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Part Number: FDC2114
Regarding to Figure 4. Remote Sensing Distance vs Capacitance for Water on datasheet page 4, my customer is asking a question.
What is meaning each curve ( 0-8cm)?
And Y axis unit(Remote Sensing Distance) is “mm”? (Typo?)
Yes, that is a typo. The x-axis should be in mm.
The legend of 0 to 8cm is for the liquid level height. So each curve shows how the capacitance reading changes as the sensor is moved away for a fixed liquid level.
The important thing is to look at the spread of capacitances at each point on the x-axis. For example, when the sensor is only 1mm away, the capacitance changes about 1300 fF from 0 to 8cm. At 10cm, the total spread has decreased to about 200fF. For sensing, you always want to maximize the signal.
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In reply to Clancy Soehren:
Thank you for reply.
My customer understood that.
I have two additional questions.
1)According to application report(SNOA935A) page 4,
When more sensitivity is needed on remote sensing, the sensor size widths need to be larger.
(Refer Table 4.)
In this case , is there any concern for more sensitivity ? (Noise? Or ambient environment(temperature)?)
2) About gap between sensor.
On datasheet, application report, gap between sensor is 2mm.
Do you have a data of this gap, or guideline?
(Theoretically, when gap between sensor is increases, the capacitance decreases.)
In reply to Tao_2199:
1) In general, the signal will increase at a faster rate than the noise. This holds true until the sensor becomes larger than the target, then you may start getting diminishing returns. You also may need to be careful if there is the possibility for interference nearby the sensor (for instance, if a hand can get close to the sensor). In that case, you may need to experiment with a few different widths to find a good tradeoff.
2.) You are correct that as the gap increases, the capacitance decreases. For this reason, we recommend minimizing the gap. How much you are able to do this is dependent on your mechanical design. The application report shows how capacitance can change as the gap changes. We do not have additional test data on this topic.
I understood about relation of sensor size/gap and capacitance.
You mentioned following.
“The application report shows how capacitance can change as the gap changes.”
I couldn’t find out it. Where is it described in application report?
I was referring to figure 4.
I informed to my customer your answer and they understood.
I will close this thread.
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