JP7768169B2 - Two-wire transmitter - Google Patents

Description

This disclosure relates to a two-wire transmitter.

Two-wire transmitters have traditionally been used in plants and factories. Two-wire transmitters can measure a variety of physical quantities, such as flow rate, pressure, and temperature.

Two-wire transmitters may have a display such as an LCD (Liquid Crystal Display). If such a display is provided, the two-wire transmitter can notify the user that an error has occurred by, for example, displaying an error symbol when an error occurs.

However, even if an error symbol is displayed on the LCD, it can be difficult to notice the error symbol if the two-wire transmitter is installed in a dark location due to poor visibility.

One way to make errors more noticeable when they occur is to turn on an LED (Light Emitting Diode). However, the measurement circuitry in two-wire transmitters typically needs to operate at a current of around 3.5 mA or less, so it is not possible to include an LED in the measurement circuit and have it light up.

As an example of a two-wire transmitter capable of lighting an LED, Patent Document 1 discloses a two-wire transmitter equipped with a battery for lighting the LED. Furthermore, Patent Document 2 discloses a configuration in which a Zener diode is connected in series with a two-wire transmitter to ensure the voltage required to light the LED.

Japanese Patent Application Laid-Open No. 2006-24067 Japanese Patent Application Publication No. 5-225484

The two-wire transmitter disclosed in Patent Document 1 is equipped with a battery inside the device to light the LED. With a configuration like this, where a battery is installed inside the device, the battery can cause electric sparks, and the device does not meet the requirements for an intrinsically safe explosion-proof structure.

The two-wire transmitter disclosed in Patent Document 2 has a Zener diode connected in series with the two-wire transmitter. With this configuration, the Zener diode drops the voltage by about 1.5 V, which increases the minimum operating voltage of the voltage source that supplies voltage to the two-wire transmitter.

As such, there was room for improvement in two-wire transmitters capable of lighting LEDs.

The present disclosure therefore aims to provide a two-wire transmitter with improved technology for lighting LEDs.

A two-wire transmitter according to some embodiments includes a measurement circuit, a current output circuit connected in parallel with the measurement circuit, an LED connected in parallel with the measurement circuit and the current output circuit, and a switch that can switch whether or not current flows through the LED. The measurement circuit includes a control unit that turns the switch off during normal operation and turns the switch on when an error occurs. Such a two-wire transmitter allows for improvements in LED illumination technology.

In one embodiment of the two-wire transmitter, the control unit may control the current flowing through the current output circuit when the error occurs so that the two-wire transmitter outputs a burn-up signal. This allows the receiving instrument to be notified that an error has occurred.

In one embodiment of the two-wire transmitter, the measurement circuit may further include a sensor, and the control unit may control the current flowing through the current output circuit during normal operation so that the two-wire transmitter outputs a current corresponding to the physical quantity measured by the sensor. This allows information on the physical quantity measured by the sensor to be transmitted to a receiving instrument.

In one embodiment of the two-wire transmitter, the control unit may turn off the switch when the error that occurred when the error occurred is resolved. This allows the transmitter to return to normal operation after the error is resolved.

In one embodiment, the two-wire transmitter may further include a resistor connected in series with the LED. This makes it possible to limit the current flowing through the LED.

In one embodiment of the two-wire transmitter, the measurement circuit may further include a display unit, and the control unit may turn on the backlight of the display unit when the error occurs. This allows the error to be notified by turning on the backlight of the display unit.

In one embodiment of the two-wire transmitter, the control unit can control the current flowing through the current output circuit so that the two-wire transmitter outputs a burn-down signal when the error occurs, and if the burn-down signal is to be output, the control unit turns off the switch when the error occurs. This makes it possible to notify the user of the occurrence of an error via the burn-down signal.

This disclosure provides a two-wire transmitter with improved technology for lighting LEDs.

FIG. 1 is a diagram illustrating a schematic configuration of a two-wire transmitter according to an embodiment. FIG. 10 is a diagram illustrating an operation during normal operation of a two-wire transmitter according to an embodiment. FIG. 10 is a diagram illustrating an operation of a two-wire transmitter according to an embodiment when an error occurs.

Figure 1 is a diagram showing the general configuration of a two-wire transmitter 10 according to one embodiment. The configuration and functions of the two-wire transmitter 10 according to one embodiment will be described with reference to Figure 1.

The two-wire transmitter 10 is connected to the DC voltage source 1 and the receiving instrument 2 via two transmission lines.

The DC voltage source 1 supplies a DC voltage to the two-wire transmitter 10. The DC voltage source 1 may be, for example, a DC voltage source capable of supplying a DC voltage of approximately 10 to 40 V.

Two-wire transmitter 10 operates using DC voltage supplied from DC voltage source 1. Two-wire transmitter 10 measures a physical quantity and outputs a current corresponding to the measured physical quantity as a transmission signal. Typically, the transmission signal output by two-wire transmitter 10 is 4 to 20 mA.

The receiving instrument 2 receives the transmission signal output by the two-wire transmitter 10.

The two-wire transmitter 10 includes a measurement circuit 11, a current output circuit 12, a switch 13, a resistor 14, and an LED 15.

The measurement circuit 11 includes a sensor 111, a control unit 112, a display unit 113, a memory unit 114, and an input unit 115.

Sensor 111 is a sensor that measures a physical quantity. The physical quantity measured by sensor 111 may be, for example, flow rate, pressure, temperature, etc.

The control unit 112 includes at least one processor, at least one dedicated circuit, or a combination of these. The processor may be a general-purpose processor such as a CPU (Central Processing Unit), or a dedicated processor specialized for a specific process.

During normal operation, the control unit 112 controls the current flowing through the current output circuit 12 so that the two-wire transmitter 10 outputs a current corresponding to the physical quantity measured by the sensor 111 as a transmission signal.

The control unit 112 controls the on/off of the switch 13. When the control unit 112 turns on the switch 13, current flows through the LED 15, causing the LED 15 to light up. When the control unit 112 turns off the switch 13, no current flows through the LED 15, causing the LED 15 to not light up.

The display unit 113 includes one or more output interfaces that display information. The display unit 113 may include, for example, an LCD (Liquid Crystal Display) or an organic EL (Electro Luminescent) display.

The memory unit 114 may be, for example, a semiconductor memory, a magnetic memory, or an optical memory, but is not limited to these. The memory unit 114 stores any information used in the operation of the two-wire transmitter 10. For example, the memory unit 114 may store system programs, application programs, various data, etc.

The input unit 115 includes one or more input interfaces that acquire input information based on user operations. For example, the input unit 115 may include buttons, etc.

The current output circuit 12 is connected in parallel with the measurement circuit 11. The current output circuit 12 can output a variable current in accordance with control by the control unit 112. The current output circuit 12 may be, for example, an NPN transistor. Figure 1 shows a case where the current output circuit 12 is an NPN transistor.

Switch 13 is a switch that can switch whether or not current flows through LED 15. The on/off state of switch 13 is controlled by control unit 112. Switch 13 may be a switch of any configuration that can be turned on/off by an electrical signal.

When the control unit 112 turns on the switch 13, current flows through the LED 15, causing the LED 15 to light up. When the control unit 112 turns off the switch 13, no current flows through the LED 15, causing the LED 15 to not light up.

Resistor 14 is a resistor connected in series with LED 15. Resistor 14 limits the current flowing through LED 15.

The LED 15 is connected in parallel with the measurement circuit 11 and the current output circuit 12. The LED 15 may be any LED that can be illuminated by passing a current through it. While one LED 15 is shown in Figure 1, multiple LEDs 15 may be connected in series.

The LED 15 may be installed in a highly visible location, such as on the housing of the two-wire transmitter 10. By lighting up, the LED 15 can alert the operator that an error has occurred.

(during normal operation)
Referring to FIG. 2, the operation of the two-wire transmitter 10 according to the embodiment during normal operation will be described.

During normal operation, the two-wire transmitter 10 outputs a current signal that corresponds to the physical quantity measured by the sensor 111. In this embodiment, the two-wire transmitter 10 is described as outputting a current of 4 to 20 mA as the transmission signal. Also, in this embodiment, the measurement circuit 11 is described as steadily flowing with a current of 3.5 mA.

The control unit 112 turns off the switch 13 during normal operation. Therefore, during normal operation, no current flows through the LED 15, and the LED 15 does not light up. In other words, the state in which the LED 15 is not lit indicates normal operation. By visually confirming that the LED 15 is not lit, the operator can determine that the two-wire transmitter 10 is operating normally.

The control unit 112 controls the current flowing through the current output circuit 12 so that the two-wire transmitter 10 outputs a current corresponding to the physical quantity measured by the sensor 111.

More specifically, the control unit 112 controls the current output circuit 12 so that a current of 0.5 to 16.5 mA flows through it, depending on the physical quantity measured by the sensor 111. In this case, because a current of 3.5 mA flows through the measurement circuit 11, the two-wire transmitter 10 outputs a current of 4 to 20 mA as the transmission signal.

(When an error occurs)
Referring to FIG. 3, the operation of the two-wire transmitter 10 according to the embodiment when an error occurs will be described.

When an error occurs, the two-wire transmitter 10 outputs a burn-up signal. The burn-up signal indicates that an error has occurred, and corresponds to the flow of a current greater than the normal transmission signal of 4 to 20 mA. In this embodiment, the two-wire transmitter 10 is described as outputting a current of 22 mA as the burn-up signal. Also, in this embodiment, it is described as causing a current of 18 mA to flow through the LED 15 when the switch 13 is turned on.

When an error occurs, the control unit 112 turns on the switch 13. As a result, when an error occurs, current flows through the LED 15, causing the LED 15 to light up. By visually confirming that the LED 15 is lit, the operator can easily determine that an error has occurred, even if the two-wire transmitter 10 is installed in a dark location.

The control unit 112 controls the current flowing through the current output circuit 12 so that the two-wire transmitter 10 outputs a current of 22 mA as a burn-up signal.

More specifically, the control unit 112 controls the current output circuit 12 so that a current of 0.5 mA flows through it. At this time, a current of 3.5 mA flows through the measurement circuit 11, and a current of 18 mA flows through the LED 15, so the two-wire transmitter 10 outputs a current of 22 mA as a burn-up signal.

Once the error is resolved, the control unit 112 turns off the switch 13 and transitions to normal operation.

(burndown signal)
The two-wire transmitter 10 may be capable of outputting a burn-down signal instead of a burn-up signal when an error occurs. The burn-down signal indicates that an error has occurred, and corresponds to a current smaller than the 4 to 20 mA current of a normal transmission signal. The burn-down signal may be, for example, a current of 3.6 mA.

The control unit 112 selects whether to output a burn-up signal or a burn-down current when an error occurs, depending on the input operation received from the operator by the input unit 115.

When a burndown signal is to be output when an error occurs, the control unit 112 turns off the switch 13 when an error occurs. The control unit 112 also controls the current flowing through the current output circuit 12 so that the two-wire transmitter 10 outputs a current of 3.6 mA as the burndown signal.

More specifically, the control unit 112 controls the current output circuit 12 so that a current of 0.1 mA flows through the current output circuit 12. At this time, a current of 3.5 mA flows through the measurement circuit 11, so the two-wire transmitter 10 outputs a current of 3.6 mA as the burndown signal.

As described above, the two-wire transmitter 10 according to one embodiment of the present invention can improve the technology for lighting the LED 15. More specifically, the two-wire transmitter 10 according to one embodiment of the present invention includes a current output circuit 12 connected in parallel with the measurement circuit 11, an LED 15 connected in parallel with the measurement circuit 11 and the current output circuit 12, and a switch 13 that can switch whether or not current flows through the LED 15. The control unit 112 turns the switch 13 off during normal operation and turns the switch 13 on when an error occurs. As described above, the two-wire transmitter 10 according to one embodiment of the present invention does not include a battery. Because batteries can cause electric sparks, including a battery would not satisfy the requirements for an intrinsically safe explosion-proof structure. However, the two-wire transmitter 10 according to one embodiment of the present invention can light the LED 15 even without a battery, thereby satisfying the requirements for an intrinsically safe explosion-proof structure. Furthermore, in the two-wire transmitter 10 according to one embodiment of the present invention, the LED 15 is connected in parallel with the measurement circuit 11. Therefore, the minimum operating voltage of the DC voltage source 1 can be kept low. In this way, the two-wire transmitter 10 according to one embodiment can improve the technology for lighting the LED 15.

It will be apparent to those skilled in the art that the present disclosure may be embodied in other forms than the above-described embodiments without departing from the spirit or essential characteristics thereof. Therefore, the foregoing description is illustrative and not limiting. The scope of the disclosure is defined by the appended claims, not by the foregoing description. All modifications within the range of equivalents of any modifications are intended to be embraced therein.

For example, the arrangement and number of each component described above are not limited to the above description and the illustrations in the drawings. The arrangement and number of each component may be configured arbitrarily as long as the component functions can be realized.

For example, in the above embodiment, the operation of lighting the LED 15 when an error occurs was described, but the two-wire transmitter 10 may also light the backlight of the display unit 113 to notify that an error has occurred. In this case, when an error occurs, the control unit 112 may leave the switch 13 off and pass current through the backlight of the display unit 113 to light up the backlight of the display unit 113.

For example, in the above embodiment, the LED 15 is illuminated when an error occurs, but the two-wire transmitter 10 may also blink the LED 15 when an error occurs.

For example, in the above-described embodiment, the current output circuit 12 is an NPN transistor, but the current output circuit 12 may be a circuit of any configuration as long as it can output a variable current.

REFERENCE SIGNS LIST 1 DC voltage source 2 Receiving instrument 10 Two-wire transmitter 11 Measuring circuit 12 Current output circuit 13 Switch 14 Resistor 15 LED
111 Sensor 112 Control unit 113 Display unit 114 Storage unit 115 Input unit

Claims (7)

A measurement circuit;
a current output circuit connected in parallel with the measurement circuit;
an LED connected in parallel to the measurement circuit and the current output circuit;
a switch capable of switching whether or not a current flows through the LED;
Equipped with
the measurement circuit includes a control unit;
The control unit turns the switch off during normal operation and turns the switch on when an error occurs. 2. The two-wire transmitter according to claim 1,
The control unit controls the current flowing through the current output circuit when the error occurs so that the two-wire transmitter outputs a burn-up signal. 2. The two-wire transmitter according to claim 1,
the measurement circuit further comprises a sensor;
The control unit controls the current flowing through the current output circuit so that the two-wire transmitter outputs a current corresponding to the physical quantity measured by the sensor during the normal operation. 2. The two-wire transmitter according to claim 1,
The control unit turns off the switch when the error that occurred at the time the error occurred is resolved. 2. The two-wire transmitter according to claim 1,
The two-wire transmitter further comprises a resistor connected in series with the LED. 2. The two-wire transmitter according to claim 1,
The measurement circuit further includes a display unit,
The control unit turns on a backlight of the display unit when the error occurs. 2. The two-wire transmitter according to claim 1,
The control unit
When the error occurs, the current flowing through the current output circuit can be controlled so that the two-wire transmitter outputs a burn-down signal;
A two-wire transmitter that, when outputting the burn-down signal, turns off the switch when the error occurs.