JP3094663B2 - Two-wire transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method in which a current is supplied from a load side via two transmission lines, a physical quantity to be measured is converted into an electric signal by a sensor, and the electric signal is processed by a signal processing circuit. The present invention relates to a two-wire transmitter for transmitting a current signal to the load side via the transmission line, and more particularly to a two-wire transmitter improved so as to be able to stably start when power is turned on.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a configuration of a conventional two-wire transmitter. The two-wire transmitter 10 is connected to an external circuit 11 via transmission lines L1 and L2.
The DC voltage Eb required 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 L1 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. A starting resistor R is provided between the emitter and the collector of the transistor Q1.
3 are 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 has a constant voltage therebetween. Primary voltage V1
Have gained.

The primary voltage V1 is supplied to the switching power supply 12
Terminal T5 and the common terminal T connected to the connection point CN1
6 between the secondary terminal T7 and the common terminal T6.
And a DC secondary voltage V2 whose voltage has been transformed is output. The secondary voltage V2 is supplied to a sensor 13 for converting a physical quantity into an electric signal, a signal processing circuit 14 having a microprocessor for processing the electric signal, and the like.

The sensor 13 converts a physical quantity such as pressure into an electric signal and outputs it to a signal processing circuit 14. The signal processing circuit 14 performs signal processing such as linearity correction on the 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-converting
A reference voltage source for generating V _R2 , and these reference voltage sources V _R1 ′ and V _R2 ′ are connected between one end of the switching terminal of the switch SW ₁ and the connection point CN ₁ .

[0008] Common terminal of the switch SW ₁ is connected to a filter FL composed of resistor R4 and the capacitor C1, it is switched by the pulse width signal PWM. Accordingly, the reference level to the common terminal of the switch SW ₁ is a voltage V _R1 and V _R2
A pulse-like signal which is switched by the pulse width signal PWM is obtained, and the filter FL smoothes this signal into a corresponding analog signal.

[0009] The analog signal is Baffuaringu by Baffua amplifier Q3 and the sensor signal V _a at its output
Is output as Inverting input terminal (-) of error amplifier Q4
A divided voltage obtained by dividing the reference voltage V _R1 by resistors R5 and R6 is applied to a non-inverting input terminal (+) of the feedback resistor R2.
Both ends the feedback voltage V _f and the divided voltage of the voltage of the sum was divided by resistors R7, R8 and a feedback resistor R2 of the sensor signal V _a generation of 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. 2 Thus, the transistor Q1 is the sensor signal V _a unification of current signals corresponding to I ₀ as (= 4mA to 20mA)
The signal is output to the reception resistor R1 via the transmission lines L1 and L2.

Accordingly, the current signal I ₀ is responsive only to the sensor signal V _a is the output signal from the sensor 13 0
16 mA of variable constant current and 4 mA of base current flowing through transistor Q1, Zener diode D3, etc.
The current is sent to the receiving resistor R1 as a sum current with the constant current of (0%).

[0012]

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

For this reason, when the signal processing circuit 14 having a microprocessor or the like which consumes a large amount of current is used at the time of starting the circuit, it is insufficient to generate the primary voltage V1 by the current flowing through the starting resistor R3. There is a problem that the power supply 12 does not start normally, the secondary voltage V2 does not reach the predetermined value, and the circuit does not start.

[0014]

According to the present invention, as a configuration for solving the above-mentioned problems, a current is supplied from a load side through two transmission lines, and a physical quantity to be measured is detected by an electric signal by a sensor. In a two-wire transmitter that converts the signal into a current signal through the previous transmission line to the load side via the previous transmission line, the current at the start of the two-wire transmitter A reference voltage source in which a reference voltage is set to a value for determining a signal, current detection means for detecting that the current consumption in the two-wire transmitter becomes a steady value and outputting a switching signal, There is provided switching means for switching between the sensor signal output from the signal processing circuit and the previous reference voltage by the previous switching signal, and the output of the switching means controls the previous current signal.

[0015]

[Operation] The reference voltage source is set to a value that determines a current signal flowing to the load side necessary for starting the two-wire transmitter, and the current detection means is the current consumption of the two-wire transmitter. , And outputs a switching signal.

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 reference voltage according to the switching signal. The current signal is controlled by the output of the switching means. In this way, it is possible to avoid a situation in which starting is impossible due to a shortage of current at the time of starting and stable starting is possible.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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. Parts having the same functions as those of the conventional two-wire transmitter shown in FIG. 4 are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

The two-wire transmitter 15 shown in FIG. 1, in that a switch SW ₂ and the reference voltage source V _R3 'downstream of the switch SW _1, differs from the two-wire transmitter 10 shown in FIG. Common terminal of the switch SW ₁ is connected to one end a of the switch end switch SW _2, the other end b of the switch end is connected a reference voltage source V _R3 'having a reference voltage V _R3 between the connection point CN1 ing.
The common end c is connected to a resistor R constituting the filter FL.
4 and the switch SW ₂ is connected to the signal processing circuit 1.
4 is switched by the switching signal SS output from the control signal No. 4.

The magnitude of the reference voltage V _R3 is selected so that V _R1 > V _R3 > V _R2 , and a current signal I _{0 of a} magnitude that can normally establish a voltage when the power is turned on can flow. Value. The signal processing circuit 14 detects the magnitude of the consumption current I _a load of the switching power supply 12 is consumed, and outputs a switching signal SS to verify that in the steady state to the switch SW _2.

Next, the operation of the embodiment configured as described above will be described with reference to the waveform diagram shown in FIG. FIG.
Before power shown in (a) (to time t _1), the switch SW ₂ is connected to the switch end side b. When power is applied at time t ₁ in this state, the reference voltage V _{R 3} is applied to Baffua amplifier Q3 sufficient flown large current signal I ₀ at its output sensor signal V _a is generated.

The error amplifier Q4 via a transistor Q2, Q1 so as to correspond to the sensor signal V _a, 2
As shown in (d), via the Zener diode D3,
A large current signal I ₀₁ to receive the resistor R1.

As a result, a primary voltage V1 that allows a sufficient current to flow across the Zener diode D3
Can be generated. The switching power supply 12 converts this primary voltage V1 into a voltage,
A next voltage V2 is generated.

The secondary voltage V2 is supplied to the signal processing circuit 14 and the sensor 13 connected to the secondary terminal T7 as an internal load.
For example, as shown in FIG. 2B, a large consumption current _Ia1 sufficient to activate the circuit can be passed.

Thereafter, the signal processing circuit 14 detects that the start-up is completed and the consumption current _Ia has stabilized to the steady value _Ia2 as shown in FIG. 2B, and based on this, the signal processing circuit 1
4 outputs the switching signal SS at time t ₂ to (FIG. 2 (c)) to the switches SW ₂ switch to switch end a side.

[0025] Consequently, as a normal operating condition, the Baffua amplifier Q3 is inputted a signal from the sensor 13, the error amplifier Q4 is a corresponding sensor signal V _a through transistor Q2, Q1, FIG. 2 (d) as shown in via the Zener diode D3, flow to the receiving resistor R1 as a current signal I _02.

FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention. In the embodiment shown in FIG.
4 outputs the switching signal SS for switching the switch SW _{2. In} this embodiment, the current consumption detecting circuit 17 is provided on the secondary side of the switching power supply 12, whereby the current consumed by the sensor 13 and the signal processing circuit 14 is reduced. detecting, a signal CS Setsu on this basis is obtained so as to output to the switch SW _2. In this case, the waveform is similar to the waveform shown in FIG.

[0027]

As described above, according to the present invention, according to the present invention, in a two-wire transmitter whose current consumption is limited, a current signal necessary for starting is previously supplied to the load side at the time of starting. Since transmission is possible, 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, can be used.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a block diagram showing a 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 symbols]

 10, 15, 16 Two-wire transmitter 11 External circuit 12 Switching power supply 13 Sensor 14 Signal processing circuit

Claims (1)

(57) [Claims] An electric 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, and the electric signal is processed by a signal processing circuit, and the electric signal is processed by a signal processing circuit. A two-wire transmitter for transmitting 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 transmitter is started; Current detection means for detecting that the current consumption of the device becomes a steady value and outputting a switching signal; and switching means for switching the sensor signal output from the signal processing circuit and the reference voltage by the switching signal. A two-wire transmitter, wherein the current signal is controlled by an output of the switching means.