Query : DMM killer

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Hi All,

Does anyone know what kind of output is provided by a ultrasonic transducer driver board, I connected my DMM to output of board. It was on Volt setting and test leads in proper position. Screen flickered as long as it was connected to board output, I took it off within few seconds.

Measured voltage of some adapter and displayed correct voltage, but when I try to match MOSFET for amplifier it flickers like it did with ultrasonic driver board, can't read anything and sometimes it reads correct value 4.60 V (IRFP240P).
 
Thankyou Guys


Yes its 50W 40kHz Ultrasonic Transducer. How much voltage do they run at?

Transducer
Ultrasonic Transducer 40KHz

Driver
50W - Ultrasonic Transducer Drive PCB Assembly

I tried removing 9V battery, DMM(Extech 430) is kind of shaken at moment. Sometime works fine, sometimes starts flickering screen and unusable. Opened it and everything looks fine from outside.

DMM should be designed to handle high frequency signals or even high voltage, don't show anything but don't die. Blow a fuse or something.
 
To get 50W from a piezo transducer I would guess many tens or hundreds of volts. Unfortunately the datasheet does not say. However, if you assume that the 50W is input to a series resistance of 20 ohms then this means 1.6A. The transducer will look main like a capacitor (4000pF) so that means a voltage of around 1600V. I have no idea if this is correct. However, 1600V of 40kHz AC is enough to blow a normal DMM.
 
If it was autoranging it might have been cooked - with fixed ranges on a high voltage setting multimeters are very robust indeed as there is a 9meg resistor in series or similar. But high frequency high voltage will couple capacitively too, but that's usually not an issue till RF frequencies.


An unloaded ultrasound driver amp will generate much higher voltages than one loaded with a piezo driver - in fact it may not be rated for no-load use, it might be a tuned amplifier with inductor.
 
Thankyou.


So is there any noob proof DMM which one can use on any type of signal one doesn't fully understand(under 10 amp, but high voltage - not the power transmission line :D ). DMM may show OL but not take damage?


Out of curiosity, what device can i use on Ultrasonic Transducer driver board to measure its output signal voltage and current while connected to Transducer?
 
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Thankyou.


So is there any noob proof DMM which one can use on any type of signal one doesn't fully understand(under 10 amp, but high voltage - not the power transmission line :D ). DMM may show OL but not take damage?


Out of curiosity, what device can i use on Ultrasonic Transducer driver board to measure its output signal voltage and current while connected to Transducer?

Without knowing your exact voltages it is hard to say. The appropriate and safest method is probably a HV differential scope probe. Most handheld DMMs are CAT III 1kV rated at best.
 
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No instrument can be totally noob proof. People will always come up with new ways to break things. As a general rule, before you measure something you should have at least a vague idea of what the result is likely to be. If not, there may be little point in measuring because even if the measurement is successful all you then have is a number but perhaps no idea how to interpret it.
 
No instrument can be totally noob proof. People will always come up with new ways to break things. As a general rule, before you measure something you should have at least a vague idea of what the result is likely to be. If not, there may be little point in measuring because even if the measurement is successful all you then have is a number but perhaps no idea how to interpret it.

Thankyou.

My intent was to find out if ultrasonic driver board output voltage is safe or not. It runs on AC 220 V but I didn't/don't know output voltage level of driver board. I made Ultrasonic cleaner using parts but wanted to make sure no dangerous parts are exposed. Example 2.5mmsq wire is soldered to ultrasonic transducer. I wanted to cover it if its dangerous.
 
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