· Diaphragm gauge
· Bourdon gauge
· Liquid manometer
· McLEOD compression manometer
· U-tube manometer
· Thermocouple gauge
· Pirani gauge
· Thermistor gauge
Picture 1 Picture 2 Picture 3
Picture 4 Picture 5 Picture 6
Picture 7 Picture 8
Mark whether the following statements are true or false
1. Typical vacuum systems require that many orders of magnitude of pressures must be measured.
2. Transducers can be classified as direct reading only.
3. Liquid wall gages and solid wall gages are direct reading gages.
4. We can combine compensated capsule or diaphragm mechanisms with sensitive and stable electronic measuring circuits.
5. There are two major mechanical liquid wall gage types: capsule and diaphragm.
6. The Bourdon gage, is used as a low vacuum gage.
7. Sensitivities and dynamic range tend to be less than those of the capacitance diaphragm gage.
8. Temperature-controlled heads or correction tables built into the electronics have been used to minimize the problem error.
Match the columns
| 1. absolute vacuum gage | a) парціальний вакуумметр |
| 2. air filter vacuum gage | b) радіометричний вакуумметр |
| 3. differential vacuum gage | c) термопарний вакуумметр |
| 4. partial-pressure vacuum gage | d) вакуумметр для виміру абсолютного тиску |
| 5. radiometer vacuum gage | e) вакуумметричний тиск |
| 6. thermistor vacuum gage | f) вакуумный індикатор забруднення повітряного фільтру |
| 7. thermocouple vacuum gage | g) диференційний вакуумметр |
| 8. vacuum gage | h) термісторний манометр; |
| 9. vacuum gage pressure | i) вакуумметр, вакуумний манометр |
Organize the following words according similar meaning.
Uncomplicated, minimize, identical, replace, magnitude, actually, essentially, change, environment, surrounding, gage, manometer, hysteresis, substitution, similar, delay, simple, transfer, reduce, size.
Discuss in groups fields of industry where vacuum measurement is used.
Each sentence has one mistake. Сorrect it. The first sentence has been done for you.
1. The flexible diaphragm deforms due to even slightly changes in pressure.
Not slightly but slight
2. The liquid column manometeris the most simplest type of vacuum gage
3. A single head can to have a dynamic range of 4 or 5 orders of magnitude.
4. Sensitivities and dynamic range tend to be little than those of the capacitance diaphragm gage.
5. The price of the strain gage type diaphragm gage is usually more lower.
6. The Pirani gage is perhaps the most oldest indirect gage that is still used today.
7. The resistance of the sensing filament is keep constant.
8. Correction for these variations can be made on the calibration curves supplied by the manufacturer if the composition of the gas will be known.
9. The gage controllers are designed to work with a specific sensor tube, and substitutions are limited to those that is truly functionally identical.
10. It have been demonstrated that a 10 W light bulb works quite well.
Translate the sentences into English
1. Головна особливість вакуумних електронних пристроїв — рух електронів проходить у вакуумі.
2. Вакуумні електронні пристрої звичайно представляють герметично запаяні скляні, металеві або керамичні трубки з різноманітними електродами всередині.
3. Рідинний манометр є найпростіший тип манометрів.
4. Вакуумні пристрої вимірювання можна розділити на такі класи: прямого зчитування і непрямого зчитування.
Read and translate the text B
TEXT B
Indirect Reading Gages
Indirect reading gages measure some property of the gas that changes with the density of the gas and usually produces an electric output. Electronic devices amplify and compensate this output to provide a pressure reading.
Thermal Conductivity Gages
Thermal conductivity gages utilize the property of gases in which reduced thermal conductivity corresponds to decreasing density (pressure). The thermal conductivity decreases from a nearly constant value above ~1 torr to essentially 0 at pressures below 10–2 torr. The gage controllers are designed to work with a specific sensor tube, and substitutions are limited to those that are truly functionally identical. Heat transfer at various pressures is related to the Knudsen number, for various heat transfer regimes. The Knudsen number can then be related to pressure through the geometry of the sensor, providing a relationship of heat transfer to pressure for a particular design thermal conductivity gage.
Pirani Gages
The Pirani gage is perhaps the oldest indirect gage that is still used today. In operation, a sensing filament carrying current and producing heat is surrounded by the gas to be measured. As the pressure changes, the thermal conductivity changes, thus varying the temperature of the sensing filament. The temperature change causes a change in the resistance of the sensing filament. The sensing filament is usually one leg of a Wheatstone bridge. The bridge can be operated so that the voltage is varied to keep the bridge balanced; that is, the resistance of the sensing filament is kept constant. This method is called the constant temperature method and is deemed the fastest, most sensitive, and most accurate. To reduce the effect of changing ambient temperature, an identical filament sealed off at very low pressure is placed in the leg adjacent to the sensing filament as a balancing resistor. Because of its high thermal resistance coefficient, the filament material is usually a thin tungsten wire. It has been demonstrated that a 10 W light bulb works quite well. A properly designed, compensated Pirani gage with sensitive circuitry is capable of measuring to 10–4 torr. However, the thermal conductivity of gases varies with the gas being measured, causing a variation in gage response. These variations can be as large as a factor of 5 at low pressures and as high as 10 at high pressures. Correction for these variations can be made on the calibration curves supplied by the manufacturer if the composition of the gas is known. Operation in the presence of high partial pressures of organic molecules such as oils is not recommended.
Thermistor Gages
In the thermistor gage, a thermistor is used as one leg of a bridge circuit. The inverse resistive characteristics of the thermistor element unbalances the bridge as the pressure changes, causing a corresponding change in current. Sensitive electronics measure the current and are calibrated in pressure units.
Compensation Tube
Thermistor gage measures approximately the same pressure range as the thermocouple. The exact calibration depends on the gas measured. In a well-designed bridge circuit, the plot of current vs. pressure is practically linear in the range 10–3 to 1 torr. Modern thermistor gages use constant-temperature techniques.
Thermocouple Gages
Another example of an indirect reading thermal conductivity gage is the thermocouple gage. This is a relatively inexpensive device with proven reliability and a wide range of applications. In the thermocouple gage, a filament of resistance alloy is heated by the passage of a constant current. A thermocouple is welded to the midpoint of the filament or preferably to a conduction bridge at the center of the heated filament. This provides a means of directly measuring the temperature. With a constant current through the filament, the temperature increases as the pressure decreases as there are fewer molecules surrounding the filament to carry the heat away. The thermocouple output voltage increases as a result of the increased temperature and varies inversely with the pressure. The thermocouple gage can also be operated in the constant-temperature mode.
Gas composition effects apply to all thermal conductivity gages. The thermocouple gage can be optimized for operation in various pressure ranges. Operation of the thermocouple gage in high partial pressures of organic molecules such as oils should be avoided. One manufacturer pre-oxidizes the thermocouple sensor for stability in “dirty” environments and for greater interchangeability in clean environments.
Дата: 2016-10-02, просмотров: 162.
