JPH03212799A - Two-wire type gauge - Google Patents

Abstract

PURPOSE:To easily detect abnormality by driving a built-in self-diagnostic circuit by the 2nd voltage to be raised fasted than a processor in the two-wire type gauge for converting a physical value to be measured into an electric signal, processing the electric signal by a microprocessor and transmitting the processed signal to a load as a current signal through two transmission lines. CONSTITUTION:The level of a terminal voltage generated between both the ends of two transmission lines l1, l2 is converted by a switching regulator 13 built in the two-wire type gauge 16 to form the 1st voltage and the terminal voltage is stabilized by a regulated power supply circuit 17 to form the 2nd voltage. The self-diagnostic circuit 18 including a reset signal generating circuit 20 and an abnormality detecting circuit 21 is driven by the 2nd voltage to execute the ON, stop and reduction of the terminal voltage, the monitor of the 1st voltage and the output of an initializing signal and an alarm signal. Thus, counterplan for abnormal operation can easily be executed by detecting the abnormality of an environment condition by the microprocessor 14 connected to the regulator 13.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention receives power from the load side via a two-wire transmission line, converts a physical quantity to be measured into an electrical signal, and converts this into an electrical signal using a microprocessor. The present invention relates to a two-wire meter that processes signals and transmits them as a current signal to a load via a transmission line, and particularly relates to a two-wire meter that has been improved to detect abnormalities in the environmental conditions of the two-wire meter.

<Prior Art> FIG. 8 is a block diagram showing an outline of the structure of a conventional so-called two-wire meter.

A two-wire instrument 10 including a microprocessor is connected to a load 11
The two-wire transmission line J2+, 12 is connected by the DC power supply 12 from the side.
A current is supplied through the input terminals T+ and T2, and this current is used to generate a circuit power supply, and the physical quantity to be measured is detected and converted into a change in the current signal through the same transmission line I+ and 12, for example, 4. It is transmitted to the load 11 in the form of a uniform unified current IL of ~20 mA.

Among these, the minimum current is 4 mA, but normally this current is required to operate at around 3.2 mA to 3.6 mA for zero point adjustment and confirmation, and there is a limit on the current consumption in the two-wire meter 10. big. In particular, recently, a microcomputer has been introduced into the two-wire meter 10 in order to meet the demand for multi-functionality, and the requirements for its power have become stricter.

An example of a specific configuration of the power supply circuit is shown in FIG.

Input terminals T1 and T2 are normally 10V as 7 terminal voltages.
level is supplied, and the power supply voltage V of the microprocessor 14
Since c is 5V, the switching regulator 13 is used to increase the supplied current by utilizing this voltage difference.

The switching regulator 13 has its input terminals T1, T
A capacitor C1 is connected to both ends of the switch SW,
The coil is connected to the power supply circuit of the microprocessor 14 through a series circuit with the coil, and one end of a diode D and a capacitor C2 are connected to both ends of the coil, and the other end of these is connected to the input terminal T2. It is connected to the.

This power supply voltage vc is detected by the control circuit 15 and compared with a predetermined built-in reference value, and a comparison signal is applied to, for example, an AND gate, and a frequency signal from a built-in oscillator that is applied to the other end of the AND gate is applied. The high oscillation frequency of is controlled on/off by the comparison signal, and the switch SW1 is controlled on/off by the switching signal obtained at the output terminal of this AND gate.

When the switch SW1 is closed, a current is injected into the coil L1, and when the switch SW is then opened, the energy stored in the coil during this time is released through the diode D1 to create the power supply voltage vc.

The power supply voltage Vc in this case can be arbitrarily changed by changing the reference voltage built into the control circuit 15 and changing the opening/closing time of the switch SW1.

Problems to be Solved by the Present Invention> However, regarding the terminal voltage 7 and the unified current I, for example, 12V≦V, ≦45V, 4mA≦work≦20m
Although it is a specification of an operating range such as A, it is required that no abnormal operation occurs even if the operating range is outside this range. In particular, V.T.
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 <12 V and I 1 <4 mA.

When a signal processing circuit consists of only analog circuits such as operational amplifiers, it is relatively easy to reduce the output in the event of an abnormality like this, but when a microprocessor is used as a signal processing circuit, it is difficult to initialize the circuit. If (reset) and alarms are not reliably executed, there will be a problem of increased chances of abnormal operation and lack of stability.

Means for Solving the Problems> In order to solve the above problems, the present invention provides two solutions from the load side.
Receiving power supply through line transmission line? l! In a two-wire meter that converts the physical quantity to be determined into an electrical signal, processes the signal using a microprocessor, and transmits it as a current signal to the load via a transmission line, the terminal voltage generated at both ends of the transmission line is measured. A switching regulator that converts the level and creates a first voltage, a stabilizing power supply circuit that stabilizes one terminal voltage and creates a second voltage, and a stabilizing power supply circuit that operates based on this second voltage and turns on, stops, and lowers the terminal voltage and the first voltage. and a signal processing means including a microprocessor operated by the first voltage and controlled by the initialization signal and the alarm signal. This is what I did.

Function> A switching regulator converts the level of the terminal voltage generated at both ends of the transmission line to create a first voltage, and a stabilizing power supply circuit stabilizes the terminal voltage to create a second voltage.

The self-diagnosis circuit is operated by this second voltage, turns on, stops, and lowers the terminal voltage, monitors the first voltage, and outputs an initialization signal and an alarm signal.

The microprocessor is operated by the first voltage and controlled by the initialization signal and the alarm signal to detect abnormal environmental conditions.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. Note that elements having the same functions as the circuits shown in FIGS. 8 and 9 are designated by the same reference numerals, and their explanations will be omitted as appropriate.

Reference numeral 16 denotes a two-wire meter, and the two-wire meter 16 includes a switching regulator 13, a stabilized power supply circuit 17, a self-diagnosis circuit 18, a signal processing circuit 19 including a microprocessor, and the like. The signal voltage Vs is applied to the input terminal T.

Signal processing diagram #
The signal is output to r19, where it undergoes signal processing and is output to output terminal T0.

The switching regulator 13 receives the terminal voltage vT, converts the level of this, and outputs the circuit voltage Vc as a first voltage to one signal processing circuit, but the rise of the circuit voltage Vc is slow with respect to the input of the terminal voltage VT. Moreover, since the load current is large, the circuit voltage (2) c generally becomes stable after the stabilized power supply circuit 17.

The stabilized power supply circuit 17 receives the terminal voltage ■T as input, and outputs a constant voltage ■k as a second voltage to its output terminal. This stabilized power supply circuit 17 includes a transistor Q1, a resistor R2, a Zener diode D2, and the like. Then, the terminal voltage vT is applied to the series circuit of the resistor R2 and the Zener diode D2, and the Zener diode D2 operates based on the Zener voltage generated across the terminals, and outputs the corresponding constant voltage vK to the output terminal. The constant voltage power supply circuit 17 operates immediately when the terminal voltage V rises to a voltage at which the circuit can operate, and can output a constant voltage to the self-diagnosis circuit 18.

In addition, in FIG. 1, the configuration is explained in which a transistor is used as the stabilized power supply circuit 17, but this transistor Q
1 is not necessarily necessary, and a series circuit of a resistor R2 and a Zener diode D2 may be used, and the voltage across the Zener diode D2 may be set to a constant voltage Vk.

The self-diagnosis circuit 18 includes resistors R3, R4, R5, R6, a capacitor C3, and inverters Q2 and R6 with hysteresis.
/S flip-flop FF1, comparator Q3, reference voltage source E1, etc., and a reset signal generating circuit 20, resistors R7, R8, reference voltage source E2, comparator Q4, etc., and an abnormality detection circuit 21, etc. It is configured.

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

A divided voltage obtained by dividing the constant voltage vK by resistors R3 and R4 is applied to the input terminal of the inverter Q2. The output terminal of the inverter Q2 is connected to the set terminal S of the R/S flip-flop 1FF1. This reset terminal R connects the circuit voltage Vc, which is the output of the switching regulator 13, to the resistor R5.
The divided voltage divided by and R6 is applied to the non-inverting input @(+), and the output terminal of the comparator Q3 to which the reference voltage E1 is applied is connected to the inverting input terminal (-). And R/S
Reset signal R from output terminal Q of flip-flop FFI
3 is output to the signal processing circuit 19.

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 c does not become a normal voltage for a while even if the terminal voltage vT rises, so the reset terminal R of the R/S flip-flop 1FFI is held at a low level and the output terminal Q is connected to the microprocessor. The reset signal (initialization signal) R8 continues to be applied to the signal processing circuit 19 including the. However, the circuit voltage VC has a certain value, for example, the reference voltage E corresponding to the lowest voltage at which the signal processing diagram B19 operates.
When it exceeds 1, the output of comparator Q3 is inverted to high level and R
The reset terminal R of the /S flip-flop FFI is set to high level, and the reset signal R5 outputted to its output terminal Q is released. For example, 4.75V is selected as the lowest value of this circuit voltage VC. As described above, the microprocessor is reliably initialized.

Next, the abnormality detection circuit 21 will be explained. Normally, the switching regulator 13 and the like include a capacitor, so even if the external power supply drops, the circuit will not die immediately.

Therefore, this abnormality detection circuit 21 detects an abnormal drop in the voltage of the DC power supply 12 as an external power supply at an early stage and sends an alarm signal A.
Output L to one signal processing circuit.

As a value for detecting this abnormal drop, for example, a specified minimum voltage is selected, and this is set by the reference voltage E2.

When the signal processing circuit 19 detects this alarm signal AL, it 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 generating circuit.

This is configured so that if the circuit voltage Vc is, for example, 4.75 V or less, it is assumed that the power has just been turned on, and the detection of the circuit voltage c also serves as the power-on.

A reset signal R3 is taken out from the output of the comparator Q4 via an inverter Q5. Note that positive feedback is applied to the comparator Q4 through a resistor R9 to provide hysteresis.

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

In this embodiment, even if the circuit voltage Vc becomes 4.75V or more, it is necessary to continue resetting the microprocessor for a certain period of time or more. In such a case, a delay circuit is used to lengthen the reset time.

The reset signal R8 is input to one end of the input of the OR circuit Q6, and the delayed signal ΔR3 delayed by a predetermined time τ by a delay circuit is input to the other end, and the OR circuit of these signals is operated in the OR circuit Q6. One signal processing circuit is reset by the reset signal R3- obtained at the output terminal of the lever.

A timing diagram in this case is shown in FIG. The pulse width of the reset signal R3- is expanded as shown in (c) by the delay signal ΔR3 which is delayed by the delay time τ shown in (b) with respect to the reset signal R3 shown in (a).

FIG. 5 is a circuit diagram showing a second embodiment of the delay circuit DL shown in FIG. 3.

In this case, a delay circuit is configured by an inverter Q7, a resistor RIO, a capacitor C4, and an inverter Q8 with hysteresis.

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

In this case, R/S flip-flop FF2.2n+1
A case is shown in which a counter CT is used.

The reset signal R3 is input to the set terminal S of the R/S flip frog F■P2 and reset #! of the counter CT. input to R. On the other hand, the tally clock signal CLK is input to the clock f@CL of the counter CT, the counting result is output from the output terminal Qπ to the reset terminal R of the R/S flip-flop FF2, and the delayed reset signal is output from the output terminal Q. SjjS- is output.

After the reset signal R3 becomes low level, the tarlock signal CLK is counted 2n and rises, and its output is applied to the reset terminal R of the R/S flip-flop FF2. As a result, the reset of the signal processing circuit 19 is canceled by the inverted reset signal R3- outputted from the output terminal Q.

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

This embodiment is configured so that a town signal DWN can also be output as an alarm signal when the voltage falls below the specification.

Terminal voltage vT is divided by resistors R8, R11, and R12, and the voltage at the connection point of resistors R8 and R11 is applied to the inverting input terminal (-) of comparator Q9 to which voltage E2 is applied, and from its output terminal. A town signal DWN is output to the signal processing circuit 19.

In addition, to detect an abnormal signal, when the duty of turning on the switch SW of the switching regulator 13 shown in Fig. 1 exceeds the specified value, the load current is larger than the input current, so this is detected. It can also be used as a warning signal.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, the self-diagnosis circuit operates with the second voltage that rises earlier than the microprocessor, so it is possible to ensure initialization when the power is turned on. Moreover, since a drop in the external power supply or a power outage is detected, it is possible to easily take measures to prevent abnormal operation on the microprocessor side. Furthermore, the second
The voltage is configured with a simple stabilized power supply, so the power utilization rate is low. Only the self-diagnosis circuit uses this, and the signal processing circuit uses the first voltage of the switching regulator, so the overall power efficiency is low. This makes it possible to reduce the power consumption of important circuits in two-wire meters.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the 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 the reset signal generation circuit. 4 is a timing diagram 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 diagram. 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, and FIG. 8 is a configuration diagram showing an outline of the configuration of a conventional two-wire meter. FIG. 9 is a block diagram showing one example of a specific configuration of the power supply circuit shown in FIG. 8. 10.16...2-wire meter, 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)

[Claims] Power is supplied from the load side via a two-wire transmission line, and the physical quantity to be measured is converted into an electrical signal, which is processed by a microprocessor and transmitted as a current signal to the load via the transmission line. In a two-wire meter, a switching regulator converts the level of a terminal voltage generated at both ends of the transmission line to generate a first voltage, and a stabilizing power supply circuit stabilizes the terminal voltage to generate a second voltage. a self-diagnosis circuit that operates based on the second voltage and executes turning on, stopping, and lowering the terminal voltage and monitors the first voltage to output an initialization signal and an alarm signal; A two-wire meter comprising an initialization signal and a signal processing means including the microprocessor controlled by the alarm signal.