JPH0625073Y2 - 2-wire signal transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention converts a physical quantity such as pressure or temperature detected by a sensor or the like into a digital signal and executes a predetermined calculation using a microprocessor to perform analog calculation. Convert to a signal and transmit this signal to the load via the two transmission lines 2
The present invention relates to a wire type signal transmitter.

<Prior Art> FIG. 3 is a block diagram showing the overall configuration of a conventional two-wire signal transmitter.

Reference numeral 10 is a sensor that converts pressure or the like into an analog electric signal. The analog signal of the sensor 10 is converted into a digital signal by the analog / digital converter 11 and input to the microprocessor 12. Microprocessor 12
Stores a digital signal read in accordance with a predetermined calculation program stored in the memory 13 in the memory 13 and takes out the data stored in the memory 13 as necessary to execute a predetermined calculation such as linearization.

The calculation result is displayed on the display 14 and is output to the pulse width / current conversion circuit 15. The pulse width / current conversion circuit 15 converts the pulse width signal PWM sent from the microprocessor 12 into a predetermined current signal and outputs it to the output circuit 16. The output circuit 16 is connected to the terminals T ₁ and T ₂ from the external power source E _L which is connected in series to the load R _L.
The current from the pulse width / current conversion circuit 15 is received in the range of 4 to 20 m while receiving the current supply via the transmission lines l ₁ and l _{2 of the} line.
The output current I _{L of A} is converted and transmitted to the load R _L.

Further, from the output circuit 16, the feedback voltage V _f proportional to the output current I _L is pulse width / pulse for stabilizing the circuit.
It is negatively fed back to the current conversion circuit 15.

These pulse width / current conversion circuit 15 and output circuit 16 constitute an analog signal converter 17.

In addition to this, a constant voltage circuit 18 is connected to the output circuit 16, and the constant voltage circuit 18 uses a part of the output current I _L to supply a constant voltage power source for use inside the two-wire signal transmitter. Make V _cc .

Further, the microprocessor 12 outputs a stop signal V _sT indicating whether or not the operation is stopped due to an abnormality to the pulse width / current conversion circuit 15, and the burnout circuit 19 outputs from the pulse width / current conversion circuit 15. A signal based on this stop signal V _sT is received, and a swing-off signal V _bT that causes the output current I _L to swing off in a predetermined direction is output to the pulse width / current conversion circuit 15 again.

When the pulse width / current converting circuit 15 receives the image blur signal V _bT, issued burnout output corresponding to the image blur signal V _bT, to burn out the output current I _L to a predetermined value.

FIG. 4 is a circuit diagram showing details of the analog signal converter shown in FIG.

The pulse width / current converter 15 includes a level conversion circuit 20, an integration circuit 21, and a driver circuit 22.

The level conversion circuit 20 has a pulse width signal P whose peak value output from the microprocessor 12 is between 0V and 5V and whose pulse width changes in accordance with the physical quantity from the sensor 10.
It is a circuit that converts WM into a pulse width signal having a specified peak value.

The power supply voltage _{V cc} applied to the terminal 1 and terminal 2 of the resistor _{R 1, R 2, R 3} , respectively voltages at _{R 4 E 1} and _{E 2} second analog configured in minutes pressurized with e.g. IC switch _{SW 11} It The common terminal 3 is connected to the connection point P ₁ via the switch SW ₁₃ .

Terminal In addition to the power supply voltage _{V cc} is applied ¹ -, 2
^- a common terminal 3 for switching this etc. ^- switch with S
W ₁₂ is added. The common terminal 3 ⁻ of the switch SW ₁₂ is output to the burnout circuit 19 via the switch SW ₁₄ .

The switches SW ₁₁ and SW ₁₂ are the microprocessor 12
Via the terminal A by the pulse width signal PWM from the terminal 1,1 ^- switched respectively to the side ^- side and the terminal 2,2.
As a result, the common terminal 3 of the switch SW ₁₁ is switched between the terminal 1 and the terminal 2 in accordance with the pulse width of the pulse width signal PWM, so that the common terminal 3 has the same pulse width as the pulse width of the pulse width signal PWM. Then, the pulse width signal PWM ₁ converted from is generated. This pulse width signal PWM ₁ is output to the connection point P ₁ via the switch SW ₁₃ . The switch _{SW 12} is the common terminal 3 be switched by a pulse width signal PWM ^- power supply voltage _{V cc} appears at the.
Further, the switches SW ₁₃ and SW ₁₄ are opened / closed via the terminal INH by the stop signal V _sT from the microprocessor 12.

In the integrating circuit 21, a negative feedback is applied from the output end of the resistor R ₇ via the filter composed of the resistors R ₅ and R ₆ and the capacitor C ₁ and the resistor R ₇ is applied from the output end thereof.
The pulse width signal P from the connection point P ₁ is fed to the operational amplifier Q ₁ which is fed back by the capacitor C ₂ to the connection point between ₅ and R _6.
WM ₁ is input and this pulse width signal PW is output at its output end.
A DC voltage E ₃ corresponding to M ₁ is obtained. This DC voltage E ₃
Is output to the next driver circuit 22.

The driver circuit 22 is configured as follows.

DC voltage _{E 3} is input via a resistor _{R 8} to the non-inverting input of operational amplifier _{Q 2} (+), an inverting input terminal (-) partial pressure power supply voltage _{V cc} by the resistors _{R 9} and _{R 10} are the The applied voltage is applied. The output terminal is connected to the inverting input terminal (−) by the capacitor C ₃ and also connected to the transistor of the output circuit 16 via the resistor R ₁₁ . Output circuit 16
, A negative feedback is applied to the operational amplifier Q ₂ via the resistor R ₁₂ .

With such a configuration, the driver circuit 22 converts the current into a current having an appropriate magnitude for driving the transistor Q ₃ of the next output circuit 16.

The collector of the transistor Q ₃ of the output circuit 16 is connected to the positive electrode of the external power supply E _L via the transmission line l ₁ and the diode D ₁ .
Also its emitter load from the negative electrode of the external power source E _L R _L,
Transmission line l ₂ , feedback resistance R _f , resistance R ₁₂ , diode D
₂ and a resistor R ₁₃ respectively. The diode D ₂ is for biasing the transistor Q ₃ . Further, Zener diodes D _{3 and} D ₄ for preventing overvoltage are connected in parallel between the collector of the transistor Q ₃ and the connection point of the diode D ₂ and the feedback resistor R _f .

Capacitors C ₄ and C ₅ are connected between the terminals T ₁ and T ₂ and the ground E, respectively, for the purpose of removing noise that enters from the outside.

In the above configuration, the base of the transistor Q ₃ are flowed output current of the operational amplifier Q ₂ is, output current I _L flows between its collector and emitter in response thereto. The output current _{I L} is converted into a feedback voltage _{V f} in the feedback resistor _{R f,} the feedback voltage _{V f, the} power supply voltage _{V cc} and the DC voltage _{E 3} of the sum voltage feedback resistor _{R f,} resistor _{R 12,} the resistor R
₁₄ and the voltage divided by the resistor R ₈ is negatively fed back to the operational amplifier Q _{2 at} its input end.

As a result, the circuit in this loop is stabilized, and the output current I _L corresponding to the DC voltage E ₃ can be passed through the load R _L.

Next, the detailed contents of the burnout circuit 19 will be described.

SW ₂ is an analog switch made of an integrated circuit (IC), inside of which a switch SW ₂₁ having terminals 1 and 2 and a common terminal 3 and a switch SW ₂₂ having terminals 4 and 5 are connected in series. ing. Power supply voltage _{V cc} to the terminal 1 of the switch _{SW 21} is, the terminal 2 is connected to a fixed potential point FV. The switch SW ₂₁ is a switch SW ₃ that determines the direction of burnout applied to the terminal A.
It is switched by a high level / low level (H / L) binary signal from.

One terminal 4 of the switch SW ₂₂ is connected to the switch SW ₂₁
, And the other terminal 5 is connected to the connection point P ₁ via the resistor R ₁₅ and connected to the cut-off signal V _bT.
Is output. The switch SW ₂₂ is opened / closed by a voltage applied to the terminal INH from the charging / discharging circuit CG composed of a parallel circuit of the resistor R ₁₆ and the capacitor C ₆ .

The charging / discharging circuit CG has a level conversion circuit 20 for which the stop signal V
_The switch SW ₁₄ is turned on by _sT to be charged by the output power supply voltage V _cc , and the switch SW ₁₄ is turned off by the stop signal V _sT, whereby the resistor R ₁₆ is turned on.
Then, the electric charge charged in the capacitor C ₆ is discharged.

Next, the operation of the embodiment shown in FIG. 4 configured as above will be described.

First, a state in which the microprocessor 12 is operating normally will be described.

In this case, if the stop signal V _sT from the microprocessor 12 is set to the low level L, the switch SW ₁ becomes the enable state (conduction state) because the INH terminal is at the L level during the normal operation. .

On the other hand, the switch SW ₂ is in the inhibit state (open state) because the power source voltage V _cc is applied to the charge / discharge circuit CG by the conduction of the switch SW ₁ to charge the capacitor C ₆ and its INH terminal becomes the high level H. The burnout circuit 19 is practically disconnected.

Therefore, in this state, the switch SW ₁₁ is opened and closed by the pulse width signal PWM having the levels of 0 V and 5 V output from the microprocessor 12, and the pulse width signal P
The pulse width signal PWM ₁ converted to a predetermined level with the same pulse width as WM is output to the integrating circuit 21 of the next stage, and then the output current corresponding to the output of the sensor 10 via the driver circuit 22 and the output circuit 16. Is output to the load R _L ,
Do the original operation.

Next, a case where the microprocessor 12 is stopped will be described.

When the microprocessor 12 stops its operation, the stop signal V _sT becomes the high level H, so that the INH terminal of the switch SW ₁ becomes H and becomes the inhibit state, and the switches SW ₁₃ and SW ₁₄ are turned off. As a result, the level conversion circuit 20 is practically disconnected.

On the other hand, when the level conversion circuit 20 is disconnected from the switch SW _2, the electric charge stored in the capacitor C ₆ is discharged through the resistor R _{16, and} thus the switch SW ₂ is released.
The inhibit terminal INH of No. ₂ gradually falls from the high level H state to the low level L state, and the switch SW ₂₂ becomes the enable state when the threshold level is crossed. That is, substantially only the burnout circuit 19 is connected to the connection point P ₁ .

In this state, the integrating circuit 21 outputs the upper limit voltage or the lower limit voltage to output the output current of the driver circuit 22 depending on whether the connection point P ₁ is pulled up or pulled down via the resistor R _15. The output current I _L of the output circuit 16 is controlled to be burnt out to the upper limit or the lower limit. In this case, whether the connection point P ₁ is pulled up or pulled down is determined by the upper / lower limit setting switch S.
Or switch the W ₃ to _the power supply voltage _{V cc} side, fixed potential point FV
Select depending on whether to switch to the side.

<Problems to be solved by the invention> By the way, a DC voltage obtained by rectifying a commercial power source is often used as the external power source of such a conventional two-wire signal transmitter, and such an external power source may be unexpected. Microprocessor malfunction due to power outage or voltage drop of external power supply,
Alternatively, there is a case where the voltage of the external power supply becomes a voltage equal to or lower than the specified value because it takes time from when the power switch is turned on until the voltage is actually established as the specified voltage.

In such a case, the constant voltage circuit does not operate normally and the contents of the memory are destroyed.

Therefore, a power supply monitoring circuit that monitors the voltage of this external power supply is provided, and when the voltage drops below a predetermined voltage, an operation stop signal is output to the microprocessor to stop the operation and set the sleep state and the contents of the memory. Hold
The burnout circuit is operated to forcibly burn out the output current to the lower limit value or the upper limit value by the analog signal converter.

In this case, when the output current is burnt out to the upper limit side, no individual problem occurs, but when the output current is burnt out to the lower limit side, hunting occurs because of the following reasons.

For example, when the input voltage of the power supply monitoring circuit that monitors the power supply voltage at the output end of the analog signal converter falls below a predetermined value due to the voltage drop of the external power supply, this power supply monitoring circuit causes the microprocessor to stop its operation. Output a control signal to stop the operation of the microprocessor. At this time, the burnout circuit operates so as to output the output current to the lower limit side, the voltage drop in the load decreases and the voltage at the output end of the analog signal converter increases.

The power supply monitoring circuit outputs a control signal for starting the operation of the microprocessor to the microprocessor when the input voltage of the power supply monitoring circuit exceeds a predetermined value. By this control signal, when the microprocessor operates, the burnout circuit is opened, and the output current increases to the normal value, so that the voltage drop in the load increases and thus the output voltage of the analog signal converter decreases.

Then, when the input voltage of the power supply monitoring circuit drops again to a predetermined value, a control signal for stopping the operation is output to the microprocessor to stop the operation of the microprocessor. Hunting occurs by repeating the above state.

<Means for Solving the Problems> In order to solve the above problems, the present invention receives a current supply from a load side through two transmission lines and converts a physical quantity into a digital signal by an analog / digital conversion means. A two-wire signal transmitter for converting and using the digital signal, a microprocessor to perform a predetermined operation, converting the result to an analog signal by an analog signal converting means, and transmitting an output current to a load through a transmission line. In the above, the burnout means for outputting the cut-off signal for cutting off the output current to the 0% side or the 100% side based on the stop signal from the microprocessor to the analog conversion means, and the output voltage of the analog conversion means are inputted. When a control signal for instructing the microprocessor to start operation is output when the output voltage rises above the first predetermined value and falls below the second predetermined value A constant is selected such that a control signal for instructing the microprocessor to stop operation is output and the difference between the first predetermined value and the second predetermined value is larger than the voltage fluctuation value of the output voltage due to the operation of the burnout means. A power supply monitoring means is provided.

<Operation> The input voltage of the power supply monitoring circuit that monitors the power supply voltage at the output end of the analog signal converter due to the decrease in the voltage of the external power supply has the second input voltage.
When the voltage falls below a predetermined value, the power supply monitoring circuit outputs a control signal for stopping the operation of the microprocessor to stop the operation of the microprocessor. At this time, the burnout circuit operates so as to output the output current to the lower limit side, so that the voltage drop in the load decreases and the voltage at the output end of the analog signal converter increases.

If the input voltage of the power supply monitoring circuit exceeds the second predetermined value,
The power supply monitoring circuit outputs to the microprocessor a control signal for starting the operation of the microprocessor when the value exceeds the first predetermined value which is larger than the predetermined value. By this control signal, when the microprocessor operates, the burnout circuit is opened, and the output current increases to the normal value, so that the voltage drop in the load increases and thus the output voltage of the analog signal converter decreases.

In these operations, hunting is performed because the circuit constants are selected so that the difference between the first predetermined value and the second predetermined value in the power supply monitoring means becomes larger than the voltage fluctuation value of the output voltage due to the operation of the burnout means. To be prevented.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the overall construction of an embodiment of the present invention. The parts having the same functions as those of the conventional two-wire type signal transmitter shown in FIGS. 3 and 4 are designated by the same reference numerals and the description thereof will be appropriately omitted.

Sensor 10, analog / digital converter 11, microprocessor 12, memory 13, display 14, pulse width /
Current converter 15, output circuit 16, analog signal converter 1
7, the constant voltage circuit 18, the burnout circuit 19, the external power supply E _L , the load R _L, etc. are the same as the circuit shown in FIG.

In FIG. 1, a power supply monitoring circuit 23 is added in addition to this.

The power supply monitoring circuit 23 has output terminals T ₁ and T ₁ of the output circuit 16.
₂ has a hysteresis in which the voltage level when the power supply voltage V _d1 associated with the output voltage of ₂ rises differs from that when the power supply voltage V _d1 decreases. Based on these voltage levels, a control signal V for instructing the start or stop of the operation is provided. _cT is output to the microprocessor 12.

When the power supply voltage V _d1 is lower than the second predetermined value, the microprocessor 1 outputs a binary control signal V _cT that stops the operation.
Output to 2. When receiving the control signal V _cT , the microprocessor 12 holds the contents of the memory 13 and _{puts the} microprocessor 12 into the sleep state to stop the operation and outputs the stop signal V _sT to the pulse width / current converter 15.

The pulse width / current converter 15 outputs the cutoff signal V according to the upper limit value or the lower limit value set by the burnout circuit 19.
_bT is output to the pulse width / current converter 15 to burn out the output current I _L in a predetermined direction.

As a result, a voltage fluctuation occurs in the load R _L and the power supply voltage V _d1
Fluctuates. Variation width of this power supply voltage (ΔI _L · R _L )
If the circuit constants are selected so that is smaller than the preset hysteresis width ΔH, then the microprocessor 12 starts operating at the first predetermined value even if the power supply voltage V _d1 rises, and the burnout circuit Is not affected by the fluctuation of the output current due to the operation of.

FIG. 2 is a circuit diagram showing the power supply monitoring circuit shown in FIG. 1 and a detailed circuit of a portion related thereto.

Supply voltage V applied to the collector of the transistor Q _{3
The voltage d1} is _divided by the resistors R ₁₇ and R ₁₈ . The divided voltage V _d2 is applied to one end of the input of the comparator Q ₄ and the reference voltage E _s is applied to the other end of the comparator Q ₄ , and the output voltage obtained by comparing these is applied to the gate of the transistor Q _5. To be done.

Further, the power supply voltage V _cc is _divided by a resistor R ₁₉ connected in parallel with the diode D ₅ and a capacitor C ₇ and output as a control voltage V _cT to the microprocessor 12, and the control voltage V _cT is a transistor. It is applied between the drain and source of Q ₅ .

The series circuit of the resistor R ₂₀ and the transistor Q ₆ has a resistor R ₁₇
And a control voltage V _cT is applied to the base of the transistor Q ₆ .

Next, the operation of the power supply monitoring circuit 23 configured as above will be described.

First, a state in which the microprocessor 12 is operating normally will be described.

In this case, since the divided voltage V _d2 is in the high level state, the transistor Q ₅ is off, and therefore the control voltage V _cT is in the high level. This high-level control voltage V _cT is transmitted to the microprocessor 12 and the microprocessor 12 is kept in the activated state.

When the stop signal V _sT from the microprocessor 12 is set to the low level L in this starting state, the INH terminal of the switch SW ₁ of the level conversion circuit 20 is set to the L level during normal operation, so that the enable state ( It becomes conductive).

On the other hand, the switch SW ₂ is in the inhibit state (open state) because the power source voltage V _cc is applied to the charge / discharge circuit CG by the conduction of the switch SW ₁ to charge the capacitor C ₆ and its INH terminal becomes the high level H. The burnout circuit 19 is practically disconnected.

Therefore, in the normal state, the pulse width signal PWM output from the microprocessor 12 is level-converted by the level conversion circuit 20, and the output current I _L is supplied to the load R _L by the same operation as in the conventional case.

Next, a case will be described in which the power supply voltage V _d1 has dropped from this normal state due to, for example, an unexpected power failure.

Now, when the power supply voltage V _d1 drops and the _divided voltage V _d2 drops below the reference voltage E _s , the transistor Q ₅ turns on, the control voltage V _cT turns to a low level, and the transistor Q ₆ turns off and the resistance is lowered. R ₂₀ is disconnected from resistor R ₁₇ . The low level control voltage V _cT stops the operation of the microprocessor 12.

The relationship between the reference voltage E _s and the power supply voltage V _d1 at this time is V _d1 = E _s (R _c + R ₁₈ ) / R ₁₈ if R _c = R ₁₇ R ₂₀ / (R ₁₇ + R ₂₀ ). (1)

On the other hand, when the operation of the microprocessor 12 is stopped, the microprocessor 12 sets the stop signal V _sT to the high level H to turn off the switch SW _1, and the burnout circuit 19
Sends a swing-off signal V _bT to the integrating circuit 21 to _swing the output current I _L in the direction set by the switch SW ₃ .
In this case, the case of setting to the lower limit side will be described.

Then, due to the decrease of the output current I _L , the power supply voltage V _d1
Rises, the transistor Q ₅ turns off, and the control voltage V
_{When cT} becomes high level, the transistor Q ₆ is turned on and the resistor R ₂₀ is connected in parallel with the resistor R ₁₇ .
The high-level control voltage V _cT starts the operation of the microprocessor 12.

The relationship between the reference voltage E _s and the power supply voltage V _d1 at this time is V _d1− = E _s (R ₁₇ + R ₁₈ ) / R ₁₈ (2).

_Here, - keep selected ^(V _{d1 -V} d1) greater circuit constant than the variation value [Delta] V _d1 of the supply voltage _{V d1} hysteresis width ΔH by the operation of the burn-out circuit 19.

On the other hand, the microprocessor 12 by the start of operation of the microprocessor 12 increases the output current _{I L} switch SW ₁ the stop signal _{V sT} as low level L on, turns off the switch SW _2, the output current _{I L} The increase causes the power supply voltage V _d1 to decrease by ΔV _d1 . However, since the circuit constants are selected so that the hysteresis width ΔH is larger than the fluctuation value ΔV _d1, there is no concern of stopping the operation of the microprocessor 12 again.

Therefore, never circuit causes hunting be set switch SW ₃ to the lower side.

In the embodiment shown in FIG. 2, the microprocessor 1
The stop signal V _sT from 2 is the pulse width / current conversion circuit 15
The switch SW ₁₃ and the switch SW ₁₄ are switched by inputting the stop signal V _sT to the burnout circuit 19 to store the switch SW ₁₄ in the burnout circuit 19. It may be done.

Further, in the embodiment shown in FIG. 2, the switching signal V _bT is input to the connection point P ₁ , but the present invention is not limited to this, and the output terminal of the integrating circuit 21 or the output terminal of the driver circuit 22 (the output circuit 16 It operates in the same way even when it is output to the input end of.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, even when the power supply is momentarily interrupted and the microprocessor is stopped and the output current is burned out to the lower limit side, the power supply monitoring circuit is provided. The circuit does not cause hunting because it has hysteresis.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the overall configuration of one embodiment of the present invention, and FIG. 2 is a circuit showing the detailed configuration of the power supply monitoring circuit shown in FIG. 1 and its related portions. FIG. 3 is a block diagram showing the overall configuration of a conventional two-wire signal transmitter, and FIG. 4 is a circuit diagram showing the detailed configuration of the analog signal converter shown in FIG. 3 and circuits related thereto. is there. 10 ... Sensor, 11 ... Analog / digital converter, 12
… Microprocessor, 13… Memory, 14… Display,
15 ... Pulse width / current conversion circuit, 16 ... Output circuit, 17
... analog signal converter, 18 ... constant voltage circuit, 19 ... burnout circuit, 20 ... level conversion circuit, 21 ... integration circuit, 22 ... driver circuit, 23 ... power supply monitoring circuit, PWM
... pulse width signal, V _{sT ...} stop signal, V _{bT ...} image blur signal, V _{cT ...} control signal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Kimura 2-9-32 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd. (56) 61-12599 (JP, B2)

Claims (1)

[Scope of utility model registration request] 1. A current is supplied from a load side through two transmission lines, and a physical quantity is converted into a digital signal by an analog / digital conversion means, and a predetermined calculation is executed by a microprocessor using the digital signal. In the two-wire type signal transmitter which converts the result into an analog signal by the analog signal converting means and transmits the output current to the load through the transmission line, the output current is changed based on the stop signal from the microprocessor. Burnout means for outputting to the analog conversion means a cut-off signal for turning off to 0% side or 100% side, and when the output voltage of the analog conversion means is input and the output voltage rises above a first predetermined value. A control signal for instructing the microprocessor to start operation is output, and when the control signal falls below a second predetermined value, the microprocessor is stopped. And a power supply monitoring means in which a constant is selected such that the difference between the first predetermined value and the second predetermined value is larger than the voltage fluctuation value of the output voltage due to the operation of the burnout means. Two-wire signal transmitter characterized by comprising