LDC1000 staple detect distance increase

bill lin14

Other Parts Discussed in Thread: LDC1612, LDC1312

Hi, I want to know how to increase the distance of inductance sensing for LDC1000, because I have a rectangular PCB Coil (around 220uH with 470p and frequency of 781KHz) with a 50 turn and long of 24cm, wide of 2.3cm to detect a office staple, the best detect distance i can get is around 0.5cm to 0.8cm, seems the radius of a coil would be the detecting distance i should get 1.1cm of detecting distance, is because my coil is a rectangular PCB or because my object staple it too small to detect.

over 9 years ago

0 Natallia Holubeva1 over 9 years ago

TI__Expert 6550 points

Hello Bill,

Please refer to the questions # 2 and 3 of our FAQ: http://e2e.ti.com/support/sensor/inductive-sensing/f/938/t/295036#Q3

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

Currently I have not reach half of wide distance 2.3cm/2=1.1cm detect distance? Is that because my LDC1000 EVM board is not setting up for high resolution?

BR
Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Bill,
Is your target approximately the same diameter as the coil?

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

When you mean diameter does it measure by the height of a rectangular PCB Coil (2.3cm), and the target of detect, a office staple height of 1mm?

BR
Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Hello Bill,

We model the coil and the target as a transformer. In your application, the coil is parallel to the target. I would like to make sure the size of the target is similar to the size of the coil.

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

When you say LDC1000 model the coil and the target as a transformer, and size of the target is similar to the size of coil, in my case my coil size is big compare to my target size, does the detect distance is very small and not able to reach the potential of half of diameter of coil.

Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Hello Bill,

The rule of a thumb is to detect up to half of the diameter of the coil when the target and the coil have similar sizes. Please, consider reducing your coil.

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

How will I need to design a PCB Coil which is aim to detect small size object like staples, pins with accuracy and quick response, would you know different patterns like rectangular, square, circle which will help increase detect distance and reduce noise?

Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Hello Bill,

For such small targets you would need to design a small rectangular allongated coil. We are currently working on similar coil deigns. The information will be released in mid to late January.

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

Do you happen to know when it comes to PCB Coil, what approach we need to know, for example I have 1 layer of PCB Coil and a 4 layer of PCB Coil with same turn, same dimension and 4 mil wide of trace, using Network Analysis, I found 1 layer of PCB Coil is around 220uH, and 4 layer of PCB Coil is around 10000uH, do you have any idea why the difference can be this huge?

BR
Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Hello Bill,

Are you designing the coils yourself or using pre-fabricated coils? Usually a 4 layer PCB would contain the same number of turns on each layer. Thus, the total inductance is 4 times of the inductance of the single layer PCB. You could open the layout in Altium or simular and confirm the number of turns.

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

What would be the cap best use for the inductance design, because I have a PCB Coil with 220uH, best working frequency 20KHz to 781KHz by using network analyzer measurement, I use cap of 470p and measure output of 500KHz, what to look for when chose the right cap?

Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Hello Bill,

470pF cap seems reasonable. Generally, you should choose the operating frequency based on the folowing constrains:

1. The frequency should be at least 20% less the self resonance frequency of the inductor.

2. You want to keep your quality factory as high as possible.

3. We recommend using COG/NPO ceramic capacitors.

Additionally, you can refer to the following blog post: http://e2e.ti.com/blogs_/b/analogwire/archive/2014/11/21/inductive-sensing-sensor-frequency-constraints

Best Regards,

Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

When the target size is small not similar size, compare to the PCB Coil, is there a way to find out what is max detecting distance it can achieve, I know that the full potential of detect distance of half of diameter of coil is not achievable, but how can I know the max distance I can achieve?

BR
Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Dear Bill,

We are working on similar project, the results of which will be available in January. The calculations of three dimentional Electormagnetic fields are quiet complex, thus we rely on experimental data. In your case, I would assume that the maximum sensing distance will depend on the coil geometries. What is the distance that you need to achieve?

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

We are looking at 5mm to 5 cm to achieve the sensing distance with plastic mylar on top of the coil. I like to know is there a minimum sensing distance that can be achieve with LDC1000 or LDC1612?

Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Hello Bill,

LDC1612 would be a better fit for the distance measurement application.

Best Regards,

Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

Any suggests on action to make the detecting distance longer?

Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Bill,

The technology is based on eddy current generation. You could try using a ferrite and adjusting offset/output gain registers on the LDC1312/LDC1612.

Best Regards,
Natallia Holubeva

0 LEE YULIN over 9 years ago in reply to Natallia Holubeva1

Prodigy 220 points

Hi Natallia:

I can't find the output gain registers in LDC1612 datasheet. How can i find about this information? thanks.

BR.

0 Natallia Holubeva1 over 9 years ago in reply to LEE YULIN

TI__Expert 6550 points

Hello Yulin,

LDC1612 is the 28 bit converter. Thus, you can achieve the highest resolution with it already. Output gain register applies to LDC1312, the 12 bit converter.

Best Regards,
Natallia Holubeva

0 bill lin14 over 9 years ago in reply to Natallia Holubeva1

Prodigy 110 points

Hi Natallia:

Change Rp(max) and Rp (min) is relate to Proximity Data I hear from Ting-Ye, Is Rp any relate to distance of detection, if I change Rp, can I gain some distance of detection?
Any news on Webench simulation for Rectangular PCB Coil?

BR
Bill

0 Natallia Holubeva1 over 9 years ago in reply to bill lin14

TI__Expert 6550 points

Hello Bill,

Rp sets the current limits for the IC. Please, refer to the FAQ #20: What are Rp min and Rp max values of LDC1000/1041/1051? It should be configured properly for the best performance. We are still working on the app note, I apologize for inconvinience.

Best Regards,
Natallia Holubeva

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LDC1000 staple detect distance increase