JP3517869B2 - Two-wire signal transmitter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-wire type signal transmitter for converting a physical quantity measured by a sensor into an electric signal and transmitting the electric signal to a load side through two transmission lines. . More specifically, the present invention relates to a device for reducing current consumption when writing data in a non-volatile memory inside a transmitter.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a configuration example of a conventional two-wire system signal. In FIG. 3, the two-wire signal transmitter 10 is
An electric signal is transmitted to the load side via the two transmission lines 31 and 32. On the load side, there is a distributor 40, for example. The distributor 40 A / D-converts (analog / digital-converts) the sent electric signal and transfers it to a computer (not shown). The communication terminal 50 is connected to the transmission line and communicates with the two-wire signal transmitter 10.

The two-wire type signal transmitter 10 comprises an input side circuit 11 for taking in a measurement input of a sensor and an output side circuit 12 for converting the taken in measurement input into an electric signal of a predetermined format and sending it out to a transmission line. Become. In the input side circuit 11, the multiplexer 111 selects one of the sensor measurement inputs S1, S2 and S3. The A / D converter 112 converts the measurement input selected by the multiplexer 111 into digital data. The photocoupler PC1 insulatedly transmits the converted digital data to the output side circuit 12. DC / DC converter CO
N is the electric power of the power supply in the output side circuit 12
Supply to 1. The power supply voltage is taken from the line L1.

In the output circuit 12, the arithmetic control section 121 reads the digital data transmitted by the photocoupler PC1 and performs a necessary arithmetic operation, and sends the arithmetic result to the output current control section 122 as output data. Output current control unit 122
Controls the transistor Q1 to convert the output data into an electric signal of a predetermined format, for example, a current signal of 4 to 20 mA, and sends it to the transmission lines 31 and 32 via the terminals 123 and 124. Calculation control unit 121 and output current control unit 122
Is composed of, for example, a microcomputer.

The arithmetic control unit 121 is an output current control unit 122.
A communication interface circuit (not shown) built in the device superimposes communication data on the output (current signal of 4 to 20 mA) to communicate with the communication terminal 50. Non-volatile memory 12
The arithmetic control unit 121 is connected to the communication terminal 5
Data such as the operation mode and the correction coefficient can be written from 0. The operation modes include, for example, types of sensors such as thermocouples and resistance temperature detectors. As a correction coefficient,
For example, there is a coefficient used when performing calibration. An EEPROM, for example, is used as the non-volatile memory 125.

The clock generator 126 is an arithmetic control unit 121.
Generates a clock that is the basis of the operation clock of. The arithmetic control unit 121 divides the clock generated by the clock generator 126 and uses the divided clock as the operation clock.

In the two-wire type signal transmitter of FIG. 3, for example, when the measured temperature of the temperature sensor is 0 ° C. to 100 ° C., the output of the transmitter is 4 to 2
It shall correspond to 0 mA. When the measurement temperature is 0 ° C., the maximum current consumption allowed for the transmitter is 4 mA, and the transmitter must operate with a current of about 3.2 mA in order to have a margin. However, since a non-volatile memory such as an EEPROM consumes a large amount of current at the time of writing, it may exceed the allowable current consumption of the transmitter of 4 mA at the time of writing. Although the maximum current consumption can be suppressed by lowering the frequency of the operation clock of the arithmetic control unit 121, there is a problem that the response of the output to the input becomes slow.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and lowers the frequency of the operation clock of the arithmetic control unit only when writing to the non-volatile memory, thereby Allow some movement,
It is an object of the present invention to realize a two-wire signal transmitter that can increase the degree of freedom in circuit design.

[0009]

The present invention is a two-wire signal transmitter having the following configuration.

(1) In a two-wire type signal transmitter for converting a physical quantity measured by a sensor into an electric signal and transmitting the electric signal to a load side through two transmission lines, the electric signal is superimposed on the electric signal on the transmission line. The non-volatile memory in which the communication data is written, the A / D converter that converts the measurement signal of the sensor into analog / digital, and the conversion data of this A / D converter are read and a predetermined calculation is performed, and the calculation result is In addition to sending it as output data, it monitors the signal sent from the transmission line.
And see the communication data in the electrical signal sent from the transmission line.
When the overlap is detected, the nonvolatile memory
And an output signal control unit that converts the output data into an electric signal of a predetermined format and sends the electric signal to a transmission line. The operation control unit is a nonvolatile memory. A two-wire signal transmitter characterized by lowering the frequency of its operating clock when writing data.

(2) The arithmetic and control unit has a frequency dividing means for generating a frequency-divided clock as an operating clock from a clock generated by the clock generator, and a frequency division ratio control means for controlling the frequency division ratio of the frequency dividing means. And a writing control means for lowering the frequency of the divided clock by sending a control signal to the division ratio control means to change the division ratio when writing to the nonvolatile memory ( The two-wire signal transmitter according to 1).

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. 1 that are the same as those in FIG. 3 are given the same reference numerals. In this embodiment, the DC / DC converter is a self-excited DC / DC converter.

The arithmetic control unit 130 includes a nonvolatile memory 12
When writing data to 5, the frequency of its operation clock is lowered. A configuration for this will be described.

In the arithmetic and control unit 130, the frequency dividing means 131 generates a frequency divided clock from the clock generated by the clock generator 126. This frequency-divided clock becomes the operation clock of the arithmetic control unit 130. The frequency division ratio control means 132 is the frequency division means 13.
Control the division ratio of 1. When writing to the nonvolatile memory 125, the writing control unit 133 sends a control signal to the division ratio control unit 132 to change the division ratio and lower the frequency of the division clock.

The writing control means 133 monitors the signal sent from the transmission line, and the communication data is superimposed on the electric signal (current signal of 4 to 20 mA in the embodiment) sent from the transmission line. When this is detected, the data is written in the nonvolatile memory 125.

FIG. 2 is a signal time chart of the write operation. As shown in FIG. 2, the nonvolatile memory 125 is controlled by the operation control unit 130 in which the clock division ratio is variable.
The frequency of the operating clock is reduced only when writing to. For example, 2 MHz during normal operation and 1 during writing
The frequency of the operation clock is switched to MHz.

When the frequency of the operating clock is lowered,
Output response to input is slightly slower, but output accuracy is maintained. Moreover, since the frequency of writing to the nonvolatile memory is low and the time required for writing is short, there is almost no practical problem.

[0018]

According to the present invention, the following effects can be obtained.

According to the inventions of claims 1 and 2, the following effects can be obtained. There is a margin in the current consumption of the transmitter when the output is small,
The degree of freedom in circuit design is increased. The output accuracy can be maintained even during writing to the nonvolatile memory.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the present invention.

FIG. 3 is a diagram showing a configuration example of a conventional two-wire signal.

[Explanation of symbols]

10 Two-wire signal transmitter 31,32 Transmission line 122 Output current control unit 125 non-volatile memory 130 Operation control unit 131 frequency divider 132 Dividing ratio control means 133 write control means

Claims (2)

(57) [Claims] 1. A two-wire type signal transmitter for converting a physical quantity measured by a sensor into an electric signal and transmitting the electric signal to a load side through two transmission lines, which is superposed on the electric signal on the transmission line. Non-volatile memory in which communication data is written, and A / D that converts the measurement signal of the sensor into analog / digital
The converter and the conversion data of this A / D converter are read, a predetermined calculation is performed, the calculation result is sent as output data, and the signal sent from the transmission line is monitored,
Make sure that the communication data is superimposed on the sent electrical signal.
When is detected, the data is written in the nonvolatile memory.
And an output signal control unit for converting the output data into an electric signal of a predetermined format and transmitting the electric signal to a transmission line. The operation control unit writes data in a non-volatile memory. A two-wire signal transmitter characterized by lowering the frequency of its operating clock. 2. The operation control unit includes frequency dividing means for generating a frequency-divided clock serving as an operation clock from a clock generated by a clock generator, and frequency-division-ratio control means for controlling a frequency division ratio of the frequency-dividing means. And a write control means for lowering the frequency of the frequency division clock by sending a control signal to the frequency division ratio control means to change the frequency division ratio when writing to the non-volatile memory. The two-wire signal transmitter according to 1.