Instrumentation & Electrical Skills - By Humayun Raza

Q1) What are the types of Transformers based on Winding/core construction? Ans) Two types: 1)Core type 2) Shell type In core type, winding is wound over laminated core's left leg and also on right leg as shown in pic below. Primary & secondary windings both are placed on same leg. Secondary is placed first over the core, primary winding is placed next after secondary. In Shell type, a three leg core is present, where the winding is wound over on the middle leg and the other two legs cover and form a shell over the single winding wound over the middle leg. Pic below demonstrates it better. Shell type Transformers have lesser core losses(because flux is divided in the extreme left & right legs, so losses become less). In applications where less physical space should be used, shell type transformers are used as they consume less winding space as only one middle leg is used for winding compared to core type where two legs are wound over with winding.

Split-ranging of Control Valves can be done by following ways: 1. Single common pnuematic signal from Controller: i.e. using a single common pnuematic signal for both Control Valves. This way requires adding Volume Boosters to Control Valves or positioner to at least one Valve because without them as air volume is from a single I/P and is dividing between two CVs, response of Control Valve action will be slower as air volume is dividing. Benchset of each CV can be set separately and calibrated but it is a time-consuming procedure compared to other easier technique available discussed below. 2. Single common electrical signal output from controller: This common electrical signal from controller is fed to two I/P converters placed in series to each other i.e. both get th same electrical signal. Instead of adjusting Benchset of each CV, each I/P can be calibrated as per Valve behaviour requirement. Also, voltage drop in one I/P's electronic circuitry should not exceed a limit wh...

Coriolis Flow Meter principle: Coriolis effect When an empty water hose is vibrated to and fro, it will oscillate with some pattern. But when the water hose is run thorough with water flow and the water hose then oscillated, then the hose will oscillate with some other frequency and pattern. More the water flow through hose, more its frequency and pattern of oscillation will vary from the empty hose oscillation pattern and frequency. This change in oscillation frequency and pattern is due to coriolis effect. This is due to the physics of forces i.e. on the flowing medium in one direction with an intertial force also on it, another perpendicular or other angled force acts on flowing medium which both forces make a resultant force vector on medium. This results in twist in the tube vibration. At inlet of coriolis, a sensor is placed and at outlet another sensor placed. When no flow is present, at inlet sensor and outlet sensor on coriolis tube, the waveform has same in-phase vibration....

Answers at the end of all questions. Q1) Which is not an applicable method to detect the presence of flammable gas A) Point Type IR Detectors B) Electrochemical sensors C) Catalytic sensors D) Open Path IR Detectors Q2) Following standard defines Procedure Automation for Continuous Process Operations A) ISA 18.2 B) None of the answers C) ISA 106 D) ISA 95     Q3) Which of the following valve types would be suitable for controlling the flow of a slurry? A) Double-seated globe B) Butterfly C) Diaphragm D) Knife edge gate     Q4) List the device that is not a common output transducer for an electronic pressure transmitter A) capacitance B) LVDT C) strain gage D) flapper-nozzle Q5) 2oo2 voting logic in fail-safe mode is following Gate A) AND B) XOR C) OR D) NAND Q6) The direct-acting actuator is ________ A) Air to Open type actuator B) Air to Close type actuator C) Piston type actuator D) a...

Why do we need split-ranging arrangement in process Control applications? Can't we keep things simple and use a single Control Valve to control process? Actually there are some product requirements when there is no other feasible/efficient solution than split-ranging Control Valves. Based on application, mainly 3 types of split-range arrangements exist: - Complementary Split-range - Exclusive Split-range - Progressive Split-range Complementary: Let's say two liquids A&B are required to be mixed in a ratio(say 60/40% respectively). Each liquid line ends in a tank. Liquid A line will have a Air-to-Open Control Valve. Liquid B line will be Air-to-Close Control Valve. For a 60/40% ratio set by Set-point option on Controller, a 10.2psi signal will be applied by Controller due to which A line CV will open 60% and B line CV will result in 40% open. Controller O/P -      A CV %    -      B CV % 3psi            ...

Aesbestos material gasket shall not be used. Flange Rating for Control Valve Carbon steel Body >= 6" shall be at least Class 150 & Class 300 for <6". Gland Packing Lubrication inlet shall not be used.  Tight Shut-Off TSO valve shall be of Class 4 & above.  TSO Class 5 valve shall be used for Compressor anti-surge & spill back service. Teflon(PTFE) material gland packings shall be used for process temperature<=205°C & Graphite for >205°C. Carbon Steel or Plated Carbon Steel shall not be used for CV Trim material. AISI 300/400 series SS Trim material shall be used.  Soft-seated TSO shall not be used for process temp>230°C nor in Flashing process nor erosive type process.