What is Sensor Calibration and Why is it Important?

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When engineers design modern process plants, they specify sensors to measure important process variables, such as flow, level, pressure, and temperature.
These measurements are used to help the process control system adjust the valves, pumps and other actuators in the plant to maintain the proper values of these quantities and to ensure safe operation.
So how does a plant maintain the operation of these sensors to guarantee that the actual value of the process is sensed and passed to the control system?
In this video, you will learn that the answer to that question is: “Sensor Calibration”.
Sensor calibration is an adjustment or set of adjustments performed on a sensor or instrument to make that instrument function as accurately, or error-free, as possible.
An error is simply the algebraic difference between the indication and the actual value of the measured variable.
Errors in sensor measurement can be caused by many factors.
First, the instrument may not have a proper zero reference.
Modern sensors and transmitters are electronic devices, and the reference voltage, or signal, may drift over time due to temperature, pressure, or change in ambient conditions.
Second, the sensor’s range may shift due to the same conditions just noted, or perhaps the operating range of the process has changed.
For example, a process may currently operate in the range of 0 to 200 pounds per square inch, but changes in operation will require it to run in the range of 0 to 500 pounds per square inch.
Third, error in sensor measurement may occur because of mechanical wear, or damage. Usually, this type of error will require repair or replacement of the device.
Errors are not desirable since the control system will not have accurate data from which to make control decisions, such as adjusting the output of a control valve or setting the speed of a feed pump.
If the calibration is too far from the accurate process conditions, process safety may be jeopardized.
To perform an “as-found” check, an accurate and precise instrument is used to develop process signals corresponding to 0%, 25%, 50%, 75% and 100% of the process range of the transmitter.
The corresponding transmitter output, in milliamps, is observed and recorded. This is called a “5-point” check.
Then, in order to check for hysteresis, a phenomenon whereby the sensor output for a process value is different going 'downscale' as it is going 'upscale', the output signals corresponding to 100%, 75%, 50%, 25%, and 0% in order are recorded.
The deviations at each checkpoint are calculated and compared to the deviation maximum allowed for the device. If the deviation is greater than the maximum allowed, then a full calibration is performed. If the deviation is less than the maximum allowed, then a sensor calibration is not required.
If we have an analog transmitter, we must adjust zero and span to reduce the measurement error. With an analog transmitter, there is a ZERO and SPAN adjustment on the transmitter itself.
Zero adjustment is made to move the output to exactly 4 milliamps when a 0% process measurement is applied to the transmitter, and the Span adjustment is made to move the output to exactly 20 milliamps when a 100% process measurement is applied.
Unfortunately, with analog transmitters, the zero and span adjustments are interactive; that is, adjusting one moves the other. Therefore, the calibration is an iterative process to set zero and span, but only 2 to 3 iterations are usually required.
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[@darrenpinto902]

This is service to mankind. Great stuff. Perfect spoken tone.

[@realpars]

Thanks a lot Darren! Great to hear. Happy learning!

[@CantStopLawling]

This video was great. I was having a lot of trouble understanding what span and zero meant and no one at work could explain it very well to me. The other day we had a service tech come in and work on a calendar machine and I was helping him check the sensor for the oil pressure in a plant, we needed to adjust the zero and span but the case made it impossible to reach with a screwdriver. In my infinite wisdom I drilled a hole over the top and one thing led to another and the zero and span pots were ripped off the board. 🤦🏻 Anyway we replaced the sensor altogether but now I at least understand what I broke!!! Lessons learned all around

[@TiberiusStorm]

I'm loving these Instrumentation & Control Engineering videos. Keep them coming!

[@realpars]

Thanks for sharing your positive feedback with us! Happy learning :)

[@kokyawnyunt3728]

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[@realpars]

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[@realpars]

You're very welcome, Marlon! Let us know if you have any questions along the way.

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[@realpars]

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[@realpars]

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[@realpars]

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[@emanuellopez3431]

Thanks RealPars, very helpful!! I recommend to modify on the video the word "guage" by gauge.

[@realpars]

You are very welcome! Thanks for the suggestion. Happy learning :)

[@shalipse]

Thank you for sharing this invaluable information

[@realpars]

You are very welcome! Thanks for your support! Please let us know if you ever have any questions. Happy learning!

[@anandatk5377]

Amazing video clip makes me a clear vision how to control and process on deviation due to inputs and power supply to sensor transmitter being excerted with Temperature including ambient and Pressure. Thanks for that benefit knowledge in automated process control....!!!

[@realpars]

You are welcome! Happy learning

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[@realpars]

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[@realpars]

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[@realpars]

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[@realpars]

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[@jackpancadao]

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[@mohsinfalah6992]

Thank you for these important informatiom

[@realpars]

You are very welcome, Mohsin!

[@adapasriharsha3720]

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[@realpars]

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[@realpars]

Happy to hear that! Thanks for your support.

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Thank you.

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[@realpars]

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[@realpars]

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[@phuciendj1572]

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[@ArunKumar-sg6jf]

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[@realpars]

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[@ericphantri96734]

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[@sagarsawant5642]

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[@haitham5084]

Thanks a lot

[@realpars]

Most welcome, Haitham!

[@ardentdfender4116]

Great stuff.

[@realpars]

Thanks a lot! :)

[@aniket7201]

Thank you Sir! for this video as you've explained it so nicely it cleared up all my doubts regarding this topic!! Thanks again for the upload 👍 I'm subscribed to your channel and I'll stay tuned for more knowledgeable content from your side, it helps alot as I'm an instrumentation engineer Fresher and in coming months i have a interview at Siemens so your videos definitely help me alot to brush my basics back up! Greetings from India!! Have a Good day Sir!

[@realpars]

That is great to hear, Aniket! We wish you a lot of luck during your interview! Happy learning! We have a free course on PLC Hardware on our website, have you seen that yet? realpars.vhx.tv/browse Happy learning!

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[@user-hu4ij9oq8o]

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[@sakerarab9894]

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[@realpars]

Thank you!

[@ericphantri96734]

The key boiled down to time shortest path on memory to processor and formula of acceleration is seems not account for fallacy in theory of limit

[@tshepompilo3914]

well played out

[@sheendelute3493]

cool and excellent my android for censor calibration

[@ericphantri96734]

The best is the calibration module contain a sound chamber had alteast 100 m vaccuum tube the measure the time sound travel in various sound speed sampling and light measure in a coil of optic cable about 1 km to 10 km lenght then use it in the room of nearly same dimension for sound and to transmit light from one building to the length of its building in air the calibration is realized

[@trungy2k2]

Instrumentation series

[@ericphantri96734]

The best is networking calubration in the lical area nrtwork connect each day to sound speed and light speed sensor speed of light and sound measuring sensor variable

[@s.ananthakumar1943]

Pls Tell about different between transducer vs transmitter

[@realpars]

Thanks for your topic suggestion! I will happily pass this on to our course developers.

[@ericphantri96734]

Self calibration sensor design...it is biggest market from speed of sound , speed light and gravity and speed acceleration is important market in car , airplane , gps ,and lidar , radar

[@clarahemin]

please can you tell me how you found the calibration numbers (last two column )?

[@realpars]

Thank you for bringing up this point. We only arrived at the last two numbers because, as we mentioned in the procedures, we showed you the instrumentation for illustration. We must follow the calibration procedures for each device as explained in the device manual, which is how we arrived at these two columns. These two columns are our target goals at 0, 25, 50, 75, and 100 percent calibration. As you can see, they should match the first columns after we perform the calibration, but because of hysteresis and wire resistance, it will not be 100% all the time. The device manual will give the tolerance range if the device is good. Happy learning!

[@aniketkulkarni5990]

👌👌👍

[@rafeequetarafe1331]

Is it possible to enter multipoint calibration values into Siemens PLC Norm X and Scale X instructions?

[@realpars]

No. It sounds like you have a non-linear input that requires the programming of a curve for calculating the value, such as a J-Thermocouple curve. The NORM_X and SCALE_X functions are linear functions and assume only two "calibration" values: 0% and 100%. You could break up your curve into multiple linear segments, one segment between every two calibration values. Then use the NORM_X function to calculate a % of range and use the appropriate "segment's" SCALE_X function to determine your transmitter value.

[@rafeequetarafe1331]

@@realpars Yes, exactly. That is one way of addressing the need. Thanks for the prompt reply. I love watching Realpars videos as they are perfectly presented with adequate details.

[@hadeersalah6888]

Please how the values of calibration were calculated ?

[@realpars]

The ideal values represent 0%, 25%, 50%, 75%, and 100% of range, which corresponds to 4ma, 8ma, 12ma, 16ma, and 20ma. The measured values are recorded from what the sensor shows when 0%, 25%, ..., 100% of the process variable is applied to the transmitter input. The deviation is calculated with the equation shown at 4:50 in the video.

[@sebastiaanstander504]

I've been hearing a lot about self calibrating instruments these days, what are the limitations of self calibrating instruments, will manual calibration disappear in future?

[@realpars]

Thank you for your inquiry, Sebastiaan. The constraints primarily lie within the engineering application and the software integrated into the device. Additionally, manual calibration is expected to remain essential for the foreseeable future. Wishing you a fulfilling learning experience from RealPars.

[@sebastiaanstander504]

@realpars thank you for your reply, I appreciate it.

[@waseemomran1341]

In order to calculate the accuracy, shall we devide by 16 ma or 20 ma ? (20,2-20,0) / 20 Or (20,2-20,0) / 16

[@realpars]

Hi there, In the 5-point check method you should use this formula: [(As found value - Ideal Value)*100 / Ideal value] in which, the Ideal value for each point is different from the other points. For instance if you apply 75% of the transmitter's range, in this point, the "Ideal Value" in the formula is 16 mA. As the same example, if you apply 100% of the pressure, the Ideal value is 20 mA and so on.

[@waseemomran1341]

@@realpars The Accuracy for most Process Instruments is usually specified in % of Span or simply % Span. The calibration Span is defined as Upper Range Value (URV) minus Lower Range Value (LRV). For Zero-based instruments, % Span is also known as % of Full Scale (% FS). Note that some instruments may be specified in % of Reading or % of Reading + % of Span, so be careful.

[@realpars]

@@waseemomran1341 Thanks for your comment. I hope I have responded to your previous question clearly, as your new explanation seems like about a different topic. The "% Of Span" is actually the "percentage" of the sensor's pressure "range". As it is illustrated in the video, for simplicity sake and for better understanding, in the typical calibration sheet no range was specified for the sensor, either it is a zero-based instrument or not. So as you expressed, for different sensors, ranges may be different and this will simply affect the pressure we are going to apply to the instrument on each point.

[@renegadeflower575]

I was number 200 liker.

[@ArunKumar-sg6jf]

Ft and Lt what means bro

[@academiceducation1087]

FT---Flow transmitter LT--Level transmitter

[@realpars]

Hi there, FT stands for "Flow Transmitter" and LT is short for "Level Transmitter". These are the standard abbreviations that we use for these sensors in the P&ID diagrams. Check out this video to learn more about P&ID diagram: kzbin.info/www/bejne/onOtn4hngq90qtU

[@ddtripathi806]

Missiles, rockets, jets, cars, engines.

[@manishmandal-78]

Sensor Calibration: Something you cannot do at home 🙂

[@davidfarfan89]

That is not a calibration. That is an adjustment and a quick verification. Calibration is a statistical method to calculate a standard deviation called uncertainty

[@yarik6468]

That's right. Therefore this video explains of calibration. Sorry my English.

[@davidfarfan89]

@@yarik6468 No problem. However what they explain is adjustment, not calibration

[@MaNemUmar]

In this sense, calibration and recalibration(adjustment) follow similar procedures . To summarize, both should only allow an adjustment performed via a more accurate test instrument and ensuring it is traceable to whatever standards it needs to adhere by.

[@davidfarfan89]

@@MaNemUmar No. I know this is something confusing. What they show is not calibration. There is no way to.find a standard deviation by the way they explain. In a calibration, you need standard deviation corrected to a gauss curve using a t student probability curve

[@MaNemUmar]

St Col I’m perfectly aware of what you are talking about. However, that technique isn’t necessary because unlike sensors for general purpose applications, most instruments used in industry (like an RTD) are linear. You aren’t calibrating a 10 dollar non linear sensor here.

[@ddtripathi806]

Nuclear reactor.

[@ddtripathi806]

Design defunct.