|Impedance:||around 50 ohm
|Cable:||RG174 (RG188 for LTH)
|Case material:||stainless steel (316L)
How to select the wright probe for your application
The first thing to do is to select the highest emitting frequency as possible, as the highest emitting frequency gives the best
spatial resolution. But unfortunately, the highest emitting frequency can often not the best choice, because:
- The maximum velocity and the maximum depth are linked. This link is given by the equation.
You can use this equation, but an easy way is to use the UDOP software.
After the selection of the default parameters (which enables the assisted mode), select an emitting frequency and the maximum
depth. The velocity button will give you the maximum measurable velocity.
- The attenuation of the ultrasonic waves depends on their frequency. The ultrasonic waves can also be attenuated and/or reflected from interfaces
(walls). Most liquids, like water or liquid metal, do not attenuate significantly the ultrasonic waves, but some, like oil,
can avoid the use of a high emitting frequency. Also the attenuation coefficient of most plastics increases with the frequency.
When the ultrasonic frequency is defined, the next step is to select the piezo diameter. The following points must be taken into account:
- A small diameter means a less sensible probe;
- A large diameter means a less diverging beam, which implies a smaller sampling volume;
- A large diameter means a longer near field, which means that the measurememt close to the probe will be affected by the oscillation
of the ultrasonic pressure field.
Again, the UDOP software helps in the selection of the probe, as it allows a visualisation of the width of the ultrasonic beam versus
depth for almost all avaialble transducers. In simulation mode (when no instrument is connected to the PC), the "tool" menu contains a
line named "Measure US field". After going in this menu, you can select a data file from a list of available measures ("Recall from file").
The last step is to select a case and a temperature range. The case has no influence on the ultrasonic properties of the probe.
Its selection should be based on the available space.
If the probe must be used in a high magnetic field environment (few Tesla) it is recommended to use the option "Deported matching impedance".
The reason comes from the fact that a high magnetic field may influence the inductive components used to match the electrical impedance
of the piezo to the instrument. For such a probe the electrical matching components are located in a small stainless steel
tube placed close to the BNC connector of the probe.