the Zero-distance calibration of ddfs

[hehuan]

when i try to use the ddfs to calculate the distance, i can't understand the comments in the README file, 

"Zero-distance calibration

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The measured values of distance measurement include an offset.

The offset value may depend on the design of the radio circuit, the antenna used, or the PCB layout.

When using a library and a sample, you need to compensate the zero-distance offset and perform the calibration manually.

To determine the offset value, place the devices at a reference distance of 60 cm from each other and collect a batch of measurement data.

The difference between the average measurement value and the actual distance can be used as an estimate of the offset."

Appreciate if you can provide your valuable comments

Thanks

[tesc]

Hi,

There will be an (unknown) offset it the distance estimates, which can be calibrated. The suggestion in the readme file is to place the devices (between which you do the distance calculations) a known distance apart, nominally 60 cm, and perform several distance measurements at that distance. If the average result from those measurements is 64 cm, then that means there is an offset of 4 cm. If the average results from those measurements is 58 cm, then that means there is an offset of 2 cm in the other direction. This offset should be taken into account for all measurements, so for the two example values I listed here, you should subtract 4 (for the 64 cm measurement) or add 2 (for the 58 cm calibration measurement). This offset will depend on the hardware, and the environment may also affect measurements.

Even though the calibration is named "zero-distance calibration", the calibration cannot be done at a distance of 0 cm. That is why the suggestion is to do the calibration at 60 cm, which is near but still not too near. You can then use the same offset regardless of what distance you measure. The offset must be added (or subtracted) on all measurements that you receive from the library. (There is no offset compensation within the library itself.)

Regards,
Terje

[Usha]

I am measuring the distance between two devices placed 60 cm apart, but the reported distance fluctuates between 0.88 m and 1.43 m. What could be causing this variation, and how can I accurately calibrate the offset?

[tesc]

Hi,

Please create a new ticket for this new question. While it may be somewhat related to the original question, it is better to have it as a new question where it is more easily found by others, and where it will not potentially clutter this thread with back-and-forth on something which was not directly related to the original question.

Regards,
Terje