The uncertainty or tolerance of measurements is given as a percentage of the full-scale range, or 100% torque value.įor standard spindles (RV-03, LV-01, HV-05, etc.), the tolerance is +/- 1% of the full-scale range.įor cone and plate viscometers, the tolerance is +/- 1% of the full-scale range.įor accessories such as the small-sample adapter, Enhanced UL adapter, etc. This uncertainty is denoted as a measurement tolerance, where the actual viscosity of the fluid being measured can be within a specified range of the measured viscosity. Understanding and calculating measurement tolerancesĮvery measurement taken with a Brookfield instrument has some amount of uncertainty associated with it. This will give a viscosity value in centipoise (cP).įor example, if an RV-04 spindle was being used on an RV torque instrument at 20RPM and the torque value displayed was 62.3%, you could determine the viscosity reading using the factor 2000/N from Appendix A of More Solutions to Sticky Problems in the following equation: To arrive at the viscosity reading being measured by an instrument, you can take the above factor, and multiply it by the percent torque, or dial reading. A spindle will have multiple factors that depend on the torque of the instrument it is installed on, so make sure to note which instrument you are calculating for (LV, RV, HA, HB, etc.) Spindle factors are listed in Appendix A of More Solutions to Sticky Problems, and are given in the form /N, where N is the selected spindle speed in RPM. These factors are empirically calculated functions that allow for a simple conversion between percent torque and viscosity. Calculating a working rangeĮvery spindle produced by Brookfield has a spindle factor. If you are trying to take a measurement, and the instrument is displaying an over-torque error (“EEEE”), or displaying a very low measurement torque (below 10%), then you can adjust your measurement method to alter the instruments working range to better fit your sample. The 100% torque value is referred to as the full-scale range. Above 100%, your instrument will state “EEEE” for the viscosity, this is the over-torque error. Below 10%, and the instrument may still report a value, but this value will not be accurate. A VALID viscosity measurement can be taken between 10% and 100%. This value is what is used to calculate the viscosity reported by the instrument. On legacy analog instruments, this is also called the “Dial reading”. The basic reading given by a Brookfield viscometer is a unitless value of “percent torque” (%) between the values of 0% and 100%. This working range will be significantly narrower than the overall ranges given for the instrument. Understanding working rangesĮvery Brookfield laboratory viscometer has a range of viscosities it is able to measure given a particular spindle and speed selection. This article will reference tables and figures in Appendix A of More Solutions to Sticky Problems. In this article, we will discuss how to calculate and understand the working range of your viscometer, as well as discuss the uncertainty or tolerance that is applied to each measurement taken with the instrument. If any of these factors change, then the working range of the instrument will also change. The working range of an instrument is determined for each measurement method, and is calculated based on the instrument torque, spindle, and spindle speed. This is the overall range of the instrument and encompasses every spindle and speed combination the instrument is capable of. For example, the RV DV2T gives a range from 100cP to 40,000,000cP. Looking at the Brookfield catalog, you may notice minimum and maximum measurements that cover a huge range of viscosities. This article applies to: All Brookfield laboratory viscometers
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