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Topic: Determine viscosity with different viscometers  (Read 9943 times)

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Offline Amber Chang

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Determine viscosity with different viscometers
« on: January 23, 2015, 12:07:36 AM »
Hi, guyes.

I want to know if the vicosity value depends on different viscometers.

My company anthorizes a product to H company.
However,  H company and my company get the different viscosity values of the same product.
The instrument and spindle types are as follow.
 
My company,
Fungilab, visco basic plus R type
Sindle TR8
Stir speed: 10 rpm
viscosity value=3000
 
H company,
Brookfield DV-II+Pro, LV type
Spindle S34
Stir speed: 10 rpm
viscosity value=4500
Do these results make sense?
I want to know what makes this difference.
 

Offline kriggy

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Re: Determine viscosity with different viscometers
« Reply #1 on: January 23, 2015, 06:33:36 PM »
If you want to know what makes the difference, then you need to compare procedure you used and they used. From top of my head it could be in temperature or sample concentration

Offline marquis

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Re: Determine viscosity with different viscometers
« Reply #2 on: January 23, 2015, 07:41:57 PM »
Are the two spindles you used (company H and Brookfield) the same size
and surface area?


Offline Amber Chang

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Re: Determine viscosity with different viscometers
« Reply #3 on: January 26, 2015, 01:12:56 AM »
If you want to know what makes the difference, then you need to compare procedure you used and they used. From top of my head it could be in temperature or sample concentration
The temperature and sample concentratio are the same.

Offline Amber Chang

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Re: Determine viscosity with different viscometers
« Reply #4 on: January 26, 2015, 01:15:54 AM »
Are the two spindles you used (company H and Brookfield) the same size
and surface area?
I know they're similar.

Offline Furanone

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Re: Determine viscosity with different viscometers
« Reply #5 on: January 26, 2015, 01:11:03 PM »
Absolutely, the viscosity results can be different between two different models of viscometer/rheometer using the same spindle, same rpm, same material/concentration, measured at same temperature, and same exact sample preparation procedure used for each product being measured.

One reason is that the springs inside are not rated the same. For example, the Brookfield DVII+ viscometer/rheometer comes in LV (Low Viscosity) and RV models (Regular Viscosity) with the torque constant for the LV at 0.09373 and torque constant for RV being 1.0 so in effect the LV model is over 10 times more sensitive (1.0/0.09373) for use with lower viscosity samples. Even with same model, two viscometers could give slightly different results if one or both are out of calibration (but likely not 3000 vs 4500 cP unless one spring has been irreversibly strained and needs replacing).

Our QC department had similar issues between our viscosity results and an ingredient supplier and the investigation turned up that the instruments used to measure (both Brookfield LV models) were calibrated well, but temprature was a factor (one country cold and other tropical) but most significant factor affecting variability was the different sample preparation SOPs. So I would say try to find out your model's torque constant, run some silicone oil viscosity standards within (3000-4500 cP range) to test your instrument in conjunction with the other company's instrument. Then if instrument spring's are comparable, start comparing step-by-step the sample preparation procedures.
"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

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