Impulse PIRAT PI Metal Detector: Understanding its Unique Pulse Change Detection System

Question

Hello On page: The PI detector is described but with a completely different pulse change detection system than in the standard PI. I will add that the detector is interesting because it is much simpler than usual. Something hard to undermine the operating principle of the last operational...

rb401 · Accepted Answer

This amplifier works as a comparator, without any feedback. In steady state, it compares (input -) the input voltage (from the potentiometer slider) with the same voltage but passed through a 2: 3 voltage divider (R14, R15). So in the static state always on the input - the voltage will be higher than the voltage on the + input. Consequently, the output voltage of this amplifier (comparator) will be as low as possible. I am constantly considering voltages in relation to the 12V power supply. But, look here, there is a C6 capacitor that introduces the inertia (time constant together with the resistor R14) of voltage changes at the + input of the comparator. That is, at sufficiently fast (faster, say, overload capacity of C6) and above a certain amplitude (1/3 of the input voltage) impulses (negative) at the input of this system, the voltage difference at the comparator's inputs will temporarily change the sign. The amplifier (comparator) will give a positive impulse at that moment. So the system is, as it is simple to say, a detector (with an activation threshold) of negative pulses with specific parameters (rate of change, amplitude).

teflon · Answer

I explained it to myself too. However, something does not suit me ... Why does the machine work on ferro and dia magnetics?

rb401 · Answer

Note that this is not a classic PI detector system, where the foundation of the method is to sample the signal at a strictly defined time (times), in a synchronous manner with the end of current pulses in the coil. And the measurement value is the absolute voltage value of these samples. And here, in this simplified detector, there is no synchronization (sampling), and the detection is practically about measuring the amplitude, completely regardless of the position relative to the pulse in the coil. So it measures properly, quite different from the classic PI. Actually, it is only detected here that the elongation time of the voltage in the coil is detected in the presence of metal. Therefore, at least for me, the expectation that the properties (i.e. the ability to recognize the type of metal) will correspond to the classical PI method is a very risky assumption. Look at this patent for example: on the fourth drawing (Fig. 8). If we introduce such a signal on this simple detector on a comparator, we will notice that in the initial range, the highest steepness will be obtained by silver, but steepness will be the same as without an object (NO TARGET). But in practice we will have this signal cut off from above due to the inevitable saturation of the first operational. So looking at the further part of the course it turns out that iron gives the greatest steepness here. But this is not important, only the global time of this response is measured, regardless of the details of its shape, which in advanced PI is used to infer about the type of metal.

bab1213 · Answer

Hello everyone, did anyone make this detector from the diagram and does it work at all

jarek_lnx · Answer

If someone did it on YT, there must be a movie

Majster109 · Answer

Hello, Yes, it works. You need to find a diagram on the net in which the Russian K157UD2 is replaced by TL072 (TL062). There are some prefabs on the web and some pretty simple DIY ones, including PCBs. The layout is quite grateful and susceptible to modification, just right for learning and experimenting. I started playing with impulse with him and I didn't get discouraged. Greetings.

Impulse PIRAT PI Metal Detector: Understanding its Unique Pulse Change Detection System

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