CN111192448B - Remote transmission liquid level transmitter system based on HART communication and use method thereof - Google Patents

Remote transmission liquid level transmitter system based on HART communication and use method thereof Download PDF

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Publication number
CN111192448B
CN111192448B CN201911344226.2A CN201911344226A CN111192448B CN 111192448 B CN111192448 B CN 111192448B CN 201911344226 A CN201911344226 A CN 201911344226A CN 111192448 B CN111192448 B CN 111192448B
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hart
host
slave
module
pressure
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CN111192448A (en
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佟志权
孙建
姚建平
刘文斌
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Zhejiang Central Control Sensor Technology Co ltd
Zhongkong Technology Co ltd
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Zhejiang Central Control Sensor Technology Co ltd
Zhejiang Supcon Technology Co Ltd
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
    • G08C19/00—Electric signal transmission systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/14—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measurement of pressure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/40—Bus networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/40—Bus networks
    • H04L12/40006—Architecture of a communication node
    • H04L12/40013—Details regarding a bus controller
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/40—Bus networks
    • H04L12/403—Bus networks with centralised control, e.g. polling
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L12/00—Data switching networks
    • H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
    • H04L12/40—Bus networks
    • H04L2012/40208—Bus networks characterized by the use of a particular bus standard

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Arrangements For Transmission Of Measured Signals (AREA)

Abstract

The invention provides a remote transmission liquid level transmitter system based on HART communication and a using method thereof, wherein the system comprises: the remote liquid level measuring device comprises a control room, a target object to be measured and a remote liquid level transmitter based on HART communication; the electronic remote transmission liquid level transmitter comprises a HART host, a HART slave and a plurality of HART bus adapters; the HART host and the HART slave are respectively arranged at a first position and a second position of the target object to be detected; the HART host and the HART slave, the HART host and the control room and the HART slave and the control room are connected through the HART bus adapter; the HART slave computer obtains a second pressure value of a second position of the target object to be detected and transmits the second pressure value to the host computer; and the HART host acquires the pressure value of the first position of the target object to be detected, and stores the difference value between the first pressure value and the second pressure value and transmits the difference value to the control room through the HART bus adapter.

Description

Remote transmission liquid level transmitter system based on HART communication and use method thereof
Technical Field
The invention relates to the technical field of transmitters, in particular to a remote transmission liquid level transmitter system based on HART communication and a using method thereof.
Background
The conventional technology of the remote transmission type liquid level transmitter is that a capillary tube is filled with silicon oil to transmit pressure, when the pressure transmission distance exceeds 20 meters, the error influence of the silicon oil cannot be ignored, a series of problems such as increase of temperature drift of a sensor, output lag, creep deformation and the like can be caused, the influence of environmental factors can be superposed due to overlong pipelines, and the anti-vibration capability is poor.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a remote transmission liquid level transmitter system based on HART communication and a using method thereof. The technical scheme of the invention is as follows:
a remote transmission level transmitter system based on HART communication, comprising: the remote liquid level measuring device comprises a control room, a target object to be measured and a remote liquid level transmitter based on HART communication;
the electronic remote transmission liquid level transmitter comprises a HART host, a HART slave and a plurality of HART bus adapters;
the HART host and the HART slave are respectively arranged at a first position and a second position of the target object to be detected;
the HART host and the HART slave, the HART host and the control room and the HART slave and the control room are connected through the HART bus adapter;
the HART host, the HART slave and the HART bus adapter are communicated with each other according to the HART protocol;
the HART slave computer is used for obtaining a second pressure value of a second position of the target object to be detected and transmitting the pressure value to the host computer;
and the HART host is used for obtaining the pressure value of the first position of the target object to be detected, storing the difference value between the first pressure value and the second pressure value and transmitting the difference value to the control room through the HART bus adapter.
Further, the HART slave further comprises: the system comprises a slave machine sampling module, a slave machine processing module, a slave machine communication module, a slave machine switch module, a slave machine power supply module and a slave machine storage module; wherein:
the slave sampling module at least comprises a second pressure sensor and is used for acquiring a second pressure value at a second position of the target object to be detected, converting a second pressure code value output by the second pressure sensor into a digital value and outputting the digital value to the slave processing module;
the slave processing module is used for processing the second pressure code value output by the slave sampling module, smoothing and filtering the second pressure code value by a peak and outputting the second pressure code value to the slave communication module;
the slave communication module is used for modulating the second pressure code value output by the slave processing module into a HART signal, transmitting the HART signal to a HART bus, and further processing the HART signal after receiving the code value by the host;
the slave switch module is used for controlling the power supply of the sampling module to realize the start and stop of the sampling function;
the slave power supply module is used for distributing power to the slave;
and the slave storage module is used for storing the setting parameters of the slave, and at least comprises the filtering parameters and HART communication parameters related to the sensor.
Further, the HART host further comprises: the host computer comprises a host computer sampling module, a host computer processing module, a host computer communication module, a host computer switch module, a host computer power supply module, a host computer storage module, a host computer current loop module and a host computer display module; wherein:
the host sampling module at least comprises a first pressure sensor and is used for acquiring a first pressure value at a first position of a target object to be detected, converting a code value output by the first pressure sensor into a digital quantity and outputting the digital quantity to the host processing module;
the host processing module is used for processing the pressure code value output by the host sampling module and obtaining a processed first pressure code value after smoothing and peak filtering;
the host processing module is connected with the host communication module, and the host communication module is connected with the slave communication module; the slave communication module transmits the second pressure code value to the host processing module through the host communication module;
the host processing module calculates the difference value between the first pressure code value and the second pressure code value, converts the pressure difference value into a pressure value PV with temperature compensation and outputs the pressure value PV to the host communication module;
the host communication module is used for modulating the PV value output by the host processing module into a HART signal, transmitting the HART signal to a HART bus and transmitting the HART signal to the control room through the HART bus adapter;
the host switch module is used for controlling the power supply of the host sampling module to realize the start and stop of the sampling function;
the host power supply module is used for distributing power to the host;
the host storage module is used for storing the setting parameters of the host, and at least comprises the filtering parameters and HART communication parameters related to the sensor;
the host current loop module is used for converting the PV value calculated by the host processing module into 4-20mA current and outputting the current;
the host display module is used for displaying the current numerical value, and at least comprises: real-time liquid level height, current value, application range and percentage.
Furthermore, between HART host computer and HART slave computer, adopt the question-answering type communication mode, further include: the slave is in a silent state after being electrified, and after receiving a host starting command, the slave starts to sample pressure code values and uploads the code values in a burst mode specified by an HART protocol; and when the slave receives the stop command, stopping sampling and communication and waiting for the next start command.
Furthermore, the HART host, the HART slave and the HART bus adapter share a HART communication link layer; the application layer command format between the HART host and the HART slave adopts a custom command frame, and the lead code is 0x 00.
Further, the sum of the power consumption currents of the HART master and the HART slave can not exceed 3.5 mA.
A use method of a remote transmission liquid level transmitter system based on HART communication comprises the following steps based on the system:
s1: the control room sends a starting command to the HART host through the HART bus, and the HART host sends a starting signal to the slave through the HART bus according to the HART protocol after receiving the command;
s2: the HART host collects and processes a first pressure value at a first position of a target object to be detected;
s3: the HART slave machine receives a starting command of the HART host machine, samples and processes a second pressure value at a second position of the target object to be detected, and transmits the second pressure value to the host machine through the HART bus;
s4: and the HART host receives the second pressure value, calculates the difference value between the first pressure value and the second pressure value, converts the pressure difference value into a pressure value PV with temperature compensation and then sends the pressure value PV with temperature compensation to the control room through the HART bus.
Further, the step S2 further includes:
the host sampling module acquires a first pressure value at a first position of a target object to be detected through a first pressure sensor, converts a code value output by the first pressure sensor into a digital quantity and outputs the digital quantity to the host processing module;
and the host processing module processes the pressure code value output by the host sampling module and obtains a processed first pressure code value after smoothing and spike filtering.
Further, the step S3 further includes:
the slave sampling module acquires a second pressure value at a second position of the target object to be detected through a second pressure sensor, converts a second pressure code value output by the second pressure sensor into a digital quantity and outputs the digital quantity to the slave processing module;
the slave processing module processes the second pressure code value output by the slave sampling module, and outputs the second pressure code value to the slave communication module after smoothing and peak filtering;
the slave communication module modulates the second pressure code value output by the slave processing module into an HART signal, sends the HART signal to an HART bus, and further processes the HART signal after receiving the code value by the host;
the slave switch module controls the power supply of the sampling module to realize the start and stop of the sampling function;
the slave power supply module is used for distributing power to the slave;
and the slave storage module stores the set parameters of the slave, and at least comprises the filtering parameters and HART communication parameters related to the sensor.
Further, the step S4 further includes:
the slave communication module transmits the second pressure code value to the host processing module through the host communication module;
the host processing module calculates the difference value between the first pressure code value and the second pressure code value, converts the pressure difference value into a pressure value PV with temperature compensation and outputs the pressure value PV to the host communication module;
the host communication module modulates the PV value output by the host processing module into an HART signal, transmits the HART signal to the HART bus and transmits the HART signal to the control room through the HART bus adapter;
the host switch module controls the power supply of the host sampling module to realize the start and stop of the sampling function;
the host power supply module is used for distributing power to the host;
the host storage module stores the setting parameters of the host, and at least comprises the filtering parameters and HART communication parameters related to the sensor;
the host current loop module converts the PV value calculated by the host processing module into 4-20mA current and outputs the current;
the host display module displays the current numerical value, and at least comprises: real-time liquid level height, current value, application range and percentage.
Further, in step S3, the slave switch module performs time-sharing control on the slave usage module, and the method further includes:
the time from the beginning of sampling to the output of the second pressure value of the HART slave is divided into four continuous time periods: the method comprises the following steps of (1) adopting time of an HART slave computer, time of uploading a sampling code value from the slave computer, adopting time of a host computer and delay starting sampling time of the slave computer;
when the HART slave computer samples, the host computer closes the host computer sampling module, and after the slave computer uploads code values, the slave computer sampling module is also closed, the slave computer sampling module is started to sample again after delaying for a period of time, and the current loop is output after the host computer processes the current loop.
Furthermore, between the HART host and the bus, the standard HART protocol is followed; when a standard HART command frame appears on the bus, the HART host and the HART slave receive the command frame at the same time; when the HART slave machine recognizes that the command frame is in the standard HART protocol format, the HART slave machine automatically stops communication and sampling, gives the control right of the bus to the HART host machine, and waits for the next starting command of the HART host machine.
Compared with the prior art, the invention has the following beneficial effects:
the invention has complete design basis, can replace the existing capillary mode, and thoroughly solves the problems of interference resistance of remote transmission and narrow measuring range. Especially in the application of the transmission distance more than 20 meters, the use value is very high.
The HART communication mode is used, the compatibility is good, the existing system structure does not need to be changed, and the use is convenient. And the high-low pressure side does not need to be distinguished during installation, and the host can automatically calculate the pressure difference value and correspond to the output current.
The invention uses two pressure sensors, and realizes differential pressure measurement by calculating the difference value of two pressure point positions. Therefore, the pressure values of the two points can be output as separate parameters, which is an advantage that the traditional flange capillary type liquid level transmitter does not have. The two-point pressure value is stored in an EEPROM module of the host in a digital quantity mode and can be read through HART commands.
The invention uses compatible universal liquid level transducer, namely two-wire system and supports HART communication, so in the invention, two-wire system and support HART communication are still adopted between the host and the slave and between the host and the system. Due to the design, the master and the slave are required to share the HART physical layer and the link layer, and the design of the communication layer has innovation points.
For a DCS system, an electronic liquid level transmitter consisting of a host computer and a slave computer is not different from a universal flange capillary type liquid level transmitter, but the performance is greatly improved, the measurable range is enlarged, and the measurement stability is better.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a block diagram of a system configuration of a remote level transmitter system based on HART communication according to an embodiment of the present invention;
FIG. 2 is a block diagram of a slave system in accordance with an embodiment of the present invention;
FIG. 3 is a block diagram of a host system in accordance with an embodiment of the present invention;
FIG. 4 illustrates a communication flow between a host and a slave according to an embodiment of the present invention;
FIG. 5 is a timing diagram illustrating time-sharing control of the master and slave devices according to an embodiment of the present invention;
FIG. 6 is a custom command frame format according to an embodiment of the present invention;
FIG. 7 is an engineering circuit diagram of a slave sampling module according to an embodiment of the present invention;
FIG. 8 is a diagram of an engineering circuit of a slave processing module according to an embodiment of the present invention;
FIG. 9 is a diagram of an engineering circuit of a slave communication module according to an embodiment of the present invention;
FIG. 10 is a diagram of an engineering circuit of a slave switch module according to an embodiment of the present invention;
FIG. 11 is a diagram of an engineering circuit of a slave power module according to an embodiment of the present invention;
FIG. 12 is a diagram of an engineering circuit of a slave memory module according to an embodiment of the present invention
FIG. 13 is a diagram of an engineering circuit of a host current loop module in accordance with one embodiment of the present invention;
fig. 14 is a circuit diagram of a host display module according to an embodiment of the invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Referring to fig. 1 to 6, the present embodiment discloses a remote level transmitter system based on HART communication, which includes: the remote liquid level measuring device comprises a control room, a target object to be measured and a remote liquid level transmitter based on HART communication;
the electronic remote transmission liquid level transmitter comprises a HART host, a HART slave and a plurality of HART bus adapters;
the HART host and the HART slave are respectively arranged at a first position and a second position of the target object to be detected;
the HART host and the HART slave, the HART host and the control room and the HART slave and the control room are connected through the HART bus adapter;
the HART host, the HART slave and the HART bus adapter are communicated with each other according to the HART protocol;
the HART slave computer is used for obtaining a second pressure value of a second position of the target object to be detected and transmitting the pressure value to the host computer;
and the HART host is used for obtaining the pressure value of the first position of the target object to be detected, storing the difference value between the first pressure value and the second pressure value and transmitting the difference value to the control room through the HART bus adapter.
In FIG. 1, POWER is a common POWER supply, P + represents a positive electrode, P-represents a negative electrode, and RCIs a resistance.
The HART slave further comprises: the system comprises a slave machine sampling module, a slave machine processing module, a slave machine communication module, a slave machine switch module, a slave machine power supply module and a slave machine storage module; wherein:
the slave sampling module at least comprises a second pressure sensor and is used for acquiring a second pressure value at a second position of the target object to be detected, converting a second pressure code value output by the second pressure sensor into a digital value and outputting the digital value to the slave processing module; the slave sampling module is the ADC and front-end circuit in fig. 2. The circuit engineering diagram corresponds to U2 and its peripheral connecting devices in FIG. 7.
The slave processing module is used for processing the second pressure code value output by the slave sampling module, smoothing and filtering the second pressure code value by a peak and outputting the second pressure code value to the slave communication module; the slave processing module is the MCU circuit in FIG. 2. The circuit engineering diagram corresponds to U3 and its peripheral connecting devices in FIG. 8.
The slave communication module is used for modulating the second pressure code value output by the slave processing module into a HART signal, transmitting the HART signal to a HART bus, and further processing the HART signal after receiving the code value by the host; the slave communication module is the HART MODEM circuit in fig. 2. The HART MODEM of this embodiment supports half-duplex communication, i.e., the slave can also receive the command of the host, thereby realizing the function of controlling the slave. The circuit engineering diagram corresponds to U1 and its peripheral connecting devices in FIG. 9.
The slave switch module is used for controlling the power supply of the sampling module to realize the start and stop of the sampling function; the reason for this design is that in two-wire HART designs, low power consumption is a key indicator of the design. The low-power-consumption design of the system can be realized by the starting and stopping functions of the sampling module and the cooperation with the HART communication time sequence. The circuit engineering diagram corresponds to U4, U8 and the peripheral connecting devices in FIG. 10.
And the slave power supply module is used for distributing power to the slave. The circuit engineering diagrams correspond to U5 and U6 in FIG. 11 and the peripheral connecting devices thereof.
And the slave storage module is used for storing the setting parameters of the slave, and at least comprises the filtering parameters and HART communication parameters related to the sensor. The slave memory module is the EEPROM circuit in fig. 2. The circuit engineering diagram corresponds to U1 and its peripheral connecting devices in FIG. 12.
The HART host further comprises: the host computer comprises a host computer sampling module, a host computer processing module, a host computer communication module, a host computer switch module, a host computer power supply module, a host computer storage module, a host computer current loop module and a host computer display module; wherein:
the host sampling module at least comprises a first pressure sensor and is used for acquiring a first pressure value at a first position of a target object to be detected, converting a code value output by the first pressure sensor into a digital quantity and outputting the digital quantity to the host processing module; the host sampling module is the ADC and front end circuit of fig. 3. The engineering circuit diagram is the same as that of the slave sampling module.
The host processing module is used for processing the pressure code value output by the host sampling module and obtaining a processed first pressure code value after smoothing and peak filtering; the host processing module is the MCU circuit in fig. 3. The engineering circuit diagram corresponds to the U3 element of FIG. 8 and its peripheral connection devices.
The host processing module is connected with the host communication module, and the host communication module is connected with the slave communication module; the slave communication module transmits the second pressure code value to the host processing module through the host communication module according to the HART protocol;
and the host processing module calculates the difference value of the first pressure code value and the second pressure code value, converts the pressure difference value into a pressure value PV with temperature compensation and outputs the pressure value PV to the host communication module.
Wherein: the process of obtaining the PV value by the host processing module is as follows: after the difference operation is carried out on the first pressure code value and the second pressure code value, the first pressure code value and the second pressure code value can be processed as a differential pressure code value. Firstly, fitting operation is carried out on a differential pressure value and a pressure value, the differential pressure value is converted into a digital pressure force NPV without temperature compensation, then Newton interpolation operation is carried out on the NPV and the temperature compensation value, and the converted digital value PV is the pressure value with temperature compensation.
The host communication module is used for modulating the difference value output by the host processing module into a HART signal, transmitting the HART signal to a HART bus and transmitting the HART signal to the control room through a HART bus adapter; the host communication module is the HART MODEM circuit in fig. 3. The engineering circuit diagram is connected with the slave communication module.
The host switch module is used for controlling the power supply of the host sampling module to realize the start and stop of the sampling function; the engineering circuit diagram is the same as the slave switch module.
The host power supply module is used for distributing power to the host; the engineering circuit diagram is the same as the slave power supply module.
The host storage module is used for storing the setting parameters of the host, and at least comprises the filtering parameters and HART communication parameters related to the sensor; the host memory module is the EEPROM circuit in fig. 3. The engineering circuit diagram is the same as the slave memory module.
The host current loop module is used for converting the pressure value calculated by the host processing module into 4-20mA current and outputting the current; the host current LOOP module is the DA & LOOP & LOD circuit in fig. 3. The current output by the host machine current loop module can be supplied to DCS, PLC and other control equipment, can reach a control room, and can also be a field display recording instrument. The engineering circuit diagram corresponds to U6, U7 and the peripheral connecting devices in FIG. 13.
The host display module is used for displaying the current numerical value and at least comprises: real-time liquid level height, current value, application range, percentage amount and instrument setting parameters. Wherein:
the real-time liquid level height H is PV/ρ g, PV is the calculated pressure value with temperature compensation, ρ is the density value of the liquid (engineering parameter, which needs to be written into the instrument), and g is the gravity acceleration.
The engineering circuit diagram of the host display module corresponds to U1, U2 and the peripheral connecting devices in FIG. 14.
The meter setting parameters include those commonly used in the art, including: filtering parameters, alarm parameters, etc.
In particular, the engineering circuits of the HART master and the HART slave are shared, wherein the HART slave does not need the engineering circuits corresponding to the master current loop module and the master display module.
As shown in fig. 4, in this embodiment, the master and the slave adopt a question-and-answer communication mode, and further include: the slave is in a silent state after being electrified, and after receiving a host starting command, the slave starts to sample pressure code values and uploads the code values in a burst mode specified by an HART protocol; and when the slave receives the stop command, stopping sampling and communication and waiting for the next start command.
Need to explain: because the standard HART protocol can judge whether the current bus is quiet, namely, the communication in the burst mode is supported, the master and the slave in the burst mode do not need to worry about not receiving the bus command.
The host, the slave and the HART bus adapter share a HART communication link layer; the difference with the standard HART protocol is that the application layer command format between the HART master and the HART slave uses custom command frames so that the slave does not respond to the commands of the bus adapter. Here, the preamble of the standard HART command frame is 0xFF, while the preamble in this design is 0x 00.
A comparison of the standard command frame and the custom command frame is shown in fig. 6. Except for the preamble, the other is identical except that the transmitted content data is different.
In this embodiment, the sum of the power consumption currents of the master and slave devices of the two-wire system cannot exceed 3.5 mA.
The device type selection is the primary factor for realizing low power consumption design, and in the embodiment, all components related to all circuits are micropower consumption components. Besides all the micro power consumption devices, an additional control mode is needed to realize low power consumption design.
Analyzing fig. 2 and 3, the module with the largest power consumption ratio is the sampling module. Therefore, the key to realizing low power consumption design is: and (5) sampling time-sharing control. Firstly, a power supply control switch mode of a sampling module is added on a circuit.
The sample-to-output of the system is divided into four successive time periods: the slave machine adopting time, the slave machine uploading sampling code value time, the master machine adopting time and the slave machine delay starting sampling time are shown in a timing diagram in figure 5. When the slave computer samples, the host computer closes the sampling module, and after the slave computer uploads the code value, the sampling module is also closed, and after a period of time delay, the module is opened for resampling, and the current loop is output after the host computer processes. Through time-sharing sampling control, the design requirement that the total power consumption current of the system is less than 3.5mA can be realized.
The design principle of the embodiment is as follows: two pressure sensors are used for replacing one differential pressure sensor, and an HART communication mode is used for replacing a capillary tube to transmit pressure signals. Because two pressure sensors are used, differential pressure measurement is realized by calculating the difference value of two pressure point positions. Therefore, the pressure values of the two points can be output as separate parameters, which is an advantage that the traditional flange capillary type liquid level transmitter does not have.
In this embodiment, the HART slave is equivalent to a pressure transmitter with incomplete functions, does not need the loop current control function, and only has the functions of pressure sampling and HART communication. And reading the pressure code value through an internal slave computer sampling module, filtering the code value, uploading the pressure code value to the HART host computer, and further processing the pressure code value by the HART host computer. The HART host is a pressure transmitter with complete functions, contains all functions of the pressure transmitter, and is also a differential pressure transmitter with complete functions. The principle of differential pressure realization is that the function of the differential pressure transmitter is realized by reading the pressure code value of the slave and performing the difference division operation with the self pressure code value.
The implementation simultaneously discloses a use method of a remote transmission liquid level transmitter system based on HART communication, and the remote transmission liquid level transmitter system based on the HART communication comprises the following steps:
s1: the control room sends a starting command to the host computer through the HART bus, and the host computer sends a starting signal to the slave computer through the HART bus according to the HART protocol after receiving the command;
s2: the host computer collects and processes a first pressure value at a first position of a target object to be detected;
s3: the slave computer receives a starting command of the host computer, samples and processes a second pressure value at a second position of the target object to be detected, and transmits the second pressure value to the host computer through the HART bus;
s4: and the host receives the second pressure value, calculates the difference value between the first pressure value and the second pressure value, converts the pressure difference value into a pressure value PV with temperature compensation and then sends the pressure value PV with temperature compensation to the control room through the HART bus.
The step S2 further includes:
the host sampling module acquires a first pressure value at a first position of a target object to be detected through a first pressure sensor, converts a code value output by the first pressure sensor into a digital quantity and outputs the digital quantity to the host processing module;
the host processing module processes the pressure code value output by the host sampling module and obtains a processed first pressure code value after smoothing and peak filtering
The step S3 further includes:
the slave sampling module acquires a second pressure value at a second position of the target object to be detected through a second pressure sensor, converts a second pressure code value output by the second pressure sensor into a digital quantity and outputs the digital quantity to the slave processing module;
the slave processing module processes the second pressure code value output by the slave sampling module, and outputs the second pressure code value to the slave communication module after smoothing and peak filtering;
the slave communication module modulates the second pressure code value output by the slave processing module into an HART signal, sends the HART signal to an HART bus, and further processes the HART signal after receiving the code value by the host;
the slave switch module controls the power supply of the sampling module to realize the start and stop of the sampling function;
the slave power supply module is used for distributing power to the slave;
and the slave storage module stores the set parameters of the slave, and at least comprises the filtering parameters and HART communication parameters related to the sensor.
The step S4 further includes:
the slave communication module transmits the second pressure code value to the host processing module through the host communication module;
the host processing module calculates the difference value between the first pressure code value and the second pressure code value, converts the pressure difference value into a pressure value PV with temperature compensation and outputs the pressure value PV to the host communication module;
wherein: the process of obtaining the PV value by the host processing module is as follows: after the difference operation is carried out on the first pressure code value and the second pressure code value, the first pressure code value and the second pressure code value can be processed as a differential pressure code value. Firstly, fitting operation is carried out on a differential pressure value and a pressure value, the differential pressure value is converted into a digital pressure force NPV without temperature compensation, then Newton interpolation operation is carried out on the NPV and the temperature compensation value, and the converted digital value PV is the pressure value with temperature compensation.
The host communication module modulates the PV value output by the host processing module into an HART signal, transmits the HART signal to the HART bus and transmits the HART signal to the control room through the HART bus adapter;
the host switch module controls the power supply of the host sampling module to realize the start and stop of the sampling function;
the host power supply module is used for distributing power to the host;
the host storage module stores the setting parameters of the host, and at least comprises the filtering parameters and HART communication parameters related to the sensor;
the host current loop module converts the PV value calculated by the host processing module into 4-20mA current and outputs the current; the current output by the host machine current loop module can be supplied to DCS, PLC and other control equipment, can reach a control room, and can also be a field display recording instrument.
The display module displays the current numerical value, and at least comprises: real-time liquid level height, current value, application range, percentage amount and instrument setting parameters. Wherein:
the real-time liquid level height H is PV/ρ g, PV is the calculated pressure value with temperature compensation, ρ is the density value of the liquid (engineering parameter, which needs to be written into the instrument), and g is the gravity acceleration.
The meter setting parameters include those commonly used in the art, including: filtering parameters, alarm parameters, etc.
In step S3, the slave switch module performs time-sharing control on the slave usage module, and further includes:
dividing the time from the beginning of sampling to the output of the second pressure value of the slave into four continuous time periods: the slave machine adopting time, the slave machine uploading sampling code value time, the master machine adopting time and the slave machine delay starting sampling time;
when the slave machine samples, the master machine closes the master machine sampling module, and after the slave machine uploads code values, the slave machine sampling module is also closed, the slave machine sampling module is started to sample again after a period of time delay, and the current loop is output after the master machine processes the current loop.
The current loop corresponds to the current of 4-20mA output by the host current module. The term "current loop" as used herein means: and in the time slot of the slave computer for delaying to start the sampling module, the host computer outputs the calculated current value to the control equipment or the control room after processing through a series of algorithms. The current passes through a loop.
The HART host computer and the bus follow the standard HART protocol; when a standard HART command frame appears on the bus, the host and the slave receive the command frame at the same time; when the slave machine recognizes that the command frame is in the standard HART protocol format, the slave machine automatically stops communication and sampling, gives the bus control right to the host machine, and waits for the next starting command of the host machine.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims (10)

1. A remote level transmitter system based on HART communication, comprising: the remote liquid level measuring device comprises a control room, a target object to be measured and a remote liquid level transmitter based on HART communication;
the remote transmission liquid level transmitter comprises a HART host, a HART slave and a plurality of HART bus adapters;
the HART host and the HART slave are respectively arranged at a first position and a second position of the target object to be detected;
the HART host and the HART slave, the HART host and the control room and the HART slave and the control room are connected through the HART bus adapter;
the HART host, the HART slave and the HART bus adapter are communicated with each other according to the HART protocol;
the HART slave computer is used for obtaining a second pressure value of a second position of the target object to be detected and transmitting the pressure value to the host computer;
the HART host is used for obtaining a pressure value of a first position of a target object to be detected, storing a difference value between the first pressure value and a second pressure value and transmitting the difference value to the control room through the HART bus adapter;
the HART slave further comprises: the system comprises a slave machine sampling module, a slave machine processing module, a slave machine communication module, a slave machine switch module, a slave machine power supply module and a slave machine storage module; wherein:
the slave sampling module at least comprises a second pressure sensor and is used for acquiring a second pressure value at a second position of the target object to be detected, converting a second pressure code value output by the second pressure sensor into a digital value and outputting the digital value to the slave processing module;
the slave processing module is used for processing the second pressure code value output by the slave sampling module, smoothing and filtering the second pressure code value by a peak and outputting the second pressure code value to the slave communication module;
the slave communication module is used for modulating the second pressure code value output by the slave processing module into a HART signal, transmitting the HART signal to a HART bus, and further processing the HART signal after receiving the code value by the host;
the slave switch module is used for controlling the power supply of the sampling module to realize the start and stop of the sampling function;
the slave power supply module is used for distributing power to the slave;
the slave storage module is used for storing the setting parameters of the slave, and at least comprises the filtering parameters and HART communication parameters related to the sensor;
the HART host further comprises: the host computer comprises a host computer sampling module, a host computer processing module, a host computer communication module, a host computer switch module, a host computer power supply module, a host computer storage module, a host computer current loop module and a host computer display module; wherein:
the host sampling module at least comprises a first pressure sensor and is used for acquiring a first pressure value at a first position of a target object to be detected, converting a code value output by the first pressure sensor into a digital quantity and outputting the digital quantity to the host processing module;
the host processing module is used for processing the pressure code value output by the host sampling module and obtaining a processed first pressure code value after smoothing and peak filtering;
the host processing module is connected with the host communication module, and the host communication module is connected with the slave communication module; the slave communication module transmits the second pressure code value to the host processing module through the host communication module;
the host processing module calculates the difference value between the first pressure code value and the second pressure code value, converts the pressure difference value into a pressure value PV with temperature compensation and outputs the pressure value PV to the host communication module;
the host communication module is used for modulating the PV value output by the host processing module into a HART signal, transmitting the HART signal to a HART bus and transmitting the HART signal to the control room through the HART bus adapter;
the host switch module is used for controlling the power supply of the host sampling module to realize the start and stop of the sampling function;
the host power supply module is used for distributing power to the host;
the host storage module is used for storing the setting parameters of the host, and at least comprises the filtering parameters and HART communication parameters related to the sensor;
the host current loop module is used for converting the PV value calculated by the host processing module into 4-20mA current and outputting the current;
the host display module is used for displaying the current numerical value, and at least comprises: real-time liquid level height, current value, application range and percentage.
2. The system of claim 1, wherein the HART master and HART slave communicate with each other in a question-and-answer mode, further comprising: the slave is in a silent state after being electrified, and after receiving a host starting command, the slave starts to sample pressure code values and uploads the code values in a burst mode specified by an HART protocol; and when the slave receives the stop command, stopping sampling and communication and waiting for the next start command.
3. The system of claim 1, wherein the HART host, HART slave, HART bus adaptor share a HART communication link layer; the application layer command format between the HART host and the HART slave adopts a custom command frame, and the lead code is 0x 00.
4. The system of claim 1, wherein the sum of the power consumption currents of the HART master and HART slave cannot exceed 3.5 mA.
5. Use of a remote level transmitter system based on HART communication, based on the system according to one of claims 1 to 4, comprising the steps of:
s1: the control room sends a starting command to the HART host through the HART bus, and the HART host sends a starting signal to the slave through the HART bus according to the HART protocol after receiving the command;
s2: the HART host collects and processes a first pressure value at a first position of a target object to be detected;
s3: the HART slave machine receives a starting command of the HART host machine, samples and processes a second pressure value at a second position of the target object to be detected, and transmits the second pressure value to the host machine through the HART bus;
s4: and the HART host receives the second pressure value, calculates the difference value between the first pressure value and the second pressure value, converts the pressure difference value into a pressure value PV with temperature compensation and then sends the pressure value PV with temperature compensation to the control room through the HART bus.
6. The method of claim 5, wherein the step S2 further comprises:
the host sampling module acquires a first pressure value at a first position of a target object to be detected through a first pressure sensor, converts a code value output by the first pressure sensor into a digital quantity and outputs the digital quantity to the host processing module;
and the host processing module processes the pressure code value output by the host sampling module and obtains a processed first pressure code value after smoothing and spike filtering.
7. The method of claim 6, wherein the step S3 further comprises:
the slave sampling module acquires a second pressure value at a second position of the target object to be detected through a second pressure sensor, converts a second pressure code value output by the second pressure sensor into a digital quantity and outputs the digital quantity to the slave processing module;
the slave processing module processes the second pressure code value output by the slave sampling module, and outputs the second pressure code value to the slave communication module after smoothing and peak filtering;
the slave communication module modulates the second pressure code value output by the slave processing module into an HART signal, sends the HART signal to an HART bus, and further processes the HART signal after receiving the code value by the host;
the slave switch module controls the power supply of the sampling module to realize the start and stop of the sampling function;
the slave power supply module is used for distributing power to the slave;
and the slave storage module stores the set parameters of the slave, and at least comprises the filtering parameters and HART communication parameters related to the sensor.
8. The method of claim 7, wherein the step S4 further comprises:
the slave communication module transmits the second pressure code value to the host processing module through the host communication module;
the host processing module calculates the difference value between the first pressure code value and the second pressure code value, converts the pressure difference value into a pressure value PV with temperature compensation and outputs the pressure value PV to the host communication module;
the host communication module modulates the PV value output by the host processing module into an HART signal, transmits the HART signal to the HART bus and transmits the HART signal to the control room through the HART bus adapter;
the host switch module controls the power supply of the host sampling module to realize the start and stop of the sampling function;
the host power supply module is used for distributing power to the host;
the host storage module stores the setting parameters of the host, and at least comprises the filtering parameters and HART communication parameters related to the sensor;
the host current loop module converts the PV value calculated by the host processing module into 4-20mA current and outputs the current;
the host display module displays the current numerical value, and at least comprises: real-time liquid level height, current value, application range and percentage.
9. The method of claim 8, wherein in step S3, the slave switch module uses time-sharing control for the slave sampling module, further comprising:
the time from the beginning of sampling to the output of the second pressure value of the HART slave is divided into four continuous time periods: sampling time of an HART slave computer, time of uploading a sampling code value by the slave computer, sampling time of a host computer and time delay starting sampling time of the slave computer;
when the HART slave computer samples, the host computer closes the host computer sampling module, and after the slave computer uploads code values, the slave computer sampling module is also closed, the slave computer sampling module is started to sample again after delaying for a period of time, and the current loop is output after the host computer processes the current loop.
10. The method of claim 5, wherein the HART host and the bus are compliant with the standard HART protocol; when a standard HART command frame appears on the bus, the HART host and the HART slave receive the command frame at the same time; when the HART slave machine recognizes that the command frame is in the standard HART protocol format, the HART slave machine automatically stops communication and sampling, gives the control right of the bus to the HART host machine, and waits for the next starting command of the HART host machine.
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