How can I prevent increasing capacitance on my homemade sensor?

In summary, the conversation discusses a capacitive water level sensor and the issue of its capacitance slowly increasing over time. The person suggests trying different methods, such as changing temperature and humidity, to see what affects the sensor's behavior. They also mention the importance of playing around with the sensor and not giving up when it doesn't behave as expected. The conversation concludes with a reminder to consider the accuracy specs of the meter being used.
  • #1
akaliuseheal
53
8
TL;DR Summary
Capacitance of sensor is not stable, why?
Hello,

I have made a capacitive water level sensor. It is a parallel plate capacitor.
While measuring the capacitance of my sensor, I measure 53 pF. I then leave it for couple of minutes, still conected to the meter, capacitance then rises to 54 pF. Capacitance is slowly increasing. Why is that and how do i prevent it?
 
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  • #2
Is this in water?
 
  • #3
Exactly how are you measuring the capacitance?
 
  • #4
hutchphd said:
Is this in water?

It is in air.

hutchphd said:
Exactly how are you measuring the capacitance?

I have the capacitor connected to the multimeter set to measure capacitance. I have it conected and turned on for couple of minutes.
 
  • #5
Can you make it move by breathing on it? Also this sensor geometry (this is the parallel trace device?) will be affected by the presence of nearby conductors...see if you can make it change by threatening it with a wire or your hand.
 
  • #6
The secret of dealing with this sort of problem is to play about with absolutely everything and see what has an effect. Try to make the effect worse by changing temperature and humidity (boil a kettle nearby for instance). Try turning off the DMM between measurements. Calibrate the depth - measure C vs height of plate above water. Min and max values as water level is varied. Are you sure that Capacitance is actually that of the plate to water? etc. etc. Measure the C of a pair of plates (not water) does the value agree (near enough) with what the sums tell you?

Most of those things may not give you a clue ( you may have done some of them) but one of them may give the crucial clue. There is a great temptation, when you make something and it doesn't behave as you expect, to put it in a cupboard and not chase the problem. Zero learning experience. A half day fiddling with it as above and you will learn so much and it may even end up working!
 
  • Like
Likes Tom.G and jrmichler
  • #7
Read the accuracy specs of your meter, they will likely be of the form xx% ±1 digit. A 1 digit jitter in any digital readout is quite common and expected for several reasons; i.e. battery voltage dropping, the actual input signal being very close to the transition value between steps (with random electrical noise occassionally forcing a transition), internal thermal drift in the meter... well, you get the idea.

Also that's only a 2%-of-reading, not bad at all in the real world.

EDIT: that accuracy of xx% may be either % of Reading or % of Full Scale

Cheers,
Tom
 
Last edited:

1. What is a homemade capacitive sensor?

A homemade capacitive sensor is a type of sensor that uses the principle of capacitance to detect changes in the electrical field. It consists of two conductive plates separated by a dielectric material, such as air or paper. When an object with an electrical charge comes close to the sensor, it alters the electrical field and changes the capacitance, which can be measured and used to detect the object's presence or movement.

2. How does a homemade capacitive sensor work?

A homemade capacitive sensor works by measuring changes in capacitance. When an object with an electrical charge comes close to the sensor, it alters the electrical field between the two plates, changing the capacitance. This change in capacitance can be measured and used to detect the object's presence or movement.

3. What materials are needed to make a homemade capacitive sensor?

The materials needed to make a homemade capacitive sensor include two conductive plates (such as aluminum foil or copper tape), a dielectric material (such as air, paper, or plastic), and a circuit to measure the capacitance (such as an Arduino board or a multimeter).

4. What are the advantages of using a homemade capacitive sensor?

One advantage of using a homemade capacitive sensor is that it is relatively easy and inexpensive to make compared to other types of sensors. It also has a wide range of applications, including touchscreens, proximity sensors, and motion detectors. Additionally, capacitive sensors are not affected by dirt, dust, or moisture, making them more reliable and durable.

5. Are there any limitations to using a homemade capacitive sensor?

One limitation of using a homemade capacitive sensor is that it may not be as accurate or sensitive as commercially available sensors. The sensitivity of the sensor can also be affected by external factors such as temperature and humidity. Additionally, the size and shape of the conductive plates and the dielectric material used can affect the sensor's performance.

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