Who knows the basic knowledge of instruments?

1. Common standard throttling devices (orifice plate), (nozzle) and (venturi tube).

2. The commonly used non-standard throttling devices are (double orifice plate), (circular orifice plate), (1/4 circular nozzle) and (venturi nozzle).

3. The commonly used methods of orifice pressure measurement are (angular pressure measurement) and (flange pressure measurement), and other methods are (theoretical pressure measurement), (radial pressure measurement) and (pipeline pressure measurement).

4. Standard orifice flange pressure measurement method, the distance between the center of upstream and downstream pressure measurement holes and the front and rear end faces of orifice plate is (25.4±0.8)mm, also called 1 inch flange pressure measurement.

5. 1 15 1 The working power supply range of the transmitter is (12)VDC to (45)VDC, and the load is (0) ohm to (1650) ohm.

6. The range of1151dp4e transmitter is (0 ~ 6.2) to (0 ~ 37.4) kPa.

7. 1 15 1 The maximum positive migration of differential pressure transmitter is (500%), and the maximum negative migration is (600%).

8. Generally speaking, the velocity of the fluid in the pipeline is maximum at (the center line of the pipeline), and the velocity at (the wall of the pipeline) is equal to zero.

9. If (Reynolds number) is the same, the motion of fluid is similar.

10. When the fluid filled with pipeline flows through the throttling device, there will be flow (local contraction) at (contraction), so that (flow) will increase and (static pressure) will decrease.

11.1151The differential pressure transmitter uses a variable capacitor as a sensitive element. When the pressure difference increases, the measuring diaphragm moves, so the capacitance on the low-voltage side (increases) and the capacitance on the high-voltage side (decreases).

When the minimum adjustment range of12.1151differential pressure transmitter is used, the maximum load transfer is (600%) of the range, and the maximum forward transfer is (500%). If it is used within the maximum adjustment range of 1 15 1,

13.1151The accuracy of differential pressure transmitter is (0.2%) and (0.25%). Note: Large differential pressure transmitter is 0.25%.

14. Common flow units, volume flow (m3/h) and mass flow (kg/h) and (t/h), and gas volume flow (Nm3/h) in standard state.

15. When measuring steam flow with orifice flowmeter, the density of steam is 4.0kg/m3 in design and 3kg/m3 in actual work, so the actual indicated flow is (0.866) times of the designed flow.

16. Measure ammonia flow with orifice flowmeter. When the design pressure is 0.2MPa (gauge pressure), the temperature is 20℃, the actual pressure is 0. 15MPa (gauge pressure) and the temperature is 30℃, the actual indicated flow is (0.897) times of the design flow.

17. The straight pipe section in front of the orifice plate generally requires (10)D, and the straight pipe section behind the orifice plate generally requires (5) d. For correct measurement, the straight pipe section in front of the orifice plate is preferably (30 ~ 50) d, especially when there is a pump or regulating valve in front of the orifice plate.

18. In order to make the flow coefficient α of orifice flowmeter tend to a constant value, the Reynolds number of fluid should be greater than the critical Reynolds number.

19. In the technical requirements of orifice plate processing, the upstream plane should be perpendicular to the center line of orifice plate without visible scars, the upstream surface and the downstream surface should be parallel, and the upstream inlet edge should be sharp without burrs and scars.

20. For what kind of fluid, the pressure position in the diagram is correct? (1)

A. gas B. liquid C. steam D. high viscosity fluid E. precipitation fluid

Principle: When measuring gas, in order to make a small amount of condensate in the gas flow back to the process pipeline smoothly without flowing into the measuring pipeline and instrument, the pressure tap should be at the upper part of the pipeline, namely 1 in the figure.

When measuring liquid, in order to make a small amount of gas separated from the liquid return to the process pipeline smoothly without entering the measuring pipeline and instrument, it is best to take the pressure port within an included angle of 0 ~ 45 degrees below the horizontal center line of the pipeline.

For steam medium, stable condensate should be kept in the measuring pipeline, and the solid medium at the bottom of the process pipeline should be prevented from entering the measuring pipeline and instrument. It is best for the pressure tap to form an included angle of 0 ~ 45 degrees with the horizontal center line of the pipeline, as shown in the figure.

2 1. What should be paid attention to when opening and closing the balance valve of differential pressure flowmeter filled with isolation liquid? What's the point?

Answer: Before opening the orifice pressure-taking valve, you must first open the balance valve, then open the pressure-taking valve on one side, and then close the balance valve after the pressure is evenly transferred to the positive and negative sides of the differential pressure flowmeter, and finally open another pressure-taking valve. Otherwise, the instrument is easily damaged by unilateral compression.

22. What is the static pressure error of differential pressure transmitter?

Answer: When the same pressure is input into the positive and negative pressure cavities of the differential pressure transmitter at the same time, the output zero position of the transmitter will shift, and the shift value will change with the increase of static pressure. This error caused by static pressure is called static pressure error.

23. Please describe how to take pressure from the throttling device?

Answer: 1. Angle connection pressure 2. Flange pressure 3. Theoretical pressure 4. Diameter distance pressure 5. Pipe connection pressure.

24. When using differential pressure transmitter to measure flow, under what conditions do I need an installation package? How to install?

Answer: when the measured medium is corrosive gas or liquid, it is necessary to add a package to protect the diaphragm and measuring conduit of the differential pressure transmitter from corrosion; When the measured medium is viscous, in order to ensure the accuracy of measurement, a package needs to be installed. The interface between the assembly and the throttle valve is the "inlet" and the interface between the assembly and the measuring conduit is the "outlet". When the density of the measured medium is less than that of the sealing liquid, the packaging should be "up and down", and when the density of the measured medium is greater than that of the sealing liquid, the packaging should be "up and down".

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Basic knowledge of instruments-classification of instruments

There are many classification methods of detection and process control instruments (usually called automation instruments), which can be classified according to different principles. For example, according to the energy used by instruments, it can be divided into pneumatic instruments, electric instruments and hydraulic instruments (rare); According to the instrument combination form, it can be divided into basic instrument, unit combination instrument and comprehensive control device; According to the instrument installation form, it can be divided into field instrument, tray instrument and rack instrument; With the development of microprocessor, tuxedo can be divided into intelligent instruments and non-intelligent instruments according to whether the microprocessor introduces instruments. According to the form of instrument signal, it can be divided into analog instrument and digital instrument. According to the functions of recording and indicating, analog and digital, display instruments can be divided into recording instruments and indicating instruments, analog instruments and digital display instruments, among which recording instruments can be divided into single-point recording and multi-point recording (indicating can also be single-point and multi-point), including paper recording or paperless recording, and recording and printing if there is paper recording. Regulating instruments can be divided into basic regulating instruments and unit combined regulating instruments. Due to the introduction of microprocessor, programmable regulator and fixed program regulator appeared. The actuator consists of two parts: the actuator and the regulating valve. Actuators can be divided into pneumatic actuators, electric actuator and hydraulic actuator according to energy source, and diaphragm actuator, piston actuator (cylinder actuator) and long-stroke actuator according to structural form. Regulating valves are classified according to their structural characteristics and flow characteristics. According to the structural characteristics, it is usually divided into straight-through single seat, straight-through double seat, tee joint, angle valve, diaphragm, butterfly valve, ball valve, eccentric rotation, sleeve (cage) and valve body separation. According to the flow characteristics, it is divided into linear type, logarithmic type (equal surface ratio), parabolic type and fast opening type. This classification method is reasonable and the coverage of instruments is wide, but it is impossible to classify all instruments into orderly wells by any classification method, and they are mutually infiltrated and communicated. For example, transmitters have many functions, such as temperature transmitter can be classified as temperature detector, differential pressure transmitter can be classified as flow detector, pressure transmitter can be classified as pressure detector, and it is difficult to accurately classify liquid level detector if it measures liquid level by pressure method, and it is also difficult to merge calculation and auxiliary units in combined instruments of Chinese and foreign units. Basic knowledge and comparison of several commonly used flowmeters Flow measurement is one of the four important process parameters (the other three are temperature, pressure and material level). Closed-tube flowmeters are classified as follows according to their technologies: differential pressure flowmeter (DP), which is the most common flow technology, including orifice plate, venturi tube and sonic nozzle. DP flowmeter can be used to measure the flow velocity of most liquids, gases and vapors. DP flowmeter has no moving parts, which is widely used and convenient to use. However, pressure loss will occur after plugging, which will affect the accuracy. The accuracy of flow measurement depends on the accuracy of pressure gauge. Positive displacement flowmeter (PD) PD flowmeter is used to measure the volume flow of liquid or gas. It introduces fluid into the metering space and counts the number of revolutions. Impeller, gear, piston or orifice plate are used to transfer fluid. PD flowmeter has high accuracy and is one of several methods to measure viscous liquid. But it will also produce unrecoverable pressure error, so it is necessary to equip with moving parts. Turbine flowmeter When the fluid flows through the turbine flowmeter, the fluid makes the rotor rotate. The rotational speed of the rotor is related to the speed of the fluid. The flow rate or total amount is derived from the average flow rate of the fluid detected by the rotor. Turbine flowmeter can accurately measure clean liquid and gas. Like PD flowmeter, turbine flowmeter will produce unrecoverable pressure error and need moving parts. Electromagnetic flowmeter can get the velocity of conductive fluid by measuring the voltage when it flows through the electromagnetic field. Electromagnetic flowmeter has no moving parts and is not affected by fluid. When the tube is full, the accuracy of measuring conductive liquid is very high. Electromagnetic flowmeter can be used to measure the velocity of mud fluid. The propagation time method and Doppler effect method of ultrasonic flowmeter are commonly used to measure the average velocity of fluid. Like other speedometers, it is an instrument for measuring volume flow. This is an unobstructed flowmeter. If the ultrasonic transmitter is installed outside the pipeline, it does not need to be inserted. It is suitable for almost all liquids, including mud, and has high precision. But the dirty pipeline will affect the accuracy. Vortex flowmeter Vortex flowmeter is to place a streamlined vortex generator in the fluid, and the velocity of the vortex is proportional to the velocity of the fluid, thus calculating the volume flow. Vortex flowmeter is suitable for measuring liquid, gas or steam. It has no moving parts and no dirt problem. Vortex flowmeter will produce noise, and it needs high velocity of fluid to produce vortex. Thermal mass flowmeter measures fluid velocity by measuring the increase of fluid temperature or the decrease of thermal sensor. Thermal mass flowmeter has no moving parts or holes, so it can accurately measure gas flow. Thermal mass flowmeter is one of the few technologies that can measure mass flow, and it is also one of the few technologies used to measure large-caliber gas flow. Coriolis flowmeter This flowmeter uses a vibrating fluid tube to generate deflection corresponding to mass flow. Coriolis flowmeter can be used to measure the mass flow of liquid, mud, gas or steam. High accuracy. However, the pipeline wall should be maintained regularly to prevent corrosion. Measuring principle of electromagnetic flowmeter: Faraday's law of electromagnetic induction proves that the movement of conductor in magnetic field induces potential. According to the principle of electromagnetic measurement, fluid is a moving conductor. The induced potential is proportional to the flow rate and is detected by two measuring electrodes. Then the transmitter amplifies it and calculates the flow according to the cross-sectional area of the pipeline. The constant magnetic field is generated by replacing the changing switching DC current with magnetic poles. The measuring system consists of a transmitter and a sensor. It has two models: integrated type, in which the transmitter and sensor form a complete mechanical unit; Separate type, transmitter and sensor are installed separately. Transmitter: Promag50 (operated by buttons and displayed in two lines) Sensor: PROMAGW (DN25...2000) Technical parameter measurement variable: flow. Measurement range of input variable: typical v=0. 1 ... 10m/s, with specified measurement accuracy, operable flow range: over 1000: 1 input signal status input (auxiliary input): U = 3...30VDC, Ri = 5kΩ, electrically isolated. Configurable: cumulative reset, measured value suppression and error information reset. Current input (Promag 53 only): active/passive optional, electrical isolation resolution: 2μA Active: 4. . . 20mA, ri ≤150Ω, Uout=24V DC, passive anti-current short circuit: 0/4. . . 20mA, Ri≤ 150ωUmax = 30V DC. Output variable output signal current output: active/passive optional electrical isolation time constant optional (0.05... 100s) full-scale value optional temperature coefficient: 0.005%o.r./℃ typical value; Resolution: 0.5 μA Effective: 0/4 ... 20mA 700Ω (HART: RL ≥ 250Ω) Passive: 4 ... 20mA Max.30VDC RI ≤150Ω Pulse/frequency output: passive open collector 30VDC250mA electrical isolation. Frequency output: full-scale frequency 2 ...1000 Hz (f max =1250 Hz) On/off ratio 1: 1 pulse width: 10s maximum. Pulse output: pulse value and pulse. Wall-mounted housing: cast aluminum sensor housing, DN25...300: powder spraying cast aluminum; DN350...2000: Type and specification of coated steel: 50W9H-UD0A1K2C4aw (DN 900) 50W is 50 series; 9H represents a diameter of 900 mm (DN 900); U represents that the base material is polyurethane; D indicates that the process connection/material is PN 10 DIN250lST37-2 flange (applicable to DN 200-DN 2000); 0 indicates that the electrode material (all electrodes) is 1.4435/3 16L stainless steel; A stands for 0.5%.3 point calibration; 1 means that no special authentication is required; The second a means there is no riot requirement; K indicates that the enclosure protection level is IP68 separated and wall mounted; 2 stands for separated self-contained 10m cable; Environmental conditions: ambient temperature -20...+60℃ (sensor, transmitter), installed in the dark, avoid direct sunlight, especially in warm climate areas. The reference conditions of measurement accuracy: DIN 19200 and VDI/VDE 264l, medium temperature: +28℃ K, ambient temperature: +22℃ K, preheating time: 30 minutes. During installation, it should be noted that accurate measurement can be obtained only when the pipeline is full, and the following installation positions should be avoided: direct installation at the highest point of the pipeline (easy to accumulate bubbles). Be careful not to install the flow tube on the inlet side of the pump, so as not to damage the flow tube lining due to pump pressure. When using reciprocating pump, diaphragm pump or plunger pump, it is necessary to install pulse throttle valve. When the length of the downward pipeline exceeds 5m, install a siphon or a bleeder valve behind the sensor. So as to avoid possible damage to the inner wall of the measuring tube caused by low pressure. Make sure the pipe is full and reduce the gas content. Installation direction: the most suitable direction helps to avoid gas accumulation and residue accumulation in the measuring tube. Vertical installation; This orientation is ideal for the pipeline system which is easy to self-empty, and the empty pipe detection electrode may not be added. Horizontal installation: the plane of the measuring electrode must be horizontal, which can prevent the electrode from being insulated for a short time due to air bubbles. Note: the empty pipe detection function can only work normally when the measuring device is installed horizontally and the transmitter shell is facing up. If the vibration is very severe, the sensor and transmitter should be installed separately. Pedestal and bracket: If the nominal diameter DN≥350, install the transmitter on the pedestal that can bear enough load. Please note that the external frame is not allowed to support the weight of the sensor. This will deform the external frame and damage the internal excitation coil. If possible, it is best to avoid valves, tees and elbows when installing sensors. Ensure the straight inlet and outlet pipe sections with the following requirements to ensure the measurement accuracy: the inlet length is 10 × DN and the outlet length is 5 × DN. The sensor and transmitter grounding sensor are grounded in the center of the pipeline. The sensor and the medium must have the same potential to ensure the measurement accuracy and avoid the corrosion damage of the electrode. Equipotential is ensured by installing a grounding reference electrode in the sensor. If the medium flows in an unlined and grounded metal tube, the grounding requirements can be met by connecting to the transmitter housing. For individual grounding, the same as above. Note: If you are not sure whether the medium is properly grounded, you should install a grounding ring. Fault diagnosis: If the electromagnetic flowmeter fails after startup or during operation, it is usually diagnosed according to the following checklist to directly find the cause of the problem and the corresponding solution. Check that there is no display and no output signal: 1, and check the power supply terminal 1, 2; 2. Check the fuse. No display but signal output: 1. Check whether the cable connection of the display module is correctly inserted into the amplifier board; 2. The display module is damaged; 3. The measuring electrode is damaged. Foreign language display text: Turn off the power, press and hold the+/-key at the same time, and power on the instrument. The display text is English (default), with the maximum display contrast. The measured value is displayed, but there is no current or pulse output signal: the measuring electrode is damaged. Display fault: the fault in the process of debugging or measurement will be displayed immediately, and the fault information will contain some symbols with the following meanings: S= fault information P= process fault = fault information! = Warning information empty pipe = fault type, that is, the measuring pipe is partially full or completely empty 03: 00: 05 = fault occurrence time, hour/minute/second #40 1= fault code current output: minimum current, 4-20ma (25ma) → 2ma, and the output signal corresponds to zero flow; Maximum current, 4-20ma (25ma) → 25ma. Note: System or process failures defined as "warning messages" have no impact on input/output.

Emphasize the basic knowledge of instruments.

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