Ultrasonic sensors help

[kunene]

hi

I have to find the equivalent circuit(internal) of the ultrasonic sensors(see attached), but I have tried on google can't really seem to find what I look for. If you guys can help I would really appreciate.

I need the equivalent circuit so I can simulate it in LTSPICE.

Thanks.

 

[ronv]

I think you need to get the spec. But maybe this will help.

https://www.electro-tech-online.com/custompdfs/2012/10/an050913.pdf

 

[kunene]

Thanks...so that is the only circuit? where is the input and output, how do I identify them?

 

[ericgibbs]

Thanks...so that is the only circuit? where is the input and output, how do I identify them?

hi k,
A couple of LTS sims with that circuit from the datasheet, also I have attached the LTS asc file.

There is an error on the datasheet values, I and a colleague are rechecking.

Its resonant at around 150KHz, not 39Khz.???

E.

 

[kunene]

hi k,
A couple of LTS sims with that circuit from the datasheet, also I have attached the LTS asc file.

There is an error on the datasheet values, I and a colleague are rechecking.

Its resonant at around 150KHz, not 39Khz.???

E.

Thanks a lot. will appreciate any update.

 

[ericgibbs]

Thanks a lot. will appreciate any update.

hi,
This works as it should, its from a SPICE web model.

The previous post simulations suggest that the circuit values are incorrect.

E.

EDIT:
If you work out the formula for L1 using that d/s equation , you will get 348mH, which makes resonance around 12KHz, so the formula is incorrect.

Use a value of 110m for L1 to give ~40KHz.

For MrAl,

The value for C1 cap of 2430pF, is common to a number of web examples.

EDIT2:
The d/s formula is correctly printed but the actual worked example is in error.

The formula for L1 is 1/[ 4* ∏^2 * fs^2 * Cs]

The example drops the ∏^2 to just ∏.
So the actual L1 = 125mH.

 

[MrAl]

Hi guys,


Eric:
I found another data sheet for a 40kHz model and they cite Cs=2500pf as i thought. So i really think they just swapped Cd for Cs. It would be harder to believe that they published a 40kHz device data sheet for a 150kHz device.
Also, if we forget about the labels Cs and Cd when we calculate the value of the series capacitance we get the exact value they quote for the 'other' cap, to within very close to 38.6kHz. Try using the 'other' cap in the resonance formula and see what you get. It calculated out to equal fs.
It would also be quite a coincidence that the parasitic capacitance worked out to be the perfect value for resonance at fs

One thing that bothered me is that i could not read the line that states the impedance. it appears with dots in it that mess up the text. Maybe you can read that and tell me what it is. We can use that to check too. Whatever values we use we have to come up with the same impedance also.

But i'll take another look anyway.

[LATER]

Ok yes, there was a problem in the calculation of the inductor value as you noted Eric.
When i did the calculations myself i found it came out to 110.8mH which is close enough to your 120mH.
So yes they forgot to square pi (ha ha).

 

[ericgibbs]

hi Al,
Please check my previous edits, they replaced the pi^2 with just pi in their worked example on the datasheet, if pi^2 is used it gives close to the correct answer for L1. ~125mH, which sims out OK.

Also the ~2500p as Cd is in common use.

Eric

 

[MrAl]

Hello again,

Ok good, it looks like you've nailed it. I get slightly different results (111mH) but that's close. You did use 38600Hz for series resonance right?

What i did was i tried to follow their logic in it's entirety. All they seem to be doing is trying to calculate the internal values from external measured data. They measured impedance, and given that and the theoretical circuit they attempt to calculate the individual internal values for the four elements.
I had to guess a little at the impedance because it's not very readable on the data sheet for some reason, but it looks like they are stating a measurement of 362 ohms at -22.8 degrees, but verification of that would be nice.
Using that data and knowing the series R and using the assumed values of 2430pf and 153.4pf and L=111.2mH, the magnitude of the impedance comes out to 357 ohms which i believe is close enough.

As shown in the diagram, to get a phase angle of -22.8 degrees or so we have to have either of those two inductance values where the (red) -22.8 degree line intersects the angles for all L. For series resonance however only the lower L value works.

 

[MikeMl]

Thanks...so that is the only circuit? where is the input and output, how do I identify them?

Where is the input and output on a resistor? A capacitor?

There is no input and output. How many pins are on the device? There are only TWO, meaning that there can only be an equivalent circuit brought out to two pins....

 

[kunene]

Thanks Eric and Mike. Really appreciate it.