US 3234781 A
Description (OCR text may contain errors)
United States Patent 3,234,781 VKSCOSITY MONITOR Charles E. Bragg, Lansing, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Filed Mar. 20, 1963, Scr. No. 266,705 8 Claims. (Cl. 73-55) This invention relates to viscosimeters and more particularly concerns the provision of a continuous viscosimeter having utility in monitoring high speed, lubricant oil, canning operations.
In the canning of lubricant oils, high speed machines are set up to can a certain quantity of a particular product. Usually a single run will be of several hours duration. The composition of the lubricant oil is known to be correct at the start of a run, but there are many factors which could, and on past occasions have, resulted in a change of composition and a quantity of canned ofispecifications material. Since such changes are rarely known before the end of the run, it is necessary to scrap all of the product canned during the run. There is a further problem in oil canning operations. When changing from one grade of oil to another, it is conventional to flush out the equipment with fresh oil. Flushing must be completed before a new run can begin, or else the initial cans will be contaminated with oil from a previous batch. It has heretofore been the practice to continue flushing for a fixed period of time known to be sufficient, but this almost invariably entails an arbitrary-and uncertain-choice between under-flushing, with the possibility of contamination or over-flushing, with the certainty of waste.
According to the invention, there is provided a simple viscosity monitoring apparatus which permits constant and instantaneous determination of oil viscosity. As a result, departures from viscosity specifications are detected instantaneously and the canning equipment can be shut down without need for scrapping the entire lot. In addition, the apparatus permits inspection of the flushing operations so that the contamination of under-flushing and the waste of over-flushing are avoided.
The inventive apparatus essentially comprises a simplified viscosimeter of the type in which a fluid at constant pressure and temperature flows through a fixed restriction, and the pressure drop across this restriction is determined as a measure of fluid viscosity. The pressure drop in the inventive apparatus is obtained with a pressure-sensitive electrical resistance element, or transducer, which constitutes one branch of a Wheatstone bridge circuit. An other branch is an adjustable electrical resistance, which is used in setting the bridge for a specified viscosity product.
To detect minimum and maximum limits of bridge imbalance corresponding to a permissible viscosity range, the Wheatstone bridge may be also equipped with a meter relay which actuates an audible or visible alarm signal when the bridge is exceptionally out of balance, i.e., when the product viscosity is lower or higher than that specified. These limits, as well as the viscosity specification itself, may be adjusted at will. As indicated earlier, a particular advantage of the inventive apparatus is its simplicity. In one embodiment, an oil preheater, a constant volume pump, and the fixed restriction are all disposed within a vessel that is heated with saturated steam. Thus, all of the mechanical components of the inventive apparatus are held at constant temperature.
The invention, in its various aspects, will be described in further detail, and additional features and advantages thereof will become more apparent, in the ensuing specification which is to be read in conjunction with the attached figures wherein:
3,234,781 Patented Feb. 15, 1966 FIGURE 1 is a schematic representation, partially in section, of the mechanical components of the invention; and
FIGURE 2 is a circuit diagram of the electrical components of the invention.
Turning first to FIGURE 1, conduit 11 withdraws a sample stream of liquid passing through conduit 12 from a reservoir to the canning machine. Conduit 11 is provided with a pressure control valve 13 to maintain constant downstream pressure leading to the viscosimeter.
The viscosimeter comprises a vessel 14, having a bottom cylindrical section 16 and a top flanged section 17, the two sections being bolted together via bolt holes 18 and bolts, not shown. Gasket 19 affords pressure tightness.
Vessel 14 is provided with several access and egress conduits. Steam, at low pressure and saturated, is admitted via conduit 21, while condensate is withdrawn via conduit 22 at the bottom of vessel 14.
Oil from conduit 11 enters vessel 14 and flows in sequence to a coiled tube preheater 23 (suitably 15 ft. in total length and having Ms outer diameter and 0.015" inner diameter), a constant volume pump 24, a fixed restriction 26 (suitably 34" of /s" OD. x 0.065" IJD. tubing) and thence discharges via outlet conduit 27. Pump 24 is suitably a gear pump which delivers a substantially constant volume independent of upstream and/ or downstream pressure; pump 24 is driven via shaft 28 (passing through bearing 29) and synchronous motor 31 The pressure drop across restriction 26 (shown coiled in the figure) is determined by a pressure-sensitive electrical resistance element 32, or transducer T. Such transducers are well known, and constitute a flexible diaphragm or bellows which actuates the wiper arm of a potentiometer. The opposite side of electrical resistance element 32 is connected to the atmosphere, that is, to the same pressure region that outlet conduit 27 discharges. For convenience, an auxiliary pressure gage 33 may be connected into the same conduit 34 to which the electrical resistance element 32 is connected.
Turning now to FIGURE 2, the electrical circuitry is shown in schematic view. Line voltage is taken via terminals 35 at volts, 60 cycle. It is brought to a low voltage isolation transformer 36 and thence to a single wave rectifier consisting of resistance 37, rectifier diode 38, and capacitor 39 (450 volts, 20 microfarad). The rectifier current, at roughly 6.3 volts, is then conducted to a voltage divider composed of resistance 41 (1,000 ohms) and resistance 42 (500 ohms).
The Wheatstone bridge is powered from taps 43 and 44 of the voltage divider and receives about 3 volts pulsating DC.
The Wheatstone bridge comprises two branches of fixed resistance, resistors 46 and 47 (SK each), one variable resistance 48 (a 5K Helipot potentiometer), the pressure-sensitive electrical resistance 32, and the balancing potentiometer 49 (1K Helipot potentiometer). Variable resistance 48 serves as a memory unit, storing a resistance value corresponding to the viscosity of a sample known to be correct at the start of a run; the bridge thus compares the instantaneous viscosity with this stored viscosity. To facilitate adjustment of variable resistance 48, or to enable the balanced bridge to measure an unknown viscosity, it may be provided with a dial calibrated to read viscosity.
The galvanometer 51, shunted with a 500 ohm resistance 52 and with a stabistor (Zener diode) 53 for overload protection, is a meter relay having both minimum and maximum contacts 54 and 56, both of which are adjustable so as to permit variation of the permissible imbalance of the Wheatstone bridge.
Galvanometer 51 will ordinarily read at zero when the bridge is balanced, but will contact terminals 54 or 56 should imbalance exceed a predetermined minimum or maximum limit.
Contact terminals 54 and 56 of galvanometer 51 are connected together and thence communicate with a double-contact double-locking relay 57. Relay 57 is connected into the power line via lines 58, and has one set of contacts 59 which are normally closed when the Wheatstone bridge is balanced; when the bridge is balanced (more accurately, when no contact is being made with contact terminals 54 or 56 of galvanometer 51), the green signal light 61 is lit, signifying a satisfactory range of viscosities. However, when contact terminals 54 or 56 are closed, contact 62 on relay 57 engages contact 63 on relay, thereby breaking the circuit to green light 61 and closing the circuit to the amber light 64, signifying unsatisfactory viscosity. To release the locking action of relay 57, a normally closed push button switch 66 is provided; this must be open to return the light from amber to green when a satisfactory viscosity is restored.
In addition to, or in place of, the visible signal lights 61 and 64, an audible alarm signal may be used which sounds an alarm when the permissible viscosity range is no longer maintained.
To employ the inventive system, oil is admitted from conduit 12 through conduit 11, preheater 23, pump 24, and flow restriction 26. In the usual case, potentiometer 48 and/ or 49 are adjusted to bring the Wheatstone bridge into balance, and push button 66 is engaged to turn on green light 61. Canning is then commenced and lubricant oil flowing through conduit 12 is continuously sampled. Should there be no variation in oil viscosity (beyond the range normally provided for by adjustment of contacts 54 and 56 on galvanometer 51) the light 61 remains green throughout the entire run.
However, should there be a departure from permissible minimum or maximum viscosity, then contacts 54 or 56 are engaged, which actuates relay 57 and switches the light from green 61 to amber 64. At the same time, an alarm may ring if such has been provided. The operator may then turn off his canning machine, discarding only th: last few cans, and resuming operation after he has ascertained the cause of the viscosity departure and has rectified the same.
At the conclusion of one canning run, and when it is desired to switch to an oil of different viscosity, potentiometer 48 is readjusted to a predetermined setting (to be illustrated subsequently) and a new grade of oil is passed from the reservoir through conduit 12 and thence to viscosimeter via valved conduit 11. By observing the dial on galvanometer 51, the operator can immediately determine when sufiicient flushing has occurred so that the oil currently involved through conduit 12 is suitable for canning; when this takes place, galvanometer 51 will be balanced.
To adjust potentiometer 48 it is merely necessary to calibrate the potentiometer 48 from previous runs with oils of known viscosity. The correlation between an oil viscosity recorder setting is generally linear, and hence only two calibration points are necessary. Also, by using oils of known viscosity, the adjustments of contacts 54 and 56 on galvanometer 51 may be adjusted to ascertain the minimum or maximum permissible ranges of viscosity.
From the foregoing description, it is evident that there has been provided, in accordance with the invention, a simple rugged, and foolproof apparatus for detecting viscosity departures in a fluid. Although the inventive apparatus is especially suited for use in conjunction with canning of lubricant oils, it is evident that it has many other uses, e.g. continuous viscosity monitoring of various oil refinery and chemical plant streams.
Further, while the invention has been described in conjunction with specific embodiments thereof, these are for illustrative purposes only, and many alternatives, modifications and variations will become apparent to those skilled in the art in light of the foregoing description. It is therefore intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.
1. In a viscosimeter which may be used to monitor the viscosity of a flowing liquid stream and which is of the type wherein a fluid at constant pressure and temperature flows through a fixed restriction and wherein the pressure drop across said restriction is determined as a measure of fluid viscosity, the combination comprising: a pressure-sensitive electrical resistance for determining said pressure drop; a Wheatstone bridge circuit having said electrical resistance as one branch thereof and having an adjustable electrical resistance as another branch thereof; means for detecting minimum and maximum limits of bridge imbalance corresponding to a permissible viscosity range; and means responsive to said detecting means for signaling departures from said permissible viscosity range.
2. Viscosimeter of claim 1 wherein said fixed restriction, a constant volume pump upstream of said fixed restriction, and a heat exchanger are all disposed within a constant temperature vessel.
3. The viscosimeter of claim 2 wherein said vessel is maintained at constant temperature by introducing steam therein.
4. The viscosimeter of claim 1 including means for adjusting the minimum and maximum limits of bridge imbalance.
5. The viscosimeter of claim 1 including overload-responsive means for shorting out said detector means at excessive bridge imbalance.
6. The viscosimeter of claim 1 wherein said signaling means comprises a colored light, said light having a color different from a second light indicating viscosity to have said permissible viscosity range.
7. A continuous viscosimeter comprising a constant temperature vessel having provisions for admitting steam therein and for withdrawing condensate therefrom; a conduit having the pressure-controlling valve therein for receiving a fluid sample; a heat exchanger within said vessel and communicating with said conduit; a constant volume pump within said vessel disposed downstream of said heat exchanger; a flow restriction disposed downstream of said constant volume pump and discharging fluid externally of said vessel; a pressure-sensitive electrical resistance for measuring the pressure drop across said flow restriction; a Wheatstone bridge including said electrical resistance as one branch thereof and having an adjustable electrical resistance as another branch thereof; means for detecting minimum and maximum limits of bridge imbalance corresponding to a permissible viscosity range; and means responsive to said detecting means for signaling departures from said permissible viscosity range.
8. The viscosimeter of claim 7 including means for adjusting the minimum and maximum limits of bridge imbalance.
References Cited by the Examiner UNITED STATES PATENTS 2,539,892 1/1951 Cook 73-398 X 2,834,200 5/1958 Rhodes et al. 7355 3,115,768 12/1963 Rhodes et al. '7355 3,116,630 l/l964 Piros 7355 3,127,586 3/1964 Heyn et a1 340240 X LOUIS R. PRINCE, Primary Examiner.
DAVID SCHONBERG, Examiner.