1. Fundamentals
1.1. What is accuracy?
Accuracy is generally defined by the deviation of the measured value vs. the true value of the property being measured.
Sensor accuracy can be affected by various factors such as calibration, environmental conditions, and the sensor. It shows how closely the sensor's measurement matches the true value of the property being measured.
In Figure 1, we can understand accuracy as always hitting the target close to the center but at different zones.
Figure 1. What is accuracy?
1.2. What is precision?
The variation that exists between multiple measurements of the same parameter of the same characteristic. A highly precise measurement indicates that the measurements are very close to each other and have minimal variation.
In Figure 2, we are hitting the target around the same area but far from the center.
Figure 2. What is precision?
1.3. What is reproducibility?
Reproducibility is when different operators produce the same measurement result with the same instrument multiple times under different conditions. Well-planned setups with controls enhance consistency and detailed protocols aid replication.
Example:
Operators 1, 2, and 3 measure the same fluid 4 times with the same sensor.
The variation in average measurements between Operators 1 and 2 is much less than the variation between Operators 1 and 3. Therefore, the gage's reproducibility is too low.
14. What is repeatability?
The repeatability of a sensor refers to its ability to produce the same measurement results under the same conditions multiple times. Therefore, if the same measurement is taken several times with the same sensor, the results should be consistent.
2. What is the relevance of measuring devices?
Accurate and precise measurements with good repeatability and reproducibility are essential for ensuring reliable data and outcomes in various fields. They form the basis for informed decision-making, quality control, innovation, and scientific progress. Efforts to improve measurement systems, reduce errors, and enhance the consistency of measurements contribute to advancements across manufacturing, engineering, and scientific domains.
3. Advantages of Rheonics inline viscometers and density meters to ensure tight process control.
Rheonics builds truly inline process instruments, to achieve that we ensure that the reproducibility and repeatability of measurements are exceptional - generally better than 0.1-1% for the SRV viscosity meter.
Rheonics runs calibration standards with NIST traceable viscosity and density standards at different times under similar conditions, ensuring each probe is evaluated for reliable and accurate measurements.
Consistency of results is essential to the success of customers' quality control programs, as it ensures that all measurements are reliable and accurate. The repeatability of measurement also allows for the easy comparison of results across different batches.
Furthermore, the repeatability of measurement allows for quick and easy troubleshooting when a process fails to meet expectations.
Based on Rheonics' proven gated phase-locked loop technology, the electronics unit offers stable, repeatable, and high-accuracy readings over the full range of specified temperatures and fluid properties.
SRV and SRD are operator-independent and measured in real-time.
Temperature effects can be compensated in real-time.
4. SRV and SRD expectations on Repeatability and Reproducibility
4.1. SRV inline process viscometer Probe R&R test setup
 Figure 6. Repeatability test done in the SRV sensor. | Test 1-Sensor A: Time:10:00AM Viscosity: 40.20 cP Temperature: 29.01 °C Test 2-Sensor A: Time:10:30AM Viscosity: 40.50 cP Temperature: 29.04 °C |
Same sensor, same fluid, agreement of measurements at two different times. Related to measurement stability | |
 Figure 7. Reproducibility test done in the SRV sensor. | Test 1-Sensor A: Time:10:00AM Viscosity: 40.20 cP Temperature: 29.01 °C Test 2-Sensor B: Time:10:30AM Viscosity: 40.32 cP Temperature: 29.06 °C |
Agreement between two sensors, different locations, different times, same fluid. | |
4.2. SRD Probe R&R test setup
 Figure 8. Repeatability test is done in the SRD sensor.
| Test 1-Sensor A: Time:10:00AM Viscosity: 154.01 cP Density: 0.8271 g/cc Temperature: 40.09 °C Test 2-Sensor A: Time:10:30AM Viscosity: 154.32 cP Density: 0.8273 g/cc Temperature: 40.08 °C |
| Same sensor, same fluid, agreement of measurements at two different times. Related to measurement stability | |
 Figure 9. Reproducibility test done in the SRD sensor. | Test 1-Sensor A: Time:10:00AM Viscosity: 154.01 cP Density: 0.8271 g/cc Temperature: 40.08 °C Test 2-Sensor B: Time:3:45PM Viscosity: 154.60 cP Density: 0.8278 g/cc Temperature: 40.05 °C |
Agreement between two sensors, different locations, different times, same fluid. | |
Do you want to know more about accuracy and viscosity? Check this support article: The myth of accuracy for inline viscosity measurements |
