Fundamentals of Instrument Calibration
Each instrument has a minimum of one input and one output. The input for a pressure sensor
would be fluid pressure, and the output would (presumably) be an electrical signal. The input of a variable-speed motor drive is an electronic
signal, and the output is electric power to the motor. To calibrate an instrument is to examine and, if required, change its response such that its output properly matches its input throughout a specific range.
Calibration service is a process that is often taken for granted in industrial facilities
. If it is not calibrated, even the most vital industrial equipment will be rendered unusable.
By calibrating a piece of equipment or a device, modifications are made to guarantee that it works as intended to give predictable, accurate, and dependable results that satisfy quality requirements. Adjustments performed throughout the calibration process must adhere to specific tolerances. These tolerances indicate minor deviations from the equipment's stated precision.
What Calibration service means
There are different ways to explain what instrument calibration is. Calibration is the process of adjusting an instrument or piece of equipment so that it meets the requirements set by the manufacturer.
Calibration can also be thought of as the process of giving information, like a report or certificate of calibration that shows that a product meets its specifications and is safe to use.
One way to calibrate an instrument is to compare its readings to those from a reference instrument, also called a calibrator. The calibration company's reference instruments are sometimes sent to a center for calibration against national standards.
When you buy an instrument, you usually get the manufacturer's calibration data. Most companies that make instruments have sets of reference instruments that are used to check the accuracy of every instrument they make.
Why Does an Instrument Need to Be Calibrated?
Almost all equipment breaks down in some way over time, and electronic equipment
, which is a key part of making things today, is no exception. As parts get older, they become less stable and steer away from what was written about them. Even normal handling can mess up the calibration, and rough handling can completely throw a piece of equipment out of calibration, even if it looks fine physically. Calibration in progress makes sure that the equipment continues to meet the requirements set at installation, and it should be checked often after that. After any kind of maintenance
, the equipment needs to be calibrated to make sure that it still fits the required calibration data.
When a calibration program is well thought out and organized, it often leads to improvements in quality, increased productivity, and more funds.
How often should calibration be done?
This can vary a lot from one industry or plant to another. Usually, the equipment's first calibration is done by the calibration company that made it. The next calibrations should be done by the consumer or, in a sense, by the manufacturer. The amount of time between recalibrations will depend on the type of equipment and the conditions where it is used. When an instrument needs to be re-calibrated depends mostly on how well it works in its application.
Still, re-calibration should be done at least once a year as a rule. In more important applications, however, this will happen much more often.
Common Terms Used in the Calibration of Instruments:
Range of Measurement
The calibration range of an instrument is defined as the region between the limits within which a quantity is measured, received, or transmitted, expressed by stating the lower (LRV) and upper (URV) range values. These limits are defined by the Zero and Span values. The lower range value, or LRV, is zero, and the upper range value, or URV, is anything above zero. For example, if a device needs to be calibrated so that it can measure pressure from 0 PSIG to 400 PSIG, then LRV = 0 and UV = 400 PSIGp. So, the range for calibration is 0 to 400 PSIG.
Span is the algebraic difference between the values at the top and bottom of the range.
Span = URV – LRV
For the example we looked at above, where the range of calibration is 0 to 400 PSIG, this means: Then our span = 400 – 0 = 400 PSIG.
The instrument range refers to the capability of the instrument. It is often written on the instrument's nameplate. On the nameplate of an instrument, it might say Instrument range: 0–800 PSIG; Output: 4–20 mA.
Don't mix up the calibration range and the range of the instrument. They are not the same thing. Although our instrument range is 0 – 800 PSIG, we may decide to calibrate it to a range of 0 – 400 PSIG or even 0 – 800 PSIG for an application with high input pressure in which case the instrument range becomes the calibration range of the device.
Ranging an Instrument
To "range" an instrument, you set its lower and upper range values so that it responds to changes in input with the right amount of sensitivity. Suppose we want to use a pressure transmitter to measure pressure in the range of 0 -100 bar to give an output of 4 – 20mA. To adjust the range of this transmitter, we just configure:
0 bar = 4mA
100 bar = 20mA
Re-ranging is similar to ranging in that you just change the lower and upper range values to a new measurement range. For example, if we want to change the range of the above transmitter so that it can now measure pressure from 50 to 150 bar, we just must reset it:
50 bar = 4mA
150 bar = 20mA.
Changes to the Zero and Span
Zero and Span Adjustments are common on both analog and smart instruments. By changing the zero and the span, we can set the instrument to measure anything within the limits set by the manufacturer. Most analog instruments let you change both the zero and the span at the same time. In other words, changing one affects the other. Changes to the span adjustment almost always change the zero point of the instrument. To accurately calibrate an instrument with interactive zero and span adjustments, you must switch back and forth between the lower-range and upper-range points many times. But for smart instruments, the zero and span adjustments don't affect each other.
Five Point Calibration
Generally, when calibrating an instrument, the data points should include readings taken at 0%, 25%, 50%, 75%, and 100% of the instrument's calibration range. Usually, this is called a "five-point calibration." During a five-point calibration, testing should be done both upscale (increasing) and downscale (decreasing) to figure out the instrument's repeatability and hysteresis.
Calibrators are used to adjust the settings on instruments that need to be adjusted. They have different shapes and functions based on the equipment or device they are used to calibrate. Some examples of calibrators are:
Temperature probes like RTDs, Thermocouples, and so on are calibrated with the help of a block calibrator and a fluidized bath.
Panel meters and temperature controllers are calibrated with the help of Signal Reference. It is a kind of calibrator that can make an electrical signal that is known. There are references for voltage, current, and the frequency of a signal. Once a signal from one of these calibrators is sent to the equipment in question, the display or output value of the equipment can be changed until it matches a known signal. Sensor output is made by the simulator, which is a special kind of signal reference. A lot of the time, signal references and simulators can both read and send signals.
Pneumatic Calibrators. These are calibrators, which are used to test or calibrate pressure instruments by giving them a controlled pressure regime. They are often used together with a source of pressure.
Calibration records are the paperwork that is kept so that the device or instrument's history doesn't get lost. It also helps figure out what's wrong if the way the instrument works changes over time. The records of calibration service should show:
- The facts as found
- The date of the last calibration
- The last calibration or data is left
- The technician's name or initials, if they are known.
- The date that the instrument needs to be checked again.
As Found Data
The data of an instrument that needs to be calibrated is the response (reading) from the device at the points of calibration (0%, 25%, 50%, 75%, and 100%) before the actual calibration exercise begins.
As Left Data
After an instrument has been calibrated, the left data is the response (reading) from the device at the points of calibration (0%, 25%, 50%, 75%, and 100%).
All calibration services should be done in a way that can be traced back to a national or international standard. Traceability is the quality of a measurement result that lets it be linked to appropriate standards, which are usually national or international standards, through a chain of comparisons that doesn't break. This means that the calibration can be linked to a national or international standard.
Traceability is made possible by making sure that the test standards we use for calibration are regularly calibrated by reference standards at a higher level.
Most of the time, the measurement standards we use in a workshop are sent to a standards laboratory where they can be tested with more accurate tools. The standards from the calibration service laboratory are then periodically checked for accuracy by higher level standards, and so on until the standards are tested against Primary Standards kept by NIST or another internationally recognized standard.
During field calibration service in the Saudi Arabia, the tool isn't taken out of the process. It is still attached to the wall. Field calibration lets the field instrument be tested or calibrated at the real process and ambient conditions. Calibration service done in the field is often very different from calibration done in the shop, and the results of each are also different. Most field instruments have isolating valve manifolds that make it easy to disconnect them from the process. Before the test or calibration signal is sent to the instrument, it is vented into the air after being disconnected.
In-Shop or Bench-Based Calibration
A bench calibration service is a process where the instrument is calibrated at a calibration bench using calibration devices to simulate the process, instead of calibrating the device in the field using the actual process as the input means. Here, the instrument is taken out of the process, cleaned, and taken to the shop, where it is put on a test stand at a calibration bench.
A bench tester is used to calibrate an instrument or device on a work surface. It is made up of a standard gauge that is very accurate and a pressure source that makes the test pressure needed to test the instrument. Most bench testers are made by instrument technicians on the job site, but some are ordered from vendors as whole systems. A standard bench should have well-labeled and organized hoses and pumps
to help technicians with the calibration services.
Calibration companies in Saudi Arabia
Calibration companies in Saudi Arabia are world-class, well-equipped instrument calibration service providers giving the best quality calibration services. Calibration companies in Saudi Arabia guarantee their calibration services by keeping your instrument at the greatest degree of precision.
Calibration companies serve a diverse range of sectors, from Manufacturing to calibration Services. These Instrument calibration companies in Saudi Arabia are among the best calibration labs.
Instrument calibration companies in Saudi Arabia are equipped with an ISO-accredited calibration facility. Unique in scope, their mobile calibration facility provides on-site, high-quality calibration services at the customer's doorstep. By doing so, Calibration companies want to increase the productivity of our customers and decrease their device downtime. Our instrument management software is similarly adaptable, with a comprehensive database of instruments, their kinds, serial numbers, and other vital information.