Calibration of level sensors typically requires complete removal of liquid to obtain a zero level. And then partial or complete filling to obtain the maximum level. This is not always possible.
Are there level sensors that do not require calibration during installation?
This refers to sensors to a depth of up to 30 feet, capable of operating in automated systems.
Please recommend a level sensor that does not require calibration and can immediately measure the liquid level without calibration procedures.
Hello,
Welcome to the DigiKey TechForum. You can take a look at these sensors to see if one will work for your application. If you can provide a more detailed description of how you’re going to be using this that may help us find a specific part that may work. What is the supply voltage you’ll be using? What type of output do you need. What is the environment this will be used in? What type of liquid will you be measuring , etc ?
Hello @alalstol,
Part of your answer depends on the sensor to PLC interface. With a simple digital (on off) sensor or pair of sensors, we would need to “teach” each sensor to recognize the upper and lower bounds. As you point out, the tank must be filled and emptied. An analog sensor such as 4-20 mA device may have the same problem. As an example, we may teach the sensor to map the empty tank to 4 mA and a full tank to 20 mA. Once again, the tank must be emptied.
There are a few ways to mitigate this problem.
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We could use an intelligent IO-Link sensor. We may still need to empty the tank. However, we may only need to do so once upon machine commissioning. A properly configured system is capable of automatically teaching an in-kind replacement sensor.
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I’m intrigued by the possibility of using radar. For example, the Banner T30R-4545 as pictured below may be used in your application. Depending on the chosen model, we could configure the radar for digital I/O, 4-20 mA analog, or IO-Link. There is also a graphical configuration tool that allows fine control of the sensor’s outputs. For example, the radar can be programmed to avoid a conveyer or support beam that partially obstructs the view. Please see Banner’s video library for additional information.
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There are many additional sensors that could be used. One example is a pressure sensors. We could install one in the base of the tank or above using a dip tube and bubbler.
Please tell us more about youu application and we may be able to narrow down the list of possibilities.
Best wishes,
APDahlen
Hello,
I need to measure the level in a tank with aqueous solutions of salts, the concentration of which may change over time. It would be preferable to have a 4-20 mA current loop at the sensor output. In a pinch I could use a digital interface.
Best wishes,
Alalstol
Hello APDahlen,
I need to measure the level in a tank with aqueous solutions of salts, the concentration of which may change over time.
In my opinion, it will be difficult to use pressure sensors. The density of the liquid changes.
The radar and pressure sensors will require calibration procedures.
Are there sensors at the output of which an analog or digital signal is generated proportional to units of the length of the liquid column?
Sorry for the simplified analogue that may not be successful - a ruler with divisions immersed in liquid.
In this case, no calibration is required.
Best wishes,
APDahlen
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Hello @alalstol,
Yes, that changes things. Without a consistent density, weight and pressure measurements are off the table.
Have you looked at industrial sensors featuring the industry standard 4-20 mA outputs? These sensors will provide an analog output proportional to the liquid level. They are like an electronic sight glass, or as you said, like a ruler immersed in the liquid.
The radar I mentioned would be a good example. Perhaps you could use this chemical resistant ultrasonic sensor:
While we are on the subject, how do you intend to display the results. One potential solution is this Red Lion process meter:
Know that I have presented good quality parts with advanced features. If you wish we can narrow down the list to find the part or combination of parts best suited for your applications.
Sincerely,
Aaron
P.S. You may still need to calibrate the sensor and verify that is does not have any unexpected surprises as the tank is filled. Once this is done you should have a long operational life. Personally, I’d still verify the reading on a routine bases.
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Hello APDahlen,
Thanks for the detailed answer.
Radar or ultrasonic sensors look tempting. They are non-contact and nothing is immersed in the liquid.
However, the calibration problem remains unresolved.
You write about standard sensors like an electronic sight glass.
As I understand it, we are talking about improved versions of a float sensor with visualization (glass window or tube) with an added electronic part. As far as I know they are short in length. Or I’m wrong?
Best wishes,
alalstol
Hello @alalstol,
Yes, many of the glass sight glasses are short. However, I have seen robust glass windowed marine applications of visual tank level indicators that are over 5 feet tall.
Yes, this is a system-level problem. It is prudent to commission each and every sensor by verifying that the system responds as expected.
Please let us know if we can assist.
Sincerely,
Aaron
Hello APDahlen,
Thanks for the answer on visual level sensors.
I have a question for you, as a professional.
Why are there no level sensors on the market that do not require calibration procedures:
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difficult to implement?
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not required ?
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high price, easier to calibrate?
In your opinion, would a level sensor that does not require calibration be in demand on the market?
Thanks in advance for your answer.
Best wishes,
alalstol
Your 3 bullet points are inextricably related to one another.
AIUI, engineers have been searching for no field calibration required liquid level sensors for well over a century now. I was part of that search for my employer in the 1990s and we never found a solution that was inexpensive enough to attract customers in our target market.
It’s been so long since I looked into this that I can’t remember most details. I do remember that at the time, even if you took a cost is no object perspective, like in a government funded science research project, there was no apparent solution.
A good place to look for literature about the cutting edge in level sensing metrology are tech publications from the worlds various space and defense agencies. e.g. NASA Tech briefs
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Thank you @PaulHutch,
The radar I mentioned is close. However, even with a digital interface, it is prudent cycle the tank as there may be obstructions or unpredictable operations.
Cordially,
Aaron
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Hello @PaulHutch,
Thanks for the interesting answer.
Do you think level meters that do not require calibration would be in demand on the market now?
Best wishes,
alalstol
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AFAIK they have always been in demand and still are, it’s just that the cost has always been too high compared to the cost of the calibration at time of installation.
Hello PaulHutch,
I have not encountered level sensors that do not require calibration during installation. If you do not take into account float and visual ones with a glass window or glass tube.
Perhaps radio waves, in which the signal travels along a steel wire? But in my opinion, even there it is necessary to calibrate the time interval between the primary and the pulses reflected from the surface of the liquid.
If you don’t mind, please provide an example of a level sensor that does not require calibration.
Best wishes,
alalstol
Neither have I, I’m guessing you’ve completely missed the point of my previous posts so I’m calling it quits now on this topic.