TDC1000-C2000EVM: NOT RECEIVING ECHO PULSE WITH THE HV CIRCUIT

Hello Isaac,

Here are the settings we had. We set a really high listening window 

When we zoomed in to the Tx pulses, this is what we observed. Our Transducer is 1MHz.

We did some additional testing to identify where the signal gets lost along the received signal path (LNAOUT (R21), PGAOUT (R27), and at R30 which connects the COMPIN)

The images below are shown in that order (

LNAOUT (R21)

 PGAOUT (R27)

 COMPIN (R30)

When we disconnected the HV, and tested the transducer without it, this is the signal at R30, which gives good results.

What adjustments can we do to make sure that we get an echo signal when we use the HV?

Semyalo,

Can you try increasing the amount of pulses you are sending out and capture the waveform so that I can see what the signal looks like?

Also I am not sure if your transducer is receiving any data. The LNA and PGA signals dont look like how we would expect them to look whenever they are getting data so my assumption would be that they are somehow now connected. 

A good way to test out your RX and TX is to test it out with another system and check if you are sending out data correctly as well as receiving data from the other system. My first thought is that perhaps the TX is not generating the pulses appropriately so if this is not sending out the transmission at the correct frequency this would explain why you are not getting anything back during the listening period. If you are transmitting properly then perhaps there is something that needs to be addressed on the RX portion.

Best,

Isaac

Hello Isaac,

We managed to generate pulses on Tx with our 1Mhz transducer we have been using playing around with the settings (image below).

The HV Circuit recommended hasn't been useful so far, so we tried it without HV on Tx, and received some good results for our 6kg (22cm high) LPG cylinder.

However, we can't be able to receive echo in a larger (130cm high) LPG cylinder. We are thinking of using a lower value transducer e.g. 500khz, 200khz

due to a significant difference in sound travel between water and our liquified gas.

We realised that the interstage filters on the EVM is set to a 1mhz. Could you please recommend the values we can change at this filter so as to accommodate less than 1mhz frequency? 

Otherwise if you have any other recommendation on how to achieve this would be of much help.

Regards,

Semyalo

Hello Semyalo,

Thanks for the patience here. A lower frequency would help as this is able to carry more energy than the higher frequency transducers the only downside is that your measurement resolution will be reduced in comparison to the higher frequency transducer.

I think changing the 51pF capacitors here to a higher capcitance will move the cutoff frequency to prevent the lower frequency signals from being attenuated. I would try something around the 150pF range for C10 and C20 above. The C15 capacitor is just a DC blocking cap so this one can probably remain the same. If its attenuating your signal try increasing it.

Best,

Isaac

Thank you, Isaac

Our lower frequency transducers are to arrive this week.

We shall be letting you know about the progress once tested.

Regards,

Semyalo

Thanks for the update Semyalo!

Let me know if there are any other questions in the meantime.

Best,

Isaac

Hello Isaac,

We have tested out the 500khz transducer (PSC500K018060H2AD2-B1) from Jiakang. We have also changed the hardware as advised, but looks like we can't have a signal get through the metallic cylinder. (we have tested it on a 22cm high metallic LPG cylinder)

Below are our settings and scope image

blue is Compin/echo, yellow is STOP pulse. Our target should be 446us

Any more advice will be much appreciated!

Regards,

Semyalo

Hello Semyalo,

The scope shot is a little too zoomed out can you try to zoom into the compin signal so that I can see what is going on?

It would also be good to know what the time divisions on your scope are set to.

Best,

Isaac