JPS6323697B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an analog/digital communication method that is applied when transmitting an analog signal and a digital signal through the same transmission path in industrial measurement, etc. .

[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 current 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 to
Since personnel must make rounds to perform maintenance and inspection work, there is a growing demand for a means that can make adjustments, check operating conditions, etc. by remote control using existing equipment.

In addition, the reception of unified signals is performed centrally at supervisory control panels, etc., which accommodates approximately 1000 transmission lines for unified signals, so When making adjustments or checking the operating status by remote control,
It has become necessary to be able to easily confirm where the other party's differential pressure transmitter, electromagnetic flow meter, etc. are installed.

[Object and structure of the invention]

The present invention has been made based on such a conventional demand, and allows digital signals to be freely transmitted and received between a transmitter such as a differential pressure transmitter or an electromagnetic flowmeter and a communication device, and also enables the transmitter to transmit and receive digital signals. The purpose of this invention is to provide an analog/digital communication method that not only transmits a digital signal containing its own individual code, but also allows a communication device to receive an analog signal, and in order to achieve this purpose. In a communication method in which a current value supplied from a power source is changed by a transmitter to produce an analog signal, a voltage drop element is inserted into a transmission path through which the analog signal passes, and the current passing through the voltage drop element is transmitted to a communication device. The transmitter changes the current value into a pulse and transmits it as a digital signal, which is then received by the transmitter and becomes the analog signal. The digital signal is transmitted as a digital signal including a code, the digital signal is received by the communication device, and the analog signal is received by the communication device based on the terminal voltage of the voltage drop element.

〔Example〕

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.
Power supply units PS _{1 to} PSn are provided to supply current to each of a plurality of two-wire transmission lines (hereinafter referred to as transmission lines) consisting of La ₁ , Lb 1 to Lan, and Lbn, and each transmission line is Transmitters Tx ₁ to Txn such as differential pressure transmitters and electromagnetic flowmeters are connected to each end, and the transmitters
Tx ₁ to Txn individually control the current value I and pass it to the transmission path as an analog signal.

In addition, in each transmission path via the terminal plate TB, two resistors R _L1 to R _L n, Rc ₁ are installed as voltage drop elements.
~Rcn are each inserted in series, and the resistor R _L n
In this circuit, this terminal voltage is applied to an analog-to-digital converter (hereinafter referred to as ADC), which converts it into a digital signal and then drives a display device such as a numeric display DP, which converts the value of the analog signal indicated by the current value I. It is supposed to be displayed after receiving it.

On the other hand, a communication device CE is selectively connected to the transmission path closer to the transmitters Tx ₁ to Txn than the resistors R _L1 to R _L n and Rc ₁ to Rcn, and this allows the current value I to be When it is changed into a pulse and sent to the transmitter Txn as a digital signal, this is received by the transmitter Txn, and in response to the reception, the transmitter Txn similarly changes the current value I, and sends it as a digital signal to the transmitter Txn.
This is to be received at the communicator CE in order to transmit it to the CE.

Note that this is the same for any oscillator Tx and resistor R _L.

FIG. 2 is a waveform diagram showing how the current value I flowing through the resistor R _L changes over time t.
The analog signal Sa determined according to the measured value of Tx is
In this case, the current flows between the line terminals T ₁ and T ₂ of the communication device CE in response to the start of transmission from the communication device CE, which varies in the range of 4 to 20 mA.
Due to Ic, the current value I is up to approximately
When the flag bit B _F is transmitted, which increases to 36 mA, the oscillator Tx stops the flow of the analog signal Sa. Therefore, during the period of the digital signal Sc, the start bit Bs, the first bit B ₁ ~
The eighth bit _B8 is transmitted.

In addition, flag bit B _F and start bit
Bs has a current value I of about 20 mA, but the first bit _B1 to the eighth bit _B8 indicating the data are, for example,
Approximately 20 mA is maintained when the logic value is "1", and approximately 4 mA is maintained when the logic value is "0".

This current value change causes a voltage drop change in the resistors R _L and Rc, which is applied to the oscillator Tx as a voltage change between the lines La and Lb on the oscillator Tx side. received by.

Then, the oscillator Tx outputs the digital signal St after a certain period of time ts ₁ after the end of the digital signal Sc.
During the period, the current value I is similarly changed by the current It, and the flag bit B _F , start bit Bs, and
The first bit _B1 to the eighth bit _B8 indicating its own individual code and data are transmitted.

As a result, a voltage change occurs between the lines La and Lb as described above, and this is received by the communication device CE.

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.

Note that the transmitter Tx returns to its original state after a predetermined period _ts2 from the end of transmission of the digital signal St, and starts distributing the analog signal Sa.

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, ADC, A/Dc, etc. are arranged around the
They are connected by a bus BUc, and the processor CPUc executes the program stored in the fixed memory ROMc, and stores the specified data in the 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 “ A transmission pulse of "H" is applied to the current control section CCc, and in response, a current Ic flows from the line terminal _T1 to _T2 .

In addition, the line voltage between the lines La and Lb is applied to one input of the comparator CPc via a wave wave device FLcd such as a band wave wave device that passes only the frequency component of the digital signal St, and the other input A comparison is made with the reference voltage Ecs given to the reference voltage Ecs.
Levels higher than Ecs are extracted as 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 ₂ is turned on. Then, the reception output indicating after the start bit Bs is given to the transmitter/receiver unit UARTc,
Transmitter Tx by indicator DPcd according to the output of this
The individual code and received data are displayed.

On the other hand, the resistors given from line terminals T ₁ and T ₃
The terminal voltage of Rc is given to an averaging unit AVRc such as an integrating circuit through a wave generator FLca such as a low frequency wave generator that blocks the frequency components of the digital signals Sc and St.
Here, the analog signal Sa is extracted, and
It is converted into a digital signal by ADC/A/DC and given to the 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.

FIG. 4 is a circuit diagram of the current control unit CCc, in which the transmission pulse from the AND gate Gc ₁ passes through a low-frequency filter for noise removal using a resistor R ₁ and a capacitor C ₁ , and is transmitted by a differential amplifier A ₁ . In addition to being amplified,
In order to turn on the field effect transistor _Q1 , a current Ic passes through the resistors _R2 and _R3 .

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.

FIG. 5 is an external perspective view of the communication device CE, in which the display devices DPca, DPcd and the keyboard KBc are arranged in a hand-held case 1, and a cord 2 is led out. track terminal
Clips 3 as T ₁ to T ₃ are connected and the line
La and Lb can be attached and detached freely.

Figure 6 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, which processes the output of the ADC/A/Dt and converts the digital signal sent out by the processor CPUt into an analog signal, and
An address setter ASTt is provided for setting individual codes using a digital switch or the like.

In addition, a power supply circuit PSt is connected to the line terminal _T1 , and in this case, it takes in a current of 4 mA from the line La, stabilizes it, and supplies it to each part as a local power supply Et, and also connects the line La and Lb. The line voltage of Sc is applied to the comparator CPt in the same manner as in Fig. 3 via a wave transducer FLt such as a band wave transducer that passes only the frequency component of the digital signal Sc. Similarly compared with the reference voltage Ets,
The comparator CPt generates a reception output, which is applied to the interface I/Ft and also to the transmitter/receiver unit UARTt via the AND gate _Gt1 .

Therefore, the flag bit of digital signal Sc
The reception output corresponding to B _F is the interface I/
Ft to the processor CPUt, and in response, the processor CPUt
Through Ft, send out gate pulse Ptg ₁ as “H” and send out control pulse Ptc ₁ , AND
At the same time as turning on gate Gt ₁ , the switch circuit
Switch SWt ₁ to AND gate Gt ₂ side.

Therefore, the start bit of the digital signal
The reception output from Bs onwards is given to the transmitter/receiver unit UARTt, where the digital signal Sc is received, and the current controller CCt is turned off, stopping the flow of the analog signal Sa.

Then, after receiving the digital signal Sc, the processor CPUt outputs an "H" gate pulse via the interface I/Ft as the period _ts1 elapses.
When transmitting Ptg ₂ and controlling the transmitting/receiving unit UARTt, a transmission pulse is transmitted via the ON AND gate Gt ₂ , and is applied to the current control unit CCt via the switch circuit SWt ₁ , resulting in a digital signal. The current flows through the current control unit CCt according to St.

However, the processor CPUt is the address setting device.
Transmits and receives individual codes according to the output of ASTt
Since the digital signal St is supplied to the UARTt, an individual code is included in the digital signal St.

When the transmission of the digital signal St is finished and the period ts ₂ has elapsed, the processor CPUt outputs the control pulse Ptc ₁
In order to stop sending out the switch circuit SWt ₁ is
The output is restored to the DAC/D/At side, and its output is given to the current control unit CCt, and the distribution of the analog signal Sa indicating the measured value of the sensor SS is resumed.

Note that the configuration of the current control section CCt is similar to that shown in FIG. 4.

In addition, the transmitter Tx is equipped with a non-volatile memory such as EAROM, in which necessary data is stored, and this data is retained even if the power is cut off. .

Therefore, it is possible to insert the resistor Rc into the terminal board etc. that accommodates the transmission line, connect the communication device CE, and perform the desired data transmission and reception with the transmitter Tx. After checking the parts, 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 also to remotely check the reception of analog signals and the operating status of the transmitter Tx. In addition to making it possible to check, the objective can be achieved by only making some additions to conventional equipment.

However, in Fig. 1, the power source for the oscillator Tx may be supplied by a separate line, or other impedance elements may be used in place of the resistors R _L and Rc, or the resistor Rc It is also possible to use only one.

In addition, in FIG. 2, a parity check bit may be added to each byte, or a specific byte may be allocated for an individual code. The structure of the diagram is
The selection is arbitrary depending on the situation, and the shape shown in Fig. 5 is not limited to hand-held type, but can also be panel-mounted type, etc.
Various modifications are possible, such as selecting and connecting transmission paths using a switch.

〔Effect of the invention〕

As is clear from the above explanation, 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 the installation of the transmitter Not only can the parts be confirmed reliably, but analog signals can also be received by the communication device, which provides a significant effect in remotely adjusting and monitoring the operating status 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 the current value, Fig. 3 is a block diagram of the communication device, and Fig. 4 is the current control in Fig. 3. FIG. 5 is an external perspective view of the communication device, and FIG. 6 is a block diagram of the transmitter. Tx ₁ ~ Txn... Transmitter, PS ₁ ~ PSn... Power supply section,
La ₁ , Lb ₁ ~ Lan, Lbn...Line, CE...Communication device,
I... Current value, R _L1 ~ R _L n, Rc ₁ ~ Rcn... 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 unit, KBc...keyboard,
DPcd, DPca……display unit, I/Fc, I/Ft……
Interface, FLcd, FLca, FLt... Wave device, CPc, CPt... Comparator, Ecs, Ets... Reference voltage, CCc, CCt... Current controller, Ec _L ... Local power supply, D/At... DAC (digital-to-analog converter), ASTt...address setter, SWt ₁ , SWt ₂ ...
...Switch circuit, Ct...Capacitor, A/Dc...
...ADC (Analog Digital Converter), 3...Clip.

Claims (1)

[Claims] 1. A communication method in which a current value supplied from a power source is changed by an oscillator to produce an analog signal, in which a voltage drop element is inserted into a transmission path through which the analog signal passes, and the voltage drop element The current flowing through the voltage drop element is changed into a pulse shape by a communication device and transmitted as a digital signal, which is received by the transmitter and converted into the analog signal.The change in current value is stopped and the current flowing through the voltage drop element is changed into a pulse shape. and transmitting it as a digital signal containing its own individual code, and receiving the digital signal in the communication device, and receiving the analog signal in the communication device based on the terminal voltage of the voltage drop element. analog and digital communication methods. 2 Using a two-wire transmission line as the transmission line,
The analog/digital communication method according to claim 1, characterized in that an oscillator whose power source is a current supplied from a power supply section is used. 3. The analog/digital communication method according to claim 1, which uses a communication device that is detachable from the transmission path. 4. The analog device according to claim 1, characterized in that a resistor is used as the voltage drop element.
Digital communication methods. 5. Analog/digital communication according to claim 1, characterized in that two voltage drop elements are used and a communication device that receives an analog signal based on the terminal voltage of one of them is used. Method. 6. The analog/digital communication method according to claim 1, which uses a transmitter and a communication device that are controlled by a processor that executes a program. 7. The analog/digital communication method according to claim 1, which uses a transmitter that transmits a digital signal containing an individual code set by an address setting device.