JPS6323693B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an analog/digital communication method and an apparatus thereof that are applied when transmitting an analog signal and a digital signal through the same transmission path in industrial measurement, etc. It is something.

[Prior art]

Conventionally, in industrial measurement, when transmitting the measurement output of a differential pressure transmitter, electromagnetic flowmeter, etc. to a remote point,
Generally, a unified signal such as 4 to 20 mA is used, and the measured value is indicated by the power supply value of this analog signal.

However, differential pressure transmitters, electromagnetic flowmeters, etc. are generally installed spread over a wide area, and in order to adjust them and check their operating status, it is necessary for staff to patrol and perform maintenance and inspection work. Therefore, there is a growing demand for a means that can make adjustments and check operating conditions by remote control using existing equipment.

[Object and structure of the invention]

The present invention has been made based on such conventional demands, and its first purpose is to transmit and receive digital signals superimposed on analog signals to and from transmitters such as differential pressure transmitters and electromagnetic flowmeters. In order to achieve this purpose, the present invention provides an analog/digital communication method in which a current value supplied from a power supply section is changed by a oscillator to produce an analog signal. changing the voltage in a pulse form to produce a digital signal, receiving the digital signal in the transmitter, superimposing it on the analog signal in the transmitter, and changing the current value in a pulse form to produce a digital signal; This system is characterized in that it receives a digital signal based on a change in the terminal voltage of a voltage drop element inserted into a transmission line through which an analog signal passes, and also receives the analog signal.

The second objective is to provide an analog/digital communication device that can freely transmit and receive digital signals in addition to analog signals between a transmitter and a communication device.
In a communication device consisting of a power supply unit that supplies current to a transmission line, and a transmitter connected to the transmission line and that changes the current of the transmission line to generate an analog signal, the communication device changes the voltage in a pulse-like manner and generates a digital signal. a voltage drop element connected in series with the power supply unit, and a circuit that receives the analog signal and a pulsed digital signal superimposed on the analog signal based on the terminal voltage of the voltage drop element. a circuit that receives the digital signal from the communication device based on a voltage change; and a circuit that superimposes the digital signal on the analog signal and changes the current value in a pulse shape and transmits it as a digital signal. The present invention is characterized in that it is provided with the above-mentioned transmitter.

Hereinafter, details of the present invention will be explained with reference to figures showing examples.

Figure 1 is a block diagram of the entire configuration, with lines L ₁ ,
A communication device CE having a power supply unit PS that supplies current to a two-wire transmission line (hereinafter referred to as a transmission line) consisting of L ₂ is provided, and at the other end of the transmission line, a differential pressure transmitter and an electromagnetic flow A transmitter Tx such as a meter is connected,
The oscillator Tx controls the current value I and passes it to the transmission line as an analog signal.

Further, in the communication device CE, a resistor Rc is inserted as a voltage drop element in series with the power supply section PS, and an analog signal is received based on the terminal voltage of this resistor Rc.

However, the voltage in the power supply section PS of the communication device CE changes in a pulsed manner, which changes the line voltage V, which is transmitted as a digital signal and received by the transmitter Tx. It has become a thing.

On the other hand, in response to the reception of the digital signal, the transmitter Tx superimposes it on the analog signal, changes the current value I in a pulse shape, and transmits it as a digital signal, so this changes the terminal voltage of the resistor Rc in the communication device CE. It is expected to be received as such.

FIG. 2 is a waveform diagram showing how the line voltage V and the current value I flowing through the transmission line change over time t. Although it is supposed to vary within the range of ~20mA, when transmission from the communication device CE is performed, the period of the digital signal Sc,
The line voltage V changes in a pulsed manner, which causes the flag bit B _F , start bit B _S , and first bit
_B1 to eighth bit _B8 are transmitted.

Each bit is indicated by an increase in the line voltage V, and the pulse width of flag bit _BF is set to be especially wide, and flag bit _BF and start bit _BS always change in the positive direction. However, the first bit _B1 to the eighth bit _B8 indicating data, for example, change in the positive direction when the logical value is "1", and remain unchanged when the logical value is "0". .

This line voltage change is detected by the transmitter Tx, thereby receiving the digital signal Sc.

Then, after a certain period ts has elapsed after receiving the digital signal Sc, the oscillator Tx changes the current value I in a pulsed manner while superimposing it on the analog signal Sa during the period of the digital signal St, and sets the flag bits B _F ,
The start bit B _S and the first bit B ₁ to the eighth bit B ₈ indicating data are transmitted in the same way as the digital signal Sc.

Therefore, in the communication device CE, the digital signal St is received as a change in the terminal voltage of the resistor Rc.

Although this example shows only the transmission and reception of one byte consisting of 8 bits, a desired number of bytes consisting of a predetermined number of bits may be transmitted and received in each of the digital signals Sc and St depending on the situation.

Also, change direction of each bit in negative direction or
The same applies to a pair of positive and negative directions.

Figure 3 is a block diagram of the communication device CE, which mainly includes a processor CPUc such as a microprocessor, a fixed memory ROMc, a variable memory RAMc, a keyboard KBc, a display device DPcd such as a numeric display, etc.
DPca, universal asynchronous transmitter/receiver (hereinafter referred to as transmitter/receiver) UARTc, and interface I/
Fc, analog/digital converter (hereinafter referred to as ADC) A/Dc, etc. are arranged around the bus line BUc.
are connected to each other by fixed memory
Processor programs stored in ROMc
CPUc executes and stores predetermined data in variable memory
Control operations are performed while accessing RAMc.

Here, if desired data is given from the keyboard KBc, the processor CPUc is
controls the transmitting/receiving unit UARTc and transmits the gate pulse Pcg ₁ as “H” (high level) via the interface I/Fc, so the AND gate Gc ₁ is turned on and the pulse sent from the transmitting/receiving unit UARTc The output shown in FIG. 2 is applied to the switch circuit SWc, and the switch circuit SWc is driven according to the waveform shown in FIG.

Then, the local power supplies Ec _L and Ec _U of different voltages constitute the power supply part PS together with the switch circuit SWc.
However, from the low voltage local power supply Ec _L to the high voltage local power supply
Ec _U is switched alternately and in a pulsed manner, and a voltage that changes in a pulsed manner is sent out between the line terminals T ₁ and T ₂ as a digital signal Sc via a resistor Rc inserted in series with these.

In addition, the terminal voltage of the resistor Rc is applied to one input of the comparator CPc via a band wave generator FLcd that passes only the frequency component of the digital signal St, and is applied to the other input of the comparator CPc. A comparison is made with a reference voltage Ecs, and a level higher than the reference voltage Ecs is extracted as a received output.

Therefore, after the digital signal Sc has been transmitted,
In response to the reception output corresponding to the flag bit B _F of the digital signal St being given via the interface I/Fc, the gate pulse Pcg ₂ is sent out as "H" from the interface I/Fc,
When AND gate Gc ₂ is turned on, the reception output corresponding to start bit Bs and after is sent to the transmitter/receiver unit UARTc.
The received data is displayed on the display device DPcd in accordance with the output thereof.

On the other hand, the terminal voltage of the resistor Rc is applied to an averaging circuit such as an integrating circuit via a wave generator FLca such as a low frequency wave generator that blocks the frequency components of the digital signals Sc and St.
AVRc, where the analog signal
Sa is extracted, converted into a digital signal by ADC/A/DC, and given to processor CPUc.

Therefore, the output of ADC/A/Dc is processed by the processor CPUc, and is also processed by the display device DPca.
The measured value represented by the analog signal Sa is received and displayed.

Figure 4 is a block diagram of the transmitter Tx, which includes the same processor CPUt and fixed memory as in Figure 3.
ROMt, variable memory RAMt, transmitter/receiver UARTt,
The interface I/Ft, etc. are connected by the bus BUt, and the processor CPUt performs control operations as shown in Figure 3, but the output of the sensor SS that detects differential pressure, flow rate, etc. is converted into digital signals. A digital-to-analog converter (hereinafter referred to as DAC) D/At is provided, the output of which is processed by a processor CPUt, and the output digital signal is converted into an analog signal.

In addition, a power supply circuit PSt is connected to the line terminal _T1 , and in this case, a current of 4 mA is taken in from the line _L1 , stabilized, and then supplied to _each part as a local power supply Et. The line voltage between _L2 and L2 is applied to the comparator CPt as in FIG. Similar to Figure 3, it is compared with the reference voltage Ets,
The comparator CPt generates a reception output and provides it to the interface I/Ft and also to the transmitter/receiver unit UARTt via the AND gate _Gt1 .

Therefore, in response to the detection of the flag bit B _F , a gate pulse Ptg ₁ of "H" is sent out, the AND gate Gt ₁ is turned on, and the digital signal Sc is received. After the reception of the digital signal Sc is completed, the period t _s
According to the progress of the process, the processor CPUt sends out an " _H " gate pulse Ptg ₂ via the interface I/Ft and controls the transmitting/receiving unit UARTt. Transmission data that changes in the positive direction is sent out and applied to one input of the adder ADD.

Note that the other input of the adder ADD is connected to a sensor.
When an analog signal corresponding to the measured value by SS is constantly given and gate pulse Ptg ₂ is not generated, only the output of DAC/D/At is sent to the current control section.
CCt, where a current with a value corresponding to the measured value passes as an analog signal Sa.
When the gate pulse Ptg ₂ occurs and the transmission data is sent from the transmitter/receiver unit UARTt, the adder ADD adds the two inputs, so the analog signal
In addition to being superimposed with Sa, the current flowing through the current control unit CCt changes in the positive direction in a pulse-like manner, and is transmitted as a digital signal St.

However, the value of the analog signal Sa and the data of the digital signal St are added in the processor CPUt, and then sent from the DAC/D/At to the adder.
The same applies if ADDt is omitted.

Further, the transmitter Tx has a nonvolatile memory such as EAROM, and stores necessary data therein, so that even if the power is cut off, these data are retained.

FIG. 5 is a circuit diagram of the current control unit CCt, and the output from the adder ADD via a low-frequency filter for noise removal using a resistor R ₁₁ and a capacitor C ₁₁ is as follows.
In addition to being amplified by the differential amplifier A ₁₁ , the internal impedance of the field effect transistor Q ₁₁ is controlled, and the current determined by this is passed through the resistor.
It is assumed that the connection passes through R ₁₂ and R ₁₃ .

However, the terminal voltage of the resistor R ₁₃ is negatively fed back to the differential amplifier A ₁₁ via the resistor R ₁₄ to maintain a current value corresponding to the output value of the adder ADDt.

Figure 6 shows the case where the auxiliary communication device CE ₂ is connected in parallel to the transmission path connecting the transmitter Tx and the communication device CE in Figure 1, and the communication device CE ₂ can be connected to any position on the transmission path. For example, the communication device CE is located in the control room and can communicate digital signals with the transmitter Tx, as well as with the communication device CE ₂ . There is. Furthermore, the communication device CE ₂ is capable of communicating with the transmitter Tx using digital signals, and is also capable of communicating with the communication device CE using digital signals.

Figure 7 is a block diagram of the auxiliary communication device CE ₂ , which includes a processor such as a microprocessor CPUc, a fixed memory ROMc, and a variable memory.
RAMc, keyboard KBc, display device DPc such as numeric display, universal asynchronous transmitter/receiver (hereinafter referred to as transmitter/receiver) UARTc, and interface I/Fc
etc. are arranged on the periphery and are connected to each other by a bus line BUc, and the processor CPUc executes the program stored in the fixed memory ROMc and performs control operations while accessing predetermined data to the variable memory RAMc. It's summery.

Here, if desired data is given from the keyboard KBc, the processor CPUc is
controls the transmitter/receiver unit UARTc and sends gate pulse Pcg ₁ as “H” (high level) via the interface I/Fc, so AND gates Gc ₁ and Gc ₂ are turned on and the output is sent from the transmitter/receiver unit UARTc. An increasing pulse Pu and a decreasing pulse Pd of “H” are applied to the current control unit CCc, and the power supply control unit CCc controls the line terminal according to the increasing pulse Pu.
While passing the current Ic from T ₁ to T ₂ , the pulse decreases
According to Pd, the control unit CCc sets the line terminal _T1 to the positive terminal,
A control voltage is sent out with the line terminal _T2 as the negative pole.

Therefore, when the current Ic passes, the resistor
The current value I flowing through Rc increases as the sum of the current It indicating the analog signal Sa and the current Ie, but on the other hand, when the control voltage is sent out, the voltage between the lines L ₁ and L ₂ increases and the current The value I decreases.

In addition, the line voltage between the lines L ₁ and L ₂ is applied to one input of the comparator CPc via a wave wave device FLc such as a band wave wave device that passes only the frequency component of the digital signal St, and the other A comparison is made with the reference voltage Ecs applied to the input of the reference voltage Ecs.
The above level is extracted as the received output.

Therefore, after the digital signal Sc has been transmitted,
In response to the reception output indicating the flag bit B _F of the digital signal St being given via the interface I/Fc, the gate pulse Pcg ₂ is sent out as "H" from the interface I/Fc, and the AND gate Gc ₃ is turned on. Then, the reception output indicating after the start bit B _S is given to the transmitter/receiver unit UARTc,
In response to this output, the received data is displayed on the display device DPc.

FIG _. 8 is a circuit diagram of _the current control unit CCc in FIG.
The increased pulse Pu from Gc ₁ is amplified by the differential amplifier A ₁ , and is also amplified by a field effect transistor or other transistor.
To turn on Q ₁ , current flows through resistors R ₂ and R ₃ .
IC is connected.

Note that the terminal voltage of the resistor _R3 is negatively fed back to the differential amplifier _A1 via the resistor _R4 , thereby maintaining the current Ic at a predetermined value.

On the other hand, an AND gate Gc ₂ through a low-pass filter similar to the one described above with a resistor R ₅ and a capacitor C ₂
The decreasing pulse Pd from Pd is inverted and amplified by the differential amplifier _A2 , and the same transistor as described above is used.
In order to turn on Q ₂ , the voltage of the local power supply Ec _L inserted in series is sent out as a control voltage via resistors R ₆ and R ₇ .

Note that the terminal voltage of the resistor R ₇ is negatively fed back to the differential amplifier A ₂ via the resistor R ₈ to maintain the current from the local power supply Ec _L at a predetermined value.

FIG. 9 is an external perspective view of the auxiliary communication device CE ₂ , in which a display device DPc and a keyboard KBc are arranged in a hand-held case 1, and a cord 2 is led out. A clip 3 is connected and can be freely attached to and detached from the lines L ₁ and L ₂ .

Therefore, the desired data transmission and reception can be performed using the transmitter Tx.
It becomes possible to update various adjustment values, setting values, etc. stored in the variable memory RAMt of the transmitter Tx by remote control, and
It becomes possible to remotely check the operating status of the transmitter Tx, and the purpose can be achieved with only a few additions to the conventional equipment.

However, in FIGS. 1, 4, and 6, the power for the transmitter Tx may be supplied by a separate line, and in FIG. add bits,
Alternatively, it is the same as adding an individual code of the transmitter Tx to the digital signal St, and the configurations shown in FIGS. 3 to 5 and 7 to 9 can be selected arbitrarily depending on the situation. , various modifications are possible.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to freely transmit and receive data to and from transmitters such as differential pressure transmitters and electromagnetic flowmeters without significantly changing existing equipment, and to receive analog signals. Since this can be performed independently of the transmission and reception of digital signals, remarkable effects can be obtained in remote adjustment and operation status monitoring of various transmitters.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention. Fig. 1 is a block diagram of the entire configuration, Fig. 2 is a waveform diagram of line voltage and current values, Fig. 3 is a block diagram of a communication device, and Fig. 4 is a transmitter. 5 is a circuit diagram of the current control section in FIG. 4, FIG. 6 is a block diagram of the entire configuration showing another embodiment, and FIG. 7 is a block diagram of the auxiliary communication device in FIG. 2. FIG. 8 is a circuit diagram of the current control section in FIG. 7, and FIG. 9 is an external perspective view of the auxiliary communication device. Tx...Transmitter, PS...Power supply, _L1 , _L2 ...Line, CE...Communicator, I...Current value, V...Line voltage, Rc...Resistor (voltage drop element) , Sa...analog signal, Sc, St...digital signal,
CPUc, CPUt...Processor, ROMc, ROMt
...Fixed memory, RAMc, RAMt...Variable memory, UARTc, UARTt...Transmission/reception section, KBc...
Keyboard, DPca, DPcd...display, I/Fc,
I/Ft...Interface, FLcd, FLca...
wave generator, CPc, CPt...comparator, Ecs, Ets...reference voltage, CCt...current control section, Ec _L , Ec _U ...local power supply, D/At...DAC (digital-to-analog converter), SWc, SWt...Switch circuit, Ct...Capacitor, A/Dc...ADC (analog-to-digital converter).

Claims (1)

[Claims] 1. A communication method in which a current value supplied from a power source is changed by an oscillator to generate an analog signal, in which the voltage of the power source is changed in a pulse form to generate a digital signal, and the digital signal is converted into an analog signal. The terminal voltage of a voltage drop element inserted into a transmission path through which the analog signal is received by the transmitter and superimposed with the analog signal in the transmitter to change the current value in a pulse-like manner into a digital signal. An analog/digital communication method characterized by receiving the digital signal based on the change and receiving the analog signal. 2. In a communication device consisting of a power supply unit that supplies current to a transmission line and a transmitter connected to the transmission line and that changes the current of the transmission line to generate an analog signal, the communication device changes the voltage in a pulse-like manner to generate a digital signal. a voltage drop element connected in series with the power supply unit, and a circuit that receives the analog signal and a pulsed digital signal superimposed on the analog signal based on the terminal voltage of the voltage drop element. a circuit that receives the digital signal from the communication device based on a voltage change; and a circuit that superimposes the digital signal on the analog signal and changes the current value in a pulse shape and transmits it as a digital signal. An analog/digital communication device characterized by comprising: the transmitter. 3 Using a two-wire transmission line as the transmission line,
3. The analog/digital communication device according to claim 2, characterized in that an oscillator whose power source is a current supplied from a power supply section is used. 4. The analog device according to claim 2, characterized in that a resistor is used as the voltage drop element.
Digital communication equipment. 5. The analog/digital communication device according to claim 2, characterized in that it uses a transmitter and a communication device that are controlled by a processor that executes a program. 6. The analog according to claim 2, characterized in that a communication device is used, which is equipped with local power supplies each having a different voltage, and is provided with a power supply unit that changes the voltage in a pulsed manner by switching between the local power supplies.・Digital communication equipment.