Any physicists, mathematicians, engineers about?

[Techmonkey]

If I've got a soundwave... and then the same wave but with a harmonic on it.... is there any way of getting a sensor hooked up to a PLC to notice when the harmonic is present? I'm thinking maybe low pass filter, but this is going to have to operate in a steelworks, so there's going to be a lot of background noise going on. Will it still be effective?

also, how powerful is a piezoelectric transducer when cranked to full voltage?


the reason I ask... we need to engineer a way of automating the emptying of a waste tank from the blast furnace. when the tank reaches a certain level, we need to tell the PLC to switch off the first pump. So we need a way of sensing when the tank is full. Having considered systems using microwaves and radar and the like, we concluded they would be too expensive and might not even withstand the constant abuse that would be dealt from the slurry. capacitance was one thought, and then resonance frequencies was another (when the transducer is vibrating in air then we'll basically be getting the fundamental wave. When submerged in slurry, it noticably distorts the waveform with harmonic(s) ?)

I don't think the rest of the system is relevant, but if anyone wants more information I'll gladly oblige.

[Pilgrim]

You may be making it too complicated. When liquid falls below a given spot on a tank, there will be changes in temperature and sound transmission in the metal of that tank at that spot.

You might very well be able to use just about ANY surface-mounted sound transducer or temp sensor on the desired spot and set it to sense a change in response. You'd need to experiment to find the right threshold for the trigger.

Does that make sense?

[ThatGermanDude]

use a pressure sensor?

[Sir Edward V]

Originally Posted by Pilgrim

You may be making it too complicated. When liquid falls below a given spot on a tank, there will be changes in temperature and sound transmission in the metal of that tank at that spot.

You might very well be able to use just about ANY surface-mounted sound transducer or temp sensor on the desired spot and set it to sense a change in response. You'd need to experiment to find the right threshold for the trigger.

Does that make sense?

I like the temperature senser idea. Place the senser at said level. Warm the air above the waste, then when the waste reaches that level, the temperature should drop to that of the waste.

I can imagine there being other complications I don't know about, but the idea is good!