A practical checklist for repeatable viscosity measurements

When two viscosity results disagree, first check whether they describe the same test. A value without its setup is difficult to investigate. A short, consistent record is often more useful than a long spreadsheet of numbers with missing conditions.

Define preparation before collecting results

Sample history matters. Storage, mixing, loading and rest can affect the state of a structured sample. Anton Paar's guidance emphasizes consistent preparation and the avoidance of entrained air when comparing measurements. [1]

Our suggested record has three parts: sample identity, preparation record and measurement record. Assign each test a unique ID so that a photograph, observation or follow-up measurement can be linked to it. If the laboratory changes its preparation procedure, record a new method revision instead of silently replacing the old instructions.

Use a record another operator can follow

Adapt this checklist to your instrument manual and approved method:

• Sample: name, batch, sampling location, collection time and operator.
• Preparation: storage history, mixing procedure, loading and resting interval.
• Setup: instrument ID, spindle ID, container and fill quantity.
• Conditions: sample temperature, speed, measurement duration and reading time.
• Result: viscosity, units, torque indication if available, and any instrument warning.
• Observations: bubbles, separation, visible damage, unusual appearance or deviations from the method.

Leave a field explicitly marked “not recorded” if historical information is unavailable. Do not substitute a guessed value. This makes it clear which comparisons are strong and which require a repeat test.

Keep different test conditions separate

ASTM D2196 addresses rotational measurements of non-Newtonian materials, including apparent viscosity and evaluations involving changing conditions. This is one reason to retain the measurement conditions alongside each reported number. [2]

For an internal report, use one row per condition, with a separate field for the method revision. Agree the acceptance limits with the responsible laboratory team before testing production batches. A new instrument or changed setup should prompt a comparison study, rather than an automatic assumption that historical limits transfer unchanged.

Investigate one change at a time

When a reading is unexpected, preserve the original record. Our suggested investigation log lists the suspected cause, the single change made, the reason for that change and the result. This avoids a situation in which a new spindle, temperature and preparation procedure all produce a different reading without revealing which change mattered.

For support on a SNB-2 or HADV-2, send the model and setup details with the record. The current SNB-2 listing includes Nos. 1–4 spindles; HADV-2 lists R2–R7 as standard and R1 as optional. Use the actual identifiers in your log. These are different configurations, so a label such as “spindle 2” needs the instrument context.

Once the cause is understood, update the method and training record together. The aim is a procedure that another operator can reproduce, with enough evidence to explain a result later.