Looking at the rotational viscometers on the market today, you'd expect to see small price differences between the instruments offered by competing brands. But what if you find one viscometer priced at $2000 and another at $9000? Is the $9000 viscometer a better instrument? Why is there such a price difference between the two instruments?
Viscometer prices depend on both the make-up of the instrument's motor, and on the technical features of the instrument (temperature probe, speed range, USB compatibility, etc.). There are two main types of rotational viscometers: those using a spring motor, and those using a servo motor.
In this article, I’m going to take a look the options available for rotational viscometers, and how those options affect the price.
Spring motors use a spring to measure the torque required to turn a spindle in the sample. For the purposes of this article, we’ll refer to these instruments as “spring viscometers”.
Springs are designed to measure a specific, limited viscosity range. That’s why you’ll see spring viscometers labeled as LV (low viscosity), RV (regular viscosity) or HV (high viscosity).
With frequent use, springs can lose the ability to give accurate readings. Transporting the instrument can also damage or de-tune the spring. That’s why, with spring viscometers, frequent calibration is essential.
During a test, spring viscometers require time to stabilize before offering a valid reading.
Within the category of spring viscometers, there is a type of instrument known as a "dial-reading viscometer". Dial-reading viscometers are extremely basic units that require a conversion factor to obtain a viscosity reading. They are quick and easy to use, but do not offer the capabilities of timed testing, multi-step testing, or data recording that you'll usually find on other spring viscometer models.
The other category of rotational viscometers utilizes a servo motor system to measure torque, bypassing the need for a spring (in this article, we’ll call this category “spring-less viscometers”).
A spring-less viscometer can measure a full viscosity range – LV, RV, and HV – in one instrument. Spring-less viscometers are more durable, and rarely need re-calibration. To be safe, unless you see irregular results, you could calibrate the instrument just once a year. Spring-less viscometers will give you instant viscosity readings.
Spring-less viscometers cost around $3500-11,000.
Keep in mind that these price ranges - for both spring and spring-less viscometers - don’t necessarily include spindles or accessory equipment (software, temperature control, etc.). These items can add roughly $500-10,000 to the total configuration costs.
Viscometer prices are also dependent on the technical features of the instrument. Speed settings, spindle compatibility, and the ability to transfer test data to a computer are just some of the features that can affect the pricing of a viscometer. A viscometer that is lower in the price range will generally have fewer technical capabilities.
Some viscometer brands include a bayonet fitting (an easy-on-and-off style of fitting) for spindles and sample tubes and touch-screens for easy navigation on every model, which can make them a little more expensive. Other viscometer brands may only offer these features as an upgrade.
Both spring and spring-less viscometers come in a range of models from the most basic to the most technical. For the purposes of this article, I am going to qualify these models as Basic Level, Mid-Level, High-Level, and Rheometer. Starting from the Basic Level, each model builds on the features of the previous model. A Basic Level model will, of course, be less expensive than a Rheometer, but it will also offer more limited capabilities.
Here are the features generally found at each model level:
Both spring and spring-less viscometers have a lot of good to offer. I hope this article has helped you understand the factors that go into the pricing of rotational viscometers. Learn more about these and other instruments that test viscosity -- download the PDF below.
'Til next time!
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