The SRV sensor measures the viscous damping caused by the fluid, this damping is directly proportional to the product of the density and dynamic viscosity of the fluid. Visit the Rheonics Operating Principle Whitepaper for more information.

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 SRV probe

1. How is the kinematic viscosity calculated by Rheonics SRV?

The SRV sensor probe measures the product of viscosity and density of a fluid (SRV Viscosity), the sensor outputs the dynamic viscosity (SRV Dyn. Visc.) of the fluid dividing the previous product by the density. This density is set to a constant value of 1.0 g/cc (1000 kg/m³) by default.

Kinematic viscosity is shown as output parameter 3 (see complete parameter list here) and is calculated by dividing the dynamic viscosity by the density, equivalent to the product divided by density squared.

If density differs from 1.0 g/cc, the sensor supports input of a different constant value or temperature-dependent density so dynamic and kinematic viscosity values can be estimated more accurately and directly output by the sensor over digital and analog channels. Review more information here.

2. Kinematic viscosity output from SRV

Through RCP Software

Rheonics Control Panel software (RCP) is used, but not limited, to monitoring, configuring, and logging measurements from the SRV sensor to a PC through Ethernet or USB connection.

To plot kinematic viscosity on the RCP Measurement tab, follow the steps below:

  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 the Measurement Tab. Check the Kinematic Viscosity is displayed (Kin. Visc.) as the Y-axis.

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

Figure 3. Kinematic Viscosity plots in RCP

            6. On the Service Tab, the Density can be set density as constant or a temperature-dependent value.

Figure 4. Density configuration for SRV through RCP

Through Fieldbus communication protocols

Fieldbus protocols in the sensor are ordered by the user upon request. To get the kinematic viscosity through any protocol (i.e. Modbus, 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 the next steps.

            1. Go to the Communication Tab, in the LCD Display box select Kinematic Visc. 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 before the order. Contact the Rheonics Support Team if a change in units is required.

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

Below is the list of units mostly used for the kinematic viscosity of fluids. All are available with Rheonics SRV sensors 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 (centimeter–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 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, lubricant degradation, fuel efficiency, heat transfer rate in heat exchangers, etc.

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


[1]: Viscosity - Wikipedia

[2]: SRV Rheonics 

[3]: Set density input to SRV inline viscometer for dynamic viscosity and kinematic viscosity outputs  

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

[5]: Real-time engine oil condition monitoring - Rheonics