TDC1011: Feasibility of distance measurement in the air

na na78,

The TDC1011 is primarily intended to be used in liquid-transmission medium applications (i.e. flow metering, liquid identification). Instead, I recommend the customer consider the PGA460, which is an integrated ultrasonic driver and receiver for air-coupled applications.

Given the customer's very short range requirement of 1cm~100cm, there are three potential solutions when using the PGA460:
1) Bi-static transformer-driven low frequency-transducer pair (30-80kHz)
2) Mono-static transformer-driven high-frequency transducer pair (180-480kHz)
3) Bi-static transformer-driven high-frequency transducer pair (180-480kHz)

The best solution is option #3 (bi-static transformer-driven high-frequency transducer pair) since the decay time at the receive only element would likely be minimized to a sub-1cm equivalent duration. High-frequency transducers are optimized for short ranging and high accuracy. For a better understanding of the three options described, refer to the PGA460 Ultrasonic Module Hardware and Software Optimization appnote (www.ti.com/.../slaa732).

For a high-frequency transducer recommendation, I suggest the Massa 200639-501 (Model E-188/220) paired with a high-freq transformer. High-freq transformer options include:
1) TDK-EPCOS B78416A2386A003 transformer
2) Wurth Electronics 750316928
When contacting either of these companies for samples, be sure to mention that you are developing an ultrasonic sensing solution using the TI PGA460. For a full-listing of air-coupled transducers and transformers, go to: e2e.ti.com/.../620399

Hi Akeem

Thank you for your reply.


In the solution you offered from 1 to 3, bi-static transformer solution requires two PGA460 devices?
Do you have reference circuitfor bi-static configuration?

BestRegards

na na78,

Only one PGA460 is required to operate in the bi-static mode. You can find a schematic/layout example for a bi-static transformer driver in the Design Files section on page www.ti.com/.../technicaldocuments as:
PGA460 Bi-static Transducer Transformer Driver Small Form Factor Design File (www.ti.com/.../slac759)

na na78,

For an additional high-frequency transducer example, refer to the Ultrasonic Distance Sensor with IO-Link Reference Design (www.ti.com/.../TIDA-01386)

Hi Akeem

Thank you for your reply.

I can see slac759 material.

Because I don't have PGA 460 EVM, so let me show the following.

Is it possible to connect second transducer for bi-static configuration using PGA460 EVM sets?
(Although it seems to be possible by using J10 header.)

I appreciate if you can reply.

BestRegare

Hi Akeem

Thank you for your reply, I understood.

BestRegards

Hi Akeem,  

We are looking at a similar application. We are trying to sense the level of liquid in a bottle, so the range is from around 1cm to 20cm, and it would be great to be accurate to +- 1mm.  
The TDC1011 IC seems ideal for this, however, our sensor will sit on the top of the bottle, so really we would be measuring the distance up to the surface of the water (where we should have a reflection). Do you still recommend the PGA460 over the TDC1011 for this?  

Many thanks,  

Pambo  

Hi Pambo,

The PGA460 or TDC1000 are both feasible options when detecting upwards of 1.5m. The limitation of this application is transducer ringing decay time rather than IC selection. Decay ring time is discussed in PGA460 Ultrasonic Module Hardware and Software
Optimization ( www.ti.com/.../slaa732.pdf ).

Because your application is focused on very short range and high accuracy performance, I recommend that you consider using the PGA460 in a bi-static transformer-driven high-frequency transducer pair (180-480kHz). This will ensure you are able to achieve downwards of 1cm at +/-1mm resolution.

If a bi-static transducer pair is too wide, then you should only use a mono-static transformer-driven high-frequency transducer. The transformer elementis important for this mode to enable best-case short ranging for a mono-static transducer. Re-posting an earlier recommendation: I suggest the Massa 200639-501 (Model E-188/220) paired with high-freq transformer:
1) TDK-EPCOS B78416A2386A003 transformer
2) Wurth Electronics 750316928

If 1cm is too short of a detectable target when the transducer is at the tip of the bottle, do you have the option to further recess the transducer to offset the minimum range. For instance, if the minimum detectable range is 3cm, could you elevate/position the transducer by an additional 2cm to detect a true bottle level of 1cm?

Hi Akeem,  

Thank you very much for your very comprehensive reply!

We were looking at a bistatic solution with 300khz transducers. I will follow your advise and investigate further.  

Our application is handheld and power efficiency is very important. Do you have any recommendations or a starting point on the driving voltage for this range (1-20cm) with a 300khz transducer?  

Many thanks,  

Pambo  

Hi Pambo,

Given your maximum range is only 20cm,  you can minimize your driving voltage to the PGA460's 6V operating requirement to ensure you also minimize the transducer's ringing decay effect to help with your minimum range measurements. You can actually supply the center-tap of transformer with a lower voltage than the PGA460's 6V minimum requirement.

The PGA460 GUI contains an embedded Power Budget Calculator. Assuming you are pinging the system at a 1Hz rate, I recommend that you use a load switch to completely disconnect power between each ultrasonic measurement. The PGA460's minimum preset record length is 4.096ms (or approximately ~70cm) for a single burst-and-listen cycle. Using the UART interface at 115.kBaud will require the PGA460 to be powered for an additional ~2ms to send the command and read the results, and an additional ~3ms to bulk configure at initial power-up. All three steps (1. bulk threshold write, 2. burst/listen command, 3. pull results) yields a total powered time of 9~10ms.

Here is an example of the power budget calculation for the high-frequency configuration recommended for this application:

Hi Akeem,  

Thats very useful, and thank you for the sample power budget! That gives us very valuable insight at this stage.  

Based on this, I wonder if we could use the TDC1011 instead so that we can operate at a lower driving voltage and reduce the power consumption and ringing decay further? Or would you not advise going much below the 6V mark for a range of up to 20cm?  

Many thanks again,  

Pambo  

Hi Pambo,

For your max range of 20cm, both the PGA460 or TDC1011 are feasible candidates, even with a lower driving voltage. If you find that the TDC1011 can provide more efficient power savings, I see no reason not to consider this device. I have a bias towards the PGA460 given my experience with the PGA460, and the fact that I have tested/proven this very short range concept.

If you have more questions on the TDC device, I can loop in our TDC specialist.

Hi Akeem,  

I'm inclined to proceed with the PGA460 actually. It might be worth asking your colleague who specialises in the TDC about the driving voltage, just to have an idea of what power savings can be made, however it does seem like the consumption is already acceptable from what you've sent previously!  

All the best,  

Pambo