JPH0631599Y2 - Two-wire transmitter - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a two-wire oscillator that transmits a signal and a power supply through the same power supply line.

[Conventional technology]

Conventionally, a switch has been provided in the transmission circuit in the two-wire type transmitter in order to switch between the measurement mode and the mode for performing zero point adjustment during installation or maintenance. This switch
Depending on its purpose, mechanical switches such as push button switches, rotary switches, and micro switches are used.
The on / off operation was performed manually from outside the transmitter body.

[Problems to be solved by the device]

However, the conventional two-wire type transmitter has a drawback that a mechanical switch is used as a switch of the transmitting circuit, so that a defect occurs due to intrusion of oil or the like and the failure rate increases. That is, a movable operator is required to directly drive the switch, but since the switch is placed inside the case of the transmitter and the operator operates from the outside of the case, this operator needs to penetrate the case. Therefore, harmful gas, liquid, or the like from the outside will come in through the gap between the operator and the case. Therefore, an expensive switch having a special structure with few contact defects is required, and assembly accuracy is also required. Further, when the atmosphere in which the transmitter is installed contains a corrosive gas, the contact life of the switch is shortened even if the airtightness is increased to some extent, which makes it practically unusable.

Also, it is conceivable that the case is hermetically sealed and the internal switch is electrically controlled from the outside, but in the case of the two-wire system, there are only two lines, so use this line as such a control line. It has the drawback that it cannot be done.

[Means for Solving the Problems]

In order to solve the above-mentioned drawbacks, the present invention provides a light emitting element that emits light by a current flowing through a power supply line, and a light emitting element that is arranged to receive light from the light emitting element, and outputs different output signals depending on whether the light is received or not. And a control plate that controls the light incident from the light emitting element to the light receiving element by moving the position.

[Action]

The light emitting element can always be made to emit light regardless of the presence or absence of a signal, and the light from the light emitting element to the light receiving element is controlled by moving the position of the control plate to perform a switch operation for mode switching of the transmission circuit.

〔Example〕

Embodiments of the present invention will be described below. FIG. 1 is a circuit diagram showing an embodiment according to the present invention. In the figure, a power source 1 and a receiver 2 are connected in series and are connected to terminals T1 and T2 of a two-wire oscillator 3 via a two-wire feeder line L. A photocoupler 4 including a light emitting element 4a made of a light emitting diode and a light receiving element 4b made of a phototransistor is provided on the (+) side internal feeder line of the two-wire oscillator 3.
Following this photocoupler 4, an oscillator circuit 6 as an oscillator is connected in series. An internal switch circuit (not shown) of the oscillator circuit 6 is connected to the light receiving element 4b. Further, the shield plate 5 as a control plate can control the conduction (on / off) of the light receiving element 4b by blocking the light incident from the light emitting element 4a to the light receiving element 4b by moving the position, and the two-wire type The structure is such that this knob can be moved manually by operating a knob from outside the transmitter 3.

Now, the two-wire transmitter 3 detects the amount of change of the object to be measured by the transmitter circuit 6, and transmits the detected amount (output current) to the receiver 2 via the power supply line L supplied with power from the power supply 1. It is a thing. Normally, the output signal current of the two-wire oscillator 3 is 4 to 20.
Since it is mA, the detection level of the receiver 2 is 4 to 20
4 to 2 because it is set to 0 to 100% corresponding to mA
The detected amount in the range of 0 mA can be measured at a level of 0 to 100%. Here, the minimum value of the output signal current is 4 mA because the receiver 2 side determines an accident such as a disconnection of the power supply line L (output signal current 0 mA).

By the way, the light emitting element 4a is connected in series to the (+) side in-container power supply line, and it is necessary to keep lighting all the time. Therefore, the specification of the light emitting element 4a is required to emit light even with the minimum value of the output signal current of 4 mA. Of course, it is natural that such a device emits light even at 20 mA. Further, it is necessary to select so that the oscillator circuit 6 is not affected by the voltage drop of the light emitting element 4a. An ordinary light emitting diode has a lower limit saturation value of about 3 mA and a voltage drop of 2 to 3 mV, which sufficiently satisfies such specifications.

Since the shielding plate 5 is usually drawn out of the photocoupler 4, light is incident on the light receiving element 4b from the light emitting element 4a in the photocoupler 4, and the light receiving element 4b is in the ON state. As a result, the output signal of "1", for example, is supplied to the internal switch circuit of the oscillator circuit 6, and the normal operation (measurement operation) is performed.

Next, when switching to the zero-point adjustment mode of the two-wire oscillator 3, the shield plate 5 is inserted into the photocoupler 4 by manually operating from outside the oscillator 3. Thereby, the light emitting element 4
The light incident on the light receiving element 4b from a is shielded by the shield plate 5, the light receiving element 4b is turned off, and the output signal changes from "1" to "0". Therefore, the internal switch circuit of the oscillator circuit 6 operates, the mode is switched, and the measurement operation is stopped. After that, work for zero adjustment is performed. Then, by pulling the shield plate 5 out of the photocoupler 4 again, it is possible to return to the measurement operation.

In this way, the two-wire oscillator 3 in this embodiment can perform the switching operation for switching the mode of the oscillator circuit 6 by inserting the shield plate 5 into the photocoupler 4.

As a result, since the case is kept sealed, it is possible to prevent a contact failure that has conventionally occurred, and it is not affected even when used in a corrosive gas atmosphere. Also, for a simple operation of blocking the light of the light emitting element 4a with the shielding plate 5,
Assembling accuracy is not required as much as in the case of using the conventional mechanical switch.

Further, in this embodiment, since the light emitting power source for the light emitting element 4a is obtained from the power source 1, it is not necessary to newly provide a power source circuit for the light emitting element 4a, and the number of parts can be reduced and the cost can be reduced.

Although the shield plate 5 is used in this embodiment, a reflector may be used to control the light from the light emitting element 4a to the light receiving element 4b.

[Effect of device]

As described above, according to the present invention, the light emitting element that emits light by the current flowing through the power supply line and the light emitting element are arranged so as to receive light, and an output signal that differs depending on whether the light is received or not is supplied to the transmitting circuit. Since it has a light-receiving element and a control plate that controls the light incident from the light-emitting element to the light-receiving element by moving the position, it is possible to prevent the contact failure that has occurred conventionally because the case can be kept airtight. Even if used in a corrosive gas atmosphere, it is not affected. Further, since the light of the light emitting element is controlled by the control plate, the assembly accuracy is not required.

Further, since the power source of the light emitting device according to the present invention is obtained from the power supply line, it is not necessary to newly provide a power source circuit for the light emitting device, and it has a remarkable effect that it can be inexpensively configured with a small number of parts. .

[Brief description of drawings]

FIG. 1 is a circuit diagram of a two-wire oscillator showing an embodiment according to the present invention. 1 ... Power supply, 2 ... Receiver, 3 ... Two-wire transmitter, 4 ...
... Photo coupler, 4a ... Light emitting element, 4b ... Light receiving element, 5 ... Shielding plate, 6 ... Oscillator circuit, L ... Feed line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Norio Sumiya, 4-28-1, Nishirokugo, Ota-ku, Tokyo Yamatake Honeywell Co., Ltd. Kamata factory (56) References

Claims (1)

[Scope of utility model registration request] 1. A two-wire oscillator for transmitting a signal output from a transmission circuit via a two-line power supply line, wherein a light-emitting element that emits light with a current flowing through the power supply line and light from the light-emitting element. And a control plate for controlling light incidence from the light emitting element to the light receiving element by position movement, the light receiving element being arranged so as to receive light, and supplying an output signal that differs depending on whether or not the light is received to the transmitting circuit. A two-wire transmitter characterized by being equipped.