The kinematic viscosity of a fluid is calculated as the dynamic viscosity divided by the density at the same temperature.

Figure 1. SME-TRD with SRD probe

1. How is the kinematic viscosity measured by Rheonics SRD?

The Rheonics SRD measures viscosity and density using a balanced torsional resonator, one end of which is immersed in the fluid of interest. This resonator vibrates torsionally at a given resonant frequency affected by the fluid’s density and has a damping as a result of the fluid’s viscosity. The sensor electronics calculate the dynamic viscosity and density based on these measurements. 

The SRD outputs the kinematic viscosity dividing the dynamic viscosity by the fluid’s measured density. It does not require any external input or customer' action to enable the readings. 

2. Kinematic viscosity output from SRD

The kinematic viscosity is given as parameter 3 of the sensor’s output readings. Review the complete output’s parameters here.

Through RCP Software

Rheonics Control Panel software (RCP) is used, but not limited, to monitor, configure and log measurements from the SRD sensor in a PC through Ethernet or USB connection. 

To plot kinematic viscosity on the RCP Measurement tab, do as follows:

  1. Use the Settings Tab, Communication box to connect the sensor to the RCP.
  2. Select the Kin. Visc. parameter in the Graph Settings. 
  3. The RCP uses cSt (centiStoke) units for Kinematic Viscosity. 

Figure 2. Enable Kinematic Viscosity in RCP

4. Go to Measurement Tab. Check the Kinematic Viscosity is being displayed (Kin. Visc.).

5.Make sure the sensor led status is green showing Running and E00 (no errors).

Figure 3. Kinematic Viscosity plots in RCP

Through Fieldbus communication protocols

Fieldbus protocols in the sensor are ordered by user upon request. To get the kinematic viscosity through any protocol (i.e. Profinet, Ethernet/IP, HART, etc.) review the manuals for each protocol here. 

Through SME-TRD display

To enable the kinematic viscosity value in the SME-TRD display follow next steps.

1. Go to Communication Tab and select Kinematic Visc. from the parameter list. This can be added in any of the three lines.

Figure 4. Enable Kinematic Viscosity in SME-TRD display

Units to be displayed in the SME-TRD display should be defined prior to order. Contact Rheonics Support Team if change in units is required.

3. What Units are available as output for kinematic viscosity from Rheonics SRD?

Below is the list of units mostly used for the kinematic viscosity of fluids. All are available with Rheonics SRD sensor and can be specified upon sensor order.


Description: This is the SI (International System of Units) standard unit for kinematic viscosity. 

Importance: This is the basic unit for kinematic viscosity (length squared divided by time) obtained from dividing the dynamic viscosity [Pa. s = 1 kg/m·s] and the density of a fluid [kg/m3]. It is the main unit used in research and development, scientific publications, and specialized technical applications. 

St - Stoke:

Description: Unit from CGS (centimetre–gram–second system of units) system. This unit is equal to 10⁻⁴ m²/s.

Importance: Named after George Stokes due to his research and job related to fluid’s mechanics and viscosity. Less common unit but can be found in older scientific publications and specialized applications.

cSt - CentiStoke: 

Description: Reduced unit from a Stoke. This is equal to 10⁻² Stokes or 10⁻⁶ m²/s

Importance: Commonly used in lubricants, automotive, oil and gas industries.

4. Why is it important to measure kinematic viscosity?

Kinematic viscosity indicates the fluid’s internal resistance to flow under its gravity. 

It is used mostly in, but not limited to, automotive, chemical, oil and gas industries. The kinematic viscosity is of relevance since it directly influences the automation quality. It can be related to the lubrication capabilities of a fluid, lubrican degradation, fuel efficiency, heat transfer rate in heat exchangers, etc.

Kinematic viscosity is also relevant for pumping systems selection, designer should know the kinematic viscosity at the min and max temperature conditions. High viscosity fluids will reduce the performance of pumps and increase the power requirements.

Kinematic viscosity is also relevant for pumping systems selection, designer should know the kinematic viscosity of the fluid to design the pump for highest efficiency. During operation, pumping characteristics can be adapted using real-time kinematic viscosity from the SRD to achieve highest efficiency. This allows pumps to be adaptable to changing fluids. Given energy consumption for pumps is the largest cost factor for pumping, operating the pumps at maximum efficiency cuts operating costs significantly.


[1]: Viscosity - Wikipedia 

[2]: rheonics SRD Density Meter inline   

[3]: Calibration verification procedure for inline viscometer and density meter  

[4]: Real-time engine oil condition monitoring » rheonics :: viscometer and density meter