JPH04230598A - Two-wire transmitter - Google Patents

Abstract

PURPOSE:To transmit a signal to a load with a certain time constant by calculating the change of the time constant based on the change of temperature of sealed liquid in a sensor and changing the time constant of software so that the time constant is a preliminarily set certain value. CONSTITUTION:A microprocessor muP2 uses data stored in a memory MEM2 to calculate the difference pressure in accordance with difference pressure calculating procedures preliminarily stored in a RAM area and transmits this difference pressure as an analog current signal IL to a load 12 through an output circuit OPC. The time constant of a sensor SRI is changed by the temperature, the classification, or the like of sealed liquid, and the capacity change is affected by the length of a capirally. These values are set by communication from a hand held terminal 13, and the sensor time constant is calculated in accordance with a calculation formula stored in the memory MEM2, and the change of the time constant is corrected to transmit a difference pressure/pressure signal to the load 12 with the certain time constant.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention converts a physical quantity to be measured by a sensor having a sealed liquid into an electrical signal by receiving power from the load side via two transmission lines, and converts the physical quantity into an electrical signal, which includes a microprocessor. Regarding the two-wire transmitter, which processes the signal using a signal calculation means and transmits it as a current signal to the load side via the transmission line, the viscosity of the liquid sealed in the sensor changes significantly depending on the temperature. This invention relates to a two-wire transmitter in which the overall damping time constant changes.

0002

2. Description of the Related Art FIG. 3 is a block diagram showing the overall configuration including a conventional two-wire transmitter. Reference numeral 10 denotes a two-wire transmitter that converts physical quantities such as process variables into electrical signals and transmits them, and is supplied with power from a DC power supply 11 via a load 12 . The electrical signal is transmitted as a current signal by the transmission lines L1 and L2, and the voltage change occurring across the load 12 is detected to determine the process variable.

[0003] The current signal is transmitted, for example, from a two-wire transmitter 10 set to a range corresponding to the pressure in the piping, from 4 to 20 meters away.
It is converted into a unified current IL of A and transmitted. In this case, it would be convenient if the two-wire transmitter 10 could be operated from outside, for example, when changing or monitoring the pressure range.

For this reason, the handheld terminal 13 is connected to the transmission lines L1 and L2 using connection lines L1' and L2' as necessary, and the handheld terminal 13 is connected to the two-wire transmitter 10. Equipped with a dedicated data communication function,
Digital data such as parameter changes is transmitted from the handheld terminal 13 to the two-wire transmitter 10. Also,
An interface 14 connected to a higher-level controller is connected to both ends of the load 12.

Next, each component configured as described above will be explained in detail. Of these, 10 two-wire transmitters
is structured as follows. Sensor SR1 is a sensor that detects pressure/differential pressure, etc. and converts it into an electrical signal.
R1a is its main body part, and SR1b is its remote part. The electrical signal converted by this sensor SR1 is analog/
It is converted into a digital signal by a digital converter AD1 and stored in a random access memory (RAM) part in a memory MEM1 via a microprocessor μP1. The microprocessor μP1 uses this stored digital signal to control the memory MEM1, for example, a read-only memory (
Predetermined calculations such as linearization and damping are executed according to the calculation procedures written in the ROM) section, and digital/
It is output to the output circuit OPC via the analog converter DA1. On the other hand, the results of predetermined calculations by the microprocessor μP1 are digitally displayed with the necessary number of digits on the built-in monitor LCD.

[0006] The output circuit OPC outputs the voltage signal converted into an analog signal by the digital/analog converter DA1.
Convert it to a unified current signal IL of 0mA and connect it to the transmission line L.
1, transmitted to the load 12 via L2. In addition, the output circuit OPC uses a part of the current signal IL to transmit data to the two-wire transmitter 1.
Create a power supply for 0's internal circuit.

The IFC is an interface for data communication with the handheld terminal 13, and is connected between the transmission lines L1 and L2 and the microprocessor μP1, and is connected to the digital signal from the transmission lines L1 and L2. It has a function of transmitting the data as parallel data to the microprocessor μP1, and conversely transmitting the data from the microprocessor μP1 as a serial signal to the transmission lines L1 and L2.

Next, the handheld terminal 13 is constructed as follows. SR1 is a setting device operated by an operator, and has a built-in monitor. Various settings or requests can be made, such as requesting a model of the two-wire transmitter 10, changing the display cycle, changing the range, detecting an abnormality, damping, or displaying the value of the current signal IL. μP'
is a microprocessor into which, for example, data from a setting device SER is input, and is processed through an interface IFC' according to a processing procedure stored in a memory MEM'.
A digital signal is sent to the wire transmitter 10. Further, the microprocessor μP' sends the response data from the two-wire transmitter 10 to the memory MEM via the interface IFC'.
', and further decoded according to the processing procedure stored in the memory MEM' and displayed on the monitor of the setting device SER.

Next, the interface 14 connected to the load 12 will be explained. A digital signal is also transmitted from the two-wire transmitter 10 to the load 12 along with the current signal IL. These mixed signals of analog and digital signals are separated by the signal conditioner SC of the interface 14, and the analog signals as PV values that require high-speed real-time performance are processed by the microprocessor CP.
The digital signals are sent to the host system via the analog input/output card I/O under the control of the microprocessor C.
It is interfaced to the high speed bus via a communication card CMN under the control of the PU.

Conversely, from the upper interface, communication card CMN, signal conditioner SC, load 1
2. A digital signal is sent to the two-wire transmitter 10 via the transmission lines L1 and L2 to realize bidirectional communication.

FIG. 4 shows the main body S of the sensor SR1 shown in FIG.
FIG. 2 is a vertical cross-sectional view showing a specific configuration of R1a and remote part SR1b. The main body part SR1a has a cylindrical body 1 in the center.
A cover flange 16 having a concave portion on the inside thereof.
, 17 are pressed and fixed from both sides of the body 15 with bolts.

Through holes 18 and 19 are formed in the center portions of the cover flanges 16 and 17, respectively. It is communicated with a distant remote section SR1b via a capillary 21. A measurement pressure P0 to be measured is applied to one end face of the remote part SR1b via a seal diaphragm 22.

On the other hand, seal diaphragms 23 and 24 are fixed to both ends of the body 15, and the interior is separated into left and right chambers 26 and 27 by a center diaphragm 25. 28 and 29 are included. Rooms 26 and 27 facing the center diaphragm 25
Electrodes 30 and 31 are fixed on the surface of the. Incidentally, a coupling part 32 is fixed to the upper part of the body 15, and a signal is taken out from there to the microcomputer.

When the measured pressure P0 is applied to the seal diaphragm 22 of the remote part SR1b, this measured pressure P0
displaces the seal diaphragm 24 via the sealed liquid 20 in the capillary 21. Seal diaphragm 2
4, the atmospheric pressure on the side of the through hole 18 displaces the center diaphragm 26 through the internal filling liquid 29 in response to the pressure transmitted through the filling liquid 28. This displacement of the center diaphragm 26 changes the capacitance between the electrodes 30 and 31 arranged oppositely on both sides of the center diaphragm 26, thereby detecting the measured pressure P0.

[0015]

SUMMARY OF THE INVENTION However, the two-wire transmitter described above poses a problem in the following cases. The response time constant of this conventional two-wire transmitter can be determined by connecting the handheld terminal 13 to the transmission lines L1 and L2 using connection lines L1' and L2', and setting the necessary time constant using the setting device SER. This is transmitted to the two-wire transmitter 10 by digital communication, and the microprocessor μP1 receives this digital signal and sets the time constant set by the setting device SER using software.

By the way, when the measured pressure Po is detected through the remote part SR1b connected to a long capillary 21 as shown in FIG. 4, the viscosity of the filled liquid 20 changes depending on the temperature, microprocessor μ
Even if the time constant set by the setting device SER is set using P1, there is a problem that the overall time constant changes depending on the temperature and is not constant.

FIG. 5 shows the results of an investigation regarding the above points. The horizontal axis shows the ambient temperature (°C), the vertical axis shows the overall time constant (seconds), and the calculated values shown by the dotted line and the actual measured values shown by the solid line are shown using the filled liquids A, B, and C as parameters. It is. As can be seen from this figure, when the ambient temperature changes, the time constant changes significantly even if the time constant is set to a predetermined value using software. In other words, setting the time constant on the handheld terminal 13 is meaningless.

[0018]

[Means for Solving the Problems] The present invention, as a main configuration for solving the above problems, measures by using a sensor that receives power from the load side via two transmission lines and has a sealed liquid. This is a two-wire transmitter that converts a physical quantity to an electrical signal, processes the signal using a signal calculation means including a microprocessor, and transmits the signal as a current signal to the load side via the transmission line. temperature detection means for detecting the temperature of the sensor and outputting temperature data; and a sensor time constant for calculating the sensor time constant of the previous sensor using this temperature data and a predetermined parameter set in advance. a calculation means, and a time constant that uses the sensor time constant to calculate a damping time constant of the signal calculation means so that the overall response time constant including the signal calculation means becomes a predetermined time constant. The computer is equipped with a calculation means.

[0019]

[Operation] The temperature detection means detects the temperature of the sealed liquid and outputs the temperature as temperature data, and the sensor time constant calculation means uses this temperature data and the influence on a preset time constant. The sensor time constant of the sensor is calculated using the given predetermined parameters. The time constant calculation means uses the calculated sensor time constant to calculate the damping time constant of the signal calculation means so that the overall response time constant including the signal calculation means becomes a predetermined time constant. Calculate and output.

[0020]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. Note that parts having the same functions as those of the conventional two-wire transmitter shown in FIGS. 3 and 4 are denoted by the same reference numerals, and the explanation thereof will be omitted as appropriate.

A temperature sensor SR2 is newly added as a sensor to the two-wire transmitter 33, and an analog temperature signal that converts the analog temperature signal detected by the temperature sensor SR2 into a digital signal and outputs it to the microprocessor μP2. /Digital converter AD2 is added.

Along with this, the calculation contents of the microprocessor μP1 and the contents of the memory MEM1 have been changed, and are provided as a microprocessor μP2 and a memory MEM2, respectively. The other parts are almost the same as the configuration shown in FIGS. 3 and 4.

Next, the operation of the embodiment configured as described above will be explained using the flowchart shown in FIG. Prior to the calculation by the microprocessor μP2, the ROM in the memory MEM2 contains the initial values necessary to start the differential pressure or pressure calculation, or the initial values necessary to start the time constant calculation. initial data is stored, which is set in step A of FIG.

Next, in the RAM in the memory MEM2,
Data necessary for calculations such as various correction coefficients such as the spring constant of the center diaphragm 25 necessary for differential pressure/pressure calculations, or correction coefficients necessary for time constant calculations are stored. Set in step B of FIG.

Thereafter, the process moves to step C, where the microprocessor μP2 reads pressure data from the sensor SR1 under its control and stores it in the RAM area of the memory MEM2.

Furthermore, the microprocessor μP2 moves to step D, and uses the data stored in the memory MEM2 in step C to update the RAM in the memory MEM2.
The differential pressure or pressure is calculated according to a differential pressure or pressure calculation procedure stored in advance in the area and transmitted as an analog current signal IL to the load 12 via the output circuit OPC.

The data reading and calculations in steps C and D are repeated to output a current signal to the load 12. In step E, it is determined whether or not this repetition has been performed a predetermined number of times. If the process has not been performed a predetermined number of times, this process is repeated, but if the process has been performed a predetermined number of times, the process moves to step F. This is to provide a difference between the differential pressure/pressure calculation and the time constant correction calculation, since the differential pressure/pressure changes quickly but the time constant changes due to temperature slowly.

In step F, the temperature data necessary for calculating the time constant is fetched from the sensor SR2 under the control of the microprocessor μP2 and stored in the RAM area of the memory MEM2.

Step G is a sensor time constant calculation step for calculating the time constant of sensor SR1. The sensor time constant Ts is the viscosity μ of the filled liquids 20, 28, and 29, and the capillary
If the volume change rate Vr of the remote part SR1b including 21 and the correction coefficient are K, then Ts=K・μ・Vr

It is shown in (1). This viscosity μ is the filled liquid 20, 28,
The rate of change in volume Vr is influenced by the length of the capillary 21. Therefore, these values are set as setting 1 by communication from the handheld terminal 13, and further, using the temperature data obtained in step F, the temperature is expressed as shown in equation (1) previously stored in the memory MEM2. The sensor time constant Ts is calculated using an arithmetic expression.

After this, the process moves to step H. This calculation step is a total time constant calculation step for calculating the time constant T of the entire two-wire transmitter 33 including the sensor SR1. The overall time constant T is set as setting 2 by communication from the handheld terminal 13, and the microcomputer of the two-wire transmitter 33 is set using the calculation formula shown in the following equation (2) stored in the memory MEM2 in advance. Calculate the damping time constant Tu by software calculation. Tu=T-Ts

(2) The result of this calculation is used in the next differential pressure/pressure calculation shown in step D.

By performing the above steps, the change in time constant due to viscosity change due to temperature is corrected, and the differential pressure/pressure signal is always transmitted to the load 12 with a constant time constant set in advance on the handheld terminal 13. can do.

[0032] In the above explanation, the remote unit SR1
Although the differential pressure/pressure transmitter having the pressure transmitter b has been described, the present invention is not limited to this, and can be similarly applied to a normal differential pressure/pressure transmitter having a sealed liquid.

[0033]

[Effects of the Invention] As described above in detail with reference to the embodiments, according to the present invention, the temperature is detected and used to calculate the change in the time constant based on the temperature change of the liquid sealed in the sensor.
Since the software time constant is changed to a preset constant time constant, even if the temperature changes, the signal can be transmitted to the load as a whole with the preset constant time constant.

[Brief explanation of the drawing]

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

FIG. 2 is a flowchart explaining the operation of the two-wire transmitter shown in FIG. 1;

FIG. 3 is a block diagram showing the configuration of a conventional two-wire transmitter.

FIG. 4 is a longitudinal sectional view showing details of the sensor shown in FIG. 3;

FIG. 5 is a characteristic diagram illustrating a problem with the two-wire transmitter shown in FIG. 3;

[Explanation of symbols]

10, 33 2-wire transmitter 11 DC power supply 12 Load 13 Handheld terminal 14 Interface 20, 28, 29 Filled liquid 21 Capillary SR1 Sensor SR1a Main unit SR1b Remote unit μP1, μP2 Microprocessor MEM1, ME
M2 memory

Claims (1)

[Claims] Claim 1: Receiving power from the load side via two transmission lines, converting a physical quantity to be measured by a sensor having a sealed liquid into an electrical signal, which is then processed by a signal calculation means including a microprocessor. In a two-wire transmitter that transmits a current signal to the load side via the transmission line,
temperature detection means for detecting the temperature of the sealed liquid and outputting temperature data; and a sensor for calculating a sensor time constant of the sensor using the temperature data and a predetermined parameter set in advance. a time constant calculating means; a time constant for calculating a damping time constant of the signal calculating means using the sensor time constant so that the overall response time constant including the signal calculating means becomes a predetermined time constant; A two-wire transmitter, characterized in that it comprises a calculation means.