measure quartz crystal oscillator value with simple circuit using oscilloscope

[ali handro]

hi everyone,
I am new at forum and looking for a answer
I'm googling but I cant undertand
please help me
my question is
I have a quartz crystal oscillator 10mhz and at-cut
and I want to measure it's value with oscilloscope.
how can I drive ocillator sine or square wave with the simplest circuit and how can I connect oscilloscope
thanx for reply
Dr. Ali Handro

 

[albbg]

Have a look to:

**broken link removed**

you have to use only the oscillator section that is IC1A and IC2B (74HC04) with, of course, the 10nF, 39pF, 68pF and 47nF capacitors and the two 1k resistors. Then connect the probe of the oscilloscope to pin4 of the IC1.
Changing the 39pF variable capacitor with a 39 pF fixed capacitor the circuit should works properly.

 

[sky_123]

As a doctor, you should know the importance of capitalization (or the lack of it), for example,
if you're a doctor of medicine you may know that 10mg of medicine means 10 milli-grams. Presume you
meant 10 Mega-Hertz, and not 10 milli-Hertz?
If you know it's frequency is 10mHz or MHz, then what benefit is there to measuring with a device that
will possibly be less accurate?

have a quartz crystal oscillator

I presume you meant you have a crystal, and not an oscillator.
You need to construct an oscillator circuit as shown here.

 

[aaaahanda]

@albbg thank you for your post, can I use such as this (https://en.wikipedia.org/wiki/File:Pierce_oscillator.svg) simpler then yours, is it possible
@sky_123 I know importance of capitalization ofcourse, I mean Mhz sorry. I found some publications about immunosensor made with this quartz crystal. according to researcher crystal's (seperate from its case) frequency changes with binding microorganism on it. yes exactly I want make ocillator circuit work with this crytal.

 

[RCinFLA]

You can create a circuit that measures the phase and amplitude across a 100 ohm resistor in series with the crystal. A 56 ohm resistor should shunt the generator input to provide termination for the generator. You must also measure or project the shunt capacitance of the crystal and cancel it out with an inductor across the crystal.

Normally a vector voltmeter would be used to measure the voltage and phase at either end of 100 ohm series resistor to ground. You could use an oscilloscope but levels necessary to read amplitude on a scope may be too high for the crystal. Too high a drive level may damage the crystal.

If you correctly cancel out the shunt capacitance of the crystal you will measure the amplitude and calculated current at zero phase crossing, along with the series resonant frequency of the crystal. You then install a series cap, about a 20 pF for a 10 MHz AT cut crystal, and adjust the freq to achieve zero phase resonance again. You now have all the info to calculate Lm and Cm of the crystal. The change in series resonance with the known value 20 pF predicts what the Lm and Cm values must be to get the measure frequency shift.

The shunt capacitance of crystal can be measured at low frequency. For a 10 MHz AT cut it will likely be in 4 to 6 pF range. If you only have a DVM with capacitance metering, use a known 5 pF cap to help calibrate the DVM reading, as the DVM may not be very accurate on its own at 5 pF range.

 

[aaaahanda]

@RCinFLA thank you for your post. I'm trying to understand basics of this circuits and I hope find a minimal circuit diagram well defined work for this purpose.

more clear for me thanx :shock::razz::!:

 

[krp]

Google "G3UUR crystal"; you will find a lot of references to this method of characterising crystals.

It's an oscillator that uses switchable capacitance; a frequency counter is required.

This is the fundamental circuit;

https://i45.tinypic.com/23icp7a.jpg

You can build it to look like my version;

https://i49.tinypic.com/zmxnjm.jpg

This will give you all the motional parameters of the crystals you are testing.

 

[aaaahanda]

it is more clear for me , thanx again, I will try this

- - - Updated - - -

hey krp thank you for your post. I am searching something definitely like this, many thanx again.

 

[albbg]

@albbg thank you for your post, can I use such as this (https://en.wikipedia.org/wiki/File:Pierce_oscillator.svg) simpler then yours, is it possible

Yes, in principle you can use it also and should works. However even if 10 MHz is not a high frequency, put care in building the circuit and use wires as short as possible to connect the various components, otherwise it could not oscillate. The use of two amplifier as in the schamtic I posted should assure a little bit more margin to assure the oscillation. However I didn't test that circuit.
Let's know if you succeded in your experiment.