Editing Viscometer (section)

==Vibrational viscometers==
Vibrational viscometers date back to the 1950s Bendix instrument, which is of a class that operates by measuring the damping of an oscillating electromechanical resonator immersed in a fluid whose viscosity is to be determined. The resonator generally oscillates in torsion or transversely (as a cantilever beam or tuning fork). The higher the viscosity, the larger the damping imposed on the resonator. The resonator's damping may be measured by one of several methods:

# Measuring the power input necessary to keep the oscillator vibrating at a constant amplitude. The higher the viscosity, the more power is needed to maintain the amplitude of oscillation.
# Measuring the decay time of the oscillation once the excitation is switched off. The higher the viscosity, the faster the signal decays.
# Measuring the frequency of the resonator as a function of phase angle between excitation and response waveforms. The higher the viscosity, the larger the frequency change for a given phase change.

The vibrational instrument also suffers from a lack of a defined shear field, which makes it unsuited to measuring the viscosity of a fluid whose flow behaviour is not known beforehand.

Vibrating viscometers are rugged industrial systems used to measure viscosity in the process condition. The active part of the sensor is a vibrating rod. The vibration amplitude varies according to the viscosity of the fluid in which the rod is immersed. These viscosity meters are suitable for measuring clogging fluid and high-viscosity fluids, including those with fibers (up to 1000&nbsp;Pa·s). Currently, many industries around the world consider these viscometers to be the most efficient system with which to measure the viscosities of a wide range of fluids; by contrast, rotational viscometers require more maintenance, are unable to measure clogging fluid, and require frequent calibration after intensive use. Vibrating viscometers have no moving parts, no weak parts and the sensitive part is typically small. Even very [[Basic (chemistry)|basic]] or [[acidic]] fluids can be measured by adding a protective coating, such as [[Vitreous enamel|enamel]], or by changing the material of the sensor to a material such as [[SAE steel grades|316L]] [[stainless steel]]. Vibrating viscometers are the most widely used inline instrument to monitor the viscosity of the process fluid in tanks, and pipes.

===Quartz viscometer===
The quartz viscometer is a special type of vibrational viscometer. Here, an oscillating quartz crystal is immersed into a fluid and the specific influence on the oscillating behavior defines the viscosity. The principle of quartz viscosimetry is based on the idea of W.&nbsp;P. Mason. The basic concept is the application of a piezoelectric crystal for the determination of viscosity. The high-frequency electric field that is applied to the oscillator causes a movement of the sensor and results in the shearing of the fluid. The movement of the sensor is then influenced by the external forces (the shear stress) of the fluid, which affects the electrical response of the sensor.<ref>W. P. Mason, M. Hill: ''Measurement of the viscosity and shear elasticity of liquids by means of a torsionally vibrating crystal''; Transactions of the ASME. In: Journal of Lubricating Technology. Band 69, 1947, S. 359–370.</ref> The calibration procedure as a pre-condition of viscosity determination by means of a quartz crystal goes back to B. Bode, who facilitated the detailed analysis of the electrical and mechanical transmission behavior of the oscillating system.<ref>Berthold Bode: ''Entwicklung eines Quarzviskosimeters für Messungen bei hohen Drücken''. Dissertation der TU Clausthal, 1984.</ref> On the basis of this calibration, the quartz viscosimeter was developed which allows continuous viscosity determination in resting and flowing liquids.<ref>{{cite web |url=http://flucon.de/produkte/quartz-viscosimeter-qvis/?lang=en |title=Viscosimeter QVis &#124; flucon fluid control GMBH |access-date=2015-07-02 |url-status=dead |archive-url=https://web.archive.org/web/20150702224834/http://flucon.de/produkte/quartz-viscosimeter-qvis/?lang=en |archive-date=2015-07-02 }}<|accessdate=2015-07-02 |</ref>

==== Quartz crystal microbalance ====
The [[quartz crystal microbalance]] functions as a vibrational viscometer by the piezoelectric properties inherent in quartz to perform measurements of conductance spectra of liquids and thin films exposed to the surface of the crystal.<ref name=":0">{{Cite journal|last=Johannsmann|first=Diethelm|date=2008|title=Viscoelastic, mechanical, and dielectric measurements on complex samples with the quartz crystal microbalance|journal=Physical Chemistry Chemical Physics|language=en|volume=10|issue=31|pages=4516–34|doi=10.1039/b803960g|pmid=18665301|bibcode=2008PCCP...10.4516J|issn=1463-9076}}</ref> From these spectra, frequency shifts and a broadening of the peaks for the resonant and overtone frequencies of the quartz crystal are tracked and used to determine changes in mass as well as the [[viscosity]], [[shear modulus]], and other viscoelastic properties of the liquid or thin film. One benefit of using the quartz crystal microbalance to measure viscosity is the small amount of sample required for obtaining an accurate measurement. However, due to the dependence viscoelastic properties on the sample preparation techniques and thickness of the film or bulk liquid, there can be errors up to 10% in measurements in viscosity between samples.<ref name=":0" />

An interesting technique to measure the viscosity of a liquid using a quartz crystal microbalance which improves the consistency of measurements uses a drop method.<ref name=":1">{{Cite book|last1=Bai|first1=Qingsong|last2=Hu|first2=Jianguo|last3=Huang|first3=Xianhe|last4=Huang|first4=Hongyuan|title=2016 IEEE International Frequency Control Symposium (IFCS) |chapter=Using QCM for field measurement of liquid viscosities in a novel mass-sensitivity-base method |date=2016|location=New Orleans, LA, USA|publisher=IEEE|pages=1–3|doi=10.1109/FCS.2016.7546819|isbn=9781509020911|s2cid=1584926 }}</ref><ref name=":2">{{Cite journal|last1=Ash|first1=Dean C.|last2=Joyce|first2=Malcolm J.|last3=Barnes|first3=Chris|last4=Booth|first4=C. Jan|last5=Jefferies|first5=Adrian C.|date=2003|title=Viscosity measurement of industrial oils using the droplet quartz crystal microbalance|journal=Measurement Science and Technology|language=en|volume=14|issue=11|pages=1955–1962|doi=10.1088/0957-0233/14/11/013|bibcode=2003MeScT..14.1955A|s2cid=250866968 |issn=0957-0233}}</ref> Instead of creating a thin film or submerging the quartz crystal in a liquid, a single drop of the fluid of interest is dropped on the surface of the crystal. The viscosity is extracted from the shift in the frequency data using the following equation

<math>\Delta f = -f_0^{3/2}\sqrt{\frac{\eta_l \rho_l}{\pi \mu_Q \rho_Q}}</math>

where <math>f_0</math> is the resonant frequency, <math>\rho_l</math> is the density of the fluid, <math>\mu_Q</math> is the shear modulus of the quartz, and <math>\rho_Q</math> is the density of the quartz.<ref name=":2" /> An extension of this technique corrects the shift in the resonant frequency by the size of the drop deposited on the quartz crystal.<ref name=":1" />