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FDC1004: Suitability for measurement of test tube, on outside of glass

Derek
Mastermind 9772 points
Part Number: FDC1004
Other Parts Discussed in Thread: TIDA-00317, FDC2214

Hello, I have an application in a product whereby I need to measure the height of an aqueous liquid in glass tubes. Tubes are 1cm x 10cm. We only need resolution of about 1cm. There will not be any hands near it; this is in an instrument. All measurement has to be done from the outside of the tube, we can't submerge anything. It looks like the FDC1004 could do this, but a couple questions:

1. How many FDC1004s do I need? Since each has four sensor inputs but only two shield drivers, I assume we need one FDC1004 for every 2 tubes?

2. Is there a way to change the I2C address of the FDC1004 so I can use multiple ICs on the same bus?

3. The reference design TIDA-00317 (custom flex circuit that plugs into the EVM) looks like a close match to what we need; is there any way to buy or borrow one of these?

4. What is better for our application - the FDC1004 or FDC2214?

Any application advice? In this application how do we use the shield driver? The tube is all glass. It wasn't clear in TIDA-00317 how the shield driver is used.

Thanks,

Derek

  • 0
    TI__Mastermind 25045 points

    Hello Derek,

    Thanks for considering to use Texas Instruments. Based on what you have described, the FDC1004 does seem like viable option for your application.

    1.  If you were to copy the TIDA-00317, three sensors from the FDC1004 would need to be used per tube.  1 for the level sensor, 1 for the reference liquid sensor, and 1 for the reference environment sensor.

    2.  Unfortunately FDC1004 device ID is read only.  So if you wanted to use multiple devices, you might consider muxing the SDA line.  Or alternatively you might consider muxing the signal and shield pins if you wanted to use fewer FDC1004 devices. 

    3.  Unfortunately we currently do not have those readily available to buy.  However, the gerber files are available under design files here.  You might be able to get a reasonably rigid-flex quote from pcbway.

    4. While the FDC2214 is designed for the same purpose, it is little trickier to set up and has had EMI issues.  We would recommend you work with the FDC1004 instead.

    So if you look at Figure 19 of the TIDA-00317 Reference Design document, you will see the blue strips corresponding to the shielding capacitive plates, which run the full length of the liquid level meter.  Then if you look at figure 10 very closely, you can see that those actually face outward from the container.  The idea is that these shield plates will be at the same potential as your sensor plates and will prevent any capacitive effects on your sensor from influences facing outside of your container.