Ladies and Gentlemen,
we use your LDC1101EVM and measured an Rp of about 4.2kOhm with the given PCB-coil and the TI-GUI. The "LDC1101EVM User Guide" shows on page 8 a table with RP@3 MHz (no target) 10.3 kΩ for the given Setup.
Is there something wrong with our measurement or is the shown value in the user guide wrong.
Your help is much appreciated.
Thanks.
Hi Kristin, hello TI-Support,
attached you can find pictures showing the Setup used with the GUI.
First three pictures show the settings and the corresponding Rp and Proximity results offered by the GUI.
If we change the RpMIN setting to 0.75kOhm no Rp is shown by the GUI only Proximity readings are shown - can you please explain that behaviour, too?
Meanwhile we measured the Rp as described in chapter 4 of your document "SNOA936–October 2015-Measuring R p of an L-C Sensor for Inductive Sensing" and received a value of 4.9 kOhm.
Thanks,
Frank.
Hi Kristin,
>>I'm also not sure why changing the Rp min value to 0.75 kOhms stopped the Rp measurements from displaying; when I tried this on my GUI with my EVM, I was still able to read an Rp measurement. Does this issue persist if you unplug the EVM and plug it back in, or if you restart the GUI?<<
The issue persists either when unplugging the LDC1101EVM or when restarting the GUI. We use following GUI:
Am I right that the Rp settings influence the drive current of the sensor? I understood that each Rp setting corresponds to an assigned drive current (e.g. Rpmin=1.5 kOhm is assigned to 300µA) and during the measurement the LDC Switches the current from the current set with Rpmax to the current set with Rpmin.
Regards
Frank
Hi Kristin,
yes, there are other settings that cause the Rp measurement to fail. Please see following tables for details:
Raw Code-Display
|
Rpmax(down) / Rpmin (right) |
0,75 |
1,5 |
3 |
6 |
12 |
48 |
96 |
|
0,75 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
1,5 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
3 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
6 |
ok |
ok |
ok |
0 |
0 |
0 |
0 |
|
12 |
ok |
ok |
ok |
0 |
0 |
0 |
0 |
|
24 |
ok |
ok |
ok |
0 |
0 |
0 |
0 |
|
48 |
ok |
ok |
ok |
0 |
0 |
0 |
0 |
|
96 |
ok |
ok |
ok |
0 |
0 |
0 |
0 |
e.g.
Rp-Display
|
Rpmax(down) / Rpmin (right) |
0,75 |
1,5 |
3 |
6 |
12 |
24 |
48 |
96 |
|
0,75 |
no graph displayed |
no graph displayed |
no graph displayed |
no graph displayed |
no graph displayed |
no graph displayed |
no graph displayed |
no graph displayed |
|
1,5 |
0 |
1 |
3 |
6 |
12 |
24 |
48 |
96 |
|
3 |
0 |
1 |
3 |
6 |
12 |
24 |
48 |
96 |
|
6 |
no graph displayed |
ok |
ok |
6 |
12 |
24 |
48 |
96 |
|
12 |
0 |
ok |
ok |
6 |
12 |
24 |
48 |
96 |
|
24 |
0 |
ok |
ok |
6 |
12 |
24 |
48 |
96 |
|
48 |
0 |
ok |
ok |
6 |
12 |
24 |
48 |
96 |
|
96 |
0 |
ok |
ok |
6 |
12 |
24 |
48 |
96 |
e.g.
"no graph displayed" shows following RP-Display:
"0" shows following RP-Display:
Can you tell me in what way the setting of the Time Constant 1 and Time Constant 2 interact with the Rp-settings?
What are These Time Constants used for? Are These Regulator Parameters used for the current switching, e.g. PT1 or PT2 Elements?
Thanks
Frank
