JP2753592B2 - 2-wire instrument - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention converts a physical quantity to be measured into an electric signal by receiving power from a load side through two transmission lines, and converts the physical quantity into an electric signal by a microprocessor. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wire instrument that performs signal processing and transmits a current signal to a load via a transmission line, and more particularly to a two-wire instrument improved to detect an abnormality in environmental conditions of the two-wire instrument.

<Prior Art> FIG. 8 is a configuration diagram schematically showing a configuration of a conventional so-called two-wire instrument.

The two-wire instrument 10 including the microprocessor receives the current from the load 11 through the input terminals T ₁ and T ₂ through the _two transmission lines l ₁ and l ₂ from the DC power supply 12 and receives a circuit from the current. a physical quantity to be measured with making power as the detected change by which the current signal is transferred to the load 11 in the form of unified unified current I _L of the same transmission line l _1, through l ₂ example 4~20mA .

Of these, the minimum current is 4 mA, but usually, this current is required to operate at about 3.2 mA to 3.6 mA to adjust and check the zero point, and the current consumption of the two-wire instrument 10 is greatly limited. In particular, recently, in order to meet the demand for multi-functionality,
A microcomputer has been introduced into the wire-type instrument 10, and the demand for its power has become strict.

 FIG. 9 shows an example of a specific configuration of the power supply circuit.

The input terminal T _1, T ₂ usually about 10V is supplied as a terminal voltage V _T, the power supply voltage V _C of the microprocessor 14 so 5V, the switching regulator 13 to increase the supply current using this voltage difference Is used.

The switching regulator 13 is the capacitor C ₁ is connected to both ends of the input terminals T _1, T _2, switch SW ₁ and a coil L
Is connected to the power supply circuit of the microprocessor 14 via a series circuit of a _1, at both ends of the coil L ₁ is connected one end of the diode D ₁ and capacitor C _2, respectively, the other end of which, such as the input terminal T ₂ It is connected.

This power supply voltage V _C is detected by the control circuit 15 and compared with a predetermined reference value stored therein.A comparison signal is applied to, for example, an AND gate, and a signal from a built-in oscillator applied to the other end of the AND gate is applied. oN / oFF control of the high oscillation frequency of the frequency comparison signal the switch SW ₁ by the switching signal obtained at the output terminal of the aND gate on /
Control off.

When the switch SW ₁ is closed is current injected into the coil L _1, the next time the switch SW ₁ is opened, during which the coil L ₁
Stored energy power supply voltage V _C is discharged through the diode D ₁ is made.

The power supply voltage V _C of the case can be varied by changing the reference voltage incorporated in the control circuit 15 arbitrarily by changing the closing time of the switch SW _1.

<Problems The present invention is to solve> However, for the unified current I _L and the electron voltage V _T is
For example, the specification of the operation range is 12V ≦ V _T ≦ 45V, 4mA ≦ I _L ≦ 20mA. In particular, it is necessary to prevent abnormal operation even when sufficient power cannot be supplied to the microprocessor 14 as a signal processing circuit such as V _T <12 V and I _L <4 mA.

When the signal processing circuit is composed of only analog circuits such as operational amplifiers, it is relatively easy to reduce the output in such an abnormal condition. (Reset)
If the alarm is not securely executed, there are many opportunities to cause an abnormal operation, and there is a problem that the stability is lacking.

<Means for Solving the Problems> In order to solve the above problems, the present invention converts a physical quantity to be measured into an electric signal by receiving power supply from a load side through two transmission lines. And a switching regulator for converting a level of a terminal voltage generated at both ends of the transmission line to generate a first voltage in a two-wire instrument that performs signal processing by a microprocessor and transmits the current signal to a load via a transmission line. A stabilized power supply circuit for stabilizing a terminal voltage to generate a second voltage, and an initialization signal and an alarm signal which are operated by the second voltage to execute turning on / off / lowering of the terminal voltage and to monitor the first voltage. Self-diagnosis circuit for outputting
It is provided with signal processing means including a microprocessor which operates by voltage and is controlled by an initialization signal and an alarm signal.

<Operation> The switching regulator converts the level of the terminal voltage generated at both ends of the transmission line to generate the first voltage, and stabilizes the terminal voltage with the stabilized power supply circuit to generate the second voltage.

The self-diagnosis circuit operates with the second voltage, performs the turning on / off / lowering of the terminal voltage and monitors the first voltage, and outputs an initialization signal and an alarm signal.

Then, the microprocessor is operated by the first voltage and controlled by the initialization signal and the alarm signal to detect the abnormality of the environmental condition.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. Elements having the same functions as those of the circuits shown in FIGS. 8 and 9 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

Reference numeral 16 denotes a two-wire instrument. The two-wire instrument 16 includes a switching regulator 13, a stabilized power supply circuit 17, and a self-diagnosis circuit.
And a signal processing circuit 19 including a microprocessor. The signal voltage V _S is outputted is detected across the input terminals T ₁ and T transmission line l ₁ which are respectively connected to _2, l ₂ resistors connected in series to R1 in the signal processing circuit 19, where signal processing is output to the output terminal T _O is made.

The switching regulator 13 is the terminal voltage V _T is input, but outputs a circuit voltage V _C as a first voltage which the signal processing circuit 19 and the level conversion, the circuit voltage V _C to the input terminal voltage V _T since the rise is slow addition load current is large, the circuit voltage V _C is stabilized becomes later generally from the regulated power supply circuit 17.

Stabilized power supply circuit 17 is the terminal voltage V _T, and outputs the constant voltage V _K as the second voltage to its output. The stabilized power supply circuit 17 includes a transistor Q1, a resistor R2, a Zener diode D2, and the like. And the terminal voltage _VT is a resistance
R2 and tools is to output a Zener voltage generated at both ends of the is applied to the series circuit Zener diode D2 to the output terminal of the operation corresponding to the constant voltage V _K as a reference with Ena diode D2, the stabilized power supply circuit 17 pin if the voltage V _T to operate as soon as the rise until the voltage that can operate circuit is self-diagnostic circuit a constant voltage V _K
18 can be output.

Although FIG. 1 shows a configuration using a transistor as the stabilized power supply circuit 17, this transistor Q1
Is not always necessary, the resistor R2 and Zener diode D2
Of the voltage across the Zener diode D2 as a serial circuit may be configured to a constant voltage V _K.

The self-diagnosis circuit 18 includes resistors R3, R4, R5, R6, and a capacitor.
A reset signal generation circuit 20 including C3, an inverter Q2 having hysteresis, an R / S flip-flop FF1, a comparator Q3, a reference voltage source E1, etc., and resistors R7, R8, and a reference voltage source E.
2. It is composed of an abnormality detection circuit 21 composed of a comparator Q4 and the like.

 First, the reset signal generation circuit 20 will be described.

A divided voltage obtained by dividing the constant voltage _VK by the resistors R3 and R4 is applied to the input terminal of the inverter Q2. The output terminal of inverter Q2 is R /
It is connected to the set terminal S of the S flip-flop FF1. This reset terminal R is a switching regulator
Is the output circuit voltage divided by the divided voltage of V _C by resistors R5 and R6 non-inverting input terminal (+) to be applied inverting input terminal 13 (-) a comparator reference voltage E1 is applied to the The output terminal of Q3 is connected. Then, the reset signal RS is output to the signal processing circuit 19 from the output terminal Q of the R / S flip-flop FF1.

With the above configuration, when the power is turned on, the R / S flip-flop FF1 is set via the inverter Q2.

On the other hand, the circuit voltage V _C for a while even the rise of the terminal voltage V _T does not become normal voltage, Therefore reset terminal R of the R / S flip-flop FF1 is held at a low level from its output terminal Q Signal processing circuit including microprocessor
The reset signal (initialization signal) RS is continuously supplied to 19.
However, when the circuit voltage V _C exceeds a certain value, for example, a reference voltage E1 corresponding to the lowest voltage at which the signal processing circuit 19 operates, the output of the comparator Q3 is inverted to a high level, and the R / S flip-flop F
The reset terminal R of F1 is set to a high level to release the reset signal RS output from the output terminal Q. Etc. The lowest value of the circuit voltage V _C eg 4.75V is selected. As described above, the microprocessor is securely initialized.

Next, the abnormality detection circuit 21 will be described. Usually, since the switching regulator 13 and the like include a capacitor, even if the external power supply drops, the circuit does not die immediately.

Thus, the abnormality detection circuit 21 detects an abnormal decrease in the voltage of the DC power supply 12 as an external power supply at an early stage, and outputs an alarm signal AL to the signal processing circuit 19. As a value for detecting the abnormal decrease, for example, a minimum specification voltage or the like is selected, and this is set by the reference voltage E2.

When detecting the alarm signal AL, the signal processing circuit 19 saves important parameters or fixes the operation to prevent abnormal operation.

FIG. 2 is a circuit diagram showing a second embodiment of the reset signal generation circuit.

This circuit voltage V _C, for example when it is assumed that immediately after the following if the power is turned 4.75V, in which the detection circuit voltage V _C is configured to serve as a power-on.

The output of comparator Q4 is reset via inverter Q5.
Take out RS. In addition, positive feedback is applied to the comparator Q4 by the resistor R9 in order to have hysteresis.

FIG. 3 is a circuit diagram showing a second embodiment of the reset signal generation circuit.

In this embodiment, the circuit voltage V _C is
Even if it becomes 4.75V or more, it is necessary to continue resetting for more than a fixed time. In such a case, the reset circuit is configured to extend the reset time by a delay circuit.

The reset signal RS is input to one end of the input of the OR circuit Q6, and the delay signal ΔRS delayed by a predetermined time τ by the delay circuit DL is input to the other end, and the OR of these signals is calculated by the OR circuit Q6. The reset signal RS 'obtained at this output terminal
Resets the signal processing circuit 19.

FIG. 4 shows a timing chart in this case. The pulse width of the reset signal RS 'is expanded as shown in (c) by the delay signal ΔRS delayed by the delay time τ shown in (b) with respect to the reset signal RS shown in (a).

FIG. 5 is a circuit diagram showing a second embodiment of the delay circuit DL shown in FIG.

In this case, inverter Q7, resistor R10, capacitor C
4. The delay circuit is composed of the inverter Q8 with hysteresis.

FIG. 6 is a circuit diagram showing a third embodiment of the reset signal generation circuit.

In this case, a case is shown in which an R / S flip-flop FF2, 2η ^{+ 1} counter CT is used.

The reset signal RS is input to the set terminal S of the R / S flip-flop FF2 and to the reset terminal R of the counter CT. On the other hand, the clock signal CLK is input to the clock terminal CL of the counter CT, and the counting is performed by the output terminal _Qη from the R / S
The signal is output to the reset terminal R of the flip-flop FF2, and a delayed reset signal RS 'is output from the output terminal Q.

Reset signal RS rises counted from the low level clock signal CLK to 2 ^eta, and applies the output to the reset terminal R of the R / S flip-flop FF2. As a result, an inverted reset signal RS 'output from its output terminal Q is output.
As a result, the reset of the signal processing circuit 19 is released.

FIG. 7 is a circuit diagram showing another embodiment of the abnormality detection circuit.

This embodiment is configured so that a down signal DWN can be output as an alarm signal when the voltage is much lower than the specification.

The terminal voltage V _T resistors R8, R11, dividing by R12, resistor R8 and R1
The voltage at the connection point with 1 is applied to the inverting input terminal (−) of the comparator Q9 to which the voltage E2 is applied, and the output terminal outputs a down signal DWN to the signal processing circuit 19.

As for the detection of an abnormal signal, when the duty for turning on the switch SW1 of the switching regulator 13 shown in FIG. ₁ exceeds a specified value, the load current is larger than the input current. May be used as an alarm signal.

<Effects of the Invention> As described above in detail with the embodiment, according to the present invention, the self-diagnosis circuit operates at the second voltage which rises faster than the microprocessor, so that the initialization is surely performed when the power is turned on. In addition, since a decrease in the external power supply and a power failure are detected, measures to prevent abnormal operation can be easily performed on the microprocessor side. Furthermore, since the second voltage is composed of a simple stabilized power supply, the power utilization rate is low, but this is used only by the self-diagnosis circuit.
Since the signal processing circuit uses the first voltage of the switching regulator, power can be effectively used as a whole, and the power of important circuits in a two-wire instrument can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of one embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of a reset signal generation circuit, and FIG. 3 is a second embodiment of a reset signal generation circuit. FIG. 4 is a timing chart for explaining the operation of the circuit shown in FIG. 3, FIG. 5 is a circuit diagram showing a second embodiment of the delay circuit shown in FIG. 3, and FIG. 6 is a reset circuit. FIG. 7 is a circuit diagram showing a third embodiment of the signal generation circuit, FIG. 7 is a circuit diagram showing another embodiment of the abnormality detection circuit, FIG. 8 is a configuration diagram showing an outline of the configuration of a conventional two-wire instrument, FIG. 9 is a block diagram showing one example of a specific configuration of the power supply circuit shown in FIG. 10, 16 ... 2-wire instrument, 11 ... load, 12 ... DC power supply,
13 Switching regulator, 14 Microprocessor, 17 Stabilized power supply circuit, 18 Self-diagnosis circuit,
19: Signal processing circuit, 20: Reset signal generation circuit, 21
…… Abnormality detection circuit.

Claims (1)

(57) [Claims] 1. A power supply is supplied from a load side via two transmission lines to convert a physical quantity to be measured into an electric signal, which is subjected to signal processing by a microprocessor, and the electric signal is processed by a microprocessor. And a switching regulator for converting a level of a terminal voltage generated at both ends of the transmission line to generate a first voltage, and a stabilization for stabilizing the terminal voltage to generate a second voltage. A power supply circuit, a self-diagnosis circuit that operates with the second voltage, performs on / off / stop of the terminal voltage, monitors the first voltage, and outputs an initialization signal and an alarm signal; A two-wire instrument comprising signal processing means including a microprocessor operated by voltage and controlled by the initialization signal and the alarm signal.