I have to add a function of liquid level detect to the probe in my task. In details, the probe goes downward to search the surface of some polar solutions, when the probe gets to the level of liquid, the sensor will give me back some signals about it, while when it goes upward back and leave the surface, the sensor will also give me back some signals about it. I think the capacitance type will help me to complete it.
But can anyone please tell a good place to buy this kind of sensor, which can be used as OEM in my task.
Are you saying the probe moves? Such probes are available but they are not capacitance based and are not necessary for finding water.
How many media do you have? How many interfaces? At the bottom you have water. Above that is air, oil, methane, or what? Please describe your application with more information.
There is quite a variety of commercially available capacitance probes used for detecting water, oil and air. Try a web search for capacitance level.
Yes, my probe can move up and down to search the liquid. Simply, there are only two media in my task. One is air above, another is polar liquid as water at bottom. The system work as an analogy to a human using his finger to touch water. He drops his hand downward to a base of water. When his finger reaches the surface of the water, he can feel it. In my work, a probe works as a 'finger', then the 'feeling' comes from some signals. Which kind of sensor can I use?
There are MANY ways of finding the height water in air. You are asking for information on one particular method that is very expensive and high in maintenance when there are many alternatives. Is there any particular reason why you are asking about a moving probe? The only times I have been involved with servo tracking level sensors is when we were looking for the height of a sand-like solid submerged within liquid. When I say we need more information, I mean we need answers to the following questions:
1 - What is the range of level you are looking for? I mean, 0 to 10 mm, 0 to 100 meters? You can see this makes a huge difference in the type of instrument selected.
2 - What is the accuracy you need? Are you looking for +/- 0.01 mm, +/- 20 mm? Again this has very big impact on the selection.
3 - Is the water clean or dirty? Some devices have a high tolerance for dirt, others cannot tolerate any. Some even require it!
4 - Is the water corrosive?
5 - Are there mechanical disturbances in the water which could interfere with any inserted device?
6 - Will there be opportunity to withdraw the device for service or is it important that the vessel never be drained?
7 - Is the environment subject to hazardous vapours such as gasoline vapour? Once again, this influences your choice.
8 - What is the maximum and minimum ambient temperature the instrument will be exposed to?
9 - What is the particular reason you are looking for a moving instrument such as you describe below? If this motion is really necessary, It is unlikely to be combined with a capacitance probe. If what you are looking for requires a capacitance probe, they can be purchased up to 10 meters in length.
Assuming that your application is exactly as you have described it, the simplest sensor would simply be a wire connected to a simple electronic circuit to detect conductivity.
I agree with Walter. There is a lot more information you need to look at in deciding the type of probe you want. If it is just water and cost is an issue then you could simply uses a float capacitive system, ultrasonic.
Check out the Vega instrumentation webiste. They offer alot of differnet sensors. Vega is just one company that manufactures level measurment devices.
If you answer the questions below then it is easy to suggest a sensor for yoru application. The only other question I woul add. Is you vessle under vacuum or positive pressure?
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