CATEGORY BENEFITS
What is a glass Capillary Viscometer?
A glass capillary viscometer measures viscosity by recording the time required for a liquid to flow through a precisely defined glass capillary under gravity at a controlled temperature. The measured flow time is used to calculate the kinematic viscosity using the calibrated viscometer constant for the specific viscometer used. This simple but highly accurate principle makes glass viscometers the reference method for viscosity measurement.
How Glass Capillary Viscometers Work
The accuracy of a glass viscometer depends on three critical factors: Capillary geometry – manufactured to tight tolerances, Temperature control – viscosity is highly temperature-dependent, Calibration traceability – ensuring reliable conversion from flow time to viscosity.When these factors are controlled, glass capillary viscometers deliver highly repeatable and comparable results across laboratories.
Best flow properties
Any irregularities in the interior surface of the glass may cause turbulence in the sample movement leading to irregular flow time determinations. This will show up as a difference between the first and the second flow time when measuring viscosity. For the best chance of getting the second flow time to agree, choose a PSL Rheotek Viscometer to measure viscosity.
Quality materials
All PSL Rheotek Capillary Viscometers are made from low thermal expansion borosilicate glass tubing.
Made in the UK
We have a complete in-house production capacity for all our products in United Kingdom We serve laboratories all over the world from our facility in Essex.
Measuring Different Liquids
For measuring transparent liquids, we recommend the ASTM Ubbelohde viscometer. The constant of this viscometer is temperature independent. Designed with an air arm, the ASTM Ubbelohde Viscometers return accurate results using an approximate quantity of sample. For measuring opaque liquids, we recommend the U-Tube reverse flow viscometer.
Certified at the highest level
All glass viscometers from PSL Rheotek are supplied complete with a UKAS (ISO 17025) Certificate of calibration, laboratory No. 0247. All certificates are fully traceable to the Master Viscometer Scale held at PSL Rheotek. All viscometers are calibrated directly against Master References in the on-site laboratory.
High Performance Glass Viscometers
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FAQ
You asked, we answered
What is a glass capillary viscometer?
A laboratory instrument that measures kinematic viscosity based on the time a liquid flows through a calibrated glass capillary.
Why is Temperature control important?
Small temperature changes cause significant viscosity variation, which is why controlled baths are required.
How often should glass viscometers be recalibrated?
Recalibration is typically recommended every two years or after any mechanical damage. Accuracy of measurement can always be monitored by measuring a certified reference standard.
What if I just measure the sample at room temperature?
Then the result will represent only an approximation. At room temperature, it is unlikely that repeatable flow times will be achieved.
Do I need to use a thermometer?
Yes, a liquid in glass or digital thermometer is essential to verify the bath temperature. The thermometer should conform to the specifications set out in a test method (e.g. ASTM D445, IP71, ISO3104) and be calibrated e.g. by an ISO 17025 laboratory.
Why do I need a chiller for the bath, when running it at 25 degrees C?
The tolerance band for temperature stability is typically +/- 0.02 degrees C. To achieve this level of temperature stability, the bath heaters are not sufficient when the test temperature is close to ambient. Even with modern high tech heaters, there will be temperature spikes, which exceed +/- 0.02 degrees C. Applying external cooling will counter these temperature spikes.
Why should I buy a PSL Rheotek branded viscometer?
The flow properties of the viscometer are determined by the interior surface of the glass. This should also be as smooth as possible in order to allow the sample to flow with the minimum of turbulence. Look out for smooth transitions between the different parts of the viscometer tube, when trying to assess the quality of a viscometer tube. At Poulten Selfe & Lee Limited, we take pride in manufacturing viscometers with superior flow properties.
I want to save money, can you sell me an uncalibrated viscometer?
Yes, we can. However, you will need to perform a calibration yourself, before you can use the viscometer tube. To perform the calibration, you will need to buy two viscosity reference standards from us and then conduct the calibration procedure as described in ASTM D446 or ISO 3105. Our preference is to sell you a capillary viscometer complete with an ISO 17025 certificate of calibration. This certificate will state the serial number of your tube as well as the viscometer constant of that specific tube to 4 significant figures. The calibrated viscometer is ready to use out of the box.
We have an audit coming up and have lost our calibration certificates, can you send us a replacement certificate?
Please contact us wia the contact form and provide us the serial number and the type of viscometer for possible reissue of certificates. If it is possible to reissue the certificate, we will send the replacement within 1-2 days. This service is chargeable.
CUSTOM SOLUTIONS
Searching for custom instrumentation for your unique requirements?
Each PSL Rheotek viscometer system is configured for the owner! A wide variety of international test method protocols are readily available in the software and company specific method protocols are also supported.
