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Original question:

FDC1004: FDC1004

I am unable to measure liquid level with FDC1004.

Lucía Valentina Eletti
Prodigy 10 points
Other Parts Discussed in Thread: FDC1004

Good morning, my name is Lucía, and I am writing from the Faculty of Engineering in Oro Verde, Entre Ríos, Argentina. Some time ago, as part of a project, we purchased the FDC1004 kit and we want to use it to measure liquid level. We have tried different electrode arrangements, following both the out-of-phase method and a conventional approach, but we have been unable to successfully measure liquid level.

There is an equation that addresses the calculation of level:



The parameter "hRL" in the equation refers to the unit height of the reference liquid sensor, which is typically set to 1. This means that "hRL" represents the height of the reference liquid sensor in the unit of measurement chosen for the system.

After using this equation, the result obtained will have units of length, typically in the same units as the dimensions used in the equation. For example, if the dimensions used in the equation are in meters (m), then the result will also be in meters (m).

If you have any further questions, feel free to ask. Regards.

  • 0
    TI__Mastermind 18545 points

    Hello, 

    I have a few extra questions for you to help us understand your issue better:

    • Can you share more information about what your capacitive sensing electrodes look like? Any layout or shape information would be helpful. 
    • What type of liquid are you using in your application? 
    • What is the range of capacitance that you get in your measurements for the liquid level change? 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 10 points


    Hello! I'm using a pair of electrodes of the same length as the container (approximately 5 and a half inches) where I measure the level. One of them is connected to one channel and the other to GND. Then I have another pair of electrodes, about 1 inch in height, where one goes to another channel and the other to GND. I set up the measurements as single-ended (non-differential). The first pair of electrodes mentioned corresponds to the level, and the second pair to the reference. As for the liquid, I'm using water. Finally, the capacitance range starts from 7.1 pF to 15 pF. I'm unable to use the sensor to measure the liquid level. Thank you.

  • 0 in reply to Lucía Valentina Eletti
    TI__Mastermind 18545 points

    Hello, 

    Does the 15pf match up with the end of your liquid level height or is the measurement saturating while the level is still changing? If it is, are you using the CAPDAC offset in your measurements? 

    Can you share a plot of the capacitance measurements for your sensor and reference over the liquid level change? 

    Thank you, 
    Justin

  • 0 in reply to Justin Beigel
    Prodigy 10 points

    Hello! The measurement reached 15pF before fully filling the container, meaning it saturated beforehand. However, we were still able to solve that saturation issue. The problem we have now is that we don't understand the equation provided in the datasheet for level calculation. Additionally, we also don't understand how to use the CAPDAC compensation in measurements because, in most cases, when the container is empty, the channels start measuring between 4 and 7.5pF.

    Thank you!

  • 0 in reply to Lucía Valentina Eletti
    TI__Mastermind 18545 points

    Hello, 

    We expect some capacitance to exist when there is no liquid in the tank. The empty container value should be used as the Clevel(0) part of the equation. You mentioned a range for this measurement, is this between different tanks/sensor electrodes or all on the same setup? If it is all the same setup, is there any difference between test setups when the capacitance range shifts? If it is not the same setup, then tolerances between assemblies could be the cause here and you may need to calibrate the zero position on each assembly. 

    For using the CAPDAC, it is a digital offset on the capacitance measurement that can be used to shift your measurement reading up to 100pF. After the CAPDAC offset, the capacitance measurement can range from -15 to +15pF. This allows the devices to measure up to 115pF depending on the CAPDAC setting. 

    Best Regards, 

    Justin Beigel