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PGA460: Discussion about short range measuring with PGA460

Zivorad Mihajlovic1
Prodigy 145 points
Part Number: PGA460
Other Parts Discussed in Thread: , ENERGIA

Hello Akeem,

I read all treads about PGA460, and I think that is good idea to summarize all possibilities and techniques that can be used for short range measuring.

I am developing device that will be used for measuring range of garbage in containers. As you can possible imagine, the reflected signal from various objects in containers will be quite a problem, but measuring bellow "blind spot" is largest problem here. I am planning to use P1 for short range, and P2 for long range. Can I use following algorithm for this:

>Set TVG for short range>>Set threshold for short range>>measuring short range>>set TVG for long range>>set thresholds for long range>>measuring long range. Any comments how to handle bot presets for  short and long range measuring that is applicable for my application. I am planning to use P1 for "20"cm to 140cm, and P2 for 50cm to 350cm.

If we use schematic of BOOSTXL-PGA460, can you tell me what is optimal setup for short range measuring (R39, R40, Q3)? Can decouple signal DECPL be used somehow for this? 

I am aware that I have to make test to find suitable values for Cdump and Rdump. I am currently use this ultrasonic sensor www.cosson.cn/.../product54.html. Can you tell can I somehow use info about capacitance of sensor (2000pF) for easy first pick of Cdump/Rdump?.

Since my ultrasonic sensor works on 40kHz and transformer B78416A2232A003 has all measuring result for 52kHz,does this mean that usage of ultrasonic sensor with 52kHz resonance frequency gives better results, especially for short range measuring (smaller decay time)? 

Generally, what is your recommendation how to recognize is there any object below "blind spot" and that can be applied for my application?

In order to minimize value of "blind spot" I am planning to use 200kHz ultrasonic sensor. I already made test board with other MCU (requested) and I adopt Energia code and it works fine for 40kHz. I am currently waiting samples of B78416A2386A003 (for 200kHz) and I notice this that this coefficients (BPF_A2_xSB, BPF_A3_xSB, and BPF_B1_xSB) must be write manually. It is good that GUI has calculator, but I didn't notice that Energia code supports writing this registers, am I right? Should I write these registers with separate function?

Since device must be very small, what is your opinion about changing electrolyte C17 with 100uF/16V tantalum capacitor? I have the same 7.6 V at output of the boost.

Thank you in advance.

Regards, Zivorad

  • 0
    TI__Mastermind 27950 points
    Hi Zivorad,

    Thanks for you very thorough message, and proactively researching these topics ahead of time. I will respond to each of your newlines.

    1) I will be releasing two application notes to help users optimize their sensors for short-ranging. The first will be an updated version of the PGA460 Ultrasonic Module Hardware and Software Optimization (www.ti.com/.../slaa732), and the second will be a new document focusing on the benefits of high-frequency transducers for short-ranging and high-accuracy.

    2) Your algorithm to dynamically reconfigure the time-varying gain profile will help optimize your short and long range measurements. (On behalf of the team here, I apologize for the inconvenience of the shared TVG profile between P1 and P2. Automotive customers typically only require a single TVG profile, and switch between P1 and P2 depending on the systematic/environmental noise, not range requirement.)

    3) If you use the BOOSTXL-PGA460, the optimal setup for short ranging when using the Murata MA58MF14-7N in mono-static mode is to use a damping resistor of 10kOhm, and a tuning capacitor value of 680pF. The decouple signal will only provide benefit to long range measurements, so you can keep the DECPL pin floating. Since you intend on using the Cosson KS-A1640H10ATR, the matching circuit values will likely different. Unfortunately, I am unable to recommend a starting set of matching values for this transducer. I usually recommend to start with no matching circuit (only transformer and transducer). If results are undesirable, begin to introduce tuning capacitance (start with 100pF, and increase). If capacitance alone is not sufficient, begin to introduce the damping resistor (start with 20kOhm, and decrease).

    4) The TDK EPCOS B78416A2232A003 transformer is ideally matched to any transducer operating at 52kHz, but this does not necessarily translate to the shortest ringing-decay. Usually an ideally matched transformer-transducer pair will yield best-case long range performance, and a smooth decay profile. Since you transducer's resonance is at 40kHz, I suspect tuning capacitance will be critical to both short and long performance.

    5) For a mono-static configuration, it is very difficult to detect the presence of an object within the saturated blind-zone. You can extract the 1MSPS ADC or DSP output using the continuous synchronous mode (master forces a clock signal to SCLK pin, and PGA460 continuously output data at TX pin), and compare the saturated region's values (for phase shift) to determine if an object is within the blind-zone. Typically, a bi-static configuration is the only means of detecting an object within the blind-zone, since the blind-zone will not be saturated.

    6) A high-frequency transducer (180-480kHz) is the best means of minimizing the decay time to sub-10cm ranges. The only issue with some high-frequency transducers is that their max range is limited to 1~2m. I recommend the Massa 200639-501 (Model E-188/220) for the best short and long range performance. Unless you are using a direct/bridge driver, you will also need a compatible high-freq transducer, since the B78416A2232A003 is not compatible with high-freq transducers.
    High-freq transformer options include:
    1) TDK-EPCOS B78416A2386A003 transformer, contact TDK-EPCOS support at: en.tdk.eu/.../product-inquiry
    2) Wurth Electronics 750316928, contact the Wurth Electronics Midcom Inc. Headquarters at: midcom@we-online.com
    When contacting either of these companies, be sure to mention that you are developing an ultrasonic sensing solution using the TI PGA460.

    7) You will need to create your own Energia functions for writing to the coefficients when using the high-frequency mode. You can use the burnEEPROM function as a reference, since this command uses a Register Write command.

    8) Since your module must be very small, you can either consider switching to a half-bridge driver to completely eliminate the charging cap and transformer, or use a smaller charging cap value. The charge cap value is more so dependent on the preset driver current limit, pulse count, and time between each burst+listen iteration. Try decreasing the charging cap value to 22uF to help conserve space. You can also decrease the value of the current limit resistor that connects VPWR to the charge cap (currently 100Ohms) to help increases the cap's recharge rate. Be cautious not to decrease this in-rush current limiting resistor value to be too low, as you may cause an under voltage condition at the PGA460 during burst.