detection current i passing through_P1Is the temperature sensor S_TOver
And the thermocouple TC, the temperature sensor S_T
For the measuring current source CS_{twenty one}Measuring current i from _A1
Is a switch SW_{twenty one}, External input terminal T_B, Temperature sensor S_T
And external connection terminal T_CVia the analog input circuit A_{twenty one}To
As it is fed back, the temperature sensor S_TResistance value R between both ends of_S
Temperature sensor measured voltage expressed by equation (6)
V_{twenty one}Occurs, and this is the A / D as the temperature sensor input signal.
Input to the controller via the converter and pull-up
Resistance R_{twenty one}Disconnection detection current i passing through_P1And thermocouple TC
Wiring resistance R_LInput voltage error V due to_e1And thermocouple TC
Input voltage V due to electromotive force_T1Is the external connection terminal T_AAnd T
_CIt occurs in the interval and this is the operational amplifier OP_{twenty one}Is supplied to
Then, the analog input signal is sent to the control device via the A / D converter.
Input voltage and input voltage V_T1Is a comparator for disconnection detection
Data CO_{twenty one}Input to the comparator CO_{twenty one}
Controls the disconnection detection signal of logical value "1" that indicates the normal state from
It is input to the device and the duplication control unit MC.

Further, in the analog input circuit A ₂₂ , the temperature sensor measurement voltage V ₂₂ becomes a voltage between the external connection terminals T _B and T _C because the output of the measurement current source CS ₂₂ is cut off, and the above analog The voltage is the same as the temperature sensor measurement voltage V _{21 of the} input circuit A ₂₁ , and the input voltage V _T2 is also cut off from the disconnection detection current i _A2 passing through the pull-up resistor R _22. It becomes a voltage between the _a and T _C, becomes the same value as the input voltage V ₂₁ of the analog input circuit a _21, the temperature sensor signal similar to the analog input circuit a ₂₁ is output, the analog input signal the operational amplifier OP ₂₂ is output from, and similar disconnection detection signal to the analog input circuit a ₂₁ is output from the comparator CO ₂₂ to the measuring circuit or the like and the duplexing control unit MC.

After all, the analog input signal, the temperature sensor input signal, and the disconnection detection signal output from both the analog input circuits A ₂₁ and A ₂₂ are unified by connecting one analog input circuit to the sensing element. The value can be the same as that of the configuration. On the other hand, in the duplex control unit MC, the switch SW _221, of the analog input circuit A ₂₂ is set so that the analog input circuit A ₂₂ is used as a master instead of the analog input circuit A _{21 .}
The master signal is supplied to SW ₂₂₂ , and these switches SW
_221, SW ₂₂₂ is turned on, the slave signal is supplied to the switches SW _211, SW ₂₁₂ of the analog input circuit A ₂₁ ,
When these switches SW _{211 and} SW ₂₁₂ are turned off,
Measurement current i _A1 from the analog input circuit A ₂₁ to the temperature sensor S _T and disconnection detection current i to the thermocouple TC
Supply of _P1 is cut off, and instead of this, analog input circuit A
Together with the measurement current i _A2 from the measuring current source CS _{22 22} is supplied to the temperature sensor S _T, in the disconnection detection current i _P2 through the pull-up resistor R ₂₂ is provided to the thermocouple TC Become.

Therefore, a temperature sensor measurement voltage V ₂₂ (= i _A2 · R _S ) represented by the measurement current i _A2 and the resistance value R _{S of} the temperature sensor S _T is applied across the temperature sensor S _T. Although generated, the measurement current i _{A2 at} this time is equal to the measurement current i _A1 of the analog input circuit A ₂₁ described above, and therefore the temperature sensor measurement voltage V ₂₂ has a value equal to the temperature sensor measurement voltage V ₂₁ described above. .

[0046] Also, the thermocouple TC, by the disconnection detection current i _P2 from the analog input circuit A ₂₂ is supplied, this wiring resistance R _L and by the input voltage error V _e2 (=
i _P2 · R _L ) is included, but the disconnection detection current i _P2 is set to a value equal to the above-described disconnection detection current i _{P1 of} the analog input circuit A ₂₁ , so that the input voltage error V _e2 becomes It has the same value as the above-mentioned input voltage error V _e1, and the input voltage V _T2 of the analog input circuit A ₂₂ generated between the external connection terminals T _A and T _C also becomes equal to the above-mentioned input voltage V _T1. temperature sensor input signal outputted from the _22, an analog input signal and the disconnection detection signal may be a value equivalent to the case of the master of the analog input circuit a ₂₁ as described above, from the analog input circuit a ₂₁ as a slave The temperature sensor input signal, the analog input signal, and the disconnection detection signal that are output can also have the same value, so even if the analog input circuit is duplicated, it is the same as when the analog input circuit is unified. And the like can be realized.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment corresponds to the above-described analog input device of FIG. 6 for the sensing element which requires two systems of a current passing through itself and a current other than that to supply the measurement current. That is, as shown in FIG. 2, the analog input device 1 has a common external connection terminal T _A and external connection terminals T _{B and} T _C for outputting a measurement current to the outside _, and an external connection as a sensing element. The resistance temperature detector Pt is connected between the terminals T _{A and} T _C , and the external connection terminal T of the resistance temperature detector Pt is connected.
_A side end and the external connection terminal T _B is connected.

The analog input device 1 has an external connection terminal T._A
~ T_CAnalog input circuits A connected in parallel to
_{twenty one,}A_{twenty two}Is equipped with. These analog input circuits A_31,
A₃₂Each has an external input terminal T_AConnected in series to
Resistance for line detection R_31,R₃₂And this resistance R_31,R₃₂One end of
DC power supply V for disconnection detection_REFOne input side is connected via
Continued and resistance R_31,R₃₂The other input side directly to the other end of
Connected disconnection detection comparator CO_31,CO₃₂When,
Resistance R on the negative side_31,R₃₂And DC power supply V_REFBetween and positive
Current source CS for measurement on the pole side_311,CS ₃₁₂; CS_321,CS
₃₂₂Through the external connection terminal T_B,T_CDC power connected to
Source VD_31,VD₃₂And one input side is the measuring current source CS
_311,CS₃₂₁And external input terminal T_BConnected between the other
Input side of the current source CS for measurement_312,CS₃₂₂And external input
Terminal T_COp-amp for measurement connected between_31,OP
₃₂And an analog input circuit A_31,A₃₂For disconnection detection
Resistance R_31,R₃₂And DC power supply VD₃₁, VD₃₂Between each other
Connected to the operational amplifier OP_31,OP₃₂From the output side of
The analog input voltage is transferred via a processing circuit such as an A / D converter.
It is input to a control device composed of a computer
Lator CO_31,CO₃₂Disconnection detection signal directly from the output side of
It has a configuration to be input to the control device.

Then, the analog input circuit A₃₁And A₃₂of
Measurement current source CS_311,CS₃₁₂And CS_321,CS₃₂₂of
Switches SW as switching elements on the output side
_311,SW₃₁₂And SW_321,SW₃₂₂Are inserted in series
Resistance for disconnection detection R ₃₁And R₃₂External connection end
Child T_ASwitch S as a switching element in series on the side
W₃₁₃And SW₃₂₃Is inserted, these switch SW
₃₁₁~ SW₃₁₃And SW_{32 1}~ SW₃₂₃Is provided outside
The master / slave signal from the redundant control unit MC
One of the analog input circuits is in the ON state, the other is
Controlled to off state, analog input circuit A_{twenty one}And A_{twenty two}
Is a switch SW₂₁₁~ SW₂₂₂Are all on
Both are controlled so that they do not become masters.

Next, the operation of the third embodiment will be described.
Now, the master signal is output to each of the switches SW _{311 to} SW ₃₁₃ of the analog input circuit A ₃₁ by the duplexing control unit MC, and these switches SW _{311 to} SW ₃₁₃ are both controlled to the ON state, and the analog input circuit A ₃₁ is also controlled. ₃₂ is output slave signals to the switch SW ₃₂₁ to SW _323, it is to the switches SW ₃₂₁ to SW _{32 3} is controlled to both turned off.

In this state, it is assumed that no wire breakage has occurred.
Then, the analog input circuit A₃₁Current source CS for measurement only
₃₁₁And CS₃₁₂To measurement current i_A11And i_A12Is outside
Part connection terminal T_BAnd T_CMeasurement by being output to
For current i_A11Via the external connection side terminal of the resistance thermometer Pt
Direct external connection terminal T_ACurrent and current for measurement i
_A12Is connected to the external connection terminal T through the resistance temperature detector Pt._AFlow
And the combined current of these is the resistance R for disconnection detection.₃₁Flow to
Temperature resistor Pt and analog input circuit A₃₁Wiring resistance between
Is "0", the operational amplifier OP₃₁Mentioned above (13)
Input voltage V expressed by the formula₃₁Is entered, and from now on
Input signal is input to the controller via the A / D converter.
Resistance for disconnection detection R₃₁Equation (14) at both ends of
Disconnection detection voltage V_D1Occurs and this is a disconnection detection
Comparator CO₃₁Will be entered in
Data CO_{twenty one}Detection of disconnection of logical value "1" indicating normal state from
The signal is input to the control device and the duplication control unit MC.

Further, the analog input circuit A₃₂Oops
Pump OP₃₂Input voltage V input to ₃₂Is the current source C for measurement
S₃₂₁And CS₃₂₂Measurement current i output from_A321Over
I _A322Is a switch SW₃₂₁And SW₃₂₂In the off state
Therefore, since it is cut off, the external connection terminal T_Bas well as
T_CThe voltage between them becomes the analog input circuit A₃₁Enter
Force voltage V₃₁The same value as the above, and the resistance R for disconnection detection₃₂
Switch SW on the input side₃₂₃Is off
To external connection terminal T_AThe combined current of the
Detection voltage V_D2Is the analog input circuit A₃₁Resistance R₃₁of
V which is voltage between terminals_D1And the analog input circuit A₃₁When
Similar analog input signal is operational amplifier OP₃₂Output from
And analog input circuit A₃₁A disconnection detection signal similar to
Comparator CO₃₂To measuring circuit, etc. and duplex control unit M
It is output to C.

Therefore, the analog input signal output from both the analog input circuits A ₃₁ and A ₃₂ and the disconnection detection signal are in a single configuration in which one analog input circuit is connected to the sensing element. It can be an equivalent value. On the other hand, in the duplex control unit MC, the analog input circuit A ₃₁
Instead of using the analog input circuit A ₃₂ as the master,
The switch SW ₃₂₁ to SW _{32 3} of the analog input circuit A ₃₂ supplies the master signal, the switches SW ₃₂₁ to SW
₃₂₃ is turned on, to supply the slave signal to the switch SW ₃₁₁ to SW ₃₁₃ of the analog input circuit A _31, when these switches SW ₃₁₁ to SW ₃₁₃ and the off state, the current for measurement from the analog input circuit A ₃₁ i instead of the _A311 and i _A312 will be measured current i _A321 and i _A322 from the analog input circuit a ₃₂ is supplied to the external connection terminal T _B and T _C.

Therefore, an input voltage V ₃₂ (= i _A322 · R _P ) is generated between the external connection terminals T _B and T _C due to the voltage difference due to the measurement currents i _A321 and i _A322 . since the current i _A321 and i _A322 equals a measurement current i _A311 and i _A312 analog input circuit a ₃₁ described above, the input voltage V ₃₂ and the input voltage V ₃₁ when the master of the analog input circuit a ₃₁ as described above It becomes equal value.

Also, the resistance R for detecting disconnection₃₂Then, the measurement voltage
Flow i_A321And i_A322This is because the combined current of
Disconnection detection voltage V according to_D2But as mentioned above
And the measuring current i_A321And i_A322And analog input circuit A
₃₁Measuring current i_A311And i _A312Is equal to, so disconnection
Detection voltage V_D2Is the analog input circuit A described above.₃₁The master
Disconnection detection voltage V_D1Is equal to
Even if the station and analog input circuit are duplicated, analog
Achieve the same operation as when the input circuit is unified
You can

In each of the above embodiments, the case where the analog input circuit is duplicated has been described. However, the present invention is not limited to this, and the present invention can be applied to the case where multiplexing of triple or more is performed. Also in this case, the multiplexing control unit controls so that only the switching element installed in any one analog input circuit is turned on and the switching elements installed in the other analog input circuits are maintained in the off state. do it.

In each of the above embodiments, the case where the analog input circuit is provided with a switch has been described.
Not limited to this, it is turned on according to the input signal of the transistor etc.
Other switching elements that are turned off may be applied.

[0058]

As described above, according to the analog input device of the first aspect, the current sneak route occurs due to the analog input circuit having the multiplexed structure.
Since switching means is provided on this wraparound route,
With this switching means, the sneak current can be interrupted, and the analog input equivalent to the unification and the disconnection detection function can be realized.

Further, according to the analog input device of the second aspect, when a plurality of analog input circuits are connected in parallel to the sensing element which outputs the measurement current by itself, the sensing element of each analog input circuit outputs the sensing element. By inserting a switching element in the sneak route of the measured current, turning on only the switching element of one analog input circuit selected by the multiplexing control unit, and turning off the switching element of the other analog input circuit. By supplying the measured current output from the sensing element to only one selected analog input circuit, an analog input signal and a disconnection detection signal equivalent to the case where only one analog input circuit is provided in each analog input circuit The effect that can be obtained is obtained.

Further, according to the analog input device of the third aspect, when a plurality of analog input circuits having the measuring current supply means are connected in parallel to the sensing element that needs to supply the measuring current. , Insert a switching element in the disconnection detection current supply route of each analog input circuit, turn on only the switching element of one analog input circuit selected by the multiplexing control unit, turn off the switching elements of other analog input circuits By supplying the measured current output from the sensing element to only one selected analog input circuit by setting the state, the analog input equivalent to the case where only one analog input circuit is provided in each analog input circuit The effect that the signal and the disconnection detection signal can be obtained is obtained.

Furthermore, according to the analog input device of the fourth aspect, when a plurality of analog input circuits having the measuring current supply means are connected in parallel to the sensing element which needs to supply the measuring current. , Insert a switching element in the measurement current supply route of each analog input circuit, turn on only the switching element of one analog input circuit selected by the multiplexing control unit, and turn off the switching elements of other analog input circuits. By supplying the measured current output from the sensing element to only one selected analog input circuit by setting the state, the analog input equivalent to the case where only one analog input circuit is provided in each analog input circuit The effect that the signal and the disconnection detection signal can be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional example corresponding to FIG.

5 is a circuit diagram showing a conventional example corresponding to FIG.

FIG. 6 is a circuit diagram showing a conventional example corresponding to FIG.

[Explanation of symbols]

1 Analog input device S Sensing element TC Thermocouple Pt Resistance temperature detector A _{11 to} A ₃₂ Analog input circuit OP _{11 to} OP ₃₂ Operational amplifier CO _{11 to} CO ₃₂ Disconnection detection comparator R _{11 to} R ₃₂ resistance CS _{21 to} CS ₃₂₂ measurement Current source MC dual control unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keizo Teshima 1 Fujimachi, Hino city, Tokyo Fujifacom Control Co., Ltd.

Claims (4)

[Claims] 1. In an analog input device in which a plurality of analog input circuits are connected in parallel to one sensing element and multiplexed, disconnection detection means for detecting disconnection of a measurement system is provided in each of the analog input circuits, and a multiplexing structure. An analog input device, comprising: a switching unit that interrupts a sneak route of a current that sometimes occurs. 2. An analog input device in which a plurality of analog input circuits are connected in parallel to one sensing element that outputs a measurement current and multiplexed, and a disconnection for detecting a disconnection of a measurement system provided in each analog input circuit. A switching element inserted in a route of a sneak current of the measuring current from the detecting means and the sensing element; and a multiplexing control section for controlling only the switching element of one selected analog input circuit to an ON state. An analog input device characterized by. 3. An analog input device in which a plurality of analog input circuits each having a measuring current supply means for supplying a measuring current to the sensing element are connected in parallel to one sensing element and multiplexed. Disconnection detection means for detecting disconnection of the measurement system provided in each of the analog input circuits, a switching element inserted in the disconnection detection current supply route of the disconnection detection means, and the switching element of one selected analog input circuit An analog input device comprising a multiplexing control unit for controlling only the ON state. 4. An analog input device in which a plurality of analog input circuits each having a measuring current supply means for supplying a measuring current to the sensing element are connected in parallel to one sensing element and multiplexed. A disconnection detecting means for detecting a disconnection of a measurement system provided in each analog input circuit, and a switching element inserted in a measurement current supply route and only one switching element of one selected analog input circuit are turned on. An analog input device, comprising: