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Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
I'm slightly off-resonance, maybe it will increase a bit.
EDIT:
I added some like 50 turns on the core but still the better resonance is in the 44Khz range, no way to bring it down to 40Khz... maybe i try to add a small tank capacitor or a series inductor..
EDIT2:
My inductance meter says the inductance of the secondary is 9.70mH, giving a resonant frequency with 2000pF Ultrasonic probe capacitance gives appros 35Khz, i dount understand why it resonates at 44KHz. Maybe saturation of the core decreases inductance I will try to regulate the inductance by increasing the air gap down to an inductance of 8mH (that in theory should give 40KHz resonance)
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
A 2nF cap gives perfect resonance at 40KHz. The probe (with 2nF capacitance) doesn't resonate. It instead resonates at 43KHz. THe transformer secondary inductance is 8mH, adgusted by air gap. THe strange thing is that it resonates correctly at 40KHz when i push the plastic cover on the ultrasonic probe. Of course no reflections... Maybe the unit (a chinese one) is defective and i should leave it alone....
EDIT:
I misunderstood my readings. The signal going down to 60Vp-p means resonance with the mechanical part! It adsorbed energy from the tank circuit. It didn't work because there was insufficient drive on the primary side (the pic port driver was half blown, so it cannot drive properly the switching transistor (i noticed it looking at the primary side). Now replaced the PIC with a new one and lowered the driver resistor on the base of the switching BJT getting 140Vp-p (with 200Vp-p at release). THe "snap" is very strong and can be heard listening carefully (reperition rate 10Hz). Now the echos are stronger (20mVp-p at 70cm) and can be amplified easily. Quite low for such power but reasonable (the transducer has a waterproof shield).
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Some questions about ultrasonic probe driving