Viscometer / Viscosity Meter

You intend to buy a viscometer?
What basic questions should you ask yourself before buying – which points should you discuss with the seller? Below you may find a short list of possible questions and answers.

What kind of viscometer (handheld-, table- or built-in device) do you need?
Do you need a table - viscometer, which you might like to use once as a mobile device – or should it be really a portable (handheld) instrument?

If you would like to use the viscometer in the process for continuous measurement of the viscous liquid, then there are a few more questions on this topic for you to answer, besides these initial ones. In this case, it makes sense to talk to one of the technicians of PCE Instruments on the telephone or to arrange an appointment with our sales representative.

What is the application area / What type of liquid do you measure (Newtonian, non-Newtonian, dilatant, thixotropic or plastic)?
As you can see from the question, you want to measure viscosity in liquids and not in gases. When it goes about measurement in liquids, first, a distinction between Newtonian liquids (linear relationship) or non-Newtonian liquids (time- and shear velocity-dependent flow process) must be made. The shear velocity-dependent flow process is called dilatancy and the time-dependent flow process is referred to as thixotropy. Please, think at once what type of the fluid you are testing. In the case of a plastic flow, a limit value of the shear stress must first be exceeded, in order to start the flow process.

What measuring range / viscosity range do the liquids to be tested have?
You can assess the viscosity range of the liquid you are testing. There are tables in the literature which approximately depict the expected viscosities of different fluids. For example, further you can see the classification of some known substances:

Substance: Viscosity η (mPa•s) Petroleum: 0.65
Water (20 °C): 1
Engine oil (150 °C): 3
Blood (37 °C): 4 - 25
Engine oil (25 °C): 100
Honey: 104
Earth’s mantle: 1021 – 1023

Is a temperature measurement / temperature control on the viscometer necessary?
The dynamic viscosity generally decreases with the fluid’s temperature increase. Therefore, in order to obtain always comparable measured values, it is recommended to use a tempering bath. In this way, the same general conditions always prevail and you can expect a high comparability of the measured values. However, it also depends on the type of the fluid to be measured, whether a temperature control is needed or not. Also, the surrounding pressure is also a critical parameter, which influences the comparability of the measured values.

Which reproducibility of the results and / or which measuring accuracy should be achieved?
Often the viscometers with an accuracy of ± 3 % can be found in the production laboratories. In the chemical laboratory, however, viscometers with at least ± 2 % should be used. Most devices from PCE Instruments offer accuracies of ± 1 %.

Is service offered? What about the provision of spare parts, e.g. spindles?
Please, make sure that the supplier / manufacturer offers sufficient amount of spare parts for the viscometer, especially it applies to measuring spindles.

Are the viscometers calibratable? Is a recalibration offered?
When ordered for the first time, all PCE Instruments viscometers are adjusted and calibrated. In the case of a recalibration, calibration oils (silicone oils) are usually used. Then, the temperature dependence matters again. Therefore, the respective temperatures are also noted on the ISO calibration certificates. The calibration oils themselves must be stored according to the manufacturer's instructions (in the dark, in closed containers), since they are not long-term stable (half a year). In addition to the check by means of calibration oils, during a traceable calibration, the check of the rotational speed / torque and the mechanical condition (essentially the concentricity of the axis for the rotary viscometers) of the device and various attachments is mandatory. If during calibration a deviation from the values specified by the manufacturer occurs, a new adjustment of the viscometer must be carried out.

Viscometer is a simple-in-operation and relatively inexpensive device which is perfect for monitoring of the production process and quality control. Modern devices have been designed in such a way that they are able to measure a wide range of viscosity, and thus, may be applied for measuring viscosity of many fluid materials, for example, paints, chemical and pharmaceutical products and asphalt. Special measuring method allows detecting the viscosity of the components (binders or bitumen) the asphalt is made of, at different temperatures (though, the standard temperature for measurements is 60 °C) and levels of mass consolidation. Bitumen in combination with the mineral materials and other components should make a homogeneous mass, and this process is under permanent control, including temperature regime and time of mixing. Asphalt quality plays an incredibly important role and thus, this process is monitored from the very beginning to the end. The color, homogeneity, bitumen presence in the mixture, water amount and water resistance coefficient – all these parameters should meet the requirements. Viscometer is just one of the device applied for the full profound check of the final product, but it helps to detect the flows in the production and eliminate them immediately, by adjusting the amount of the components and conditions of the production process.

Vacuum capillary viscometer is the most widely applicable type of viscometers for asphalt measurements. To provide reliable and accurate measurement the device must comply with the standards (ASTM D 2171) and be calibrated. To determine the asphalt characteristics a few samples are usually takes from the mixture and carefully studied and checked in the laboratory, for this purpose laboratory model of viscometer is recommended.

Slurries find application in many branches of industries, that is why the knowledge about their flow behavior is so important. it is quite a challenging task, since they often have inhomogeneous structure. Rheological characteristics of the slurry suspensions give a better understanding of how the process should be organized, so that to make the desired final product or process flowless. Slurries have got a number of solid parts (sometimes of different size), various additives which, if not considered, may affect the viscosity and flow tremendously. Besides, temperature and other factors also have their own influence on the fluid, and therefore it is even more important to study the character of the liquid in use. For example, it may be important for choosing the correct pipeline, if it goes about mining or industry.

Depending on the type of slurry (which may contain sand particles, cement, clay and many others), different methods of viscosity measurements may be selected.

In fact, both, rheometer and viscometer (rotational and tube) can be applied for slurry measurements, but the use of the latter makes more sense, since it is easier in operation and provides sufficient information about viscosity of the slurry, without determination of other extra characteristics, which rheometer is used for. A lot depends on the slurry itself and the process, in which it is used. As a rule, its behavioral characteristics are like of the non-Newtonian fluids, and to give a correct description of the slurry flow abilities, several measurements are to be taken. Viscosity is directly connected with the shear rate the fluid demonstrates. It is not obligatory that this rate remains one stable value, that is why viscosity may also differ in the parts with high shear rate form the parts with low shear rate, even though it may be the same slurry. That is why it is recommended to apply a few instruments, depending on the characteristics of a particular part under control (speed, shear rate, temperature) to get accurate results about slurry behavior in a process flow.