Testing componets

[studentguy]

How could i test a crystal oscialltor in-circuit?
its a xco in a pierce type oscillator, all i have access to is the crystal and thats all i need to test for correct frequency operation.

could i just use it like a filter and it should pass the desired tone easily?

 

[Gary B]

I would just apply power and look at its output with either a scope having a calibrated time base or a frequency counter. If it is a really fussy application, might go so far as to use a spectrum analyzer but, I can’t think of an application off hand where it would be justified.

 

[MikeMl]

Why not just power the circuit, and see if it oscillates at the right frequency? If you are worried about loading it with a scope probe, you can just listen for it on a shortwave receiver from across the room.

 

[studentguy]

i cant power the oscillator circuit, i can only power and test the crystal.

Since the crystal oscillates at a certin frequency - would't it , in a way, act as a bandpass fiter that i could test for?

 

[MrAl]

Hi,

What kind of accuracy are you looking for?

 

[JimB]

We need to be clear about the terminology here.

Crystal - a passive device made from quartz (usually) which exhibits the characteristics of a very high Q tuned LC circuit.
Usually enclosed in a sealed metal can with two pins or wires for connection to a circuit.

Crystal oscillator - either an active device with a crystal and an amplifier, when a DC supply is applied to two of the pins, the amplifier will oscillate at a frequency determined by the crystal.
Usually enclosed in a sealed metal can with four pins or wires to connect to the external circuit.
The four wires are: 0v, +5V, output, the fourth wire is often not connected but may sometimes be used as an enable/disable signal to start/stop the oscillator.

Since the crystal oscillates at a certin frequency - would't it , in a way, act as a bandpass fiter that i could test for?

If the device is a crystal rather than a crystal oscillator then yes you could test the crystal to find its resonant frequency, you will need a signal generator with very fine frequency control, a frequency meter if the sig gen does not have a built-in counter, a suitable test jig to hold the crystal and provide defined circuit conditions, and connections for the test equipment, and some means of measuring the output voltage from the test jig, an oscilloscope or RF voltmeter would do.

i can only power and test the crystal

You cannot "power" a crystal, a crystal oscillator yes, but not a crystal.

JimB

 

[studentguy]

Really guys thank you.

It is a crystal -piezoelectric 100k hz frequency.

So,
If I was to sweep signals through the pins with a function generator, can I test for voltage and see where the highest response is?
And thereby Testing for the center frequency?

 

[JimB]

If I was to sweep signals through the pins with a function generator, can I test for voltage and see where the highest response is?
And thereby Testing for the center frequency?

In theory yes, but in practice your function generator probably does not have sufficiently fine control of the frequency to make meaningfull measurements.
But dont just take my word for it, try it and see what happens.
And anopther thing, dont overdrive the crystal or it will break, keep the generator output less than 1 volt.
(Dont ask me how I know!)

JimB

 

[studentguy]

Thank you!

can you recommend any other ways to test it?

Yea i was looking at the schematic - max power 1uW