EP4684381A1

EP4684381A1 - 2-wire transmitter

Info

Publication number: EP4684381A1
Application number: EP23928792.3A
Authority: EP
Inventors: Shogo Wakuda; Makoto Ishii
Original assignee: Yokogawa Electric Corp
Current assignee: Yokogawa Electric Corp
Priority date: 2023-03-22
Filing date: 2023-12-14
Publication date: 2026-01-28
Also published as: JP2024135330A; CN120836048A; WO2024195226A1; JP7768169B2

Abstract

A 2-wire transmitter 10 includes a measurement circuit 11, 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 able to switch whether current is applied to the LED 15. The measurement circuit 11 includes a controller 112. The controller 112 turns off the switch 13 during normal operation and turns on the switch 13 at a time of error occurrence.

Description

2-WIRE TRANSMITTER

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of Japanese Patent Application No. 2023-045957 filed March 22, 2023, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a 2-wire transmitter.

Background

Conventionally, 2-wire transmitters are used in plants, factories, and the like. 2-wire transmitters are able to measure various physical quantities such as flow rate, pressure, temperature, and the like.

A 2-wire transmitter may include a display, such as a liquid crystal display (LCD). With such a display, a 2-wire transmitter is able to report that an error has occurred by, for example, displaying an error symbol at a time of error occurrence.

However, even when an error symbol is displayed on an LCD, noticing the error symbol may be difficult due to poor visibility, such as when a 2-wire transmitter is installed in a dark location.

One way to make an error easier to notice at a time of error occurrence is to turn on a light emitting diode (LED). However, the measurement circuit included in a 2-wire transmitter must normally operate at a current of 3.5 mA or less, and therefore including an LED in the measurement circuit and making the LED light up is not possible.

As a 2-wire transmitter capable of lighting an LED, for example, Patent Literature (PTL) 1 describes a 2-wire transmitter including a battery for lighting an LED. Further, PTL 2 describes a configuration in which a Zener diode is connected in series with a 2-wire transmitter to secure a voltage required to light an LED.

PTL 1: JP 2006-024067 A
PTL 2: JP H05-225484 A

Summary

(Technical Problem)
The 2-wire transmitter described in PTL 1 includes a battery inside the device to light the LED. Such a configuration including a battery inside the device cannot meet the requirements for an intrinsically safe explosion-proof structure because the battery may be a source of electrical sparks.

The 2-wire transmitter described in PTL 2 includes a Zener diode connected in series with the 2-wire transmitter. With such a configuration, voltage drops by about 1.5 V at the Zener diode, resulting in a higher minimum operating voltage for a voltage source supplying voltage to the 2-wire transmitter.

Thus, there was room for improvement in 2-wire transmitters capable of lighting LEDs.

Therefore, it would be helpful to provide a 2-wire transmitter with improved technology for lighting an LED.
(Solution to Problem)

A 2-wire transmitter according to at least one embodiment comprises: 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 able to switch whether or current is applied to the LED, wherein the measurement circuit comprises a controller, and the controller turns off the switch during normal operation and turns on the switch at a time of error occurrence. According to such a 2-wire transmitter, the technology of lighting an LED is improved.

In the 2-wire transmitter according to an embodiment, the controller controls current flowing through the current output circuit so that the 2-wire transmitter outputs a burnup signal at the time of error occurrence. This allows a receiver to be notified that an error has occurred.

In the 2-wire transmitter according to an embodiment, the measurement circuit further comprises a sensor, and during normal operation, the controller controls current flowing through the current output circuit so that the 2-wire transmitter outputs a current corresponding to a physical quantity measured by the sensor. This allows information on the physical quantity measured by the sensor to be transmitted to a receiver.

In the 2-wire transmitter according to an embodiment, the controller turns off the switch when the error that was occurring at the time of error occurrence is resolved. This allows returning to normal operation after the error is resolved.

The 2-wire transmitter according to an embodiment further comprises a resistor connected in series with the LED. This limits current flowing to the LED.

In the 2-wire transmitter according to an embodiment, the measurement circuit further comprises a display, and the controller turns on a backlight of the display at the time of error occurrence. This allows the error to be reported by the backlight of the display being turned on.

In the 2-wire transmitter according to an embodiment, the controller is able to control current flowing through the current output circuit so that the 2-wire transmitter outputs a burndown signal at the time of error occurrence, and when the burndown signal is output, turns off the switch at the time of error occurrence. This allows reporting that an error has occurred by a burndown signal.
(Advantageous Effect)

The present disclosure provides a 2-wire transmitter with improved technology to light an LED.

In the accompanying drawings:
FIG. 1 is a diagram illustrating a schematic structure of a 2-wire transmitter according to an embodiment;
FIG. 2 illustrates normal operation of a 2-wire transmitter according to an embodiment; and
FIG. 3 illustrates operation at a time of error occurrence of a 2-wire transmitter according to an embodiment.

DETAILED DESCRIPTION

FIG. 1 is a diagram illustrating a schematic structure of a 2-wire transmitter 10 according to an embodiment. Structure and functions of the 2-wire transmitter 10 according to an embodiment are described, with reference to FIG. 1.
The 2-wire transmitter 10 is connected to a direct current (DC) voltage source 1 and a receiver 2 via two transmission lines.
The DC voltage source 1 supplies DC voltage to the 2-wire transmitter 10. The DC voltage source 1 may be, for example, a DC voltage source able to supply a DC voltage of 10 V to 40 V.
The 2-wire transmitter 10 is operated by a DC voltage supplied from the DC voltage source 1. The 2-wire transmitter 10 measures a physical quantity and outputs a current corresponding to the physical quantity measured as a transmission signal. Normally, the transmission signal output by the 2-wire transmitter 10 is 4 mA to 20 mA.
The receiver 2 receives the transmission signal output by the 2-wire transmitter 10.
The 2-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 controller 112, a display 113, a storage 114, and an input 115.
The sensor 111 is a sensor that measures the physical quantity. The physical quantity measured by the sensor 111 may be, for example, flow rate, pressure, temperature, or the like.
The controller 112 includes at least one processor, at least one dedicated circuit, or a combination of at least one processor and at least one dedicated circuit. Each processor is a general-purpose processor such as a central processing unit (CPU) or a dedicated processor specialized for specific processing.
The controller 112 controls current flowing through the current output circuit 12 so that during normal operation, the 2-wire transmitter 10 outputs a current corresponding to the physical quantity measured by the sensor 111 as a transmission signal.
The controller 112 controls on/off states of the switch 13. When the controller 112 turns on the switch 13, current flows to the LED 15 and the LED 15 lights up. When the controller 112 turns off the switch 13, no current flows to the LED 15 and the LED 15 does not light up.
The display 113 includes one or more output interfaces that display information. The display 113 may include, for example, a liquid crystal display (LCD) or an electroluminescent (EL) display.
The storage 114 includes, but is not limited to, semiconductor memory, magnetic memory, optical memory, and the like. The storage 114 stores any information used in operation of the 2-wire transmitter 10. For example, the storage 114 may store a system program, an application program, various data, and the like.
The input 115 includes one or more input interfaces that obtain input information based on a user operation. For example, the input 115 may include buttons and the like.
The current output circuit 12 is connected in parallel with the measurement circuit 11. The current output circuit 12 is able to output variable current in response to control by the controller 112. The current output circuit 12 may be, for example, a negative-positive-negative (NPN) transistor. FIG. 1 illustrates a case where the current output circuit 12 is an NPN transistor.
The switch 13 is a switch able to switch whether or not current is applied to the LED 15. The on/off state of the switch 13 is controlled by the controller 112. The switch 13 may be a switch of any configuration that may be turned on or off by an electrical signal.
When the controller 112 turns on the switch 13, current flows to the LED 15 and the LED 15 lights up. When the controller 112 turns off the switch 13, no current flows to the LED 15 and the LED 15 does not light up.
The resistor 14 is a resistor connected in series with the LED 15. The resistor 14 limits current flowing to the 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 may be lit by electric current flow. In FIG. 1, one LED 15 is illustrated, but a plurality of the LED 15 may be connected in series.
The LED 15 may be installed in a highly visible location, such as on a housing or the like of the 2-wire transmitter 10. The LED 15 may be lit to inform an operator that an error is occurring.
(Normal operation)
Normal operation of the 2-wire transmitter 10 according to an embodiment is described, with reference to FIG. 2.
In normal operation, the 2-wire transmitter 10 outputs current corresponding to the physical quantity measured by the sensor 111 as a current signal. According to the present embodiment, the 2-wire transmitter 10 outputs a current of 4 mA to 20 mA as a transmission signal. Further, according to the present embodiment, the measurement circuit 11 has a steady current flow of 3.5 mA.
The controller 112 turns off the switch 13 during normal operation. Therefore, during normal operation, no current flows to the LED 15, so the LED 15 does not light up. In other words, the LED 15 is not lit during normal operation. An operator may ascertain that the 2-wire transmitter 10 is operating normally by seeing that the LED 15 is not lit.
The controller 112 controls current flowing through the current output circuit 12 so that the 2-wire transmitter 10 outputs a current corresponding to the physical quantity measured by the sensor 111.
More specifically, the controller 112 controls the current output circuit 12 so that a current of 0.5 mA to 16.5 mA flows through the current output circuit 12, according to the physical quantity measured by the sensor 111. At this time, a current of 3.5 mA is flowing through the measuring circuit 11, and therefore the 2-wire transmitter 10 outputs a current of 4 mA to 20 mA as a transmission signal.
(Time of error occurrence)
Operation at a time of error occurrence of the 2-wire transmitter 10 according to an embodiment is described, with reference to FIG. 3.
At a time of error occurrence, the 2-wire transmitter 10 outputs a burnup signal. A burnup signal is a signal indicating that an error is occurring, and a current greater than the normal transmission signal of 4 mA to 20 mA corresponds to a burnup signal. According to the present embodiment, the 2-wire transmitter 10 outputs a 22 mA current as a burnup signal. Further, according to the present embodiment, a current of 18 mA flows through the LED 15 when the switch 13 is turned on.
The controller 112 turns on the switch 13 at a time of error occurrence. Accordingly, at a time of error occurrence, current flows to the LED 15 and the LED 15 lights up. By seeing that the LED 15 is lit, an operator may easily ascertain that an error is occurring, even when the 2-wire transmitter 10 is installed in a dark location.
The controller 112 controls current flowing through the current output circuit 12 so that the 2-wire transmitter 10 outputs a current of 22 mA as a burnup signal.
More specifically, the controller 112 controls the current output circuit 12 so that a current of 0.5 mA flows through the current output circuit 12. At this time, a current of 3.5 mA is flowing through the measurement circuit 11 and a current of 18 mA is flowing through the LED 15, and therefore the 2-wire transmitter 10 outputs a current of 22 mA as a burnup signal.
When the error that had occurred is resolved, the controller 112 turns off the switch 13 and transitions to normal operation.
(Burndown signal)
The 2-wire transmitter 10 may be able to output a burndown signal instead of a burnup signal at a time of error occurrence. A burndown signal is a signal indicating that an error is occurring, and a current less than the normal transmission signal of 4 mA to 20 mA corresponds to a burndown signal. The burndown signal may be, for example, a current of 3.6 mA.
The controller 112 selects whether to output a burnup signal or a burndown current at a time of error occurrence, according to an input operation received from an operator by the input 115.
When outputting a burndown signal at a time of error occurrence, the controller 112 turns off the switch 13 at the time of error occurrence. Further, the controller 112 controls current flowing through the current output circuit 12 so that the 2-wire transmitter 10 outputs a current of 3.6 mA as a burndown signal.
More specifically, the controller 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 is flowing through the measuring circuit 11, and therefore the 2-wire transmitter 10 outputs a current of 3.6 mA as a burndown signal.
According to the embodiment of the 2-wire transmitter 10 as described above, the technology of lighting the LED 15 is improved. More specifically, the 2-wire transmitter 10 according to an embodiment includes the current output circuit 12 connected in parallel with the measurement circuit 11, the LED 15 connected in parallel with the measurement circuit 11 and the current output circuit 12, and the switch 13 that is able to switch whether or not current is applied to the LED 15. Further, the controller 112 turns off the switch 13 during normal operation and turns on the switch 13 at a time of error occurrence. Thus, the 2-wire transmitter 10 according to an embodiment does not include a battery. Batteries may cause electrical sparks, and therefore the requirements for an intrinsically safe explosion-proof structure are not met when a battery is included, but the 2-wire transmitter 10 according to an embodiment is able to light the LED 15 even without a battery, thereby satisfying the requirement for an intrinsically safe explosion-proof structure. Further, in the 2-wire transmitter 10 according to an embodiment, the LED 15 is connected in parallel with the measurement circuit 11. Therefore, the minimum operating voltage of the DC voltage source 1 may be kept low. Thus, according to an embodiment of the 2-wire transmitter 10, the technology of lighting the LED 15 is improved.
It is obvious to a person skilled in the art that the present disclosure may be realized in defined forms other than the embodiments described above, without departing from the spirit or essential features of the present disclosure. Accordingly, the preceding description is illustrative and not limiting. The scope of the present disclosure is defined by the appended claims, not by the preceding description. Any modifications that fall within the scope of equivalence are intended to be included in the scope of the present disclosure.
For example, the arrangement, number, and the like of each of the above components are not limited to those illustrated in the above description and drawings. The arrangement, number, and the like of each component may be configured arbitrarily, as long as the function thereof is achievable.
For example, the operation of turning on the LED 15 at a time of error occurrence is described according to an embodiment above, but the 2-wire transmitter 10 may turn on a backlight of the display 113 to report that an error has occurred. In such a case, the controller 112 may leave the switch 13 off and apply current to the backlight of the display 113 to turn on the backlight of the display 113 at a time of error occurrence.
For example, the operation of turning on the LED 15 at a time of error occurrence is described according to an embodiment above, but the 2-wire transmitter 10 may cause the LED 15 to flash on and off at a time of error occurrence.
For example, a case in which the current output circuit 12 is an NPN transistor is described according to an embodiment above, but the current output circuit 12 may be a circuit of any configuration as long as variable output current is possible.

1 DC voltage source
2 receiver
10 2-wire transmitter
11 measurement circuit
12 current output circuit
13 switch
14 resistor
15 LED
111 sensor
112 controller
113 display
114 storage
115 input

Claims

A 2-wire transmitter comprising:
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 able to switch whether or not current is applied to the LED, wherein
the measurement circuit comprises a controller, and
the controller turns off the switch during normal operation and turns on the switch at a time of error occurrence.
The 2-wire transmitter according to claim 1, wherein
the controller controls current flowing through the current output circuit so that the 2-wire transmitter outputs a burnup signal at the time of error occurrence.
The 2-wire transmitter according to claim 1, wherein
the measurement circuit further comprises a sensor, and
during normal operation, the controller controls current flowing through the current output circuit so that the 2-wire transmitter outputs a current corresponding to a physical quantity measured by the sensor.
The 2-wire transmitter according to claim 1, wherein
the controller turns off the switch when the error that was occurring at the time of error occurrence is resolved.
The 2-wire transmitter according to claim 1, further comprising
a resistor connected in series with the LED.
The 2-wire transmitter according to claim 1, wherein
the measurement circuit further comprises a display, and
the controller turns on a backlight of the display at the time of error occurrence.
The 2-wire transmitter according to claim 1, wherein
the controller
is able to control current flowing through the current output circuit so that the 2-wire transmitter outputs a burndown signal at the time of error occurrence, and
when the burndown signal is output, turns off the switch at the time of error occurrence.