GB2250597A

GB2250597A - Buoyant hydrometer

Info

Publication number: GB2250597A
Application number: GB9022407A
Authority: GB
Inventors: Luciano Ceresa
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-10-16
Filing date: 1990-10-16
Publication date: 1992-06-10
Anticipated expiration: 2010-10-16
Also published as: GB9022407D0; GB2250597B

Abstract

A hydrometer 10 comprises a buoyant body. and electronic sensors for sensing the level of liquid on the body. A central processing unit 42 powered by a battery 18 automatically determines the liquid's density according to the sensed liquid level and displays the result, e.g. on L.C.D. 40. A plurality of sensors 26 are spaced spirally around the stem 14 of the device and energised by drivers 30 under control of the c.p.u. The stem is formed by a hollow, multi-layer p.c.b. The sensors may be of conductive type, or temperature-dependent resistors with adjacent copper heating pads which are intermittently energised. The device may also be set to show the temperature of the liquid. <IMAGE>

Description

BUOYANT HYDROMETER The invention relates to a buoyant hydrometer.

The operation of a hydrometer is based upon the principle that a buoyant body will sink into a liquid until it displaces a volume of the liquid equal in weight to that of the object. The density of a liquid can be determined by how far the hydrometer submerges in the liquid.

Prior art hydrometers have been analog and required a scale located on the hydrometer to be read by the naked eye. Such hydrometers have consequently been restricted in precision.

Accordingly this invention aims to provide a hydrometer having improved precision and to increase the ease with which density measurement can be achieved.

In accordance with the present invention a hydrometer comprises a buoyant body, electronic sensing means for sensing the level of liquid on the buoyant body, means responsive to the sensing means for automatically determining the liquid's density and means for displaying the determined density.

The buoyant body may include a stem formed from printed circuit board having a hollow centre for improved buoyancy.

The means for sensing may include a plurality of sensors each comprising a conductive pad, and means for providing an electrical signal to each of the conductive pads. The level of liquid is determined by detecting a signal on a feedback line separated from each pad by a gap that provides electrical insulation in air, but transmits a signal when immersed in a conductive liquid.

The means for sensing may alternatively include a plurality of sensors each comprising a resistive element that has a resistance that varies in response to a change in temperature and means for providing a predetermined heating energy to each of the elements. A difference in the resistance of adjacent elements is registered and used to locate the position of the liquid level. An electrical impulse provides the predetermined heating energy to each resistive element.

In both alternative systems the sensors are preferably disposed on the buoyant body at regular intervals for progressive immersion in the liquid as the buoyant body is submerged. It may also be preferable for the electrical signals to be delivered to each of the sensors in succession.

The invention will be described in further detail below by way of example only and with reference to figures 1 to 7 of the drawings of which: Figure 1 is a perspective view of a hydrometer of this invention; Figure 2 is a section through the hydrometer of Figure 1; Figure 3 is a perspective view with cut away showing the construction of the stem of the hydrometer of Figure 1; Figure 4 is a schematic representation of the electric circuitry of the hydrometer of Figure 1; Figure 5 is a schematic representation of a current sensory system for sensing liquid level for a hydrometer; Figure 6 is a schematic representation of a heat sinking sensory system for sensing liquid level for a hydrometer; and Figure 7 is a plan view of one sensor of the heat sinking sensory system of Figure 6.

A hydrometer 10 of this invention is illustrated in Figures 1 and 2. The hydrometer 10 includes a bulb 12, a stem 14 and a display holder 16.

The hydrometer 10 is buoyant so that the level of liquid on the device can be used to determine the volume of liquid displaced as the hydrometer is submerged in a liquid allowing the density of liquid displaced to be calculated.

The bulb 12 is water tight and contains a battery 18 for supplying power, and also most of the electronic components for operation of the device.

The battery 18 may be a primary or rechargeable battery. The bulb 12 also provides a cavity 20 for storage of lead shot 22, or other weights, to provide the hydrometer 10 with a desired characteristic mass.

An optional feature of the hydrometer 10 illustrated in this example is a temperature sensor 24. This enables the hydrometer 10 to be used to determine the temperature of the liquid and also provides the option for the device to be used to provide the density of a particular liquid under test at standard temperature even if the liquid is not actually at the standard temperature, the device being dedicated for use with that liquid. This can be achieved by preprogramming the device with a liquid expansion table or a conversion table.

A plurality of sensors 26 are arranged in spiral formation on both sides of the stem 14. The sensors 26 are equally spaced in regular formation along the length of the stem 14. The sensors 26 are driven by electrical signals issuing from a plurality of drivers 30, driven by a driver control, controlled by a Central Processing Unit (CPU) 42. The driver control can hold 50 or more drivers located in the water tight bulb 12. The stem 14 is narrower than the bulb 12 and very light in weight in order for there to be a significant change in position of the liquid level on the hydrometer 10 for liquids having a relatively small difference in density.For example, to achieve a precision of 0.001 gum'3, is desirable. The change in immersion of the hydrometer for a given density change can vary from 0.5 mm to 5 mm depending on the construction of the hydrometer, that is the ratio between the body bulb and the stem. To achieve the desired precision, the stem 14 is made from printed circuit board (PCB) 28 which has a central cavity to reduce weight.

Figure 3 shows the construction of the hollow PCB in greater detail. The stem 14 is an empty multi-layer PCB. The stem 14 can be fabricated using well-known multi-layer PCB technology with a difference. Conventionally, a multilayer PCB is made by sticking different layers of copper and epoxy resin together. This creates a multilayer PCB which can have various thicknesses. The copper layer is patterned to form the conductive circuit, and the epoxy resin layer helps complete the circuitry of the PCB by acting as a non-conductive material. The PCB of this invention differs from conventional multilayer PCB in that it includes an internal frame 34 providing the central cavity. The frame may also be hollow for reduced weight.A pair of inner panels 36 that contain the conductive lines are attached directly to the frame and a pair of external panels 38 provide the outer surfaces of the stem to which the sensors 26 are attached. The double-sided PCB can also be used for low-precision hydrometers that rely on visual scale readings and subsequent conversion by an operator.

The display holder 16 is situated at the top of the stem 14 so that it remains out of the liquid for ease of viewing at all times during operation. It is also water tight and contains a liquid crystal display (LCD) 40. The LCD 40 alternately displays the density and temperature of the liquid. The display holder 16 also contains the central processing unit (CPU) 42 of the device. This is the instrument's controller and once programmed controls the signals output by the drivers 30, and analyses data received from the sensors 26. Once the data has been analysed and the level of liquid on the hydrometer determined, the CPU 42 calculates the density of the liquid under test and displays the result on the LCD 40.

The hydrometer's electric circuitry is designed to drive the sensors 26 to provide information from which the density of the liquid under test can be calculated. To this end the drivers 30, under control of the CPU 42 provide signals to the sensors 26 in a predetermined sequence eg. beginning with the topmost sensor and ending with the bottommost or vice versa. A feedback line 44 delivers signals from the sensors 26 to the CPU 42 where they are analysed. The CPU 42 can optionally provide a choice of operating conditions including scale gradation, type of density degree, (ie. API, BE, DIN, ALCOHOL, GRAVITY, etc), and resolution. If the thermometer is used the temperature scale OF or OC can also be chosen.

The CPU 42 remains in a standby condition until actuated by being dipped into a liquid. In the standby condition, the CPU with scan the bottom or the top sensors of the hydrometer every 'X' seconds. If the hydrometer is outside the liquid, no feedback signal will be sent from the sensor. If immersed in liquid, there will be a feedback signal and the CPU will move out of standby and start working by scanning all the sensors of liquid. The calculated density is immediately displayed by the LCD 40. The reading cycle is repeated at intervals of Y seconds. If a different density is calculated the displayed density output is changed. After a fixed number of scans at intervals of Y seconds have provided the same density display, the sensors are scanned less frequently once every Z seconds where Z > > Y.After displaying the density for a fixed period, the CPU 42 may switch to display the temperature of the liquid determined by the temperature sensor 24. The CPU 42 will revert to a standby condition if no liquid density is calculated when the device is removed from the liquid.

The liquid level sensory system can be one of two distinct types, namely either a current sensory system or a heat sink system, illustrated in Figure 5 and Figures 6 and 7 respectively. Turning firstly to Figure 5, the layout of the current sensory system can be seen. In this embodiment, the sensory mechanism operates by utilizing the difference in electrical conductivity that exists between air and liquids.

The sensors 26 are copper pads 50 that have been treated against corrosion. They are spaced equidistantly one from the other along the direction of immersion of the stem in regular spiral formation on the stem 14. Each pad 50 is electrically connected to a respective driver 30. As the buoyant hydrometer is dipped in the liquid, the CPU is activated by the process described above and sends addresses to the drivers 30 whereupon AC or DC voltage signals are sent in sequence to the pads 50. A feedback line 44 is located along the stem 14. There is a gap 54 between each pad 50 and the line 44.This gap 54 is insulative in air but as a result of the natural conductivity of most liquids, becomes conductive on immersion Consequently, no signal on the feedback line 52 will be received from sensors 26 above the liquid level whereas there will be signals received from those sensors 26 below that level. By scanning the sensors 26 in sequence, the CPU 42 detects a transition in the signal received from adjacent sensors 26 at the liquid level. By knowing the address of the sensors at the transition from liquid to air, the CPU 42 automatically determines the level of the liquid relative to the stem and calculates the density of the liquid under test from knowledge of the mass and volume of liquid displaced.

As there are some liquids that are not electrically conductive, the sensory system illustrated in Figures 6 and 7 provides an alternative method for sensing the level of liquid on the stem 14 of the hydrometer 10. In this system, the difference between the thermal conductivity of liquids and that of air or other gases is exploited. The difference corresponds to a ratio of about 1/10 air to water.

The sensors 26 are operated in pairs, each sensor comprising a pair of copper pads 56, 58 one connected to a respective driver 30 and the other to one of first and second feedback lines 60, 62. The copper pads 56, 58 are electrically connected by a strip of resistive paste or ink 64 all of which have a similar positive or negative temperature coefficient.

Adjacent sensors 26 are connected to different ones of the two feedback lines 60, 62. It is important to operation of this particular embodiment that the resistance of the resistive strips 64 of adjacent sensors 26 are adjusted to be substantially equal during construction. The sensors 26 are placed equidistantly one from the other in spiral formation as in the previous embodiment.

A heating effect is created in each sensor 26 by delivering a constant voltage impulse, AC or DC, to each of the sensors 26 a-k for a specific time, sufficient to raise the temperature of each strip 64 by 300C to 600C above that of the ambient temperature.

The energy input in Joules = V x I x t = I2Rt where V = voltage, I = current, R = resistance and t = time.

The difference in thermal conductivity between a liquid and a gas such as air results in more heat being conducted away from a resistive strip 64 immersed in liquid than from one exposed to the air.

The quantity of heat transmitted in calories, Q = MxCxDT where M = mass in grammes, C is the thermal conductivity in cal/g C and T = change in temperature in degrees centigrade. The temperature of a strip 64 immersed in liquid will consequently be lower than that for one in air, whereas if both sensors are in the same environment (air or liquid) the resistance of both will be the same. As all the resisitive strips 64 have either a positive or a negative temperature coefficient, the resistance of a sensor 26 in liquid and one in air will be different. Adjacent sensors 26 straddling the liquid level with therefore provide signals having different voltages on the first and second feedback lines 60, 62 respectively. To detect a liquid level between any of the adjacent sensors each scanning cycle includes two scans.In the first, sensors 26a and 26b, 26c, 26d etc are analysed together and any difference in the output voltage between them detected. This allows a liquid level between sensors a+b, c+d, etc to be detected.

In the second, sensors 26b+26c, 26d+26e are analysed together to detect a liquid level between sensors b+c, d+e, etc.

The signals on the first and second feedback lines 60, 62 are delivered to a differential voltage comparator 66 that delivers a signal to the CPU 42 when there is a voltage differential between the two lines 60, 62. A signal is received by the CPU 42 when a pair of adjacent sensors 26 are straddling the liquid level on the stem. The CPU 42 drives the sensors 26 in sequence to determine the position of the liquid level. The density of the liquid under test is then calculated and displayed in a similar manner to that described in the previous embodiment.

The automatic calculation and display of the density of a liquid by the hydrometer avoids the problems of lack of precision and difficulty of use inherent with the prior art analog hydrometers.

The invention being thus described, it will be obvious that the same may be varied in many ways.

Such variations are not to be regarded as a departure from the scope of the invention.

There are described above novel features which the skilled man will appreciate give rise to advantages. These are each independent aspects of the invention to be covered by the present application, irrespective of whether or not they are included within the scope of the following claims.

Claims

CLAIMS:

1. A hydrometer comprising: a buoyant body; electronic sensing means for sensing the level of liquid on the buoyant body; means responsive to the sensing means for automatically determining the liquid's density according to the sensed liquid level; and means for outputting the determined density.

2. A hydrometer according to claim 1 wherein the electronic sensing means comprises a plurality of sensors each comprising a conductive element, driver means for providing an electrical signal to each of the conductive elements, and a feedback line separated from each element by a gap electrically insulative in air, such that electrical conduction is effected between the element and the feedback line on immersion in a conductive liquid.

3. A hydrometer according to claim 2 wherein the sensors are disposed on the buoyant body for progressive immersion as the body is progressively submerged.

4. A hydrometer according to claim 3 wherein the driver means is operable to supply an electrical signal to the plurality of sensors in succession.

5. A hydrometer according to claim 1 wherein the electronic sensing means comprises a plurality of sensors each comprising a resistive element having a resistance that varies in response to a change in temperature, means for providing a predetermined heating energy to each of the resistive elements, and means for detecting a difference in the resistance of adjacent resistive elements.

6. A hydrometer according to claim 5 wherein the means for detecting a difference in the resistance of adjacent resistive elements comprises a differential voltage comparator arranged to receive output signals from adjacent resistive elements.

7. A hydrometer according to claim 5 or 6 wherein the means for providing the predetermined heating energy is adapted to supply an electrical impulse to each resistive element.

8. A hydrometer according to claim 7 wherein an electrical signal is supplied to a pair of adjacent resistive elements simultaneously.

9. A hydrometer according to claim 8 wherein the electrical signal is- applied to each pair of adjacent resistive elements in succession.

10. A hydrometer according to claim 8 wherein each sensor is paired alternately on successive applications of the electrical signal with first and second adjacent sensors respectively

11. A hydrometer according to claim 5 wherein the sensors are disposed on the buoyant body for progressive immersion as the body is progressively submerged and the electrical signal is supplied to the plurality of sensors in sequence.

12. A hydrometer according to any one of claims 2 to 11 wherein the sensors are equally spaced one from the other along the direction of submersion of the buoyant body.

13. A hydrometer according to any one of claims 1 to 12 wherein the buoyant body includes a stem formed from printed circuit board having a hollow centre.

14. A hydrometer according to any one of claims 1 to 13 wherein the means for displaying the calculated density is a digital display.

15. A hydrometer according to any one of claims 1 to 14 further comprising means for measuring and displaying the temperature of a liquid.

16. A hydrometer according to any one of claims 1 to 15 wherein the means for sensing the level of liquid is activated on immersion in a liquid.

17. A hydrometer according to claim 16 when dependent on claim 11 wherein the electrical signal is supplied to the plurality of sensors at a first frequency immediately on actuation and at second frequency smaller than said first on a predetermined number of similar successive determinations of the liquid density.

18. A hydrometer according to claim 14 wherein the means for sensing the level of liquid shuts down a fixed period after activation.

19. A hydrometer comprising a buoyant body having a stem formed from a printed circuit board having a central cavity.

20. A hydrometer substantially as hereinbefore described with reference to the accompanying drawings.