TDC1000-GASEVM: How to setup TDC1000

Rolf Crapp

Part Number: TDC1000-GASEVM

We need help, how to setup TDC1000 with the following measurement setup?

We measure the Speed of Sound of air with different O2 conzentration . (Speed of Sound depends on temperature, humidity, O2 conzentration).

the speed of Sound change from

314m/s @0°C and 100% O2

360m/s @50°C and 21% O2

We use the TDC1000-GASEVM board with a audiowell 200khz transducers.

the distance between the transducers is 0.024m.

The calculated runningtime of the pulses is between (min) 66.52us and (max) 76.24us. This means the maximum pulse shift is 9.72us.

At 200khz the time from one to another pulse is 5us.

The measurements look good within a small area. But as soon as the range is increased and the time difference becomes greater than 2us, the TDC jumps to the next pulse and we get a jump of 5us in the TOF values.

See Picture to see the Jumps

for example we tried:

- 1 Tx pulse with dampening.and a ECHO_QUAL_THLD of -125mV

- 5 Tx pulse with ECHO_QUAL_THLD of -775mV

Questions:

1. According to my understanding shift of TOF greater than 5us is possible. (see div. examples from TI).

2. How could we prevent the jump to the next pulse. Dampening and Blanking doesnt help.

over 8 years ago

0 Scott Cummins over 8 years ago

TI__Mastermind 31655 points

Hi Rolf,

Could you please reupload the picture? It is not showing up for me.

Regards,

0 Rolf Crapp over 8 years ago in reply to Scott Cummins

Prodigy 30 points

Hi Scott

I hope it works this time.

i did some more measurements with a Osziloscope, were the jump is shown.

I tried a lot of settings, but no one works over the full range.

thanks for your help

0 Scott Cummins over 8 years ago in reply to Rolf Crapp

TI__Mastermind 31655 points

Hi Rolf,

Thank you, I can see the plots now.

First, just to clarify, the distance between the transducers is fixed for all of these tests, correct? The only change is in the concentration of the gas? First, I would experiment with the number of transmit pulses until you are sure that it is outputting the maximum SPL and you are getting the best quality return echo. There will be a point where the transducer saturates, so the maximum TX pulses available (31) may be more than is necessary. Once you have chosen your TX pulse number, then adjust the threshold with the goal of triggering on the same return echo peak across your range of concentrations. I suggest turning the damping setting off unless you are having trouble with the ringing obscuring your return echo.

Another way to approach this would be to set the TDC1000 to use single-echo mode (in register CONFIG 4), and to have multiple stops (register CONFIG 1)-- don't forget to set the number of stops expected in the TDC7200 tab as well. This will generate a stop for each peak in the RX signal. From there you will have to devise your own method for determining which of the stops is the correct one.

Regards,

0 Rolf Crapp over 8 years ago in reply to Scott Cummins

Prodigy 30 points

Hi Scott

Thank you for your Reply.

The Distance of the transducers is the same. Just the concentration changes.

For all measurements we used the single-echo mode, in some datasheet or Applikation note ti wrote that the Mutli echo mode is only suggested for levelmeasurement.

In the meantime we did some more measurements with different distance of the transducers.

Fortunately a distance greater than of 0.028m has turned out to be better. With this distance we measure no jumps of the signal.

I think the problem is the ringdown signal from tx path which give us the problem on rx path.

Unfortunately we need a small distance between the transducers because of space in the device.

How can we reduce the ringdown of the transducers? Is there any way without exchanging the transducers?

Regards.

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TDC1000-GASEVM: How to setup TDC1000