JP3199097B2 - Two-wire transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method in which a current is supplied from a load side via two transmission lines, a physical quantity to be measured is converted into an electric signal by a sensor, and the electric signal is processed by a signal processing circuit. The present invention relates to a two-wire transmitter that transmits a current signal to a load side via a transmission line as a current signal.
It relates to a wire type transmitter.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the configuration of a conventional two-wire transmitter. The two-wire transmitter 10 is connected to an external circuit 11 via transmission lines L1 and L2.
The DC voltage Eb required to supply the circuit power of the two-wire transmitter 10 and the receiving resistor R1 are connected in series to the transmission lines L1 and L2 via terminals T1 and T2. This transmission line L
The other ends of L1 and L2 are connected to terminals T3 and T4 of the two-wire transmitter 10.

A diode D is provided between terminals T3 and T4.
1. The emitter and base of the transistor Q1, the collector and emitter of the transistor Q2, the diode D2, and the feedback resistor R2 are connected in series. A starting resistor R is provided between the emitter and the collector of the transistor Q1.
3 are connected.

Further, a Zener diode D3 is connected between a connection point CN1 between the diode D2 and the feedback resistor R2 and a connection point CN2 between the starting resistor R3 and the collector of the transistor Q1.
Are connected, and a primary voltage V, which is a constant voltage, is connected between them.
I have one.

The primary voltage V1 is supplied to the switching power supply 12
Terminal T5 and the common terminal T connected to the connection point CN1
6 between the secondary terminal T7 and the common terminal T6.
And a DC secondary voltage V2 whose voltage has been transformed is output. The secondary voltage V2 is supplied to a sensor 13 for converting a physical quantity into an electric signal, a signal processing circuit 14 having a microprocessor for processing the electric signal, and the like.

The sensor 13 converts a physical quantity such as pressure into an electric signal and outputs it to a signal processing circuit 14. The signal processing circuit 14 performs signal processing such as linearity correction on the electric signal and outputs it as a pulse width signal PWM. At the same time, it is output and displayed on the liquid crystal display element LCD as needed.

Reference numerals 15 and 16 denote reference voltages V _R1 and V _R2 for converting the pulse width signal PWM to a predetermined level.
Is a reference voltage source that generates
5,16 connection point between one end of each of the switch end switch SW ₁ C
N1.

[0008] Common terminal of the switch SW ₁ is connected to a filter FL composed of resistor R4 and the capacitor C1, it is switched by the pulse width signal PWM. Accordingly, the reference level to the common terminal of the switch SW ₁ is a voltage V _R1 and V _R2
A pulse-like signal which is switched by the pulse width signal PWM is obtained, and the filter FL smoothes this signal into a corresponding analog signal.

[0009] The analog signal is Baffuaringu by Baffua amplifier Q3 and the sensor signal V _a at its output
Is output as Inverting input terminal (-) of error amplifier Q4
A divided voltage obtained by dividing the reference voltage V _R1 by resistors R5 and R6 is applied to a non-inverting input terminal (+) of the feedback resistor R2.
Both ends the feedback voltage V _f and the divided voltage of the voltage of the sum was divided by resistors R7, R8 and a feedback resistor R2 of the sensor signal V _a generation of is applied.

The error amplifier Q4 controls the base current of the transistor Q2 so that these divided voltages match, and as a result, the base current of the transistor Q1 is controlled by the collector current of the transistor Q2. 2 Thus, the transistor Q1 is the sensor signal V _a unification of current signals corresponding to I ₀ as (= 4mA to 20mA)
The signal is output to the reception resistor R1 via the transmission lines L1 and L2.

[0011]

However, in the two-wire transmitter 10 as described above, when an abnormality occurs in this transmitter, the liquid crystal display element LCD displays "Erro".
This abnormality is notified to the outside by displaying characters such as "r", but the liquid crystal display element LCD is difficult to be seen in a dark place unless a backlight is provided, and there is a problem as an abnormal display element.

Therefore, it is conceivable to use a light emitting diode LED. However, in order to make the light emitting diode LED emit light, it is necessary to supply a current of several mA.
In the two-wire transmitter 10 that needs to be operated with the following current signal I ₀ , the light emitting diode LED is not used as an abnormal display element.

[0013]

According to the present invention, as a configuration for solving the above-mentioned problems, a current is supplied from a load side through two transmission lines, and a physical quantity to be measured is detected by an electric signal by a sensor. In a two-wire transmitter that converts the signal to a signal processing circuit and processes the signal as a current signal via the previous transmission line to the previous load side, it is connected in series to the main current path through which the current signal flows Light-emitting element, a switch element connected in parallel with the light-emitting element, and when an abnormality occurs in the previous two-wire transmitter, the previous switch element is opened to cause the previous light-emitting element to emit light and to cause the previous light-emitting element to emit light. And a driving circuit for notifying the abnormality to the outside in a lighting state.

[0014]

[Function] The light emitting element receives a current from the load side through two transmission lines, converts a physical quantity to be measured into an electric signal by a sensor, processes the electric signal by a signal processing circuit, and processes the signal by a signal processing circuit. It is inserted in series with the main current path through which the current signal flows to the load side via the wire.

A switch element is connected in parallel with the light emitting element, and the drive circuit opens the previous switch element and emits light when the two-wire transmitter has an abnormality. The abnormality of the destination is notified to the outside in the lighting state even in a dark place.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 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. Parts having the same functions as those of the conventional two-wire transmitter shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

The two-wire transmitter 20 shown in FIG. 1 includes a CPU monitoring circuit 21, a driving circuit 22,
A switch element 23, a light emitting diode (LED) 24, and the like are added.

Transistor Q1 and switching power supply 12
A switching element 23 composed of a P-channel MOS type FET having a low on-resistance is provided between the switching element 23 and the primary terminal T5.
Is connected. Further, a light emitting diode (LED) 24 is connected to the switch element 23 in parallel.

The switching element 23 has a source S on the collector side of the transistor Q1, a drain on the primary terminal T5 side, and a driving circuit 22 on the gate G.
Drive signal S ₃ is applied from.

[0020] CPU monitoring circuit 21 is energized by the secondary voltage of the switching power supply 12 V2, and outputs a status signal S ₂ by monitoring whether there is abnormality in the signal processing circuit 14 for mounting the CPU.

The driving circuit 22 includes transistors Q _5, Q ₆ ,
Inverter Q _7, it is configured of a resistor R ₉ to R _13. Transistor Q ₅ is obtained by dividing the divided voltage at receiving the status signals S ₁ resistor R ₉ and R ₁₀ from the signal processing circuit 14 is applied to the base, the transistor Q in the collector
Voltage V ₀ which ₁ is applied through a resistor R _11, and the emitter is connected as the common potential point to the connection point CN1.

In this case, the status signal S ₁ is output when the CPU in the signal processing circuit 14 is normal, but the peripheral circuit is abnormal, for example, when the sensor 13 fails and exceeds the normal range of the normal sensor signal. For example, the level is changed and output.

A divided voltage obtained by dividing the status signal S ₂ by the resistors R ₁₂ and R ₁₃ is applied to the base of the transistor Q ₆ ,
Emitter connection point CN1, its collector connected to the collector of the transistor Q ₅ as a circuit configuration of the wired OR.

The status signal S _{2 in} this case is output when the CPU in the signal processing circuit 14 is abnormal. For example, the status signal S ₂ has a built-in watch dock timer and the like. The counter is cleared, but when an error occurs, the counter causes a flow, etc., so that the software is judged to be abnormal and the level is changed and output.

[0025] In addition, the collector of the transistor Q ₅ is,
Is applied to the input terminal of the inverter Q ₇ which is biased by the voltage V _0, the switching element 2 in the driving signal S ₃ appearing at its output
The gate of the P-channel MOS type FET constituting 3 is driven.

Next, the operation of the embodiment configured as described above will be described. Normally, since the switch 23 is on, the sensor 13 converts a physical quantity such as pressure into an electric signal and converts the physical quantity into an electric signal, as in the case shown in FIG.
The signal processing circuit 14 performs signal processing such as linearity correction on the electric signal and outputs the signal as a pulse width signal PWM.

The pulse width signal PWM is supplied to the switch SW
₁ , filter FL, buffer amplifier Q3, error amplifier Q
4, the transistor Q2, the reception resistive via the transmission line L1, L2 as a current signal I ₀ through the transistor Q1 R1
Has been transmitted to.

Next, the operation of the added circuit including the driving circuit 22 will be described. First, it is assumed that the status signals S ₁ and S ₂ are configured to be “L level” when normal, and to “H level” when abnormal.

Therefore, in the normal state, the status signal
No. S₁, S_TwoIs at the “L level”.
Jista Q_Five, Q₆Is off. Because of this
TA Q ₇Of the output terminal becomes "H level" and the output terminal
Status signal S_ThreeIs "L level".

Therefore, the gate voltage of the P-channel MOS FET constituting the switch 23 is biased to near 0V, so that the switch 23 is turned on. In this case, the main current path through which current signal I ₀ is a path of transistor Q1- switching element 23-diode D3- feedback resistor R2.

In this case, the drain /
Since the resistance value between the sources is 5Ω or less, the voltage across the light emitting diode 24 is about 100 mV even at a current signal I ₀ of 20 mA, while the lighting voltage of the light emitting diode 24 is 1 V or more. 24 does not light.

In the abnormal state, since the status signal S ₁ or S ₂ is at “H level”, the transistor Q ₅ or Q ₆ is turned on. Thus the input terminal of the inverter Q ₇ is "L level" and the status signal S ₃ of the output terminals
Becomes "H level".

Then, the gate voltage of the P-channel MOS type FET constituting the switch element 23 is biased to near the source voltage, so that the switch element 23 is turned off. In this case, the main current path through which current signal I ₀ is a path of transistor Q1- emitting diode 24 diode D3- feedback resistor R2. Therefore, the light emitting diode 24 is turned on, and the occurrence of an abnormality can be notified to the outside.

It should be noted, in any case, the power supply voltage of the inverter Q ₇ is less than the sum of the voltage drop of the light emitting diode 24 and the diode D2, the maximum rating of the inverter Q ₇ may be configured so as not to exceed.

FIG. 2 is a partial display section showing the vicinity of the display surface of the two-wire transmitter shown in FIG. By disposing the light emitting diode 24 in the vicinity of the liquid crystal display element LCD,
Even in a dark place, the abnormality can be easily visually recognized by turning on the light emitting diode 24.

[0036]

According to the present invention, as described above in detail with the embodiments, even in a two-wire transmitter subjected to current limitation, light emission can be achieved by using a current signal effectively. An abnormality can be easily visually recognized outside even in a dark place by using a light emitting diode requiring a large current.

[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 partial display section showing the vicinity of a display surface of the two-wire transmitter shown in FIG.

FIG. 3 is a block diagram showing a configuration of a conventional two-wire transmitter.

[Description of Signs] 10, 20 Two-wire transmitter 11 External circuit 12 Switching power supply 13 Sensor 14 Signal processing circuit 21 CPU monitoring circuit 22 Drive circuit 23 Switch element 24 Light emitting diode

Claims (1)

(57) [Claims] An electric current is supplied from a load side through two transmission lines, and a physical quantity to be measured is converted into an electric signal by a sensor, and the electric signal is processed by a signal processing circuit, and the electric signal is processed by a signal processing circuit. In a two-wire transmitter for transmitting a current signal to the load side, a light emitting element connected in series to a main current path through which the current signal flows; a switch element connected in parallel to the light emitting element; A two-wire transmitter, comprising: a drive circuit that opens the switch element to emit light when an abnormality occurs in the wire transmitter to notify the abnormality to the outside in a lighting state.