Dear Norliana,

It seems that you have a pressure sensor which converts the variation in pressure dP in units of mmHg into frequency change df for an oscillator. The frequency change df here is in parts per million ppm. The ppm unit = df/ f0 where f0 if the nominal value of the frequency of the oscillator.

So, in order to determine df in Hzas you want , f0 must be known. Then df= ppm x f0/one million.

Best wishes

This might be usful for you : http://www.rfwireless-world.com/calculators/ppm-to-Hz-converter.html

Dear Abdelhalim Zekry,

How to find the nominal value of the frequency of the oscillator? Is it the same value to self resonance frequency? If I am referring to article I attach below, Is it the f0=196MHz?Thank You

Dear Norliana,

The resonance frequency f0 as zero pressure as in the paper is 95 MHz.

Best wishes.

Dear Abdelhalim Zekry,

As mentioned in the paper, the resonant frequency change in the range 95-103MHz for pressure range 0-50mmHg.

Hence, the sensitivity of sensor (in Hz/mmHg) =

(105 MHz - 95 MHz) / 50mmHg = 200kHz/mmHg.

But, in the paper, the sensitivity mentioned in ppm = 1580 ppm/mmHg.

I still can't understand how 1580ppm/mmHg = 200kHz/mmHg?

Could you please correct me if I'm wrong?

Thank You very much.

Dear Norliana,

Having 1580 ppm/mmHg= 1580 x 10^-6 xf0 Hz/ mmHg= 1580 x95 MHzx 10^-6= 150.1 KHz/mmHg. To obtain 200 KHz/mmHg, one must have ppm =(200/ 150.1) 1580= 2105 ppm.

Dear Norliana, there is some mistake: your calculations must be 95-103 MHz which gives 8MHz/ 50= 160 kHz/ mmHg not 200 as you calculated. This gives sensitivity in ppm as 160k/ 95 MHz= 1684 ppm/mmHg. You may get a better quantity by taking the the average resonance frequency rather than the initial value which is (95 + 103)/2= 198/2. It gives ppm = 150kHz/ 99MHz= 1616 ppm.

Best wishes

Thank You very much Prof Abdelhalim Zekry...and Tomer Noyhouzer ...for your respond.

I am sincerely grateful.

nicely explained by Abdelhalim Zekry