How to check if Rheonics sensor needs calibration? : Rheonics Support

TABLE OF CONTENTS

1. What products are involved?
2. How do we know if our Rheonics sensor needs calibration?
3. Rheonics vibrational sensor technology
4. What are the df and fres?
5. Quick verification of SRV calibration in air
6. Quick verification of SRD calibration in air
7. Accepted fres and df air values for the SRV and SRD
8. What to do if the air values are non-zero?
9. Always check the infosheet
10. References

1. What products are involved?

Rheonics SRV viscometer and SRD density-viscosity meter.

2. How do we know if our Rheonics sensor needs calibration?

Rheonics sensors are factory-calibrated and do not require re-calibration in the field. However, periodic verification or re-calibration may be necessary to meet regulatory requirements (e.g., ISO, FDA).

Note: Performing a periodic air check is a simple method to determine if the sensor requires calibration.

3. Rheonics vibrational sensor technology

The SRV and SRD are based on a balanced torsional resonator (BTR), unaffected by external vibrations. Fluid properties sensors based on vibrating resonators fall into two categories: density and viscosity measurement. A resonant structure immersed in a fluid is influenced in two ways: Damping and resonant frequency.

More information about the operation principle can be found here Rheonics vibrational sensor technology: demystified

4. What are the df and fres?

The damping(df) refers to the process by which energy is dissipated in a system. It is increased by viscous dissipation in the fluid. The friction of the fluid being sheared by its movement carries energy away from the resonator. This energy dissipated by the fluid increases the damping of the resonator.

The resonant frequency(fres) is the frequency it would oscillate at if excited by an impulsive force. It is depressed by mass loading of the resonator by the fluid. Its apparent mass is increased by the fluid it moves due to its own motion. This increased apparent mass decreases the frequency of the resonator.

fres and df can be observed in the RCP software on the “Measurement” tab.

Figure 1. RCP software showing df and fres in air

This “air check” is useful for quickly verifying the SRV and SRD calibration and baseline. The sensor does not use moving parts, so if readings in the air are zero, there is no way that the factory calibration has been affected, or any long-term drift has occurred. Figure 2 above shows the values for fres and df which are 2 parameters that are important to validate the correct operation of the probe.

5. Quick verification of SRV calibration in air

Figure 2. SME-TRD with SRV probe

Remove the SRV from the process
Clean the SRV if the probe is dirty
Leave the SRV in the air, and verify that nothing is in contact with the sensing element
Verify the viscosity reading is zero. This can be checked through the SME-TRD display, RCP software, or any external integration system (e.g. PLC).

6. Quick verification of SRD calibration in air

Figure 3. SME-TRD with SRD probe

Remove the SRD from the process
Clean the SRD if the probe is dirty
Leave the SRD in the air, and verify that nothing is in contact with the sensing element
Verify the viscosity and density readings are zero. This can be checked through the SME-TRD display, RCP software, or any external integration system (e.g. PLC).

7. Accepted fres and df air values for the SRV and SRD

Below is a table with the accepted fres and df when the probe is in the air, a correct operative probe will have.

Sensor type	SRV	SRD
fres[Hz]	7400	7650
df[Hz]	1	1
tolerance fres[Hz]	check infosheet provided by Rheonics	check infosheet provided by Rheonics
tolerance df[Hz]	check infosheet provided by Rheonics	check infosheet provided by Rheonics

Table 1. Accepted fres and df values for the SRV and SRD

8. What to do if the air values are non-zero?

If the values are non-zero, the next step is to use the scaling tab to baseline the 0 cP. Deposits on the probe could cause drift, so it’s important to clean the probe. If the value reads zero after cleaning, the issue is resolved.

If it remains non-zero, the scaling tab can correct the drift. open the RCP software and go to the “Scaling tab” in expert mode.

8.1. This offset can be observed in the “Measurement tab” where viscosity is a non-zero value.

Figure 4. Viscosity reading with offset.

8.2. Using the “Scaling tab” to fix the viscosity offset.

Check this support article for more information: Scaling: How to create correlation between lab and inline measurements?

Figure 5. Scaling tab, setting correct viscosity

8.3. Once properly scaled the viscosity output goes down to zero.

Figure 6. Scaled viscosity output when non-zero viscosity reading

9. Always check the infosheet

Rheonics provided an infosheet with the sensor, where users can input values to verify that the sensor is within the operational range when in air. An example of what can be observed in the infosheet can be found in Figure 7.

Figure 7. Infosheet information.

If we calculate the air frequency and damping values and compare them with the values observed in the RCP software (Figure 2), a correctly functioning sensor should fall within this range.