JPH05342495A - Two-wire transmitting device - Google Patents

Abstract

PURPOSE:To provide the improved two-wire transmitting device capable of the stable actuation when the power is applied. CONSTITUTION:In a two-wire transmitting device 15, the current is applied from the side of a load through two transmission lines, and the physical amount to be measured is converted into an electric signal by a sensor 13, which is signal-processed by a signal processing circuit 14 and transferred through the transmission line to the load side as a current signal. It is provided with a reference voltage source VR3 setting the reference voltage to the value deciding the current signal at the time of actuating the two-wire transmitting device 15, a current detecting means outputting the switching signal by detecting the consumption current in the two-wire transmitting device 15 becomes the normal value, and a switching means switching a sensor signal to be outputted from the signal processing circuit 14 and the reference voltage by means of the switching signal. The current signal is controlled by the output of the switching means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention receives a current from a load side through two transmission lines, converts a physical quantity to be measured into an electric signal by a sensor, and processes the electric signal by a signal processing circuit. The present invention relates to a two-wire type transmitter that transmits a current signal to the load side via the transmission line, and more particularly, to a two-wire type transmitter improved so that stable startup can be performed when power is turned on.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing the structure of a conventional two-wire type transmitter. The two-wire transmitter 10 is connected to an external circuit 11 via transmission lines L1 and L2.
The DC voltage Eb necessary 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 1 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. Further, a starting resistor R is provided between the emitter and collector of the transistor Q1.
3 is connected.

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, and a constant voltage is applied between them. Primary voltage V1
Is getting

The primary voltage V1 is the switching power supply 12
Common terminal T connected to the primary terminal T5 and the connection point CN1
6 and its secondary terminal T7 and common terminal T6.
A DC secondary voltage V2, which has been voltage-transformed between the two, is output. The secondary voltage V2 is supplied to the sensor 13 that converts a physical quantity into an electric signal, the signal processing circuit 14 equipped with a microprocessor that processes the electric signal, and the like.

The sensor 13 converts a physical quantity such as pressure into an electric signal and outputs it to the signal processing circuit 14. The signal processing circuit 14 performs signal processing such as linearity correction on this electric signal and outputs it as a pulse width signal PWM.

V _R1 ′ and V _R2 ′ are the pulse width signals PWM
A reference voltage V _R1 for level conversion of
A reference voltage source for generating V _R2 , and these reference voltage sources V _R1 ′ and V _R2 ′ are connected between each one of the switching ends of the switch SW ₁ and the connection point CN1.

The common end of the switch SW ₁ is connected to a filter FL composed of a resistor R4 and a capacitor C1 and is switched by a pulse width signal PWM. Therefore, at the common end of the switch SW _1, the levels are the reference voltages V _R1 and V _R2.
A pulse-shaped signal which is switched by the pulse width signal PWM is obtained between the two, and the filter FL smooths this signal to obtain a corresponding analog signal.

This analog signal is buffered by the buffer amplifier Q3 and the sensor signal V _{a is} output at its output end.
Is output as. Inverting input terminal (-) of error amplifier Q4
Is applied with a divided voltage obtained by dividing the reference voltage V _R1 by the resistors R5 and R6, and the feedback resistor R2 is applied to the non-inverting input terminal (+) thereof.
A divided voltage obtained by dividing the voltage of the sum of the feedback voltage V _f generated at both ends of the sensor signal V _a by the resistors R7, R8 and the feedback resistor R2 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. As a result, the transistor Q1 outputs 2 as a unified current signal I ₀ (= 4 mA to 20 mA) corresponding to the sensor signal V _a.
The data is output to the receiving resistor R1 via the book transmission lines L1 and L2.

Therefore, the current signal I ₀ responds only to the sensor signal V _a which is the output signal from the sensor 13 0 to
Variable constant current of 16mA and base current of 4mA flowing through transistor Q1 and Zener diode D3.
It is sent to the receiving resistor R1 as a current that is the sum of the constant current of (0%).

[0012]

However, the two-wire type transmitter as described above has a high starting resistance R at the time of starting.
The current flowing through 3 causes a current to flow through the Zener diode D3,
A primary voltage V1 is generated at both ends of this, and the circuit is started using this, but since the current consumption of the two-wire type transmitter is limited, the current flowing through the starting resistor R3 cannot be increased.

Therefore, when the signal processing circuit 14 equipped with a microprocessor or the like which consumes a large amount of current at the time of starting the circuit is used, it becomes insufficient to generate the primary voltage V1 due to the current flowing through the starting resistor R3, and thus switching is performed. There is a problem that the power supply 12 does not start normally, the secondary voltage V2 does not reach a predetermined value, and the circuit does not start.

[0014]

In order to solve the above problems, the present invention receives a current supply from a load side via two transmission lines and at the same time, a sensor measures the physical quantity to be measured. In the 2-wire type transmitter that converts the signal into a current signal by the signal processing circuit and transmits it as a current signal to the load side via the transmission line, the current at the start of the 2-wire type transmitter A reference voltage source in which a reference voltage is set to a value that determines a signal, a current detection unit that detects that the consumption current in the preceding two-wire type transmitter reaches a steady value, and outputs a switching signal, The sensor signal output from the signal processing circuit and the reference voltage are switched by the switching signal, and the current signal is controlled by the output of the switching means.

[0015]

[Operation] The reference voltage source has a reference voltage set to a value that determines the current signal flowing to the load side required for starting the 2-wire type transmitter, and the current detection means uses the current consumption of the 2-wire type transmitter. Is detected as a steady value and a switching signal is output.

The switching means switches between the sensor signal output from the signal processing circuit to which the electric signal from the sensor is input and the previous reference voltage according to the previous switching signal. The current signal is controlled by the output of the switching means. In this way, it is possible to avoid a situation where the current becomes insufficient at the time of startup and the system cannot be started, and stable startup is possible.

[0017]

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. The parts having the same functions as those of the conventional two-wire transmitter shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be appropriately omitted.

The two-wire transmitter 15 shown in FIG. 1 is different from the two-wire transmitter 10 shown in FIG. 4 in that a switch SW ₂ and a reference voltage source V _R3 ′ are provided after the switch SW ₁ . The common end of the switch SW ₁ is connected to one end a of the switching end of the switch SW ₂ , and the other end b of this switching end is connected to a reference voltage source V _R3 ′ having a reference voltage V _R3 between it and the connection point CN1. ing.
The common end c is connected to the resistor R that constitutes the filter FL.
4, the switch SW ₂ is connected to one end of the signal processing circuit 1
It is switched by the switching signal SS outputted from the No. 4.

[0019] The reference voltage V _R3 is, V _R1> V _R3> These size relationships V _R2 is selected such that can flow the current signal I ₀ of a magnitude normally voltage can be established when the power is supplied It is considered to be a value. The signal processing circuit 14 detects the magnitude of the consumption current I _a consumed by the load of the switching power supply 12, confirms that the steady state is reached, and outputs the switching signal SS to the switch SW ₂ .

Next, the operation of the embodiment configured as described above will be described with reference to the waveform chart shown in FIG. Figure 2
Before the power is turned on (up to time t ₁ ) shown in (a), the switch SW ₂ is connected to the switching end b side. In this state, when the power is turned on at the time point t ₁ , the reference voltage V _{R 3} is applied to the buffer amplifier Q3, and _a sensor signal V _a sufficient to allow a large current signal I ₀ to flow at the output terminal is generated.

The error amplifier Q4 is connected to the sensor signal V _a via the transistors Q2 and Q1 so as to correspond to the sensor signal V _a .
As shown in (d), via the Zener diode D3,
A large current signal I _{01 is} passed through the receiving resistor R1.

As a result, a primary voltage V1 capable of flowing a sufficiently large current across the Zener diode D3.
Can be generated. The switching power supply 12 voltage-transforms the primary voltage V1 and outputs the voltage to the secondary terminal T7 of 2
The next voltage V2 is generated.

This secondary voltage V2 is connected to the secondary terminal T7 as an internal load by the signal processing circuit 14 and the sensor 13.
For example, as shown in FIG. 2B, a large consumption current I _a1 sufficient to activate the circuit can be supplied.

After that, the signal processing circuit 14 detects that the start-up is completed and the consumption current I _a is stabilized at the steady value I _a2 as shown in FIG. 2B, and based on this, the signal processing circuit 1
4 outputs the switching signal SS (FIG. 2 (c)) to the switch SW ₂ at time t ₂ to switch to the switching end a side.

As a result, in a normal operation state, the signal from the sensor 13 is input to the buffer amplifier Q3, and the error amplifier Q4 outputs the corresponding sensor signal V _a via the transistors Q2 and Q1 as shown in FIG. 2 (d). As shown in FIG. 5, the current signal I ₀₂ is passed through the Zener diode D3 to the receiving resistor R1.

FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention. In the embodiment shown in FIG. 1, the signal processing circuit 1
4 outputs the switching signal SS for switching the switch SW ₂ , but in this embodiment, the consumption current detection circuit 17 is provided on the secondary side of the switching power supply 12 to reduce the consumption current consumed by the sensor 13 and the signal processing circuit 14. The switch signal CS is detected and the switching signal CS is output to the switch SW ₂ based on the detection. Also in this case, a waveform diagram similar to that shown in FIG. 2 is obtained.

[0027]

As described above in detail with reference to the embodiments, according to the present invention, in a two-wire type transmitter whose current consumption is limited, a current signal necessary for starting is previously sent to the load side at the time of starting. Since the data can be transmitted, stable operation can be ensured even if a signal processing circuit equipped with a microprocessor that requires a large current consumption at the time of startup, which cannot be used conventionally, is used.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating the operation of the embodiment shown in FIG.

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

FIG. 4 is a block diagram showing a configuration of a conventional two-wire transmitter.

[Explanation of reference numerals] 10, 15, 16 2-wire type transmitter 11 External circuit 12 Switching power supply 13 Sensor 14 Signal processing circuit

Claims (1)

[Claims] 1. A 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, which is signal-processed by a signal processing circuit, and then transmitted through the transmission line. In a two-wire type transmitter that transmits a current signal to the load side, a reference voltage source having a reference voltage set to a value that determines the current signal when the two-wire type transmitter is started, and the two-wire type transmission device. A current detection means for detecting that the consumption current in the power supply reaches a steady value and outputting a switching signal, and a switching means for switching the sensor signal output from the signal processing circuit and the reference voltage by the switching signal. A two-wire type transmitter, characterized in that the current signal is controlled by the output of the switching means.