JP5531900B2 - 2-wire transmitter - Google Patents

Description

  The present invention relates to a two-wire transmitter that is connected to an external circuit with two transmission lines and outputs a predetermined current to the external circuit while using the external circuit as a power source.

  A two-wire transmitter is a device that is connected to an external circuit with two transmission lines, uses the external circuit as a power source, replaces predetermined information (physical quantities) obtained from sensors, etc., with current signals, and outputs them to the external circuit. is there. The 2-wire transmitter does not require dedicated power supply wiring and can be installed at low cost. Therefore, it is widely used as a field device such as a differential pressure / pressure transmitter and a temperature transmitter in each plant. A two-wire transmitter used as a field device replaces a physical quantity with a DC current of 4 mA to 20 mA, which is a world standard, as a signal in the field device, and transmits it as a current signal to an external circuit.

  In a two-wire transmitter, processing by a processing unit (CPU) is performed in the process of replacing a physical quantity with a current signal. The CPU performs processing according to a program stored in the storage device. A general field device including a two-wire transmitter includes a ROM (flash ROM or the like) and a RAM as a storage device (for example, Patent Document 1). A plurality of programs are stored in the flash ROM, and necessary programs are transferred to a RAM having a higher read / write speed (read / write) than the flash ROM, and processed by the CPU in accordance with the programs developed in the RAM. ing.

  In a conventional two-wire transmitter as a conventional field device (4 mA to 20 mA), a flash ROM provided has a capacity of about several hundred kbytes, whereas a RAM has a capacity of about several tens of kbytes. In this case, the power consumption is also proportional to the capacity, and the power consumption of the RAM is about 1/10 that of the flash ROM. For this reason, the flash ROM and the RAM can be operated in parallel even in a two-wire transmitter with limited power consumption.

JP 2009-145934 A

  Here, in recent years, a further increase in processing speed has been demanded for the two-wire transmitter. As described above, the RAM is faster than the flash ROM with respect to the read / write speed. For this reason, once all the programs are transferred from the flash ROM to the RAM and are operated on the RAM, it is unnecessary to access the flash ROM thereafter, and an increase in processing speed may be achieved. If this method is adopted, the rewriting frequency of the flash ROM is also reduced, so that it is possible to extend the life of the flash ROM (a general number of rewrites of the flash ROM is several hundred times). However, in order to develop all programs in RAM, a RAM having a larger capacity than before is required. A large-capacity RAM has a large power consumption. In particular, in a two-wire transmitter with limited power consumption, it is difficult to further operate a large capacity RAM and a flash ROM in parallel when other circuits are operating. For this reason, it is difficult to implement all the programs in the flash ROM in the RAM.

  In view of such a problem, the present invention can operate a RAM having a large capacity in parallel with the flash ROM, and can increase the processing speed and extend the life of the flash ROM. It aims to provide a transmitter.

  In order to solve the above problems, a typical configuration of a two-wire transmitter according to the present invention is connected to an external circuit with two transmission lines, and a predetermined current signal is sent to the external circuit while the external circuit is used as a power source. A two-wire transmitter for outputting, a sensor circuit for converting a physical quantity into an electrical signal and outputting it, a flash ROM for storing a program describing a predetermined process, and a RAM for developing a program stored in the flash ROM And a processing unit that executes predetermined processing on the electrical signal output from the sensor according to a program developed in the RAM, a display circuit that displays the processing result of the processing unit to the outside, and power received from the external circuit An output circuit for determining a current signal to be output to an external circuit according to a processing result of the processing unit, a first power supply line for supplying power from the output circuit to the flash ROM, and a first power supply line A first switch that opens and closes, a second power supply line that supplies power from the output circuit to the sensor circuit and the display circuit, a second switch that opens and closes the second power supply line, and controls the opening and closing of the first switch and the second switch. An open / close control unit, wherein the open / close control unit opens the second switch when the first switch is closed.

  According to the above configuration, the flash ROM, the RAM, and the peripheral device can be powered on individually. Therefore, even if the power is turned on when everything is turned on, if the power is turned on only to the flash ROM and RAM, all the programs stored in the flash ROM can be expanded to the RAM immediately after the power is turned on. is there. This RAM needs to have a larger capacity than before. Further, since the flash ROM and the RAM operate in parallel when the program is developed, the power consumption in the two-wire transmitter increases. However, in the above configuration, when the power is turned on, the power of the sensor circuit and the display circuit can be turned off to save power consumption. Therefore, even in a two-wire transmitter with limited power consumption, it is possible to operate a RAM having a larger capacity and a flash ROM in parallel than in the past. Further, once all the programs are expanded in the RAM, it is not necessary to access the flash ROM having a low read / write speed, and the processing speed can be increased. Furthermore, since the number of rewrites to the flash ROM is also reduced, the life of the flash ROM can be extended.

  At the time of turning on the power of the two-wire transmitter, the open / close control unit opens the second switch, closes the first switch, the processing unit transfers the program stored in the flash ROM to the RAM, The open / close control unit has a determination unit that determines whether or not the transfer of the program from the flash ROM to the RAM has been completed, and opens the first switch in response to the completion of the transfer of the program. It should be closed.

  In the above configuration, when the development of the program from the flash ROM to the RAM is completed, the parallel operation of the flash ROM and the RAM ends. Accordingly, power consumption is also reduced, so that the sensor circuit and the display circuit can be started without any problem. Further, with the above configuration, it is possible to cut the static power consumption of the flash ROM and contribute to saving power consumption.

  According to the present invention, it is possible to operate a RAM having a large capacity in parallel with a flash ROM, and to provide a two-wire transmitter capable of increasing the processing speed and extending the life of the flash ROM. It becomes possible.

1 is a circuit diagram of a two-wire transmitter according to an embodiment of the present invention. It is a flowchart which shows the flow of operation | movement at the time of power activation of the 2-wire transmitter of FIG. It is a figure explaining the prevention measure of the inrush current of the 2-wire transmitter of FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a circuit diagram of a two-wire transmitter 100 according to an embodiment of the present invention. As shown in FIG. 1, the two-wire transmitter 100 is connected to the outside by two transmission lines La and Lb, and uses the external circuit 10 as a power source. The two-wire transmitter 100 is embodied as a field device such as a differential pressure / pressure transmitter and a temperature transmitter, and outputs a predetermined current signal Iout indicating a physical quantity to the external circuit 10.

  The two-wire transmitter 100 includes a sensor circuit 102. The sensor circuit 102 converts physical quantities such as pressure and temperature into electrical signals and outputs them to the processing unit 106 in the microprocessor 104.

  The processing unit 106 (CPU) performs a predetermined process on the electrical signal output from the sensor circuit 102. The predetermined processing is processing such as linearity correction (distortion correction) or noise removal. These processes are performed according to the processing procedure specified by the program. The processing result obtained by the processing unit 106 is output to the output circuit 114 as an electrical signal.

  The flash ROM 108 is a non-volatile IC memory, and stores a program describing a predetermined process as an instruction to the processing unit 106. Although the flash ROM 108 can rewrite data, the number of times that data can be rewritten is generally limited to several hundred times.

  The RAM 110 is a volatile IC memory, and a program stored in the flash ROM 108 is expanded. The processing unit 106 executes a program expanded in the RAM 110. The RAM 110 can access stored data in any order, and the read / write speed is faster than that of the flash ROM 108. Therefore, the processing time can be shortened by transferring (downloading) the program in the flash ROM 108 to the RAM 110 and executing the processing. In the two-wire transmitter 100, all programs stored in the flash ROM 108 are downloaded to the RAM 110. Therefore, a RAM 110 having a capacity comparable to that of the flash ROM 108 is employed.

  The display circuit 112 mainly displays the operation state of the two-wire transmitter 100. Further, the processing result by the processing unit 106 may be displayed outside. The display circuit 112 is a type of human machine interface (HMI) that mediates information transmission between the processing unit 106 and a human. Examples of the display circuit 112 include an LED, an indicator, and a liquid crystal. In the present embodiment, the display circuit 112 is given as a representative example of the HMI, but the present invention is not limited to this, and a speaker or a mechanical display may be provided.

  The output circuit 114 determines a current signal Iout (4 mA to 20 mA) to be output to the external circuit 10 in accordance with a processing result (processed sensor signal) by the processing unit 106. By this current signal Iout, the external circuit 10 acquires a physical quantity measurement result. The output circuit 114 is located upstream of the power supply line in the two-wire transmitter 100 with respect to other components. Then, power is supplied to the other components through the output circuit 114.

(Operation at power-on)
Next, a further configuration of the two-wire transmitter 100 will be described along the flow of operation when the power is turned on. FIG. 2 is a flowchart showing an operation flow when the power of the two-wire transmitter 100 of FIG. 1 is turned on. The two-wire transmitter 100 provides a time difference in power supply from the output circuit 114 to each component when the power is turned on.

  First, referring to FIG. 1 again, the components related to the operation when the power is turned on will be described. In the two-wire transmitter 100, independent power lines are wired from the output circuit 114 to other components, and power is supplied. A first power supply line L 1 is wired from the output circuit 114 to the flash ROM 108. A second power supply line L2 is wired from the output circuit 114 to the sensor circuit 102 and the display circuit 112 (block B). A third power supply line L3 is wired from the output circuit 114 to the RAM 110 and the processing unit 106 (block A).

  A switch for opening and closing each power supply line is provided on each power supply line. A first switch SW1 is provided on the first power supply line L1. A second switch SW2 is provided on the second power supply line L2. A third switch SW3 is provided on the third power supply line L3.

  The two-wire transmitter 100 is provided with an open / close control unit 116 that controls opening and closing of the first to third switches (SW1 to SW3). The opening / closing control unit 116 is provided upstream of the first to third switches (SW1 to SW3), and receives power supply when the power of the two-wire transmitter 100 is turned on together with the output circuit 114. The open / close control unit 116 opens and closes the first to third switches (SW1 to SW3) so that the total power consumption of each component is within the limit range when the program is downloaded from the flash ROM 108 to the RAM 110.

  When the power is turned on to the two-wire transmitter 100, in step 200 of FIG. 2, the open / close control unit 116 opens the second switch SW2 (OFF). In subsequent step 210, the first switch SW1 and the third switch SW3 are closed (ON).

  When the first and third switches SW3 are turned on, in step 220, the processing unit 106 starts downloading all the programs from the flash ROM 108 to the RAM 110. Since the RAM 110 has a larger capacity than the conventional one and the flash ROM 108 and the RAM 110 operate in parallel, the power consumption in the step 220 increases more than the conventional one. However, since the second switch SW2 is turned off in the preceding step 200, the power consumption by the block B (see FIG. 1) is reduced. Therefore, step 220 can be performed within the power consumption limit range.

  As shown in FIG. 1, the opening / closing control unit 116 includes a determination unit 118 that determines whether or not downloading of a program from the flash ROM 108 to the RAM 110 is completed (step 230). If determination unit 118 determines that the download has been completed by a notification from processing unit 106 (YES in step 230), the process proceeds to subsequent step 240. If it is still being downloaded (NO at step 230), the process enters a standby state.

  When downloading of all the programs is completed (YES in step 230), it is no longer necessary to operate the flash ROM 108 thereafter. Therefore, in step 240, the opening / closing control unit 116 turns off the first switch SW1 connected to the flash ROM 108. Thereby, the static power consumption of the flash ROM 108 can be cut, and the power consumption can be saved. In subsequent step 250, the opening / closing control unit 116 turns on the second switch SW2. Thereby, the sensor circuit 102 and the display circuit 112 can be started without a problem in power consumption. Then, a series of processing ends.

  According to the above configuration, the RAM 110 and the flash ROM 108 having a larger capacity than the conventional one can be operated in parallel even in a two-wire transmitter with limited power consumption. Further, once all the programs are expanded in the RAM 110, it is not necessary to access the flash ROM 108 having a low read / write speed, and the processing speed can be increased. Further, since the number of rewrites to the flash ROM 108 is also reduced, the life of the flash ROM 108 can be extended.

(Measures to prevent inrush current)
FIG. 3 is a diagram for explaining measures for preventing inrush current in the two-wire transmitter 100 of FIG. The two-wire transmitter 100 is provided with measures for preventing inrush current when turning on the first to third switches (SW1 to SW3). In FIG. 3, the second switch SW2 is taken as an example to represent the first to third switches (SW1 to SW3). Hereinafter, measures for preventing inrush current will be described with reference to FIG.

  The second switch SW2 includes a low-pass filter LPF, an operational amplifier Q1, and a transistor Q2. The opening / closing control unit 116 controls the opening / closing of the second switch SW2 by outputting a PWM signal (Pulse Width Modulation) to the second switch SW2. Specifically, the PWM signal from the open / close control unit 116 is input to the operational amplifier Q1, and the conduction of the transistor Q2 is controlled by the output of the operational amplifier Q1.

Here, for example, when the voltage rises steeply as the voltage V _RC of conventional operational amplifier Q1 is input, the output is applied to the transistor Q2, resulting as in the conventional example of the current signal Iout (B) An inrush current is generated. If an inrush current occurs, the element may be destroyed, or a voltage drop may occur due to a reaction that is less than the operating limit, which may cause a malfunction in the circuit operation.

In order to prevent the occurrence of the inrush current, in the two-wire transmitter 100, the opening / closing control unit 116 outputs a PWM signal so that the duty ratio gradually increases. This PWM signal is smoothed by the low-pass filter LPF and becomes an analog signal in which the voltage V _RC rises gently. When this analog signal is input to the operational amplifier Q1, a current signal Iout (B) that gently rises flows through the transistor Q2 that has received the output, and the voltage Vout also rises gently. As a result, in the two-wire transmitter 100, even if a plurality of switches are provided, it is possible to prevent inrush current from being generated in each component.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be used for a two-wire transmitter that is connected to an external circuit with two transmission lines and outputs a predetermined current to the external circuit while using the external circuit as a power source.

La, Lb ... transmission lines L1 to L3 ... first to third power supply lines Q1 ... operational amplifier Q2 ... transistors SW1 to SW3 ... first to third switches 10 ... external circuit 100 ... two-wire transmitter 102 ... sensor circuit 104 ... Microprocessor 106 ... processing unit 108 ... flash ROM
110 ... RAM
DESCRIPTION OF SYMBOLS 112 ... Display circuit 114 ... Output circuit 116 ... Opening / closing control part 118 ... Determination part Iout, Iout (B) ... Current signal LPF ... Low-pass filter VRC ... Voltage Vout ... Voltage

Claims (2)

A two-wire transmitter that is connected to an external circuit with two transmission lines and outputs a predetermined current signal to the external circuit while using the external circuit as a power source,
A sensor circuit that converts a physical quantity into an electrical signal and outputs the electrical signal;
A flash ROM for storing a program describing predetermined processing;
A RAM for developing a program stored in the flash ROM;
A processing unit that executes a predetermined process on the electrical signal output from the sensor according to a program developed in the RAM;
A display circuit for displaying the processing result of the processing unit to the outside;
An output circuit that receives power from the external circuit and determines a current signal to be output to the external circuit according to a processing result of the processing unit;
A first power supply line for supplying power from the output circuit to the flash ROM;
A first switch for opening and closing the first power line;
A second power supply line for supplying power from the output circuit to the sensor circuit and the display circuit;
A second switch for opening and closing the second power line;
An opening / closing control unit for controlling opening / closing of the first switch and the second switch;
With
The two-wire transmitter, wherein the open / close control unit opens the second switch when the first switch is closed. When powering on the 2-wire transmitter,
The open / close control unit opens the second switch, closes the first switch,
The processing unit transfers the program stored in the flash ROM to the RAM,
The open / close control unit includes a determination unit that determines whether or not the transfer of the program from the flash ROM to the RAM is completed, and opens the first switch in response to the completion of the transfer of the program. The two-wire transmitter according to claim 1, wherein the second switch is closed.

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