industrial instrumentation basics

 Ultrasonic Level Transmitter The Ultrasonic sensor are also used in industrial applications to measure the level of liquids, slurries and solid. The Ultrasonic level transmitter operates on the basic principle of using sound or acoustic  waves to determine liquid, solid or slurries level. These devices measure the distance from a reference point in the vessel or tank to the level interface, using ultrasonic waves. Frequency range of ultrasonic level sensor Ultrasonic level transmitter measures actual distance, by issuing an ultrasonic pulse of ranging in the freaquency of 40 kHz to 70 k Hz. The lower frequency of ultrasonic pulses can use to measure long range. Mostly used frequency is 58 k Hz , at this frequency the resolution is  1 cm and sensing range of ultrasonic level sensor will be 11 meter.  Working principle of ultrasonic level transmitter  Ultrasonic level transmitter’s measure actual distance by issuing an ultrasonic pulse and measuring the time req...

 Radar Level  Radar level transmitter are used to measure level in industrial applications. Radar level measurement method is an advanced method. In radar level transmitter time of flight method is used to measure the level. By calculating this time of flight we measure the level of liquid or solids.  RADAR level have a transmitter which transmit microwave or radar waves after colliding with material they return back to the receiver.  The time from the transmitter to the echo return to the receiver, is calculated, which is proportional to the level. This time is calculated by the formula:  Distance = (Speed of light x time delay) / 2 This calculation is done by a built in microprocessor and the level is displayed on screen or lcd, a signal proportional to level in 4 to 20 mA is output of level transmitter , this standard current signal of 4 to 20 mA is for plc or dcs. Time of Flight technology  Time of flight technology is used in  devices that are mu...

Instrumentation terms and definition instrumentation Instrumentation is a branch of science which deals with the measurement and control of process variables in a process. Process  It is defined as the adoption of series of steps or methods to acquire a predefined result.  In other words, it can be defined as a physical system we want to measure and control by implementing instrumentation devices Examples of process are:  boilers oil refinery chemical plants power plants etc Measurement It is a way to associate physical quantities with numbers, so by measurement we can find the number which shows us the amount or quantity of an entity. Process Variable   It is a variable in the process that we are attempting to maintain, measure or control in a process. process variable maybe  pressure temperature flow level  quality vibration etc. Setpoint In-process control system, the setpoint is a point we set for a process value to be achieved this is a value we desir...

  Calibration  of flow meter All flow meters require an initial calibration.  Manufacturers of the flow meter usually calibrate a  flow meter for specific service conditions.  The need to recalibrate usually depends on how well the meter fits the application. Some liquids passing through flow meters are corrosive or acidic or abrasive. So after sometime portions of the meter will deteriorate and the performance of the meter is reduced   The procedure of flow meter calibration  First flushing the transmitter.  Flush both the impulse lines.  Adjust the zero when there is no flow or by equalizing in case of od DP transmitter if necessary.  Close one of the valves either H.P. or L.P. open the equalizing valve. The O/P should read zero. For span, calibration passes a flow of known value preferably span value of flow meter, and calibrates the span. again check zero. Common faults in flow meter * No power * Impulse line leak or block * any wea...

  Thermocouple Thermocouple Working principle Thermocouple working principle based on see back effect. See back effect  This states that an electric current flows in a closed circuit of two dissimilar metals, having temperature differences at both junctions. In thermocouple two dissimilar metals have joined on one end, This is called hot junction and it is exposed to the temperature we want to measure, the other junction which is called cold junction or reference junction is usually made ar transmitter.  One junction is at a reference temperature (like 0 oC) and the other junction at the temperature to be measured.  A temperature difference will cause the voltage to be developed at the reference junction and produced voltage is directly proportional to the temperature.    A thermocouple produces mv (DC). External Reference Junction Techniques Reference junction technology is usually considered one of the main problems of any thermocouple installation. Indi...

 Infrared Gas Analyser IR Gas analyzer:  An infrared gas analyzer measures or traces a specific gas in a sample gas, this measurement is comprised by determining the absorption of an emitted infrared light source. Gases on Earth's atmosphere are getting excited to a specific wavelength in the infrared range. So by testing how much of the infrared light of a specific wavelength is absorbed by the sample we can measure a specific gas concentration.  Fortunately, different molecules of gases in the atmosphere absorb different frequencies of infrared light. Air with a high concentration of a certain gas will absorb more quantity of a certain frequency of infrared light, allowing the sensor to report a high concentration of the corresponding molecule of gas in the sample, Types of Infrared analyzer  Infrared or IR Gas analyzer are divided into  two  main types  1. Non-Dispersive IR-Analyzer  2. Dispersive IR analyzer  Working Principle of infrare...

Level measurement What is Level The level is a measure of the difference in altitude of two points. The height of the water column, liquid, or powder in the desired range between the minimum and maximum values is called their level. There are different measurement methods implied for the level measurement.   Units of level Meter Foot Percent Types of level measurement There are two main methods to measure level. 1. Direct or visual method  2. Indirect method Direct Methods (Visual Methods) The direct method is used to measure the height of a substance above a point marked as zero points. Direct methods for level measurement are preferably used when level changes are slow and small, for example,  to measure the level of Sump tanks and Bulk storage tanks. Direct level measurement methods are simple and are considered very reliable.  Types of direct methods Direct level measurement devices are divided into four types: a. Dip-sticks & Dip-Rods b. Weighted gauge tape...

 Pressures Measurement in instrumentation In the following pages, we will discuss all the basics of pressure measurement, such as, What is pressure,  what is the definition of pressure,  units of pressure measurement, types of pressure sensors, working principle of different pressure primary elements, and applications of different sensors, pressure transmitter, and their calibration procedure.  What is Pressure? The force per unit area is called pressure. Three main methods are used to measure pressure, absolute pressure, gauge pressure, and differential pressure.  Pressure varies depending on the altitude of the site where we are measuring pressure.  Weather, pressure fronts, and other conditions also affect the measurement of pressure in a process. The measurement of pressure is relative to all these factors of weather and climate, and pressure measurements are carried out in two main scales  1. gauge pressure  2. absolute pressure. Gauge press...