Unit-4 part 2.pdf
- 1. What is Psychrometer? A psychrometer is a hygrometer made up of two thermometers that are identical. One thermometer’s bulb is kept wet, causing it to record a lower temperature than the dry-bulb thermometer due to evaporation cooling. A psychrometer is a device for measuring air humidity. It does so by measuring the temperature difference between a dry thermometer bulb and a wet thermometer bulb that has lost some moisture due to evaporation. A psychrometer tests both the dry and wet bulb temperatures at the same time. A wet wick mounted over the thermometer bulb is used to determine the temperature of the wet bulb. Practically any kind of thermometer can be used. Sling Psychrometer The relative humidity, which is calculated as a percentage, can be determined using a sling psychrometer. It’s calculated by multiplying the amount of moisture in the air at a given temperature by the maximum amount of moisture the air could hold at the same temperature, dividing by 100, and multiplying the quotient by 100. A wet-bulb thermometer and a dry-bulb thermometer are kept in a sling psychrometer. Using regular tables and maps, a sling psychrometer may be used to calculate the physical and thermal properties of moist air. It’s usually used to figure out relative humidity.
- 2. The wet bulb is covered in muslin, which is soaked in water and acts as a wick. When the web bulb is removed from the bath, it cools due to evaporation. A sling psychrometer is one that has the bulb whirled around to speed up evaporation. Design of Psychrometer A wet-bulb thermometer and a dry-bulb thermometer are kept in a sling psychrometer. Psychrometric charts are complicated graphs that show the dry- bulb temperature, wet-bulb temperature, relative humidity, specific volume, dew point temperature, humidity ratio, and enthalpy of moist air at a specific atmospheric pressure. A dry-bulb thermometer is a regular thermometer, while a wet-bulb thermometer is one with a cloth-wrapped bulb that has been moistened with distilled water. One bulb is dripping wet, while the other is completely dry. To test the temperature, we expose the dry bulb to the cold. We wrap a cloth wick around the wet-bulb and soak it in water until it’s ready to use. Working of Psychrometer The amount of evaporative cooling on the psychrometer’s wet bulb is proportional to the amount of moisture in the air. Drier air absorbs more moisture from the bulb, which causes it to cool down faster. The temperature does not change as much because the warmer air cannot retain as much water from the bulb. In other words, the more humid the air is, the greater the change in the wet bulb temperature. Much information about atmospheric conditions, such as humidity, air temperature, surface temperature, and dew point, can be shown on a digital screen at once. However, these devices must be calibrated to local conditions for 20 to 30 minutes before use, and the wet bulb sensor will dry out if not used for a prolonged period of time.
- 3. As a result, despite needing a little more legwork on the part of the user, the good old manual psychrometer retains its appeal. They would use a psychrometric chart to determine the final humidity reading after reading both bulb temperatures. Uses of Psychrometer While psychrometers are no longer widely used, they are still sometimes used to calibrate humidistats, which regulate the internal humidity of air conditioning and heating systems in buildings. Psychrometers were once used in the construction of building ventilation systems. A psychrometer tests both the dry and wet bulb temperatures at the same time. A wet wick mounted over the thermometer bulb is used to determine the temperature of the wet bulb. Practically any kind of thermometer can be used. In some ships, the primary wet bulb temperature measurement system is an electric psychrometer. They use it as a backup for air temperature and dew point sensors that are automatically mounted. Psychrometers are used for musical instruments such as pianos, guitars, and violins, which can be affected by excessive humidity. Paints are susceptible to humidity, so it’s used in the coating’s industry.
- 4. Dynamometers Introduction This article takes an in depth look at dynamometers. You will learn more about topics such as: What is a dynamometer How dynamometers are used Types of dynamometers Dynamometer test procedures
- 5. A dynamometer is a measuring device used to determine the torque, force, speed, and power required to operate the drive on a machine or motor, which can be measured by evaluating the torque and rotational speed of a motor simultaneously. Beyond the common use of dynamometers, there are other uses for them, such as tests of engine management controllers and the examination of combustion. When force is applied to a flexible metal ring on a dynamometer, it bends and measures the applied force. The measurement of force using dynamometers is an essential part of automobile production to determine horsepower, power absorption, and rotary speed. To maintain their instruments and ensure the accuracy of readings, users regularly calibrate and test dynamometers. How a Dynamometer Works The best explanation of how a dynamometer works is to envision a spring in a two part mounting. One end of the spring is anchored to a base with the other end connected to the force to be measured. As the spring is stretched by the force, a reading registers on a scale. This simplistic representation of a dynamometer is very similar to a spring balance but provides readings in units of force or Newtons (N). Though this simple example can provide a reading, it does not have the strength to measure the power of a 250 hp engine. A more sophisticated and technical device is required for that type of job, which is much larger and resembles an electric motor or gas engine.
- 6. A large dynamometer is a variable load that is attached to the drive of an engine or motor. As the motor powers up, the dynamometer absorbs the power being produced to provide data on the torque and power of the motor. As the power is absorbed, the dynamometer dissipates the massive amount of power generated through electromagnetism. As can be expected in the modern era, the data produced by a dynamometer is fed into a computer. There are several varieties of software available to collect dynamometer readings. Though DOS tends to be going out of existence, a few versions of DOS software are still being used. The most common type is Windows based. The readings from the software include: ambient temperature barometric pressure humidity oil and coolant temperature exhaust temperatures airflow exhaust oxygen throttle position engine rpm manifold pressure crankcase blowby With the use of dynamometer software, it is possible to measure, record, observe, and assess any kind of data from an engine. Most manufacturers and producers use dynamometers for basic data readouts. Dynamometer producers know that the more things you measure and quantify, the better will be the quality of the final product. With every test being performed consistently since any aspect of the process can create variations in the results. Compiling a wide range of data can account for any possible fluctuations and variables.
- 7. What is Dew Point? The Dew Point is the lowest temperature that allows water vapour to remain in a gas without condensing to a liquid state. As the air or gas temperature drops, its ability to absorb water vapour drops until it becomes completely saturated and below this dew point temperature, water droplets will start to form. In pressurised systems such as compressed air distribution networks, the dew point is directly related to the temperature AND system pressure. As pressure increases, the dew point temperature also rises meaning that the potential for vapour to condense out occurs at a higher temperature. In practice this can mean that instead of the condensing temperature being quite low, the dew point could be at or above ambient temperature. Why do I need Dew Point Measurement? Industrial compressed air and gas systems can suffer damage from water contamination directly or through the water subsequently freezing and expanding. Having water vapour in the air or gas can also affect process or product quality. Removing water contamination through filters and drying systems is common practice but as the dew point (and potential for damaging condensation) changes with pressure, the risk of damage will vary throughout a plant. ISO 8573-1 defines a range of purity classes for compressed air including water with the measurement expressed in terms of pressure dew point. ISO 8573-3 is the section that defines measurement methods for humidity and ISO 8573-9 for liquid water. Measuring the dew point can be a simple process and should be continuously monitored according to the plant risk analysis recommendations. This needs to occur at the drying plant before the distribution network and also at critical points of use. By measuring the dew point, efficient control of the drying/filtering system can be achieved to optimise the running costs of the compressed air/gas system. Particular emphasis should be placed on any part of the system where the pressure increases or the ambient temperature decreases as these are the situations where problems can occur quickly. For example, the air ring main leaves one building to go to another and the ambient outside air is or can be significantly lower than the indoor ambient. Additional drying capability may be needed and monitored in order to prevent condensation as the pipe leaves the building. Monitoring the dew point is a key indicator of system health that can be used to guide maintenance tasks as well as maintain plant compliance with the purity classes set in ISO 8573-1.
- 8. Dew Point Sensors S211 -60degC Dew Point Sensor S212 -50degC Dew Point Sensor S215 -20degC Dew Point Sensor
- 9. S220 -100degC Dew Point Sensor S230 - S231 -100degC Dew Point Sensors
- 10. S305 Dew Point Monitor
- 11. S520 smart dew point meter S201 Dew point sensor
- 12. COSA Xentaur Corporation 84 Horseblock Road Unit H Yaphank, NY 11980 Tel: 631-345-3434 Email: sales@cosaxentaur.com Hygrocontrol COSA Xentaur GmbH Mosel Str. 2B 63452 Hanau, Germany Tel: +49 1618192790 Email: info@hygrocontrol.de I N N O VAT I V E M E A S U R E M E N T S O L U T I O N S MOISTURE MEASUREMENT OF GASES “Moisture and humidity are significant factors affecting us directly and indirectly through their meteorological aspects, their contribution to the quality and cost of natural and synthetic products, their influence on the chemical, electrical, physical and parasitic life support characteristics of most manufactured and processed goods, their relationship with storage life, energy cost and conservation, material degradation, etc.” The amount of water vapor in air and many different gases is vital to a wide variety ofindustrial processes--especially the manufacture of electronic components, and is one of the variables in most fields of research which must be accurately measured and controlled. Until the age of modern electronics there was no alternative to the wet-and-dry bulbhygrometer for measurement of relative humidity and this simple device remains as one of the cheapest and most accurate forms of measurement. Making measurements when the moisture content is drier than about 20% relative humidity is a very different matter. The development of the aluminum oxide sensor drastically changed the science of moisture measurement. The invention of the capacitance sensor opened up such possibilities that new applications for the technique were discovered almost on a daily basis--indeed new applications are still being found for this highly versatile sensing device forty years later. The sensor is a variable capacitor with an ultra high purity aluminum core and porous gold film outer electrode with a special dielectric layer between. It rapidly comes into equilibrium with the surrounding atmosphere, and the capacitance of the sensor varies in direct proportions to the water vapor content. Cosa Sensors are manufactured in a variety of measuring ranges to meet the needs of applications as varied as making sure that periscope prisms remain clear, medical gases in hospitals are not contaminated, plastic bottles for carbonated drinks don’t burst, and that the highly specified gases used in VLSI (very large scale integration) silicon chip manufacture are within specification. With such a large market it is natural that many other manufacturers have tried to develop aluminum oxide sensors. However, none have come anywhere near the performance of the Cosa product for these very good reasons: 1) Accuracy: Xentaur XTR-100 sensors are produced in a robotized manufacturing system and vigorous QC procedures assure high uniformity. One curve correction function fits all sensors, making sensors freely interchangeable. 2) Capacitance Change: The capacitance change of a XTR-100 sensor over the full measuring range is about 60 times larger than that of a conventional Al2O3 sensor. In addition, the capacitance change per 1°C change of dewpoint at the dry end is approximately 500 times larger. The much larger signal change makes it easier to handle the sensors signal electronically. The result is more stable and accurate readings, which are less prone to other influences such as drift, temperature and electrical noise. 3) Automatic Calibration: Any measuring system needs to have its calibration checked from time to time. With the Xentaur sensor it takes about one minute and needs no other equipment or operator skill. The XTR-100 sensors flatten out at the top and saturate at a predesigned level above +20°C. With other types the sensor (or even the complete instrument) must be returned to the manufacturer, or the user has to buy extremely expensive calibration equipment.
- 13. COSA Xentaur Corporation 84 Horseblock Road Unit H Yaphank, NY 11980 Tel: 631-345-3434 Email: sales@cosaxentaur.com Hygrocontrol COSA Xentaur GmbH Mosel Str. 2B 63452 Hanau, Germany Tel: +49 1618192790 Email: info@hygrocontrol.de I N N O VAT I V E M E A S U R E M E N T S O L U T I O N S 4) Speed: The XTR-100 sensor responds significantly faster to a change in water vapor content than conventional sensors. Xentaur sensors dry down from -40°C to -60°C in 90 seconds. In dry to wet change conditions response speed is virtually instantaneous. 5) Temperature Coefficient: Xentaur sensors have a small and uniform temperature coefficient. Conventional sensors exhibit a substantial coefficient (i.e. readings vary significantly with temperature changes). Some other manufacturers supply their sensors in thermostatically controlled chambers in order to obtain a stable reading. OTHER PRICIPLES OF OPERATION The capacitance sensor is not, of course, the only way of measuring small amounts of water vapor in air and other gases, but it is certainly the easiest, most reliable, and usually the cheapest. 1) Chilled Mirror Instruments: Generally accepted as the standard to which other instruments are measured against. This is a very simple instrument in principle, although complicated and expensive in practice. The air or gas passes over a very small mirror on which shines a light source. The mirror is chilled, usually by using a Peltier device, until its temperature is below the sample dewpoint temperature. Condensation or frost forms on the mirror, scattering the light beam and detection of the scattered light is used to control the mirror temperature. Cosa offers the MBW line of chilled mirror hygrometers. These analyzers are laboratory grade instruments, extremely accurate and very expensive. Normally used as standards, these analyzers are not well suited to industrial applications. 2) Electrolytical Instruments: These have a cell which is coated with Phosphorus Pentoxide. The theory is that the sample gas passes through the cell at a closely controlled flow rate and all the moisture is absorbed into the desiccant. Platinum wires embedded in the desiccant carry a current which electrolyzes this water into hydrogen and oxygen and Faraday’s law is used to convert the required current into a moisture measurement. Fine so far--but did you spot the deliberate mistake? The desiccant absorbs ALL the moisture: clearly impossible, and the reason for quite large errors when measuring at 10 parts per million moisture content and drier. The other disadvantages are the need to accurately control sample flow rate, the very limited cell life, and the several days it takes to obtain stable readings from a new cell. 3) Oscillating Crystal Instruments: These are very high-tech devices which use a tuned crystal coated with a hygroscopic polymer. The sample gas passes over the crystal, the polymer absorbs the moisture and the resonant frequency between the two gases is used to measure the sample moisture content. (In some versions two crystals are used to give a differential measurement). Not only do these instruments assume near total absorption of the sample’s moisture but they also rely on their own reference gas having an absolutely constant known moisture content close to zero--both being equally unlikely. These are impressive instruments--extremely expensive--but having questionable reliability when measuring very dry samples. The type of hygrometer chosen by the user to perform a particular process measurement of control function depends to a great extent on the compatibility of the moisture measurement technique of the hygrometer type with the process of interest. Xentaur aluminum oxide sensor technology is certainly the easiest, most reliable, and usually the least expensive method of measurement for the vast majority of applications measuring moisture. Specify Cosa dewpoint sensors for all your hygrometer requirements.