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TDC1000 Delta TOF

Burak Sönmez
Prodigy 20 points
Other Parts Discussed in Thread: TDC7200

Hi,

I am using 200 KHz transducers and gasevm board. I measure flow so I use TDC in mode 2 in flow mode. I see reasonable DELTA TOF AVG and TOF STDEV. However, when I give air pipe from different directions, I got the same direction. I mean, when I blow from one side of the pipe, delta TOF value increases to 2000 ns for example. When I blow from other side of the pipe, again I got about 2000 ns even I expect to see -2000 ns. 

If I blow slowly, I see what I expect( increasing to 700 ns from one side, decreasing to about -700 ns in other side). If I blow little bit faster, directions are changing as I explained above. I suspect that when I blow faster, the amplified signal passes the threshold shifts 5000 ns ( 1/200 KHz = 5000 ns )

Here are the configurations of TDC and oscilloscope screen:

I tried to change threshold, number tx pulses, short tof blank period and gain. I could not get the desired result

No flow Delta TOF

Could you help me with this issue?

Thanks.

  • 0
    TI__Mastermind 21685 points
    >>>>If I blow slowly, I see what I expect( increasing to 700 ns from one side, decreasing to about -700 ns in other side). If I blow little bit faster, directions are changing as I explained above. I suspect that when I blow faster, the amplified signal passes the threshold shifts 5000 ns ( 1/200 KHz = 5000 ns )

    I think you might be right about this. One thing to try is to set "NUM_RX" in Config1 register to 5 and also select in TDC7200 the "Number of Stops" to 5. Then from graph tab, you can set "TDC_Select" as Start to Stop2, or Start to Stop3, or other values (average of multiple stops). Usually selection Start to Stop3 or Start to Stop4 should help. Can you also show TDC7200 & Graph tab settings? Otherwise, please upload saved register config file.

    Thanks,
    Vishy