The most common measurement method has been to dip a cup with a known shape into a coating reservoir, take it out, and then measure how long it takes for the fluid to flow through a hole in the bottom of the cup. The longer it takes, the higher the viscosity. Unfortunately, this method is inaccurate. Ten different operators will get ten different measurements.
If product quality and customer satisfaction are important to you ... if you want consistent product delivered day in and day out, ... and especially if you recirculate coatings and evaporation is possible, an autoviscometer will be invaluable.
Your autoviscometer should:
Our patented viscometer has no moving parts and no seals that can wear out or gum up. A stainless steel sensor measures viscosity and temperature simultaneously. There are no wet/dry interfaces to introduce errors and the viscometers typically clean themselves during normal line cleaning.
After a system reaches stability the controller output will stabilize at some value. The Expected Control Output (ECO) is an estimate of that value input by the operator. The estimate can be based on experience (the results last time), or knowledge of the system.
Set the Expected Control Output, then when "Control as Set" Mode is begun the ViscoPro2000 system positions the proportional band so the ECO value is at the set point. If your estimate is right and the proportional band is set wide enough to prevent oscillation, the system will converge to the Set Point as fast as is possible with PI control.
If you want to guarantee that the system will not overshoot and are willing to take longer to get to the set point, set the ECO value to zero and the proportional band wide enough to guarantee no oscillation. With this strategy the output will approach quickly to within two times the "Semi-Proportional Band", then very gradually ease toward the Set Point under the influence of the Integral adjustment. As a rule of thumb it will take up to three times the System Stabilization Time" to reach stability at the Set Point. This is a very safe strategy that is sometimes used the first time if recovery from an overshoot is difficult. Difficult recovery from an overshoot is usually not the case with thermal control of viscosity (e.g. HFO control), since most systems cool as readily as they heat. On the other hand, when viscosity is adjusted by the addition of a solvent and recovery depends on gradual evaporation, recovery may be very slow and overshoot needs to be avoided. Of course in these cases it is also helpful to reduce the rate of solvent addition so the process is more symmetric.
In viscometers with rotating spindles or piston rods, which are usually mounted in coating tanks, the wet/dry interface presents commonplace problems. As tank levels drop, some coating dries on the spindle or rod and then drags on the viscometer which artificially raises the viscosity reading. Water-based coatings exacerbate this problem. When this happens, the viscometer sends a signal to add solvent to thin the coating; the result—bad product and lost production.
If the proportional bandwidth is reduced, the response of the controller will be faster and, in general, the offset will be smaller. If the proportional band is set too small the system will oscillate. As a rule of thumb, set the proportional band as small as possible without inducing oscillations.
To visualize the oscillation process, imagine that the proportional band is set to zero. With temperature-based control, if the temperature is below the set point the heat will be ON full. Full heat application will continue until the thermal detector reaches the set point temperature. At that point the heat application will go full OFF, but by then the system will be overheated and will overshoot the set point. When the temperature detector cools to the set point, the heat will switch ON full, but by then much of the system will have cooled below the set point. The result is oscillation.
The heart of our autoviscometer is a stainless steel sensor and piston, along with electronics and connecting cable. For coating control applications, both a control valve and a needle valve can be included.
Simply and inexpensively. Just add a “tee” fitting into the existing coating line that goes to the applicator. Install the sensor and run the cable back to the electronics, which come in a NEMA4 enclosure for protection and can be mounted hundreds of feet from the sensor, if necessary. Install the valves for your solvent addition and wire the solenoid back to the electronics. That’s it.
The Cambridge autoviscometer is virtually maintenance free in a wide variety of coating applications. We recommend a calibration check at least once a year for most applications. Re-calibrations can be performed in the field or in our facility.
We guarantee the system will perform to your satisfaction or you can return it within thirty days for a full refund. To ensure your success, our people are available to see that the system is installed correctly and to train your personnel on its proper operation. And you have our portfolio of successful worldwide installations to further secure your peace of mind.
Yes. Cambridge Viscosity holds several domestic and international patents on its technology:
Dynamic reciprocating-bob rheometry
Application US2008023625A1, Cambridge Viscosity, Inc.
Priority 2007-03-27 • Filing 2007-03-27 • Publication 2008-10-02
A sensor for making rheological measurements takes the form of a ferromagnetic bob alternatively driven through a sample fluid in opposite directions by magnetic force from two alternately driven coils. The bob's position affects the mutual ... <MORE>
Viscosity measurement of liquids at subambient temperatures
Grant US9335242B2, Cambridge Viscosity, Inc.
Priority 2013-03-07 • Filing 2013-10-30 • Grant 2016-05-10 • Publication 2016-05-10
An apparatus and method is shown for determining the pumpability limit, freeze point and/or pour point of liquids, particularly fuels, at sub-ambient temperatures. A sample is placed in a viscometer which is rapidly cooled by a ... <MORE>
High precision reciprocating bob viscometer
Grant US9562840B2, Patrick Riley, Cambridge Viscosity, Inc.
Priority 2014-12-03 • Filing 2015-01-09 • Grant 2017-02-07 • Publication 2017-02-07
A high precision, reciprocating bob viscometer is shown that has two coils (A and B) encircling a reciprocating bob. Coil A is energized with a combined sinusoidal and DC signal, while coil B senses the position of the reciprocating bob, ... <MORE>
Grant US6584831B1, Patrick Riley, Cambridge Viscosity, Inc.
Priority 2011-12-21 • Filing 2001-12-21 • Grant 2003-07-01 • Publication 2003-07-01
Electrical current driven through one or the other of two coils (20 and 22) draws a ferromagnetic bob ( 28 ) along a chamber ( 26 ) containing a liquid whose viscosity is to be measured. The current that flows through the coil includes and AC ... <MORE>