JPH0442720B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a two-wire transmitter that transmits signals and supplies power via a common two-wire transmission path. More specifically, the present invention has a microcomputer on the transmission end side, processes the signal to be transmitted by this microcomputer, and transmits it to the reception end side via a two-wire transmission line.
This relates to wire transmitters.

(Prior art) As a conventionally known two-wire transmitter, for example,
There is one described in 49-42936.

This device, as shown in the block diagram of Figure 2,
Current adjustment means 1 for adjusting the current flowing to load Lo
Then, the signal ei to be transmitted is applied to the current adjusting means 1.
, a feedback resistor 3 that obtains a voltage according to the load current IL, and a feedback circuit 4 that negatively feeds back the voltage generated across the feedback resistor to the input side of the voltage response means 2. There is.

Conventional equipment with this configuration
It has the advantage of being able to supply a load current IL that accurately corresponds to ei to the load Lo, but it is also possible to correct the signal to be transmitted with another signal, or perform predetermined calculations, such as linearization. It is not possible to perform calculations, square root calculations, etc., and there is a drawback that performing such calculations requires a more complicated circuit.

Therefore, a system has been proposed in which a microcomputer is provided at the transmission end and various calculations are performed there. In this case, an A/D converter to convert analog signals into signals that can be handled by the microcomputer, a D/A converter to convert digital signals to analog signals, etc. are required around the microcomputer, and the transmission end side Since the power consumption increases, unified standard signals (e.g. 4-
20mA), it becomes difficult to operate the transmission end.

(Problems to be Solved by the Invention) The present invention has been made in view of such problems in the prior art, and its purpose is to provide a two-wire transmission line while providing a microcomputer at the transmission end. The aim is to realize a two-wire transmitter that can operate the transmission end with a small amount of power supplied through the wire.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, includes current adjusting means for adjusting the current flowing through the two-wire transmission line, and electric power sent through the two-wire transmission line. an analog signal holding means which is always operated and provides a signal for controlling the current regulating means; a clock generating means which is always operated by the electric power sent through the two-wire transmission line; A power supply circuit includes a means for accumulating the transmitted power, a switch that is intermittently turned on for a predetermined period of time by a signal from the clock generating means, and the power is supplied through this switch to operate. A microcomputer that processes signals to be transmitted; and a D/A converter that operates upon being supplied with power through the switch and converts the digital signal from the microcomputer into an analog signal and outputs it to the analog signal holding means. It is composed of:

(Embodiment) FIG. 1 is a block diagram showing an example of a device according to the present invention. In the figure, is the transmitter installed on the transmission end side, is the receiving end side, and there are 2
They are connected via line transmission line ln.

In the transmitter, 1 is a current adjustment means that adjusts the load current IL flowing through the two-wire transmission line ln, 2 is an amplifier that controls the current adjustment means 1, and 3 is a load current IL.
It is a feedback resistor that obtains a voltage ef according to . 4 is a detection end that outputs a signal _e1 corresponding to the process quantity to be transmitted such as temperature, pressure, flow rate, etc.; 5 is a buffer amplifier that inputs the signal _e1 from the detection end 4; 6 is an input multiplexer; and 7 is an input multiplexer. 6 is a comparator which receives the selected signal as one input; 8 is a microcomputer to which the signal from comparator 7 is input; 9 is a battery-backed RAM connected to this microcomputer 8; 10 is a D/A converter that converts a digital signal output from the microcomputer 8 into an analog signal, and its output terminal is connected to the other input terminal of the comparator 7. Reference numeral 11 denotes a setting means for setting calculation constants, zero points, and span values, which are adjusted by means of a knob 12, for example, by active movement, and the setting signal _e2 obtained here is sent to the input multiplexer 6.
is applied to the comparator 7 via. 13 is a switch driven by a signal from the microcomputer 8, 14 is a capacitor, and 15 is an amplifier, which constitute an analog signal holding circuit 16 that holds the analog signal from the D/A converter 10. . The output signal of this analog signal holding circuit 16
e ₀ is applied to the input terminal of amplifier 2, and
It is applied to a comparator 7 via an input multiplexer 6. Further, the output signal e ₀ of the analog signal holding circuit 16 is indicated by an indicator 17. 17 is the feedback voltage ef generated in the feedback resistor 3
is applied to the comparator 7 via the input multiplexer 6.

18 is a Zener diode connected to the two-wire transmission line ln via a resistor 19, and 20 is a capacitor that stores the constant voltage obtained by the Zener diode 18 via a resistor 21. These operate each circuit on the transmission end side. It constitutes a power supply circuit 22 for
The amplifiers 2 and 15 are constantly supplied with a constant voltage as a power supply voltage. 23 is a clock generation circuit which is operated by being supplied with power from the power supply circuit 22, and 24 is this clock generation circuit 23.
This is a switch drive circuit that inputs the clock output at regular intervals and turns on the switch SW at regular intervals. Switch SW
is connected at one end to the power supply circuit 22, and supplies power from the power supply circuit 22 to each power supply terminal of the buffer amplifier 5, input multiplexer 6, comparator 7, microcomputer 8, and D/A converter 10 at regular intervals. is supplied to.

At the receiving end, BT is a DC power supply, Lo is a load, and these are connected in series to the two-wire transmission line ln.

The operation of the apparatus configured in this way will be explained next. From the receiving end side, via the two-wire transmission line ln,
For example, a current of 4 mA to 20 mA is constantly supplied. At the transmission end, the amplifiers 2 and 15 and the clock generation circuit 23 are all supplied with a constant voltage by the Zener diode 18 in the power supply circuit 22, and are constantly operating. The clock generation circuit 23 uses the switch driver 24 to turn on the switch SW for a predetermined time at regular intervals. As a result, the buffer amplifier 5, input multiplexer 6, comparator 7, microcomputer 8, and D/A converter 10 operate by being supplied with power from the power supply circuit 22 for a predetermined time at regular intervals. When power is being supplied, the microcomputer 8
reads the signal _e1 from the detection end 4 through the buffer amplifier 5, input multiplexer 6, and comparator 7, and converts it into a D/A converter formed by the comparator 7, microcomputer 8, and D/A converter 10. A conversion loop converts it into a digital signal. In the same way,
Signal e ₂ from setting means 11, feedback signal ef from feedback resistor 3, output signal from analog signal holding means 16
Each of e ₀ is also converted into a digital signal. Next, the microcomputer 8 uses the converted digital signal to perform predetermined calculations such as initialization calculation, correction calculation, and linearization calculation. What kind of calculation should we perform here?
It is determined by the type of detection end 4, the form of the transmission signal, etc. For example, if the detection end 4 is a pressure detector that detects a pressure difference depending on the flow rate, for example, _a square root calculation or a 4mA
Conversion calculations to convert to ~20mA signal, linearization calculations to make the load current IL have a comparative relationship with the flow rate, etc. will be performed. PID calculations are also performed to control the flow rate to be measured, if necessary.

This calculation result turns on the switch 13,
The signal is held in the analog signal holding means 16 via the D/A converter 10. Further, various data for successively performing the above calculations are stored in the nonvolatile memory 9 backed up by the battery.

The analog signal held in the analog signal holding means 16 is applied to the current adjusting means 1 via the amplifier 2 to adjust the load current IL. This load current
IL is detected by feedback resistor 3 and the load current
The voltage ef corresponding to IL is read into the microcomputer 8 via the feedback circuit 17, and the load current
IL is controlled so that it corresponds accurately to the calculation result to be transmitted.

The above operations are repeatedly performed within a predetermined period of time (for example, 20 mS) while the switch SW is on. After this predetermined time has elapsed, the switch SW is driven off and the power supply to the amplifier 5, input multiplexer 6, comparator 7, microcomputer 8 and D/A converter 10 is stopped. This reduces the average power consumption at the transmission end. While the power supply to the peripheral circuits including the microcomputer 8 is stopped, a load current based on the analog signal held in the analog signal holding means 16 continues to flow.

After a certain period of time (for example, 80 mS) has elapsed, the switch SW is turned on again and the operation described above is performed. Here, in the microcomputer 8, various data immediately before the power supply is stopped is stored in the memory 9, and by reading the data from there, the output signal e ₀ of the analog signal holding means 16 can be read out if necessary. Alternatively, by reading the feedback voltage ef and performing an initialization calculation, the
Continuous calculation results can be obtained. In addition, since most process quantities do not change rapidly, by appropriately selecting the time to turn on the switch SW and the time to turn it off, it is possible to operate it without any problems.

In the above embodiment, the transmission end inputs the signal _e1 from one detection end, but it may also input signals from other detection ends. For example, a signal from a detection end that detects the density of the fluid to be measured and a signal from a detection end that detects the flow rate of the fluid to be measured may be input. In this case, the microcomputer 8 can calculate both signals and obtain a mass flow rate signal.
Moreover, although the case where one calculation constant setting means 11 is provided is illustrated, a plurality of calculation constant setting means 11 may be provided so that a plurality of calculation constants can be set. Moreover, each analog signal is selected by the input multiplexer 6 and applied to the comparator 7, but if a comparator is provided corresponding to each analog signal, the input multiplexer 6 is unnecessary. Furthermore, here, the A/D conversion operation is performed in a loop including a comparator, a microcomputer, and a D/A converter.
An AD converter may be provided on the input side of the microcomputer 8, and the digital signal converted there may be input to the microcomputer 8. Furthermore, although the power supply circuit 22 at the transmission end stores power using the capacitor 20, a secondary battery may be provided here to store power.

(Effects of the Invention) As explained above, the present invention is capable of intermittently supplying power to peripheral circuits including microcomputers and D/A converters that consume relatively large amounts of power at the transmission end. The switch
Assuming that the time when the SW is turned on is t, and the time when it is turned off is T, and the power consumption in amplifiers 2 and 15 is ignored, the average power consumption at the transmission end will not affect normal operation. Instead, it can be reduced to t/(t+T). Therefore, according to the present invention, although a microcomputer capable of performing various tasks is provided on the transmission end side, it is possible to operate the transmission end with a small amount of power supplied via a two-wire transmission line. A two-wire transmitter can be realized.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing an example of a device according to the present invention, and FIG. 2 is a connection diagram showing an example of a conventional device. DESCRIPTION OF SYMBOLS 1...Current adjustment means, 2...Amplifier, 3...Feedback resistor, 4...Detection end, 8...Microcomputer, 10...D/A converter, 16...Analog signal holding means, 22... Power supply circuit, 23...Clock generation means, SW...Switch, ln...2-wire transmission line.

Claims (1)

[Claims] 1. Current adjustment means for adjusting the current flowing through the two-wire transmission line; analog signal holding means that is constantly activated by the electric power sent through the two-wire transmission line and provides a signal for controlling the current adjustment means; a power supply circuit including a clock generating means that is constantly operated by the electric power sent through the two-wire transmission line, and a means for accumulating the electric power sent through the two-wire transmission line;
a switch that is driven on intermittently for a predetermined period of time by a signal from the clock generating means;
A microcomputer is supplied with power through this switch and operates to process the signals to be transmitted, and a microcomputer is supplied with power through the switch and operates to convert the digital signal from the microcomputer into an analog signal and A two-wire transmitter equipped with a D/A converter that outputs to analog signal holding means.