Precision Tools and Industry Automation
Measuring Tools
Are used for measuring:
■ Physical properties such as temperature, pressure, humidity, light intensity, atmosphere pressure, length, distance, weight, mass, force etc.
■ Chemical properties such as PH, carbon dioxide sensor, gas detector, oxygen sensor, smoke detector, etc.
Some of these instruments are used in our daily life. For example thermometer we use in our home to show the temperature or the one that controls temperature of cooking oven, ruler, measuring tape, tire pressure meter when we inflate our car tires. Important features which are considered for choosing right measuring unit are accuracy, response time, repeatability and range of measurement.
Precision Tools
Precision tools in fact are basis of control system and industry automation. Some of precision tools which are used in many industries are: different types of controllers, monitors, displays, transmitters, recorders, laser distance meters, radius gauges, dial calipers, etc. These tools are used for measuring, displaying, transmitting, recording and controlling important parameters in various fields of industry.
Different Functions of Precision Tools
■ Tools which control temperature, humidity, pressure, level of liquids,… and called “controllers”.
■ Tools which display measured values by controllers and called “indicators”.
■ Tools which transmit data and measured values in form of signals which are called “transmitters”.
Analyzing and Testing Equipment
Equipment which are used for measuring thickness, vibration, roughness,
Non-destructive testing (NDT) and also machines which are used for measuring electrical parameters, analyzing gas, are vital for industries. Instruments which are used for measuring voltage, electric current or some other tools which are used for aligning motor shafts, vibration of machines, toughness measurement and insulation test, are only few of these equipment. These equipment are used to keep different parameters within standard values.
Industry Automation
Industry automation covers broad range of tools and equipment that automate operation in various industries. Equipment such as programmable logic controllers (PLC), monitoring systems, recording equipment, shaft encoders, proximity sensors, timers, counters…. all are examples of systems which are used in this area.
Some measuring and automation equipments are:
■ Ultrasonic Level meter: This equipment is used in especial environment such as explosive environment or areas where corrosive materials exist. These level meters operate on the basis principle of using sound waves to determine liquid/solid/slurries level. Besides, they can monitor open channel flow, measure volume, determine the actual volumetric throughput in lift stations, measure differential level and control the pumps output.
They are consist of two elements; A) a high efficiency transducer and, B) an associated electronic transceiver. Working together, they determine the time for a transmitted ultrasonic pulse and its reflected echo to make a complete return trip between the non-contacting transducer and the sensed material level.
■ Floating Level Meter: One of the very first types of level meters which still are used widely is, floating level meter. Mechanical floating level meters are easy to use, inexpensive, suitable for controlling level of open or pressure containers.
■ Vibration Level Meters (Vibration Fork Level Instruments): Are designed to vibrate at its frequency by a pair of piezoceramic discs. When the forks come in contact with the medium the frequency and amplitude changes. That change is detected and converted into a switch signal. Tuning forks are particularly good for high viscosity materials such as fluids and powders.
■Level Transmitters: Provide continuous level measurements over the range of the system rather than at a single point and produce an output signal that directly correlates to the level in the vessel. The output signal generated can be used to display the depth or to actuate control functions.
■ Level Indicators / Controllers: Level indicators utilize a mechanical device, such as a float, or a sensor with output signal to indicate the level within a tank. Level controllers are, essentially, indictors with integrated control output which allows for functions such as on/off, alarms, etc.
■ Depth/Pressure: Pressure based level instruments use pressure sensors at the bottom of a tank to measure the force exerted per unit area. For level applications, that force is the weight of the medium to be measured plus any pressure acting on the surface. By knowing the density of the medium and compensating for the effect of ambient pressure, the resulting value can be converted to a level measurement. The output signal generated can be used to display the depth or to actuate control functions.
■ Level Switches: Are point level measurement instruments used to mark a single, preset level condition such as high or low level condition that would trigger an alarm or switch.
■ Radar: Radar level instruments measure the time required for a microwave pulse and its reflected echo to make a complete round trip between the transducer and the sensed material level. That value is then converted into a level measurement.
Radar level instruments utilize non-contact measurement unaffected by changes in temperature, pressure or the presence of vapor. Accuracy of radar level instruments depend upon bandwidth and frequency but is unaffected by density, conductivity or dielectric constant of the medium.
■ Capacitive: Capacitance level instruments operate on the electrical characteristics of a capacitor. A capacitor is made of two conductive plates isolated from one another by a dielectric. Capable of storing an electrical charge, that charge varies depending upon the conductivity of the dielectric.
In level applications, the medium to be measured serves the dielectric while the tank wall and sensor are the conductive plates. As the tank fills the sensor probe is exposed to a more conductive material than air and the capacitance value of the probe increases. This value is converted to an output signal that can be used to display the level or activate a switch or control.
Capacitance level instruments do not work well with low capacitance materials like plastic, sand, etc. or with materials having a large particle size (and thus a lot of air pockets). Material build-up along the probe can also make readings inaccurate.
■ Conductive: Conductivity level sensors use a low-voltage, current-limited power source applied across separate electrodes to detect the medium's resistance when their electrodes are covered by the process material. Normally used with water, wastewater, water-based liquids; conductive level probes are simple to install and use. They have the added benefit of being solid state.
Conductivity level sensors provide point level detection and are adept at switching functions for minimum, maximum or differential applications. If build up insulates the probe from the medium, it will stop working properly.
■ Optical: Optical level instruments contain an infrared LED and a light receiver. Light from the LED is directed into a prism which forms the tip of the sensor. With no liquid present, light from the LED is reflected within the prism to the receiver. When rising liquid immerses the prism, the light is refracted out into the liquid, leaving little or no light to reach the receiver. Sensing this change, the receiver actuates electronic switching within the unit to operate an external alarm or control circuit.
■ Pressure Gauges: Pressure gauges are used for measuring pressure in various equipments which might use air, steam, fluids, oil and etc.
Some types of pressure gauges have been introduced below:
■ Air or Pneumatic Pressure Gauge: Air pressure or pneumatic gauges measure the amount of air needed to maintain the optimum use of the object containing this gas. A common container of air is a tire. Using an air pressure gauge ensures the correct amount of air fills the tire for optimum performance. Too little air in a tire eventually makes it flatten while too much air makes it wear unevenly or even explode.
■ Hydraulic Pressure Gauge: Hydraulic pressure gauges are used for measuring pressure in environments that are subject to mechanical vibrations or in applications where pressure pulses may take place. They are ideal for precise measurement and recording of hydraulic tool pressures. Some gauges may be liquid or glycerin filled so they are able to give a perfect vibration display and smooth pointer movement, even in conditions of heavy load and strong vibration. The lubricating effect of the glycerin also provides protection to the system against mechanical wear. The pressure gauges are designed and manufactured keeping in mind increased reliability and extended service life. Digital pressure gauges have become popular.
■ Differential Pressure Gauge: A Differential pressure gauge indicates the difference in pressure between two points. These gauges contain two entrance ports with each connected to one of the monitored pressure capacities. Using this type of pressure gauge allows one the ability to read the pressure difference between two points with one gauge rather than having to check two pressure gauges and calculate the difference. These gauges are particularly useful for checking the filter conditions HVAC or dust collection systems thus preventing the need to check the filters manually.
■ Digital Pressure Gauge: Digital pressure gauges convert pneumatic, hydraulic, or differential pressure into signals that read out in numerical displays. Digital pressure gauges are becoming more and more popular due to their smaller size and greater accuracy and readability. The digital pressure gauge can be use in almost any application that a conventional gauge is being used. As the prices of these gauges continue to decline, the use of the digital pressure gauge will inevitability increase in the years to come.
