Coriolis flow meters Coriolis flow meter operate on the principal that, if a particle inside a rotating body moves in a direction toward or away from the center of rotation, the particle generates inertial forces that act on the body.  The operation of a Coriolis flow meter is based on the mechanics of motion. The Coriolis force happens when a mass moves in a rotating inertial frame. The rotation is created by vibrating two opposing tubes on the flow meter. When a fluid flows through the opposed vibrating tubes, the tubes twist due to the Coriolis force. The twisting alternates with the vibration and creates two phase-shifted sinusoidal wave forms on coils mounted to the tubes. The amount of shift is proportional to the mass flow rate. In addition, the frequency of vibration is proportional to the fluid density. Coriolis Flow Meter Principles The basic operation of Coriolis flow meters is based on the principles of motion mechanics. As fluid moves through a vibrating tube it...

  Types of Fast-acting On/Off Valves with Built-in Actuators Solenoid Valves Solenoid valves operate using a linear sliding obstructer that opens and closes the valve, or changes the flow from one outlet to another. There are many different types of obstructers used including plunger, shuttle, spool, and diaphragm. The linear motion is achieved by energizing an electromagnetic coil to pull the obstructer in one direction. A spring drives the obstructer back in the opposing direction when the coil is de-energized. 2-position on/off valves are the most common type of solenoid valves, but there are a vast number of others, including 3-position where there are 2 coils that pull the obstructer in opposite directions, using springs to center it when neither is energized. There are even proportional solenoid valves that can be used for flow control. In these valves, the coil moves the obstructer varying distances based on the voltage supplied to it. Solenoid valves are relatively small. T...

  Types of Rising Stem (multi-turn) Valves Gate Valves A gate valve functions by moving a wedge shaped disc obstructer up and down to open and close the flow path through the valve. This linear motion is provided by a threaded rising stem. Turning this threaded stem requires multiple revolutions (multi-turn) to travel from open to closed. The number of revolutions required is usually the valve size in inches x 3 + 2. So a 6 inch valve will require 20 turns of the stem [(6 x 3) + 2 = 20]. They should only be used for on/off applications as throttling for an extended period of time will damage both the obstructer and seals. Use of a gate valve for throttling is also not very effective since most of the reduction of flow will increase in the last 10% of closure. Globe Valves Globe valves operate by having a convex disc shaped plug raise and lower via a rising stem into a circular seat around the inside of the globe shaped body at the “equator”. The flow enters the “lower hemisphere” f...

  Types of (Quarter-turn) Rotary Valves Ball Valves Quarter-turn 2-way ball valves are by far the most common type of process control valve. They are 2-way (inlet and outlet), 2-position (open and closed) valves that are used for shut-off or isolation of a system, or a loop or component within a system. The basic construction of a ball valve includes a ball as the obstructer which is sandwiched between two cup shaped seals referred to as “seats”. Typically the ball has a bore straight through it. Media flows through this bore when the valve is open. When the ball is rotated 90˚, the flow of media is stopped by the sides of the ball which now completely fill the opening in the seats. Plug Valves The basic construction of a plug valve is practically identical to that of a ball valve with the exception of the shape of the obstructer used. In this case, the ball is replaced by a slightly tapered cylinder. This cylinder has a bore through it just like a ball valve, and it operates the s...

  Types of Valves Rotary Valves These types of valves rely on the rotary motion of the flow obstructer In most cases this rotation is limited to 90 degrees (one quarter-turn), however, there are valves that operate using a larger degree of rotation and have more than 2 positions that are used in regular operation. Valves that are truly quarter-turn are completely closed at 0˚ and completely open at 90˚. Examples of quarter-turn valves are ball valves, plug valves, and butterfly valves. Linear Valves There are 2 distinct types of linear valves: rising stem (multi-turn) and axial. While both valve types rely on the linear motion of the flow obstructer, they are very different in construction and operation. Multi-turn rising stem valves move the obstructer by the rotation of a threaded rod (stem) which is attached to the obstructer Examples of multi-turn valves are gate valves, globe valves, pinch valves, diaphragm valves, and needle valves. These valve types are commonly used for flo...

    Operational Amplifier (Op-amp) What is an Operational Amplifier (Op-amp)? An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output. Pin configuration V+: non-inverting input V−: inverting input Vout: output VS+: positive power supply VS−: negative power supply Operational Amplifier Clasifications There are four ways to classify operational amplifiers: Voltage amplifiers take voltage in and produce a voltage at the output. Current amplifiers receive a current input and produce a current output. Transconductance amplifiers convert a voltage input to a current output. Transresistance amplifiers convert a current input and produces a voltage output. O...

  Bourdon Tubes Bourdon Tubes are known for its very high range of differential pressure measurement in the range of almost 100,000 psi (700 MPa). It is an elastic type pressure transducer. The device was invented by Eugene Bourdon in the year 1849. The basic idea behind the device is that, cross-sectional tubing when deformed in any way will tend to regain its circular form under the action of pressure. The bourdon pressure gauges used today have a slight elliptical cross-section and the tube is generally bent into a C-shape or arc length of about 27 degrees. The detailed diagram of the bourdon tube is shown below. As seen in the figure, the pressure input is given to a socket which is soldered to the tube at the base. The other end or free end of the device is sealed by a tip. This tip is connected to a segmental lever through an adjustable length link. The lever length may also be adjustable. The segmental lever is suitably pivoted and the spindle holds the pointer as shown in t...

  Pressure Measurement   This module will examine the theory and operation of pressure detectors (bourdon tubes, diaphragms, bellows, forced balance and variable capacitance). It also covers the variables of an operating environment (pressure, temperature) and the possible modes of failure. General Theory   Pressure is probably one of the most commonly measured variables in the power plant. It includes the measurement of steam pressure; feed water pressure, condenser pressure, lubricating oil pressure and many more. Pressure is actually the measurement of force acting on area of surface.  We could represent this as:  Pressure = Force/Area or P=F/A The units of measurement are either in pounds per square inch (PSI) in British units or Pascals (Pa) in metric. As one PSI is approximately 7000 Pa, we often use kPa and MPa as units of pressure. Pressure Scales   Before we go into how pressure is sensed and measured, we have to establish a set of ground rules. Pr...

  Why Calibration of instrument is important The main reasons for calibration are to ensure the reliability of the instrument, that it can be trusted. To determine the accuracy of the instrument and to ensure the readings are consistent with other measurements. It could also void your warranty if your instrument is not calibrated. What is Calibration ? Calibration is the activity of checking by  comparison with a standard ,the accuracy of a measuring instrument of any type. It may also include adjustment of the instrument to bring it into alignment with the standard. Purpose of instrument calibration ? Calibration is the process of comparing the output of an instrument to that of a reference (i.e., known accurate) instrument given the same input. When an instrument is calibrated, the proper output is confirmed by the technician over the range of measurement. Before any adjustments are made, the output is recorded. This is called the as-found calibration. If any adjustments are...

  Q & A For Flow Measurements 1.Convert the flow of 3 Cu ft/min into Cu meters/hour. Solution 1 Cu ft/min = 1.699 Cu meters/hour So, 3 Cu ft/min = 3 x 1.699 Cu meters/hour  = 5.097 Cu meters/hour  2 .Convert the flow of 9 Imp. Gallons into Barrels(oil). Solution 1 Imp. Gallons = 0.0286 Barrels So, 9 Imp. Gallons = 9 x 0.0286 Barrels  = 0.2574 Barrels 3.Convert the flow of 2 lb./sec into gm/min. Solution 1lb./sec = 27220 gm/min So, 2 lb./sec = 2 x 27220 gm/min  = 54440 gm/min 4. Convert the flow of 10 meter/sec into cm/sec.  Solution 1 meter/sec = 100 cm/sec So, 10 meter/sec = 10 x 100 cm/sec  = 1000 cm/sec   5. Convert the flow of 18 ft/sec into meter/min . Solution 1 ft/sec = 18.29 meter/min So, 18 ft/sec = 18 x 18.29 meter/min  = 329.22 meter/min 6. Convert the flow of 57 ft/min into meter/sec. Solution  1 ft/min = 0.005080 meter/sec  So, 57 ft/sec =57 x 0.005080 meter/sec  =0.28956 meter/sec 7. Convert the flow of 10 Imp...