Rheonics resonators are influenced by fluids in two ways:
The denser the fluid, the lower the resonant frequency. A denser fluid increases the mass loading of the resonator.
The more viscous the fluid, the broader and smaller the resonant peak of the sensor, Friction between the resonator and the fluid increases its damping.
The measurable properties of the resonator – its resonant frequency and damping – are both influenced by the properties of the fluid.
Shape of the resonator - determines the measurements
The shape of the resonator determines the way in which it responds to the fluid in which it is immersed. Rheonics’ SRV series of sensors are cylindrical, vibrating parallel to their own surfaces. They are influenced primarily by shearing forces, and are therefore relatively insensitive to mass loading effects. They are useful for measuring viscosity but not density.
Rheonics’ DV series of sensors have flattened end masses. Parts of their surfaces vibrate parallel to themselves and therefore shear the fluid. These contribute to the damping of the resonator and determine its sensitivity to viscosity. Other parts of the surface vibrate perpendicular to themselves, and therefore displace the fluid. This results in mass loading of the sensor, and determines its sensitivity to density.
The Balanced Resonator Advantage
Resonant sensors fall into two further geometric categories – balanced and unbalanced.
A tuning fork is a typical balanced resonator. Its two tines vibrate in opposite directions, balancing out bending forces that are otherwise transmitted to the sensor’s mounting.
A single transversely vibrating beam ( a “half tuning fork” ) by comparison, exerts large reaction forces on its mounting, resulting in large energy loss compared to the balanced tuning fork geometry.
A vibrating wire, on the other hand, is an unbalanced resonator, and exerts substantial forces on its mounting structures.
In order to reduce the effects of mounting conditions on unbalanced resonators, their anchors must be relative large and massive compared to the size of the actual sensing element.
Insensitive to mounting conditions
Rheonics’ sensors use balanced resonators (patents pending). The DV series uses a torsional tuning fork configuration, in which the two tines twist in opposite directions. The SRV series uses a unique patented coaxial resonator, in which the two ends of the sensor twist in opposite directions, cancelling out reaction torques on their mounting.
Get to know the technology
Schedule a conversation
with Joe Goodbread
8406 Winterthur, Switzerland
Tel: +41 52 511 3200
3 Sugar Creek Center Blvd, Ste 100
Sugar Land, TX, 77478
Tel: +1 832 998 0606