Introduction
Instrumentation is a technical discipline present in any industry with a process involving chemical, physical, electrical, or mechanical steps to aid in the manufacturing of a product in a very large scale.
In oil and gas, measuring instruments can be found in all cycles from upstream during exploration to downstream at the pump station. Processes are present from midstream while producing crude oil or natural gas to downstream separating the product at refinery plants.
Each cycle requires instrumentation qualified personnel during engineering phase, construction/installation, or maintenance during operation phase.
Instrumentation discipline involves a combination of knowledge from numerous fields such as electronics, electrical, chemical, physics, process, fluid mechanics, safety, and environment and relates to the devices of measure and control installed on a system.
And here below I’ve divided the article into different sections to explain the main aspect of instrumentation and how it applies to the oil and gas industry. Click below and be directed to the section of your interest.
Now let’s dive right in!
Definition
Instrumentation devices are divided into two categories:
- measure
- control
Every instrument either of measure or control relates to one physical variable such as temperature, level, flow… and connects to the process of a system or its environment, to operate productively, with quality, safety, environmental principles, of the system objectives.
Measure
Measure devices combine a sensor element and a transmitter.
A sensor is a device that detects environment events or physical changes of the physical variable causing it to send information by an output signal or mechanism motion.
While the transmitter has a microprocessor that converts the specific sensor output to a usable standardized output signal sent to a computer for logic interpretation.
Thus, an instrument with a combination of a sensor measuring pressure and transmitter, is commonly called a pressure transmitter.
Accuracy Traceability Metrology
The immediate concern when measuring is if the reading value is valid and accurate. Evidence and preferably proof should be requested before taking any value into consideration.
The metrology is a system to ensure the suitability of measurement by calibration method and quality control. Calibration is a verification or adjustment of instrument measure using another instrument as reference to guarantee measurement precision by ensuring its accuracy. The quality control involves traceability by accreditation from an international level with high precision calibration instruments.
In practice, the accuracy of instruments installed on the plant is guaranteed by the periodic calibration using certified testing equipment tools. The certification also involves periodic calibration of these references executed by an accredited external laboratory using high accuracy instruments and includes a traceability sticker (usually valid for one year).
Each instrument is then specifically manufactured / selected for the function that is designed with an acceptable tolerance between the real value and the measured value.
An instrument that is very accurate will unnecessarily increase costs; inaccurate may cause performance errors that make the project uncontrollable. Accuracy is important but complex as the entire chain of measure must be considered.
THE DEVIATION BETWEEN MEASURED VALUE AND REAL VALUE SHOULD BE WITHIN THE INSTRUMENT TOLERANCE, IF NOT IT’S A DISCREPANCY BECAUSE THE ACCURACY IS NOT RESPECTED.
Standard signal and loop
The term “loop” refers to a “current loop” which is the standardized analogic output signal (4-20 mA) from transmitter to the Industrial Control System (ICS) that is part of a program providing reading indication to the station operator and may have thresholds generating logical actions.
The general term “loop” as “single loop” is also used to quantify workload in project based on an overall number of instruments, being either measuring or controlling instruments, and regardless of the signal if analogic or not.
Each instrument is then specifically manufactured / selected for the function that is designed with an acceptable tolerance between the real value and the measured value.
An instrument that is very accurate will unnecessarily increase costs; inaccurate may cause performance errors that make the project uncontrollable. Accuracy is important but complex as the entire chain of measure must be considered.
THE DEVIATION BETWEEN MEASURED VALUE AND REAL VALUE SHOULD BE WITHIN THE INSTRUMENT TOLERANCE, IF NOT IT’S A DISCREPANCY BECAUSE THE ACCURACY IS NOT RESPECTED.
Industrial Control System
Instruments are located outdoor within an installation, commonly called “field”, and provides signals across cables. Single instrument cables are routed to junction boxes then connected to marshalling cabinets via multicables. The master computing system called Industrial Control System (ICS), is a collection of hardware and software components communicating to each other as a whole architecture to control the plant by a program displaying information to an operator in the control room.
Smart instrument
Older instruments were pneumatic-based devices where measures were displayed locally on gauges or using Pressure/Intensity convertors. Instrument’s calibration was performed by adjusting screws, and control loop was executed via local single-loop controller. If data needed to be saved automatically and analyzed, the solution was a local chart recorder using paper. A major step forward occurred when microprocessors became small and robust enough for direct installation on field instruments, enabling local digital-based data for signal, configuration, and diagnostics as well as suitable for transmission over a network.
The term “smart” is attributed to an instrument equipped with a microprocessor managing digital information and includes one or more digital network communication options such as HART, FIELDBUS or more recently wireless.
Hydraulic pneumatic
Other than electric signals and also part of instrumentation, hydraulic (compressed oil) and pneumatic (compressed air) allows strong mechanical motion.
Units
There exist several units worldwide, to quantify physical variable and is used based on practice or geographical location. Originally, two systems were in practice:
- Imperial System
- Metric system
Nowadays, the International System of Units (SI) has been implemented, to unite national systems of measurement with those used in other countries, making conversion between systems possible with high precision and to standardize mathematical formulas. SI plays a role in international agreements as standard units, meaning that scientific and economic figures can be commonly understood. SI is now the most widely used system of measurement that specifies the unit symbols and names to state multiples and fractions of each unit.
Despite this, the fact could not be ignored that non-SI units of measurement still appear in the industry as it has been engrained so deeply in history, cultures or are more suitable to the measuring scale, that they will continue to be used for a long time to come. Instrument technicians are required to be familiar with common units used and to be able to convert it with ease.
Symbols
The instrumentation discipline uses numerous symbols in reference to international standards such as International Standard Organization (ISO) or company practices. It helps to simplify systems for process design or understanding, such as the Piping Instrumentation Diagram (PID).
Acronyms and abbreviations
The oil and gas industry and especially instrumentation discipline uses a lot of acronyms and abbreviations to limit text hence simplifying drawings, less time to say, easier and faster communication.
An abbreviation is typically a shortened form of words used to represent the whole INS for INSTRUMENTATION while an acronym contains a set of initial letters (such as PT for Pressure Transmitter).
It is important to learn these terms to be able to communicate with people from the industry and understand drawings.
Environment
Instrument also differs based on the environment in which they will be installed. In plants there will be extremes of temperature, vibration, dust, chemicals, and abuse. Instruments for use in plants are very different from those that are designed for laboratory use. A key feature of any system design must be the reliability of the equipment in that condition.
Acting devices
Acting devices can be defined as influencing components of a system to the physical variable, in such a way as to force it to operate in accordance with certain assumed requirements. Inversely to measuring instruments categorized as Inputs, the acting devices, Outputs, receive signals from the ICS. Generally, the control instruments are valves influencing flow or indirectly a level (if directed into a tank), or temperature (using heating or cooling fluid).
There are two types of acting instrument:
- on/off instruments
For instance, valve featuring only open or close state.
- control instruments
For instance, control valve featuring a positioner controlling the travel for flow adjustment
Control loop / Process control
A group of interconnecting instruments, combining measuring and controlling instruments, working in conjunction to maintain a process variable of a system at a desired set point. A controlled process is always surrounded by the environment in which it exists, undergoing controlled or uncontrolled influences of this environment called disturbances or perturbations. The measuring signal is permanently monitored for deviation from the desired set point and generates a manipulated signal in a form of decision.
Calculation functions are automatically and continuously applied to the deviation, to determine this output signal value sent to the control instrument to produce desired behaviors. Previously the calculation was executed by an individual control computer called controller in a form of algorithms and now by a “control block function” in the program, performing the same operation. The calculation functions being: Proportional, Integral, and Derivate.
Domestic example
Let’s take a refrigerator. The internal temperature is crucial to preserve the products stored and must be controlled.
Refrigerator being the system, the process is the temperature control inside the refrigerator.
A refrigerator’s ideal internal temperature is 4°C for best conservation (the “set point”). The temperature is measured using a sensor located in the food compartment.
The acting device decreasing the temperature is a cooling system controlled by running and stopping a compressor, generating cold fluid flowing across a condenser. In control process on/off, we set positive and negative thresholds around the set point, allowing certain amount of time between run and stop conditions.
Below graph illustrates each value over a period of time. Temperature increases slowly if the compressor is not running. In the event of a user opening the door, the temperature suddenly increases, reaching the temperature threshold high activating the compressor to cool down internal temperature. The compressor OFF when low temperature threshold reached.
Safety
Oil and gas plants involve highly dangerous substances, particularly flammable and toxic gases. To reduce risks to personnel, fire and gas detectors devices are installed all around the installation as early warning. These devices, part of the instrumentation’s responsibility, is crucial. It provides early detection to anticipate dangerous conditions and so time for personnel to evacuate hazardous areas.
Common scenario is the emergency process shutdown initiated to stop the supply of flammable substances and launch the firefighting system such as water deluge.
Technology
A car has retained the same function over decades even though it has never stopped changing and evolving. New technologies, especially in the fields of micro-electronics and industrial computer science, have changed cars. These arise due to widely varying constraints such as increasing safety, reliability, ease with which problems can be diagnosed and repairs can be made, and costly. The car is thus an illustration of an impressive technological progression that can be easily compared with instruments 50 year ago and now.
Instrumentation discipline is definitely an escape from routine jobs by constantly encountering new devices with different operating principles that must be approached with a long learning mindset as the technology evolves.
I hope this article provides you with a clearer understanding of what instrumentation is, and hopefully encourages you to pursue a career in this discipline.
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