Accuracy The accuracy of a viscometer is dependent not
only on the engineering of the instrument it- self, but also on how precisely temperature can be controlled. It is common to make repeated viscosity measurements that are averaged to achieve a result with an associated accuracy.
Viscosity standards are used to check the ac- curacy of a viscometer and can be important for verifying compliance with industry quality systems. Check that the manufacturer pro- vides standards suitable for your application. Brookfield Silicone and Mineral Oil Standards provide a fluid viscosity value that is constant at 25 °C. The company recommends replacing viscosity standards on an annual basis.
Temperature control The viscosity of most materials reduces as
temperature increases. Materials such as en- gine oils are subject to routine temperature variations in use, and the measurement of viscosity is required at different temperatures. Therefore, it is very important for viscometers to have precise temperature controls.
The Black Pearl Viscometer from ATS
RheoSystems (Bordentown, NJ; www.
atsrheosystems.com) comes with built-in Peltier temperature control for all measuring systems. Some systems have the option of adding cooling equipment, leading to tem- perature ranges below 0 °C.
Sample volume and
microvolume capability Sample volume is important for biological samples, especially in the clinical laboratory. The SV-A Series from A&D Weighing (San Jose, CA;
www.andonline.com/weighing) allows for the accurate measurement of sample sizes as small as 2 mL with 1% accuracy. The Cannon- Manning Semi-Micro Extra Low Change U-tube Viscometer from CANNON Instrument Co. will measure kinematic viscosity with as little as 0.5 mL of sample.
Automation and
computer interfacing The simplest viscometers allow one mea- surement at a time, but for continuous measurements, or measurements at different
temperatures, it is useful to have an automated system. Semi-Automatic Kinematic Viscosity Systems from UIC, Inc. (Joliet, IL; www.uicinc. com) can determine the viscosities of up to 12 samples simultaneously and independently.
Some automated instruments can be interfaced to a PC. Check whether the manu- facturer’s software can be interfaced to your in-house laboratory system if required.
WinCT-Viscometer software from A&D Weighing uses an RS232C interface to display measurement progress from the SV series Sine-wave Vibro Viscometer in real time on a PC. Measured results can be saved or analyzed.
The DV2T Viscometer from Brookfield Engineering Laboratories (Figure 2) features a 5-in. color display to guide users through test creation and data gathering. Multistep test protocols can be created using the Program Generator software and uploaded to the DV2T through a USB flash drive. Test data can be printed or sent to a PC.
Regulatory requirements and
industry standards Be sure that your chosen viscometer is certi- fied for your required ASTM or ISO industry standards.
The Thermo Scientific HAAKE Falling Ball Viscometer type C from Thermo Fisher Scientific measures the viscosity of transpar- ent Newtonian liquids and gases. It meets the ISO 12058 standard and is accepted as an of- ficial reference instrument.
The PolyVISC® Automatic Glass Capillary Viscometer from CANNON Instrument Co. is a benchtop unit for dilute solution polymer vis- cosity analysis. Both transparent and opaque samples can be measured with the accuracy required by ASTM D 2857.
Viscometer manufacturers A list of viscometer manufacturers is given in Table 1. For more information, please visit
www.labcompare.com.
Katriona Scoffin,
B.Sc., is a freelance science writer; e-mail:
articles@scoffin.co.uk.
AMERICAN LABORATORY • 31 • SEPTEMBER 2013
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