How Can I Check a Vortex Flowmeter?

What does the instrument manufacturer have to say? After all, it is still under warranty, isn't it?

I understood you correctly that you want to know the pressure value of your Vortex flowmeter and you are confused because you are reading the value in mm of water from the Vortex while you are measuring the Oxygen? if that is a case then you should not do any conversion as a standard measurement of most equipments would use mm of water, Pa, Bar or psi as a pressure difference so if your equipment only give mm of water and you want to know Pa for instance then you just convert the mm water to Pa by x 9.81 and that will give you pressure value in Pa

It's a flowmeter, not a pressure sensor. Flow is related to the frequency of the vortex street coming off the back of the sensor.

I would simply call up the mfg of the vortex sensor and ask for their assistance.

Usually sensors set up for water will not work well for gas as the the sensitivity of the vortex sensing equipment in the sensor will not be at the proper gain.

About Vortex Sensors:

Need to measure a gas get a sensor set up for gas.

Need to measure a liquid get a sensor set up for liquid.

Anything else is using the incorrect tool for the job.

Cheers,
Ducdude

thank you very much for all your comments, I've been looking for technical documentation and now it´s getting clearer.

the frequency of vortex shedding is proportional to the volume flow.

Pulses = K Factor * unit volume

The K-factor is Used as a proportional constant:

Within the application limits of the device, the K-factor depends only on the geometry of the device. It is independent of the fluid velocity and the fluid density and viscosity properties. In this way, the K-factor is independent of the type also of matter that is to be measured, regardless of Whether this is steam, gas orliquid

Consequently I can use the calibration with water to obtain oxygen flowrate, after applying the gas density in the conditions of pressure and temperature will get mass flow, I have to take into account that the Reynolds number is adequate for the range of measurement I need