LDA Sensor: Types, Function & Applications

Hello!

I would like to install a Lane Departure Assist system in my vehicle.
However, I'm stuck in a dilemma when it comes to choosing the right sensor!

When I use a differential pressure sensor like the MPX4250DP, I cannot measure negative pressure (For those who are not clear about this: /viewtopic.php?t=3224).

"With an absolute pressure sensor like the MPX4250AP, the zero-point offset needs to be corrected. However, atmospheric pressure is known to fluctuate, so the zero-point would need to be adjusted depending on the weather conditions and altitude."

"Quote:"
The average air pressure at sea level is approximately 1013 millibars.
He fluctuates with the weather conditions at sea level, approximately between 985 and 1035 millibars (the absolute extreme values are about 880 and 1080 millibars).

What does the practical application look like? Are weather-dependent pressure changes noticeable on the LDA (Laser Doppler Anemometer)?

Best regards, Wolfi.

What do you think about that?

Use two absolute pressure sensors and then use a differential amplifier to convert the reading into relative pressure for display.

Yes, that would be a possibility. But unfortunately, it's an expensive .

What interests me much more is the question of how strongly atmospheric pressure fluctuations are visible on the LDA.

... and why don't you get an analog one with a pointer ?

It can display charging pressure and suction, and it automatically calculates the external pressure due to its internal system .

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

That was also true.
But I wanted to connect the LDA to the auxiliary instrument for battery voltage measurement. I would just need to change the scale and possibly amplify the signal.

I'm just a bit of a perfectionist , and this is what it would look like if it were completely original.

Hi,

I don't understand the problem.

Take two identical sensors: one for outside pressure and the other for load cell (LD). Then, using an operational amplifier (op-amp), subtract the value from one sensor from the value of the other. (Analog computer)

The result corresponds exactly to the boost pressure above atmospheric pressure.

However, the atmospheric pressure doesn't fluctuate as much with the weather; it changes more significantly with altitude (1 millibar per 8 meters).

This is especially true since the VTG doesn't reproduce much better than 50 mB anyway (hysteresis).
With an accuracy of 1 millibar, the whole thing is useless.

You will notice that the display becomes very jittery when you show individual MB values with four digits. However, if you switch to displaying three or two digits, you can save on the expensive compensation circuitry.


Then you simply connect an operational amplifier to the existing laser diode sensor, and from there to your digital voltmeter, and that's it. (As described in this forum).

garth.brooks wrote:

You will notice that the display becomes very jittery when you show individual MB values, especially with a 4-digit format.

This should be an analog display! (As described).

garth.brooks wrote:

Take two identical sensors: one for outside pressure and the other for LD (likely referring to a specific measurement). Then, using an operational amplifier (op-amp), subtract the value from one sensor from the value of the other. (Analog computer)

I already understand that! As Joerg also mentioned. However, two sensors are not exactly cheap!

garth.brooks wrote:

This is even more true considering that the VTG doesn't reproduce much better than 50mB anyway.

What does this sentence mean?
Do you mean that the engine control unit isn't using a higher resolution? Then there would always be quite strong pressure fluctuations in the turbocharger! I can't really imagine that. But I'm happy to be proven wrong .


I'm just wondering if a change in atmospheric pressure would actually be noticeable on a pointer instrument.

Why not make it cheap? You can tap into the existing pressure sensor and also use the ambient pressure sensor in the control unit. Just be careful to do that with a relatively high impedance. Then, subtract all those values and output them on an analog meter! What's the problem? It's not that expensive!

However, this won't help you identify a faulty boost pressure sensor!

No, not that. But you have to compromise! Either it's cheap and potentially flawed, or more expensive and safer... (although the more expensive solution can also be flawed).
'Two sensors aren't any more expensive than a decent mechanical LVDT, and those few resistors and maybe two op-amps shouldn't add much to the overall cost.'

@joergs
Yes, you're right. Mechanical LDAs are more expensive than I thought.

But I just had an idea:
You could connect a differential pressure sensor so that the high-pressure side is located after the turbocharger and the low-pressure side is located in the air filter housing (after the filter). This way, you measure what the turbocharger actually has to deliver. If the filter is not clogged, approximately 50 mbar higher boost pressure will be displayed (due to pressure loss in the filter). If the filter is clogged, the reading will be even higher, allowing you to detect the problem. However, this method cannot be used to monitor a bypass valve, but the 1Z engine doesn't have one anyway.

It doesn't sound too bad, or .