JP2555195B2 - Received signal conversion circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a received signal conversion circuit provided in a receiving device among devices including a terminal and a receiving device.

[Prior Art] FIG. 3A is a configuration diagram showing a conventional received signal conversion circuit.

There is a device in which data to be measured is converted into a voltage or current magnitude by a terminal 30 installed at a remote location and directly transferred to a receiving device 31.

Between the receiving device 31 and the terminal 30, there are power supply lines 32 and 33 for the operating power supply of the terminal 30, and a signal line 34 provided for another purpose. A predetermined voltage (up to several tens of V) is applied between the power supply lines 32 and 33 by the power supply 35.

The data of the terminal 30 uses the power supply line 32 and the signal line 34, and the detection resistor 3 provided between them.
6. The differential amplifier 37 operated by the power supply 35 is used to detect the change in voltage or current amount.

Further, FIG. 3 (b) shows that the power supply line 32 on which the data is superposed has a ground potential, and a differential amplifier 39 which is operated by another power source 38 based on this is provided. .

Further, as shown in FIG. 3 (c), the isolation amplifier 40 is used, and the data is fetched by the variation obtained by separating the direct current component from the power supply voltage.

[Problems to be Solved by the Invention] However, according to the configuration of FIG. 3 (a), since the power supply voltage is directly input to the differential amplifier 37 in the receiving device, the change data is considered. Then, a device with a large dynamic range must be used, which is expensive, and maintenance and the like are in a dangerous state due to this voltage.

Further, as shown in FIG. 3 (b), although the differential amplifier can operate near the ground potential by setting the resistance ground, the power supply line itself has a high voltage.

The isolation amplifier 40 shown in FIG. 3 (c) is expensive.

Then, since the power supply voltage at the end of the receiving device 31 increases almost in proportion to the distance between the terminal 30 and the receiving device 31, the power supply line itself becomes dangerous to the human body.

The present invention has been made in view of the above problems, and provides a reception signal conversion circuit capable of detecting a response signal superimposed on a high-voltage power supply line without using a special circuit element. Is intended.

[Means for Solving the Problems] In order to achieve the above object, the reception signal conversion circuit of the present invention is a response signal im transmitted between one line of a power supply line and between signal lines
The detection voltage of the current detection resistor that detects the current is input, the operation power supply is divided by the resistance, and the operation amplifier is connected to the power supply line at the division point, and the output of the differential amplifier is input. And a level shift circuit for level shifting the voltage to near the ground potential by connecting one end to the ground, and a low voltage for performing processing corresponding to the response signal im by the output of the level shift circuit. And a processing circuit.

[Operation] According to the above configuration, the response signal weighted by the high-voltage power supply line is detected by the differential amplifier and then level-shifted to the ground potential by the level shift circuit, so that the low-voltage drive is performed. It will be processed in the subsequent circuit.

[Embodiment] FIG. 1 is a configuration diagram showing an embodiment of a received signal conversion circuit according to the present invention.

The terminal 1 is provided at a position remote from the receiving device 2 (several tens of kilometers), and has a detection circuit 1a for detecting a measurement target and a response circuit 1b for transmitting data to the receiving device 2.
It consists of.

Power supply lines 4 and 5 and a signal line 6 are provided between the receiving device 2 and the terminal 1 for operating power of the terminal 1. Voltages of ± are applied to the ground lines of the power supply lines 4 and 5 by a power source 6 whose midpoint is the same potential as the ground voltage. As a result, the voltage of the power supply lines 4 and 5 can be set to ± 1/2 of that of the conventional one, and safety is increased.

A current detecting resistor 7 is provided in series on the power supply line 4 and the signal line 6, and both ends of the current detecting resistor 7 are connected to the input of the differential amplifier 8.

The power supply line for operation of the differential amplifier 8 is operated by the resistors 9 and 10 and the power supply 11 which are connected across the power supply line 4. By making the values of the resistors 9 and 10 the same, it is possible to use the differential amplifier 8 that operates at ± 1/2 of the voltage of the power supply 11, and also to set the direction in which the response signal im flows arbitrarily. it can. Here, the power supply 11 sets the dynamic range of the differential amplifier 8 to a voltage including im · Rm.

The output of the differential amplifier 8 is connected to the bases of the transistors forming the level shift circuit 12. The emitter is connected to the power supply line 4, and the collector is connected to the ground terminal 14 having the earth potential via the resistor 13. By fixing the ground terminal 14 to the ground of the receiving device 2, the circuit in the subsequent stage can be configured by a low-voltage general-purpose element.

Both ends of the resistor 13 are connected to the input of the level adjusting amplifier 15. The dynamic range of the level adjustment amplifier 15 is the collector current ic of the level shift circuit 12 × the resistance 13
The value of the resistor 13 is set so as to include the range of the value of.

The processing circuit 17 is composed of an A / D, a CPU, etc., receives the output of the level adjusting amplifier 15, processes the data of the terminal 1, and digitally outputs the measurement result from the terminal 17.

The level adjusting amplifier 15 and the processing circuit 17 are power supplies.
Works with 16.

 Next, the operation of the above configuration will be described.

The measurement in the detection circuit 1a of the terminal 1 flows as a response signal im in the response circuit 1b as a current proportional to the measured value.

This response signal im induces a voltage proportional to the measured value across the current detection resistor 7. Here, since each of the power supply lines 4 and 5 has a voltage of 1/2 of the maximum power supply voltage, safety can be improved.

The differential amplifier 8 amplifies the voltage induced by the current detecting resistor 7, and the level shift circuit 12 uses the amplified voltage.
The transistor crector current ic is controlled. Since the differential amplifier 8 is fixed to the power supply line 4 by the resistors 9 and 10 and is operated across the potential of the power supply line 4, the differential amplifier 8 and the power supply 11 have a low voltage lower than the voltage of the power supply line. You can use anything that works with, and you don't need to use anything special.

Then, the resistor provided in the latter stage of the level shift circuit 12
A voltage proportional to the collector current ic is obtained at both ends of 13,
This voltage is proportional to the response signal im and has a reduced voltage. As a result, the level adjustment amplifier 15
The processing circuit 17 can be driven at a low voltage, and can be composed of general-purpose circuit components.

Next, FIG. 2 is a configuration diagram showing another embodiment of the received signal conversion circuit according to the present invention.

In the above-described embodiment, the signal line 6 for the response signal is used, but other than that, as shown in FIG.
In a device having a meeting line 20 provided between them, the meeting line 20 may be used in place of the signal line 6 of the above-mentioned embodiment, and in this case, the same effect as that of the above-mentioned embodiment can be obtained. it can.

[Effects of the Invention] According to the present invention, the differential amplifier and the level shift circuit level-shift the response signal superimposed on the high-voltage power supply line to the ground potential, so that no special circuit element is used. A general-purpose low-voltage drive circuit element can process the response signal, which can reduce the cost, and the low voltage can improve the safety during maintenance work. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a received signal conversion circuit of the present invention, FIG. 2 is a block diagram showing another example of the circuit, FIG. 3 (a),
(B), (c) is a circuit block diagram which shows the conventional receiver, respectively. 1 ... Terminal, 1a ... Detection circuit, 1b ... Response circuit, 2 ...
Receiver, 4,5 ... Feed line, 6 ... Signal line, 7 ... Current detection resistor, 8 ... Differential amplifier, 9,10 ... Resistor, 11 ...
Power supply, 12 ... Level shift circuit, 13 ... Resistance, 14 ... Ground terminal, 15 ... Level adjustment amplifier, 16 ... Power supply, 17 ...
... processing circuit.

Claims (1)

(57) [Claims] 1. A terminal provided at a remote place, and a power supply line and a signal line for operating the terminal provided between the terminal and the receiving device, the receiving device being provided on the receiving device side of the device. This is a received signal conversion circuit, in which the detection voltage of the current detection resistor that detects the response signal im transmitted between one line of the power supply line and the signal line is input, and the operating power supply is divided by the resistor connected to the power supply line. Differential amplifier, a level shift circuit that inputs the output of the differential amplifier, and has one end connected to the ground to level shift the voltage to near the ground potential, and the response by the output of the level shift circuit. A received signal conversion circuit comprising: a processing circuit that performs a process corresponding to the signal im.