ve flowmeter

I. Introduction

Ground scale measurement is one of the main means of enterprise material measurement. But in the actual work, the cheating phenomenon in the ground scale measurement is quite common, and more complex, the harm can not be underestimated.

1, manual invoicing loopholes.

Most enterprises still use manual billing, due to the randomness of manual counting is very large, there is no constraint, and some enterprises' individual division scale personnel even take the scale statement and signature home, at home billing signature.

2. Car body positioning and dynamic weighing measurement problems.

Nowadays, industrial scales are measured on the basis of static weighing, and buyers or sellers often collude with weighing personnel. When the truck passes slowly through the scale body table, only the front wheel or the rear wheel is on the scale body table, press the print button and begin to print the measurement bill. In this way, the weight value is often several tons.

3. Cheating on repeated scales.

Due to the lack of effective technical control, buyers or sellers often repeat the measurement of the same truck by buying the weighing personnel and the warehouse management personnel, repeatedly printing the scale code, and the warehouse management personnel also sign for it.

4, change the car back to the scale cheating.

The technical control measures taken by some enterprises have certain loopholes, and the weighing personnel take the same car number, the big car weighing, the small car back, or the small car weighing, the big car back to the skin to achieve the purpose of cheating.

In order to effectively limit and overcome the work of the measuring staff, it is necessary to have more comprehensive technical control measures and sound management system constraints. And the technical control measures are the foundation of the establishment of a management system, in this case, the flow meter measurement system has played a strong advantage, received good results, to the enterprise has brought benefits.

Second, composition structure

The system diagram is as follows:

The protocols used are as follows:

Third, serial communication technology introduction

RS-232C and RS-485:

The data transmission between computer and computer or between computer and terminal can adopt serial communication and parallel communication. Serial communication is widely used because of its few lines and low cost, especially in remote transmission, which avoids the inconsistency of the characteristics of multiple lines. In serial communication, both sides of the communication are required to adopt a standard interface, so that different devices can be easily connected for communication. RS-232-C interface (also known as EIA RS-232-C) is one of the most commonly used serial communication interfaces. Its full name is "Technical Standard for Serial Binary Data Exchange Interface between Data Terminal Equipment (DTE) and Data Communication Equipment (DCE)" and the standard specifies the use of a 25-pin DB25 connector.

As the RS-232-C interface standard appeared earlier, it is inevitable that there are shortcomings, mainly the following four shortcomings:

(1) The signal level value of the interface is high, easy to damage the chip of the interface circuit, and because it is incompatible with the TTL level, it is necessary to use a level conversion circuit to connect with the TTL circuit.

(2) The transmission rate is low, and the communication baud rate ranges from 0 to 20Kbps.

(3) The interface uses a signal line and a signal return line to form a common ground transmission form, which is easy to produce common mode interference, so the anti-noise interference is weak.

(4) Transmission distance is limited, the maximum transmission distance standard value is 50 feet, in fact, it can only be used within 15 meters.

In view of the shortcomings of RS-232-C, there are some new interface standards, and RS-485 is one of them. When the communication distance is required to be tens of meters to thousands of meters, RS-485 serial bus standard is widely used. RS-485 uses balanced transmission and differential reception, so it has the ability to suppress common-mode interference. Coupled with the high sensitivity of the bus transceiver, it can detect voltages as low as 200mV, so the transmitted signal can be recovered from kilometers away. RS-485 works in half duplex mode, and only one bit is in the sending state at any time. Therefore, the transmitting circuit must be controlled by the enable signal. RS-485 is very convenient when used for multi-point interconnection and can eliminate many signal lines. Application RS-485 can be networked to form a distributed system, the maximum transmission distance of RS-485 interface standard value of 4000 feet, in fact, generally up to 3000 meters, so that users can use a single RS-485 interface to easily establish a network of equipment. (Figure 2)

RS-485 interface has the advantages of good anti-noise interference, long transmission distance and multi-station capability, which makes it the preferred serial interface. The half-duplex network composed of RS-485 interfaces generally requires only two connections, so RS-485 interfaces are transmitted by shielded twisted pair cables. The RS-485 interface connector adopts the 9-pin connector of DB-9, and the RS-485 interface of intelligent terminal adopts DB-9 (hole), and the keyboard interface of RS-485 connects with the keyboard adopts DB-9 (pin).

Multi-serial Converter card (CI-134) :

Since most of the standard serial ports used on the current computer are RS-232C interfaces, if you want to use RS-485 for communication, it requires an interface conversion card for data conversion. The Industio CI-134 is an RS-422/485 four-port serial card designed for communication applications in industrial environments. It supports four independent RS-422/485 serial ports and can control up to 128 devices in one-to-multipoint communication applications. To make RS-485 2-wire half-duplex operation easier, each CI-134 card has automatic data flow control (ADDC), which requires no software operation. Therefore, the RS-485 half-duplex protocol can be controlled in Windows applications without additional coding. To meet the requirements of highly reliable products for industrial environments, this product offers optional photoelectric isolation (2 KV) and surge protection (25 kV ESD). And built-in terminal resistance, can be easily used in remote communication. The serial card is widely used in: multi-point data acquisition; Factory automation, remote serial device control, industrial control, embedded industrial machinery and SCADA systems.

Fourth, function detailed explanation

The following article will take the automobile loading system of the sixth branch of petrochina Daqing Natural Gas Corporation as an example to briefly explain the principle and function of the flowmeter measurement system.

4.1 System Principles

The flowmeter metering system includes a computer monitoring management program (force control 2.0 configuration software, that is, ForceControl2.0), multi-serial port conversion card (CI-134IS), mass flowmeter (Rosemount), automatic shut-off valve (two-stage type), control system (OPTOMUX B100), emergency stop reset button, The control mode can be fully automated. In this system, the loading status of the site is completed by using Daqing 3D configuration software force control 2.0, and the control system, mass flow meter (Series 2000) and display screen (Daqing 3D system) are communicated through multiple serial port cards. Among them, the control system is connected to the quick cut-off valve, the emergency stop reset button and the ground signal on the site; The mass flowmeter is used to calculate and convert the instantaneous flow rate, temperature, density, volume cumulant and mass cumulant of the medium in the pipeline. Because it is a digital signal transmission, it avoids the problem of single data transmission by analog or pulse, and the precision deviation of pulse cumulant, ensuring the accuracy and reliability of the measurement data. The force control software processes the data collected from the transmitter of the mass flow meter, and then sets it to the special display installed in each loading crane position, so that the operator and the driver on the site can understand the loading progress very conveniently.

In case of emergency, the field operator and the control room operator can use the button to close the quick stop valve, the process is: the control system (PLC) collects the switch signal obtained by the switch, and then locks or resets according to the need to control the state of the quick stop valve.

4.2 Control Process

In order to store, query and generate daily, monthly, quarterly and annual reports of loading data while monitoring and management, status monitoring and data management are implemented separately in the upper computer of this set of measurement system. Force control 2.0 collects and sends on-site data through multiple serial cards, that is, the upper configuration, and then interfaces with ODBC data source. The loading quantity and loading crane number are sent to the database management module developed by Microsoft Visual FoxPro 6.0, so that the computer can automatically print the settlement bill and generate the report. Their specific functions are:

Force control: real-time collection and display of field data, control of loading process, automatic voice prompt and alarm, real-time and diachronic trend display, network data release, dual-system hot backup, etc

Database management (VFP) : calculate preload, store load records, query, retune records, generate reports, etc

The complete loading process of this flowmeter metering system is:

Force control: real-time collection and display of field data, control of loading process, automatic voice prompt and alarm, real-time and diachronic trend display, network data release, dual-system hot backup, etc

1. When the vehicle is ready to load, the vehicle management data is recorded in the control room first, and the operator records it into the database management program, and the computer automatically calculates the amount of pre-loaded vehicles according to the tank volume and media density input by the operator.

2. When the vehicle arrives at the loading crane and is ready, the operator of the control room gives the estimated loading quantity and sends it to the LED display screen while the quick cut-off valve automatically opens fully. When it is close to 95% of the loading target value, the control system will adjust the quick cut-off valve to a small flow state (such as 5% of the full flow), and issue an audible and visual alarm to remind the loading personnel to pay attention. When the actual loading volume reaches the predetermined target value, the control system closes the cut-off valve and stops the loading on site.

It is also possible to fill a loading position with only one flowmeter, using a thick and thin two pipelines, respectively controlled by two valves. When approaching the loading target value (such as 95%), first turn off the valve on the thick pipeline, and then close the valve on the fine pipeline to ensure the loading accuracy.

3. When the control room sends out the valve closing action, the data is automatically transmitted from the monitoring software to the database management module, which is controlled by the operator to print the loading and metering statement and provide it to the user. At this point, the whole loading process is completed.

4. In order to ensure the needs of loading progress, any position of each loading station can be loaded at any time, and the computer can meet the requirements of parallel loading without conflict.

5. Voice prompt function:

Database management (VFP) : calculate preload, store load records, query, retune records, generate reports, etc

The complete loading process of this flowmeter metering system is:

Two explosion-proof speakers are installed on the site loading trestle, and a microphone is installed in the control room for voice communication with the site. When the loading starts, the configuration software triggers a previously recorded sound file, such as "second crane loading starts"; When the loading volume reaches 95% of the pre-loading volume, the computer outputs a sound file to the scene, such as "the second crane loading is ready to end"; At the end of loading, output another sound file, such as "Second crane loading end". Thus, the site operator can master the progress of loading and make the loading work proceed smoothly.

4.3 Dual-System Hot Backup

When the two upper computers are equipped with multiple serial port conversion cards, the force control software has the dual-system hot backup function, that is, you can specify one machine as the host and the other as the slave. The content of the slave machine is synchronized with the content of the host in real time, and the slave machine monitors the host status in real time. Once the host stops responding, it takes over the control. The "dual-system backup" mechanism can also greatly improve the reliability of system operation. When the host stops for some reason and cannot receive the data of the remote device, it can immediately replace the status of the host as a backup and continue the work of data collection. The system operation does not have to stop because of this, which greatly reduces the pressure of users when the system is shut down. At the same time, enterprises can reduce the loss caused by system outage.

V. Summary

The multi-serial card plays a very important role in the loading and measuring work. Because RS-485 has the characteristics of stable communication, strong anti-interference, long communication distance, etc., the system increases the practicability. This system can also be connected to the serial device network Server (Nport Express), connect with other networks, realize resource sharing, and through the power control Web Server to generate all the records and reports to other management or control networks of the enterprise. The leader of the company can see the loading status of the site at any time in his office, as well as the relevant reports in the computer, which facilitates the integrated management of the company and increases the scalability of the system.