LDC 1614 + MSP4302553

Hello Santosh,

LDC1000 measure both Inductance and Proximity(aka parallel resistance). LDC1614 only measures Inductance. Does the Inductance measurement work for you? If you could describe the application (target composition, distance, what kind of measurements you are doing), that would be helpful.

Best Regards,
Natallia Holubeva

Best Regards,
Natallia Holubeva

Hello Natallia,
I need to detect the presence of the target at a distance of 4-5 cm. I used webench tool and for my application it suggested 1614. Target composition is steel. In my case, resolution is not an important thing. Can we use inductance values to detect the presence? I think 'yes'

Hello Santosh,

Yes, an L measurement can definitely be used to detect presence. For a range of 4 to 5cm, a sensor size of 10cm would be recommended; the LDC1614 can detect at distances larget than 1 coil diameter, but the response will be larger with a larger coil. How large is the target? How quickly do you need to determine the presence? Do you need presence only or position?

Regards,

ChrisO  

Hello Chris,

Sorry I didn't see your reply. I need to detect presence and I want a sensor that gives the distance to inductance graph as linear as possible. I played with the LDC webench tool but the graphs are not satisfactory. 

I want a response something close to the blue lines for a range of 5 to 7 cm. The target is a steel wheel as shown in the figure below. If the graph is linear, I can map inductance to distance values. (In the above case, 0.5cm to 7cm, the inductance value is same)

The wheel thickness will be 3cm, will be exposed on the sensor. 

Hello Santosh,

You should look into a larger sensor - for sensing at 7cm, you will need a sensor diameter of >14cm; and going larger will produce a more 'linear' response (i.e. the error from a true linear response will be reduced). Can you use a 20-25cm diameter coil?

Regards,

ChrisO 

Hello Chris,

I want to keep the coil as minimum as possible. Is there any other alternative like increase number of layers >4 etc...

Hello Santosh,

The target needs to interact with the magnetic field generated by the sensor, so therefore the magenetic field needs to reach that distance. The "size" of the generated magnetic field is primarily determined by the diameter of the sensor and not the overall inductance.

If you cannot make the sensor larger, then perhaps you could change the location of the sensor and detect a different target or target movement?

Regards,

ChrisO

Hello Chris,
Is it possible to have a sensor coil in rectangular shape whose area will be same as 14 cm diameter circular coil. I read in the faq's that the effective area will be contributed by the smallest side of the rectangle (the largest circle that can be inscribed in the rectangle). Can you elobrate on this. I can't change the position of the coil.

Hello Santosh,
With a rectangular coil, you have a sensing range equivalent to the shorter side (e.g. a 20mm X 50mm rectangular coil will have about the same sensing distance as a 20mm diameter circular coil).
One tradeoff with a rectangular coil is that it will have a lower Q than an equivalent size circular coil, as a circular coil has the largest area vs. perimeter (the perimeter corresponds to the length of trace needed to route the shape, and hence the resistance of the trace, while the inductance is a function of the area).
Regards,ChrisO

Can I use a coil (non pcb) and test it? I don't want to print a huge pcb before I test the sensor with my application. To sense a target at 7cm, how should I choose capacitor, no of windings, diameter (as you told before >14cm)?

Hello Santosh,
Yes, you can make a coil using magnet wire windings (for example). You can get a set of calculator tools from www.ti.com/.../technicaldocuments: take a look at the Inductive Sensing Design Calculator Tool, which is an excel based suite of calculation tools and includes an estimator for spiral coil design.
Regards,ChrisO

Hello Chris,

That's great. I will start with a hand made coil first. By the way the link to the calculator is no a valid one. Could you please send me the exact link for the coil design calculator?

I found the excel calculator. It is also based on pcb spiral coil. can I use a handmade coil? and can you tell me what factors should be taken into consideration while designing a sensor coil?

my requirements:
diameter of the coil: 8cm
sensing distance: 4cm
how do I pick capacitor value?

Hi Santosh,

You can take a look at the blog post http://e2e.ti.com/blogs_/b/analogwire/archive/2014/11/21/inductive-sensing-sensor-frequency-constraints which gives a good amount of information. For the LDC1000, the sample rate is also a function of the sensor frequency.

Regards,

ChrisO