sorry for the delay responding,
I haven't logged in for a while.
When measuring the viscosity online a great deal depends on the selection of the viscometer and the installation.
Marimex I know have been working on this but I couldn't tell you how successful they are. Their sensors are suitable for dynamic viscosity at very very much higher viscosities than here but measure the dynamic viscosity only. However, in pipeline applications it is necessary to measure the density as this is a critieria also applied to the accetable pipeline limits.
Many of the successes in Canada have been with the Emerson 7827 digital viscometers (that measure density from the resonant frequency and hence also the kinematic viscosity necessary for the ASTM D341 calculations but while accurate enough for the viscosit, not accurate enough for the density control.
A more recent viscometer, the LEMIS DC 52 ViscoAnalytic, is comparable to the Emerson 7827 but has fiscal density accuracy capability.
Note that the LEMIS and Emerson sensors displae the fluid and can measure density an dynamic viscosity and hence generate the kinematic viscosity. The Marimex uses torsional vibration which does not displace the fuid and a different method of determining the viscosity from the vibrational sensor (amplitide sensing I believe rather than bandwidth) and hence needs separate density measurement.
In real terms the Emerson and Lemis sensors are routinely used for viscosities greater than 400cSt. For example in marine bunker fuel applications where the viscosities of the commonest fuels are around 380cSt and higher with some fuels.
It is necessary to use the appropriate installation methods, which is typically the flow chamber, appropriate fixed flow rates e.g. around 25//min and PTFE or similar non-stick coatings for the sensors and to insulate well. A static mixer is also often recommended for the upstream section to ensure homogeneity of the fluid entering the chamber.
(examples of both the Emerson and Lemis sensors are found on www.viscoanalyser.com along with photos of some installations in Canada - the "bitumen" and Russia - heavy fuel oils)
The key to the success of this method also depends on the sensor accuracy and the accuracy of both viscosity and temperature measurements.
So it is quite feasible to heat or cool (or both, cooling for one sensor and heating for the other) but in the Canadian pipeline applications it has been usual for the first viscometer to measure at the sample original temperature i.e close to the pipeline temperature but subject to any ambient temperature effects on the sample line and use an electric heater between the viscometers to generate a sufficient temperature difference.
Note that in some applications such as where the oil is very waxy, it is necessary that both measurements are made above the wax point which is then sometimes above the reference temperature. So it is not necessary that either viscometer operates at the reference temperature though with more viscous product it is advisable to operate in the region of the reference temperature with one of the viscometers if possible.
The advantage of the method is that using indirect (calculation) methods, the temperatures do not have to be precisely regulated as is the case with the capillary viscometers and when the instalation is well designed and the viscometers properly specified, the on stream factor is very high and service, calibration and cleaning are then only needed in exceptional circumstances.
This is one of the reasons that until the advent of the Emerson (then Solartron) 7827 with accuracy, response time and methodology (callculation methods) along with a good understanding of process application installation practise, pipeline blending applications tended to rely on sampling and off line methods which necessarily also then involved "safe" blending i.e. use of excess distilate to ensure the density and viscosity were within limits.
These installations, including the civils, environmental enclosures etc. tend to be expensive but the pay back periods are very quick.
If you need further assistance, please follow the contact page on www.viscoanalyser.com