Posted by(ÀÛ¼ºÇϽŠºÐ) i need to buy a Kinematic Viscosity bath with several specs ASAP - do you know where i can buy one, my name is Todd Blue, can you please get back to me soon, thank you. ( May 11, 2001 at 08:28:59: )

In Reply to(¿ø¹®) : Re: Viscosimeter self calibration
posted by(¿ø¹® ÀÛ¼ºÀÚ) : Jon Watson, Solartron Mobrey on January 30, 2001 at 09:51:55:

: Calibration fluids are a very good means of calibrating process instruments but they are often best used in a laboratory environment. In a process environment the moment you open the container, you risk contamination. We use them for laboratory calibration of our process viscometers and routinely overcheck them with capillary viscometers because of cross contamination (traces of one calibration fluid adhering to the instrument as it is transfered to the next fluid). They often must be used in significant quantities in a process environment and the cost can escalate. Used with care they are an excellent means to obtain a calibration because the viscosity of the fluids is well certified. An alternative approach, often the best practical approach and commonly used in the process environment for critical measurements, is to take samples of the actual process fluid for laboratory evaluation: take a process viscosity and temperature reading from the instrument and then take a sample. Here the problem is to ensure the laboratory instruments are capable of good measurement. Glass capillaries can be obtained to ASTM D445 complete with temperature controlled baths. Great care must be taken and the laboratory measurement must be fastidiously conducted. API 555 suggests statistical evaluation of the lab results which i can fully endorse. Site calibrating our own instruments in the oil fields and refineries using the control room instruments and technicians we have found that even $80,000 does not ensure good readings if the instruments are not used correctly. Run the same oil sample several times and ensure good sample handling techniques. Clean carefully after each use.
: Be sure to get very good temperature measurements. MaxMet spoke of the ASTN D341 relationship which we rely on in our process viscometer systems for real time determination fo the kinematic viscosity at the reference temperatures from process temperature measurements. This is a logarythmic relationship and small viscosity errors or small temperature errors at process conditions can mean very significant errors at the reference temperature. In the laboratory many benchtop density meters such as from Paar, give excellent density which can be reverse API referred to the appropriate temperature to convert dynamic viscosity readings to kinematic if the lab viscometer is dynamic. Most process instruments are dynamic but usually, if capillaries, use a process density meter for kinematic viscosity determination. (analytical measurements; for behavioral measurements e.g. fuel oil heating,accuracies are more open and various "fixes" are used to compensate the dynamic measurement to a kinematic. One manufacturer claims to calibrate on "kinematic fluids" by which they mean they use the kinematic viscosity of the calibration fluid to calibrate the dynamic measuring process viscometer. A bit of a waste because the moment the oil changes quality, the density changes and the calibration is in error.
: Heavy Fuel oil viscometers, used to control the heating of heavy fuel oils to burners in power stations and petrochemical plant or to large diesel engines aboard ship, are periodically checked using a Hoppler (or is it Hoffler?) falling ball viscometer in a temperature controlled jacket to determine the dynamic viscosity and a hydrometer is used to find the desnity at the same temperature. This enables them to find the kinematic viscosity. Simple equipment but properly used, as it must be to obtain reasonable accuracies, it can be time consuming. Ashland Chemicals (sorry, i don't have the web site) are one supplier of this type of equipment, or Kittywake (www.Kittiwake.com)another.