Instrumentation application fields:
Instrumentation has a wide range of applications, covering industry, agriculture, transportation, science and technology, environmental protection, national defense, culture, education and health, people’s life and other aspects. Due to its special status and great role, it has a huge doubling and pulling effect on the national economy, and has a good market demand and huge development potential.
Instrument fault diagnosis: the method is as follows
1. percussion hand pressure method
When we use the instrument, we often encounter the phenomenon of good and bad when the instrument is running. Most of this phenomenon is caused by poor contact or virtual welding. In this case, tapping and hand pressing can be used.
The so-called “knock” is to tap the board or component lightly through a small rubber cockroach or other percussion object to see if it will cause an error or downtime. The so-called “hand pressure” means that when a fault occurs, after turning off the power, press the plugged parts, plugs and sockets firmly by hand again, and then start the machine again to try whether the fault will be eliminated. If you find that tapping on the casing is normal, and hitting it again is abnormal, it is best to reinsert all the connectors and try again.
2. Observation method
Use sight, smell, touch. Sometimes, damaged components will discolor, blister or have burnt spots; burnt components will produce some special odor; shorted chips will become hot; virtual soldering or desoldering can also be observed with the naked eye.
3. Exclusion method
The so-called elimination method is a method of judging the cause of the failure by plugging in some plug-in boards and devices in the machine. When the instrument returns to normal after a plug-in board or device is removed, it means that the fault occurs there.
4. Substitution method
Two instruments of the same model or sufficient spare parts are required. Replace a good spare with the same component on the faulty machine to see if the fault is eliminated.
5. Contrast method
It is required to have two instruments of the same model, and one of them is in normal operation. Using this method also requires the necessary equipment, such as a multimeter, oscilloscope, etc. According to the nature of comparison, there are voltage comparison, waveform comparison, static impedance comparison, output result comparison, current comparison and so on.
The specific method is: let the faulty instrument and the normal instrument operate under the same conditions, and then detect the signals of some points and then compare the two groups of signals measured. If there is a difference, it can be concluded that the fault is here. This method requires the maintenance personnel to have considerable knowledge and skills.
6. heating and cooling method
Sometimes, the instrument works for a long time, or when the temperature of the working environment is high in summer, it will malfunction. The shutdown and inspection are normal, and it will be normal after stopping for a period of time and then restarting. After a while, the failure occurs again. This phenomenon is due to the poor performance of individual ICs or components, and the high temperature characteristic parameters do not meet the index requirements. In order to find out the cause of the failure, the heating and cooling method can be used.
The so-called cooling is to use cotton fiber to wipe the anhydrous alcohol on the part that may fail to cool down when the failure occurs, and observe whether the failure is eliminated. The so-called temperature rise is to artificially increase the ambient temperature, such as using an electric soldering iron to approach the suspicious part (be careful not to raise the temperature too high to damage the normal device) to see if the fault occurs.
7. Shoulder riding
The shoulder riding method is also called the parallel method. Put a good IC chip on the chip to be checked, or connect good components (resistor capacitors, diodes, transistors, etc.) in parallel with the components to be checked, and maintain good contact. If the fault comes from the internal open circuit of the device or Reasons such as poor contact can be ruled out by this method.
8. Capacitor bypass method
When a certain circuit produces a relatively strange phenomenon, such as a display confusion, the capacitor bypass method can be used to determine the part of the circuit that is probably faulty. Connect the capacitor across the power supply and ground of the IC; connect the transistor circuit across the base input or collector output to observe the effect on the fault phenomenon. If the failure phenomenon disappears when the capacitor bypass input terminal is invalid and its output terminal is bypassed, it is determined that the fault occurs in this stage of the circuit.
9. State adjustment method
In general, before the fault is determined, do not touch the components in the circuit casually, especially the adjustable devices, such as potentiometers. However, if the double reference measures are taken in advance (for example, the position is marked or the voltage value or resistance value is measured before being touched), it is still allowed to be touched if necessary. Maybe after the change sometimes the glitch will go away.
10. Isolation
The fault isolation method does not require the same type of equipment or spare parts to be compared, and is safe and reliable. According to the fault detection flow chart, the division and encirclement gradually narrow the fault search range, and then cooperate with methods such as signal comparison and component exchange to find the fault location very quickly.
Six types of common instrumentation principle diagram:
1. Principle of pressure instrument
1). Spring tube pressure gauge
2). Electric contact pressure instrument
3). Capacitive pressure sensor
4). Capsule pressure sensor
5). Pressure thermometer
6). Strain-type pressure sensor
2. Principle of temperature instrument
1). Structure of thin film thermocouple
2). Solid expansion thermometer
3). Outline drawing of thermocouple compensation wire
4). Thermocouple Thermometer
5). The structure of the thermal resistance
3. Principle of flow meter
1). Target flowmeter
2). Orifice flowmeter
3). Vertical waist wheel flowmeter
4). Nozzle flow
5). Positive displacement flowmeter
6). Oval gear flowmeter
7). Venturi flowmeter
8). Turbine flowmeter
9). Rotameter
Fourth, the principle of liquid level instrument
1). Differential pressure level gauge A
2). Differential pressure level gauge B
3). Differential pressure level gauge C
Principle of ultrasonic measurement of liquid level
5. Capacitive level gauge
Five, valve principle
1). Thin film actuator
2). Piston actuator with valve positioner
3). Butterfly valve
4). Diaphragm valve
5). Piston actuator
6). Angle valve
7). Pneumatic membrane control valve
8). Pneumatic piston actuator
9). Three-way valve
10). Cam deflection valve
11). Straight through single seat valve
12). Straight-through double seat valve
6. Control principle
1). Cascade uniform control
2). Nitrogen sealing split range control
3). Boiler control
4). Heating furnace cascade
5). Furnace temperature measurement
6). Simple and uniform control
7). Uniform control
8). Material transfer
9). Liquid level control
10). The principle of measuring molten metal with invasive thermocouples
Instrumentation product features:
1. Softwareization
With the development of microelectronics technology, the speed of microprocessors is getting faster and the price is getting lower and lower, and it has been widely used in instrumentation, which makes some real-time requirements very high. software to achieve. Even many problems that are difficult to solve or simply cannot be solved by hardware circuits can be solved well by software technology. The development of digital signal processing technology and the widespread adoption of high-speed digital signal processors have greatly enhanced the signal processing capabilities of the instrument. Digital filtering, FFT, correlation, convolution, etc. are commonly used methods of signal processing. The common feature is that the main operations of the algorithm are composed of iterative multiplication and addition. If these operations are completed by software on a general-purpose computer, the operation time The digital signal processor completes the above multiplication and addition operations through hardware, which greatly improves the performance of the instrument and promotes the wide application of digital signal processing technology in the field of instrumentation.
2. Integration
With the development of large-scale integrated circuit LSI technology today, the density of integrated circuits is getting higher and higher, the volume is getting smaller and smaller, the internal structure is getting more and more complex, and the functions are getting stronger and stronger, thus greatly improving each module and thus the entire instrument system. of integration. Modular functional hardware is a powerful support for modern instrumentation. It makes the instrument more flexible and the hardware composition of the instrument is more concise. For example, when a certain test function needs to be added, only a small amount of modular functional hardware needs to be added and then called The corresponding software can be used to use this hardware.
3. Parameter setting
With the development of various field programmable devices and online programming technologies, the parameters and even the structure of the instrumentation do not have to be determined at the time of design, but can be inserted and dynamically modified in the field where the instrumentation is used.
4. Generalization
Modern instrumentation emphasizes the role of software, selects one or several basic instrument hardware with commonality to form a general hardware platform, and expands or composes instruments or systems with various functions by calling different software. An instrument can be roughly decomposed into three parts:
1) Data collection;
2) Analysis and processing of data;
3) Storage, display or output. Traditional instruments are built by manufacturers in a fixed manner according to the functions of the above three types of functional components. Generally, an instrument has only one or several functions. Modern instruments combine general hardware modules with one or more of the above functions to form any instrument by compiling different software.
Post time: Nov-21-2022