JPH0682437B2 - Signal transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a signal transmitter for converting a physical quantity such as pressure, differential pressure or flow rate into an electric signal and transmitting a load via a two-wire transmission line. In particular, the present invention relates to a status display for displaying the status of its output current.

<Prior Art> FIG. 6 is a block diagram showing a configuration of a conventional signal transmitter. This block diagram receives electric power from the outside through a two-wire transmission line and uses all of the circuit power with this electric power. The example of the signal transmitter of the type which covers is shown.

10 is a signal transmitter and 11 is a receiving instrument. The output terminals T ₁ and T _{2 of the} signal transmitter 10 and the input terminal T ₁ ′ of the receiving instrument 11,
_Two transmission lines l ₁ and l ₂ are connected between T ₂ ′ and the input terminal
A series circuit of a resistor R _L and a DC power source E _B is connected between T ₁ ′ and T ₂ ′.

Reference numeral 12 is a conversion unit that receives a physical quantity such as the pressure P and converts it into a corresponding electric signal.

13 receives the output current I _L from the DC power supply E _B via the transmission lines l ₁ and l ₂ , and uses a part of this output current I _L to transmit the signal.
It is a constant voltage power supply unit that produces 10 circuit voltages Vi.

The converter 12 receives the circuit voltage Vi generated by the constant voltage power supply 13, performs signal processing corresponding to the physical quantity such as the pressure P, and outputs the signal to the inverting input terminal (-) of the operational amplifier 14. The output of the operational amplifier 14 is applied to the base of the transistor 15 functioning as a current control element via the resistor R _O.

The collector of the transistor 15 is connected to the output terminal T ₁ , and its emitter is connected to the common potential point COM via the series circuit of the diode D ₁ and the resistor R ₁ . Further, between the common potential point COM and the output terminal T ₂ , a parallel circuit of a photodiode D ₂ and an analog meter M and a feedback resistor Rf are connected in a series circuit.

A voltage obtained by dividing the sum of the circuit voltage Vi and the voltage generated in the feedback resistor by resistors Rf, R ₂ and R ₃ is applied to the non-inverting input terminal (+) of the operational amplifier 14.

With the above configuration, the conversion unit 12 performs predetermined signal processing such as linearization in response to a physical quantity such as the pressure P and outputs a voltage corresponding to the physical quantity to the transistor 15 via the operational amplifier 14. The transistor 15 converts this voltage into a current and transmits it to the resistor R _L via the output terminals T ₁ and T ₂ . Output terminal
In addition, T ₁ and T ₂ include the current flowing in the constant voltage power supply unit 13, and are transmitted as an output current I _L of 4 to 20 mA as a whole.

Of these, 0 is controlled by transistor 15.
The range is from 4 mA corresponding to% to 20 mA corresponding to 100%.

According to the above configuration, the photodiode D ₂ has the output current I _L
Is continuously lit when is flowing, it is possible to determine whether or not the output current is flowing even from a distance, without approaching the meter M for confirmation.

<Problems to be Solved by the Invention> However, according to this conventional configuration, it is possible to determine whether or not the output current is flowing, but it is inconvenient that the output current cannot be determined from a distance. was there.

In particular, it was inconvenient to check the output status when the signal transmitter was installed in a dark place or at night.

<Means for Solving the Problems> In order to solve the above problems, according to the present invention, a signal corresponding to an input physical quantity is mainly processed by a conversion unit, and a current control element outputs a two-wire signal as a current signal. In a signal transmitter for transmitting to a load via a transmission line, an LED element connected so that a current related to a current signal flows and a switch element connected in series or in parallel with this LED element, and a conversion unit. A pulse signal related to the current signal is output from the device, and the opening and closing of the switch element is controlled by this pulse signal.

<Operation> In the converter, signal processing is performed according to the physical quantity, the output voltage is passed as an output current through the current control element to the load, and the pulse signal related to this output current is output from the converter. This pulse signal causes the LED element to blink corresponding to the output current, and the approximate value of the output current is known from the degree of blinking of this LED element.

<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. The elements having the same functions as those of the signal transmitter shown in FIG. 6 are given the same signals, and the description thereof will be appropriately omitted.

In FIG. 1, only the signal conversion unit 16 is shown. The converter 17 is the same as the signal transmitter shown in FIG. 6 in that the converter 17 performs predetermined signal processing such as linearization on the physical quantity such as the pressure P. In addition to this, in the present embodiment, the converter 17 uses a pulse width signal PW whose duty ratio changes in accordance with the output current I _L.
It has a built-in PWM oscillation circuit that outputs M.

On the other hand, the output terminal T ₁ , the constant voltage power supply unit 13 and the transistor 15
A photodiode D ₂ is connected between the connection point of the collector of and the connection point of, and a switching element SW is connected to both ends of the photodiode D ₂ .

This switch element SW ₁ is the pulse width signal PWM from the converter 17.
It is opened and closed by.

FIG. 2 is a characteristic diagram showing the relationship between the output current and the pulse width signal shown in FIG.

The horizontal axis shows the output current I _L , and the vertical axis shows the duty ratio D of the pulse width signal PWM (= t ₁ / t ₂ , t ₁ is the pulse off period, and t ₂ is the pulse field repetition period). When the output current I _L is 0%, the duty ratio D is 100%, and as the output current increases, the duty ratio D increases and the lighting period when blinking gradually increases.

FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention.

In this case, a photodiode D ₃ is connected between the other end of the photodiode D ₂ whose one end is connected to the output terminal T ₁ , the connection point of the constant voltage power supply unit 13 and the collector of the transistor 15, and The switch element SW ₂ is connected to both ends. This switch element SW ₂ is opened / closed by the pulse width signal PWM from the conversion unit 17, whereby the photodiode D ₃ blinks.

FIG. 4 is a block diagram showing the main configuration of the third embodiment of the present invention.

In this case, a resistor R ₄ is connected between the output terminal T ₁ and the collector of the transistor 15, and a series circuit of a photodiode D ₄ and a switch SW ₃ is connected in parallel with this. The switch SW ₃ is opened / closed by the pulse width signal PWM ′, and the lighting of the photodiode D ₄ is controlled.

Pulse width signal PWM 'is controlled as shown the switch SW ₃ in FIG. 5. The horizontal axis in FIG. 5 represents the output current I _L , and the vertical axis represents the open / closed state of the switch SW ₃ .

When the output current I _L is 0% or less, the switch SW ₃ is turned off to turn off the light. When the output current I _L is 0% to 100%, the switch is turned on continuously. It is designed to blink.

Even if the signal transmitter is installed in a dark place by such a configuration, it is necessary to immediately identify whether the current output is within the normal output range or where the output current I _L is out of range. You can

The photodiode D ₁ and the switching element shown in FIG.
By combining SW ₁ with the photo diode D ₄ , resistance R ₄ , and switch element SW ₃ shown in Fig. ₄ , the signal transmitter is installed in a dark place from the display state of the _two photo diodes D ₂ and D _4. Even if the current output is within the normal output range from the display state of the photodiode D _{4 and} the output value is known from the display state of the photodiode D ₂ and the range is exceeded. Can be identified immediately.

In the above description, the configuration in which all the internal power of the signal converter is covered from the receiving instrument 11 side has been described, but the present invention is not limited to this, the power source is obtained from another transmission line, but the signal is transmitted through the transmission line l. It can be similarly applied to a signal converter configured to transmit via ₁ and l ₂ .

<Effects of the Invention> According to the present invention as specifically described above with reference to the embodiments, since the photodiode is turned on by the pulse width signal related to the output current, the signal transmitter is installed in a dark place. Even if it is, the output status can be easily identified by lighting or blinking the LED.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a characteristic diagram showing the relationship between the pulse width signal and the output current shown in FIG. 1, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a block diagram showing a configuration of an example, FIG. 4 is a block diagram showing an essential part of a third embodiment of the present invention, and FIG. 5 is a characteristic diagram showing a relation between a switch state and an output current in FIG. FIG. 6 is a block diagram showing a configuration of a conventional signal transmitter. 10, 16 …… Signal transmitter, 11 …… Reception instrument, 12,17 …… Converter, 13 …… Constant voltage power supply, 14 …… Operational amplifier, Vi ……
Circuit voltage, D ₂ ~D ₄ ...... photodiode, PWM ...... pulse width signal, I _L ...... output current.

Claims (2)

[Claims] 1. A signal transmitter in which a signal corresponding to an input physical quantity is signal-processed by a converter and transmitted as a current signal by a current control element to a load via a two-wire transmission line. LEs connected to carry the relevant current
A D element and a switch element connected in series or in parallel to the LED element are provided, and a pulse signal related to the current signal is output from the conversion unit, and opening / closing of the switch element is controlled by the pulse signal. Characteristic signal transmitter. 2. The pulse signal when the current output is 0%
The signal transmitter according to claim 1, wherein the LED element is continuously turned on in a range of 100%, and the LED element is blinked at a current output exceeding 100%.