level sensors

[Alex1015]

Most sensors on the market measure intermediate parameters: resistance, conductivity, pressure, capacitance, time interval and others. Their calibration is carried out in the field. Filling and draining liquid from the reservoir. This is quite labor intensive.

To what extent can level sensors that do not require calibration procedures be in demand on the market?

I don't mean visual level sensors (glass windows or tubes).

Let me explain my question in more detail.

I mean continuous level meters: hydrostatic, capacitive, conductivity, ultrasonic and others.
During manufacturing, sensors are calibrated by measurements of the signal (parameter) used.
For example, hydrostatic level sensors are calibrated to specified pressure values.
These results can be converted either into percentages or into units based on the density of pure fresh water.
In this case, on-site calibration may not be necessary if you are dealing with clean fresh water.

If you work with salt solutions, then the parameters of the solutions will differ significantly from the parameters of pure water. Sweating, conductivity, dielectric constant and others. The temperature dependences of these parameters will also change.

As a result, the liquid level values ​​will change and the temperature compensation of the sensors will not work correctly.

 

[Heaviside1925]

OP,
You are making some broad statements with your premise which do not really equate in reality.
Do you mean level devices that only change state when detecting a level at a certain fixed point? ie. level switches
or
Do you mean level devices which provide a continuous output in proportional to the liquid level? ie. Level transmitters

Most sensors on the market measure intermediate parameters: resistance, conductivity, pressure, capacitance, time interval and others. Their calibration is carried out in the field. Filling and draining liquid from the reservoir. This is quite labor intensive.

Is this in your opinion? Calibration should take place in a controlled environment, not the field. Now, it will be field checked, once installed, but only after it's been calibrated.

To what extent can level sensors that do not require calibration procedures be in demand on the market?

There already is, they are called float switches.

Maybe I am misunderstanding your question, if so, I am unsure of what you are asking.

 

[3DDave]

Since level sensors are typically used to estimate volume, but are not able to directly detect volume, the only use for a level sensor otherwise is things like sump pumps, which don't require calibration.

 

[TugboatEng]

What do you mean by calibration? Most level sensors I have purchased require entry of a few parameter and you're up and running.

 

[waross]

I had to field calibrate a level control system for a flood water pumping station.
This was a bubbler system with a large chart recorder, and multiple micro switches mounted on the indicating mechanism.
There were several pumps which were called into service and stopped depending on the level, which was determined by the bubbler system.
The system was factory calibrated, but in reverse of what it should have been.
It was a long way back to town to get a calibration set.
So I used a piece of hose connected to the bubbler system and a tape measure.
For each set point, I determined what the bubbler back pressure would be. (actually in feet and inches of water column.
I measured that distance from the end of the hose and marked the hose.
I lowered the end of the hose into the sump until my mark was at the water level.
I then set the micro switch accordingly.
I repeated this with different measurements and marks until all of my set points were located.

Often a level switch may be calibrated by measuring and lowering it a predetermined distance.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Some systems are calibrated by the depth that the electrodes are lowered into the conducting liquid.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[IRstuff]

ANY measurement instrument requires calibration, whether you notice it or not. Additionally, what objection do you have with time of flight? It's the closest thing you can get to using a measuring stick. And if you don't like calibration, then why not use a measuring stick?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[waross]

Filling and draining liquid from the reservoir. This is quite labor intensive.

Or in the calibration shop, with precision calibration instruments.



--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

I'd say that you're most likely picking the wrong level measuring system if you must drain and fill the reservoir to calibrate it.

 

[waross]

I'd say that you're most likely picking the wrong level measuring system if you must drain and fill the reservoir to calibrate it.

I agree completely.
I have installed a lot of different types of level controls over the years.
I can't think of any that needed a reservoir to be drained and refilled to calibrate.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Heaviside1925]

OP, I see you have edited your post. You are making assumptions based off of an inaccurate understanding. A 2 hour read on Wikipedia will gain you much more knowledge than the time you spend on here. Now to your additional "ideas?"

I mean continuous level meters: hydrostatic, capacitive, conductivity, ultrasonic and others.
During manufacturing, sensors are calibrated by measurements of the signal (parameter) used.
For example, hydrostatic level sensors are calibrated to specified pressure values.
These results can be converted either into percentages or into units based on the density of pure fresh water.
In this case, on-site calibration may not be necessary if you are dealing with clean fresh water.

If you work with salt solutions, then the parameters of the solutions will differ significantly from the parameters of pure water. Sweating, conductivity, dielectric constant and others. The temperature dependences of these parameters will also change.

As a result, the liquid level values ​​will change and the temperature compensation of the sensors will not work correctly.

Calabration is only to provide a predictable, repeatable, proportional response to the variable it is measuring. You are referring to range selection, not calibration. As far a temperature compensation. If an instrument's accuracy is temperature dependent, it will provide its own self correction. If the fluid property the instrument is measuring is temperature dependent, then correction may take place internally in the instrument or externally in the device that is receiving the proportional output signal. This is not calibration.

 

[waross]

This is not calibration.

Agreed.
Any calibration shop is able to calibrate for any density.
DP cells may be used (after a different type of calibration) to determine the density of the fluid that will be measured.
DP cells are also used to determine the head of fluid that may be under varying head pressure.
This was being done many years ago, with pneumatic instruments and air pressure signals.
You cannot look at (and possibly misunderstand) one or two applications and become an knowledgeable instrumentation engineer.
An introductory course on industrial instrumentation can only give a simple glimpse of the field in 30 or 35 hours.
And we have not yet touched on communication protocols nor PID controllers.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

Try this forum: Control Systems Engineering
Link

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

For clarification, I didn't mean to say that sensors don't need calibration. Many come calibrated out of the box. I prefer level sensors that see the surface of the fluid because they tend to not require additional field calibration (for atmospheric vented tanks). Even if your conditions are not a standard atmosphere there are sensors that are unaffected such as radar.

 

[LionelHutz]

No matter what you want to call the field setup, you still should be able to pick a solution that doesn't require draining and filling a reservoir.

 

[IRstuff]

I would suspect that draining/filling the tank is for calibrating the tank to the sensor data processing, rather than calibrating the sensor per se, particularly if the tank has, say, a double-wall construction or if your data processing is in terms of percent fill of the tank.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[waross]

Further to IRstuff,
I am thinking an irregular shaped tank where level is not proportional to volume.
Years ago a friend of mine designed and built a system to determine the volume and weight of product in a his tanker trailer.
He had a DP cell across fixed points to determine the density.
I don't remember how he determined the level, but then he used a look up table to compute the weight from the density and level.
He picked up petroleum product from storage tanks at remote wells.
The density varied from well to well, and he had to cross DOT scales.
His hauls were quite long and the ability to carry maximum weight meant more money in his pocket.
Before that he had to load light to avoid overweight fines.
When he had his system working well he phoned me to tell me about it.
He said that I was the only person he knew who could understand what he had done.
Many years ago,he and I made a ten day canoe trip down the Big Salmon River in the Yukon Territory.
10 days from Quiet Lake to Carmacks village.
We brought a moose out with us.
Almost sank the canoe. grin
It's a one-way river, once you start down you are committed and there is no going back save waiting for winter and going back on the ice.
Recently some folk have video'd the trip and posted to U-Tube.
Big Salmon River
More Big Salmon

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LionelHutz]

OP is saying the sensor is the reason for draining and filling, not the shape of the reservoir. Determining the level is solvable without draining and refilling unless you're forced to use the wrong solution.

 

[Parchie]

OP believes it is best to test the sensor in-situ. That's the main problem. Unless he thinks out of that box, he'll never see that are many ways to do it.

 

[IRstuff]

I think the OP may be mixing different "calibrations"

> There is a calibration of the sensor's innate performance, ToF measurement, etc. This does not need to be done in-situ and does not require draining of any tank

> This is a calibration of the tank w.r.t. to the sensor, i.e., what level represents 0% fill and what level represents 100% fill or any other fill level that isn't represented as an absolute height or volume. Nevertheless, process software may tend to be written around %-fill, and perhaps it's too old and might not have the means for a manual entry, i.e., 49.35 ft = 0% fill and 1.27 ft = 100% fill; in such as case, only physically draining the tank would allow the user to set those values.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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