JPS6234299A - Two-wire type transmitter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to a two-wire transmission device that converts a physical quantity to be measured into an electrical signal and transmits current to a remote load via a two-wire line. In particular, the present invention relates to the effective use of power source energy obtained via a two-wire line.

<Prior art> Fig. 4 As a two-wire transmission device since K12m,
6434r Title of Invention: Transmitter" (corresponding U.S. Pat. No. 4,084,155) and will be described.

10 is a sensor such as a vortex flow meter, which outputs a frequency signal corresponding to the flow rate. This frequency signal is transmitted to the amplifier 11
The signal is amplified and applied to the Schmitt circuit 12. The Schmitt circuit 12 generates a square wave pulse 1 whose rate of return corresponds to the frequency of the borrow signal. This frequency is frequency/11! A pressure converter 13 converts it into an analog voltage (2) corresponding to the flow rate, and a conversion circuit 14 converts this analog voltage (5) into a unified current of, for example, 4 to 20 mA.

The conversion circuit 14 has a load 15 such as an indicator, terminals T10 and T
Two-wire line 11 connecting terminals T2o and T21 respectively
ゝ■、1. When a current is supplied from the σ current power supply 16 via L2, the conversion circuit 14 controls the current to correspond to the current iAK, for example.

A diode 17, a current control transistor 8, a Zener diode 19, and a resistor 20 are connected in series between the terminals T2 and T2, and a battery 21 is connected in parallel to both ends of the Zener/diode 19.

The voltages +V and -V generated across the series connection of the Zener diode 19 and the resistor 20 are applied across the series circuit of the constant current diode 22 and Zener diode 23, and A reference voltage ■ is obtained at the connection point.

This reference voltage (2) is applied to the positive input terminal of the differential amplifier 24, and a constant voltage v'6 is obtained at its output terminal. This constant voltage V
is voltage-divided and applied to the positive input terminal of the differential amplifier 25 as a predetermined bias voltage.

Its negative input terminal has frequency/1! An analog voltage V corresponding to the output signal of the sensor 10 from the output end of the pressure transducer 13
is applied, and the corresponding voltage developed at its output controls the transmission current flowing through the current control transistor 18.

26 is a counter circuit whose power supply +V5. -Vb is a battery 21 that is independent of the power supply +V and -V of the conversion circuit.
The square wave pulse P of the Schmitt circuit 12 is frequency-divided by the frequency dividing circuit 27, and the pulses are counted.

Transmission flowing to load 16? tl:#L is, for example, 4-4-
In this case, when the output from the sensor 10 is zero, the circuit excluding all the counter circuits 26 operates T! i style is 4. It is selected to consume all mA or less, for example 3! maintain circuit power with crystals. Therefore, the battery 21 is charged with 1 mA to 17 mA. counter 26
The current consumption in the battery 21 increases as the output of the sensor 10 increases, but at the same time the transmission current also increases, so the discharging rate and charging rate per unit time in the battery 21 are balanced, the energy utilization rate is averaged, and the counter 26 causes the transmission current to be substantially unaffected.

Power for all circuits except the counter 26 is supplied from voltages +v and -vK.

<Problems to be Solved by the Invention> However, in such a conventional two-wire transmission device, when the battery 21 is discharged, both ends of the Zener diode 19 are short-circuited, causing problems such as in the differential amplifier 24 and 25. The problem arises that no power supply voltage is applied and no transmission current of 4-20 mA is transmitted.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a load, a two-wire line, a first constant voltage element, a t-current control means for controlling the transmission current flowing through the load, and a battery. are connected in series to a DC power supply to form a transmission path, and a second constant voltage element is connected in parallel to an I series circuit in which at least a current regulating means and a tg1 constant voltage are connected in series via a constant current circuit. and applying a constant voltage across the second constant voltage element as a circuit power supply of a signal conversion circuit that converts the physical liquid to be measured into an electric signal corresponding to the physical liquid to be measured,
When this battery completes charging in parallel with the battery, ′r! 1. A third constant voltage element that allows current to flow is connected, and the voltage across the first constant voltage element is set so that the voltage is higher than the sum of the lowest voltage that does not impair the constant current characteristics of the constant current circuit and the constant voltage of the second constant voltage element. The battery power supply is connected as a power supply for another auxiliary circuit independent of the circuit power supply, and the current control means is controlled by the output of the signal conversion circuit.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. Note that parts having the same functions as those of the two-wire transmission device shown in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

A Zener diode 28 is connected between terminals T11 and T21.
, current control transistor 18. Zener diode 19,
A feedback resistor 29 is connected in series.

Furthermore, a Zener diode 28, a current control transistor,
A series circuit of a constant current circuit 30 and a Zener diode 31 is connected in parallel to both ends of the series-connected circuit of the Zener diodes 19.

Voltage across Zener/diode 31 +V, -V
For example, it is used as a power supply voltage for the sensor circuit 32, digital processing circuit 33, analog circuit 34, etc.

A series circuit of a diode 35 and a battery 21 is connected in parallel to the 1i1ii end of the Zener diode 19. Voltage terminal %+-Vb at 1ifii end of battery 21
is used as a power source for the auxiliary circuit 36. Auxiliary circuit 36
Information is exchanged with the digital processing circuit 33 via line 37 and controlled. The auxiliary circuit 36 includes, for example, a liquid crystal indicator 1 voice device.

Further, the voltage across the resistor 290 is fed back to the analog circuit 34 via the line 38 as a voltage proportional to the transmission current (2).

The sensor circuit 32 converts, for example, flow rate or pressure into a physical analog voltage. The converted analog voltage is input to the digital processing circuit 33.

The digital processing circuit 33 includes, for example, an analog/digital converter, a microprocessor, a memory, and a digital/analog converter, digitizes the input analog voltage completely, performs necessary digital operations, converts it into an analog voltage, and converts the input analog voltage into an analog voltage. Output to 34. Digital processing circuit 33
also instructs the auxiliary circuit 36 to operate, for example, a liquid crystal indicator in the auxiliary circuit 36, if necessary.

The analog circuit 34 receives the output voltage of the digital processing circuit 33 and controls the current control transistor 18 so that the differential voltage between the feedback voltage 1 and the pressure generated across the resistor 29 becomes zero.

The transmission current 5 controlled in this manner is transmitted to the load 15, and a value corresponding to the physical quantity detected by the sensor circuit 32 can be determined from the voltage generated across the load 15.

By the way, the consumption T in the constant current circuit 30! i-style I. For example, if the number of people is 3.8m, a current of (IL -3,8,) flows through the am control transistor 18, the battery 21 is charged with this current, and the auxiliary circuit 36 is further charged with this current.
to drive. When charging of batch 1J21 is completed, the signal current controlled by current control transistor 18 is shunted by Zener diode 19.

This is to prevent radiation from occurring.

The Zener diode 28 is for ensuring the minimum voltage that the constant current circuit 30 exhibits constant current characteristics, and even if the battery 21 is discharged, the constant current circuit 30K
For example, the constant voltage value of the Zener diode 28 is selected so that an Oi2E current of I c =3-8 mA flows. For example, the constant voltage value of the Zener diode 31 is 6.4 (V).

If the constant current circuit 30 exhibits constant current characteristics at 1 V or more, the constant voltage value of the Zener diode 28 is 7.4 (V).
The value shall be above. Note that the Zener diode 31 is selected so that normal voltages +V and -VK are obtained when the current consumption in the constant current circuit 30 is 4 mA or less, for example, 3.8 mA.

C Also, the current consumption from the battery 21 is selected so that when the control signal from the digital signal processing circuit 33 to the auxiliary circuit 36 is zero, the current consumption from the battery 21 is zero.

According to such a configuration, even if the battery 21 is completely discharged and the Zener diode 19 is short-circuited, a transmission current of 4 to 20 mA corresponding to the output of the sensor circuit 32 can be transmitted to the load 15. can be supplied.

FIG. 2 is a partial block diagram showing an entire embodiment of the pond of the present invention. In this case, a Zener diode 19 is inserted on the collector side of the current control transistor 18, and a Zener diode 28 for maintaining the circuit voltage when the battery 21 is completely discharged is placed on the emitter side of the current control transistor 18. Accordingly, a level shift circuit 39 for changing the operating level of the auxiliary circuit 36 is inserted on the control input side of the auxiliary circuit 360. Even with this configuration, even if the battery 21 is completely discharged, current transmission of 4 to 20 mA, which is the basic function of a two-wire transmission device, is ensured.

In the embodiment shown in FIG. 3, in addition to the basic configuration shown in FIG. 1, a Zener diode 4o is inserted between the connection point between the constant current circuit 30 and the Zener diode 28 and the terminal T11, and a diode 41 and a Batteries 42 are connected in series, and the power supply voltages of the auxiliary circuit 36 are +Vb and -Vb. In this case as well, the level shift circuit 43 is inserted on the control input side of the auxiliary circuit 36, as in the embodiment shown in FIG.

Even with such a configuration, the object of the present invention can be achieved.

11 in each example! As the current control transistor 18, not only a bipolar transistor but also a MO8FETK may be used.

Furthermore, when this two-wire transmission device is installed in a hazardous location, a resistor is connected in series to the battery 21 to limit energy release.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, even in a two-wire transmission device, which is limited in terms of electric energy, a unified current of, for example, 4 to 20 mA can be achieved.
It is possible to operate in an auxiliary circuit that requires a current consumption of 4 to 20 mA, which corresponds to the physical quantity in the sensor circuit, even if the battery (21) is discharged and the drowsy energy is gone. The basic function of transmitting the current can be ensured.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a partial block diagram showing a first modified embodiment of the invention, and FIG.
The figure is a partial block diagram showing a second modified embodiment of the present invention.
FIG. 4 is a block diagram showing the configuration of a conventional two-wire transmission device. 1o...sensor, 12...Shemitt circuit, 13.
... Frequency 'voltage converter, 14... Conversion circuit, 15
...Load, 16...DC power supply, 18...Current control transistor, 19.28.31゜40...Zena diode, 21.42...Battery, 26...Counter circuit, 3o... ... constant current circuit, 32... sensor circuit. 33... Digital processing circuit, 34... Analog circuit, 36... Auxiliary circuit, 39.43... Level shift circuit.

Claims (1)

[Claims] A load, a two-wire line, a first constant voltage element, a current control means for controlling the transmission current flowing through the load, and a battery are connected in series to a DC power source to form a transmission path, and the current control means and the first A signal conversion circuit which connects a second constant voltage element in parallel to a series circuit in which at least one constant voltage element is connected in series through a constant current circuit, and converts a physical quantity to be measured into an electrical signal corresponding to the series circuit. A constant voltage is applied across the second constant voltage element as a circuit power source, and a third constant voltage element is connected in parallel with the battery to allow current to flow when this battery completes charging, thereby controlling the constant current circuit. The voltage across the first constant voltage element is selected to be greater than the sum of the lowest voltage that does not impair current characteristics and the constant voltage of the second constant voltage element, and the power source of the battery is connected to the circuit power source. is connected as a power source for another independent auxiliary circuit, and the two-wire transmission device is characterized in that the output of the signal conversion circuit controls the current control means.