JPH0465974B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION This invention relates to the field of meters, and more particularly to the field of meters for measuring the concentration of water in water-ink mixtures.

Lithographic printing presses use a mixture of ink and an aqueous dampening solution. This dampening solution is water containing small amounts of specialized additives to increase the water dampness of the printing plate. A continuous stream of ink and dampening solution is supplied to the press. These are as a mixture of ink and dampening solution;
Or it can be supplied as separate streams of ink and dampening solution depending on the shape of the press. In any case, useful printing mixtures on presses include both ink and water. In keyless ink systems, for economical operation, the ink-water mixture should be recycled, since only a fraction of the ink mixture is always consumed by the printing process.

Proper amounts of water and ink in the mixture must be maintained for best printing results. This can be done at startup when fresh water-ink mixture is added by using the proper proportions to make the mixture.
However, over the course of printing, the ratio of ink and water changes within the recirculating mixture. Currently, printers associated with presses do not have a means to automatically and continuously monitor the water concentration in the recirculating water-ink mixture. The user must rely on his experience and printing results to evaluate the concentration of water in the mixture.

Meters are known that measure the dielectric constant of a mixture to determine the water content of a substance or the concentration of a mixture. Some of these prior art meters use Wheatstone bridge type circuits to measure dielectric properties (eg, US Pat. No. 3,696,299). Others use two oscillators to obtain a frequency difference related to the dielectric properties of the material being tested (eg, US Pat. No. 4,048,844). Still other meters use oscillators with peak detectors (e.g.
U.S. Pat. No. 4,399,404) or logic circuits (eg, U.S. Pat. No. 4,130,796). However, what the printer needs is a simple meter that automatically provides a direct reading of the concentration of water in the ink.

SUMMARY OF THE INVENTION It is an object of this invention to provide a meter for conveniently measuring the concentration of water in a mixture consisting of water and ink.

According to this invention, the mixture to be measured is
Forming a dielectric between the plates of a capacitor in a special capacitor cell. This cell provides capacitance to the audio oscillator. When the inductivity of the mixture changes due to a change in the water content of the mixture, the output frequency of the oscillator changes. The oscillator output frequency is converted to a voltage proportional to the oscillator output frequency. This voltage is then converted into a second voltage proportional to the logarithm of the first mentioned voltage. This second voltage is read at the display device. The concentration of water in the water-ink mixture is
Since it is proportional to the logarithm of the dielectric constant of the mixture, the display can be set to provide a direct reading of the proportion of water in the water-ink mixture.

In a preferred embodiment, a special condenser has an inlet and an outlet and is connected in series to the recirculating water-ink mixture system in the press by suitable tubular configuration. This meter can then give a continuous reading of the water in the mixture.

These and other objects and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A microwave cavity was used to study the dielectric properties and microwave absorption of water and lithographic ink mixtures. During these studies, it was discovered that the logarithm of the real part ε′ of the dielectric constant ε=ε′+iε″ is linearly related to the concentration of water in the water-ink mixture. This relationship is Defined by Eq.

logε=logε ₀ ′+kC, where ε′ is the real part of the complex dielectric constant ε (as described above), ε ₀ ′ is the value of ε′ for the ink without added water, and C
is the concentration by weight of water (or water containing dampening solution) and k is the proportionality constant.

Additional tests show that this relationship is reproducible and
and has been shown to be applicable to many different types of lithographic inks. Figure 1 shows
This logarithmic relationship for three different newsprint inks supplied by Flint Ink Co., of Detroit MI is shown in curve 2 for black ink, curve 4 for yellow ink, and curve 6 for magenta ink. There is. These curves were obtained for the mixtures tested at 23°C. Tests at temperatures ranging from 10°C to 40°C showed that the ink-water mixture had an anomalously small temperature dependence. This result was surprising since water itself shows a strong temperature dependence. Apparently, this anomalous reaction is related to the microstructure of the water-ink emulsion. In any case, the small temperature dependence and reproducible phenomenological response (Fig. 1) provide a theoretical basis for a meter for measuring the concentration of water in water-ink mixtures, as explained below. giving.

FIG. 2 is a block diagram of a capacitance-type meter according to the invention for obtaining a linear reading of the concentration C of water (or dampening solution) in an ink-water mixture. In this meter, the mixture acts as a dielectric material for the capacitor 8. The capacitance of the capacitor 8 depends on the dielectric constant ε' of the mixture and (as mentioned above and shown in FIG. 1) this in turn depends on the concentration C of water in the mixture.

Condenser 8 is part of the circuit of audio frequency oscillator 10 . The oscillator 10 has a capacitor 8
gives a square wave frequency that is inversely proportional to the dielectric constant of the mixture. This is expressed by the following equation.

f=1/2R _f C _p ε′・1/1n [(1+β)/(1−β
)] where Rf is the feedback resistance determined by the type of ink being measured;
β is the resistance of the positive feedback loop of the oscillator and C ₀ is the capacitance of the cell 8 in the absence of the mixture.

Once the square wave signal f is generated, the signal is
A frequency-to-voltage converter 12 is used to convert into a voltage E proportional to 10 ^-kc /ε ₀ '. As shown in Figure 1, the logarithm of the dielectric constant is the solution C in the storage container.
There is a linear relationship with the concentration of Hence,
E ₁ is converted into a base 10 logarithm by a logarithmic amplifier 14 . Since a limited logarithmic range is required, unit 14 can be constructed from an inexpensive operational amplifier and a suitable NPN transistor, or it can be purchased as a modular unit as shown later in the schematic diagram. .
In fact, low concentrations of water (e.g. 0-20% water)
In, the relationship between water concentration and dielectric constant ε′ is
It is linear enough to provide ±1% accuracy without a logarithmic amplifier. Thus, for meters used only to measure water concentrations below about 20%, logarithmic amplifier 14 can be eliminated. The output voltage E ₂ is proportional to the water concentration C offset by some arbitrary voltage given by the relationship E ₂ ∝kC+logε ₀ '. logε′ is
Constant for the particular type of ink being tested.

The final stage of the water-ink mixture meter is an amplifier 16 for conditioning the signal from the logarithmic amplifier 14.
and a display device 18 for reading out this signal. Amplifier 16 provides a voltage output of 0 V when the concentration of water in the water-ink mixture is 0 (C=0) and when the concentration is 50% (C=50%).
It has an adjustable offset voltage and an adjustable gain between 0.95 and 20 to give a voltage output of 5V.

A functional schematic diagram of the meter is shown in FIG. This unit is an oscillator (multivibrator) using amplifier A1 shown in the top left hand corner.
It consists of Three position switches are used to select the appropriate feedback capacitor to set the frequency based on some reference point (eg, an empty cell or a known ink-water system). The output from the oscillator is
The magnitude set by the positive gain setting (50+
2) is amplified by /x (amplifier A2), where x
is the resistance (KΩ) between the wiper and ground potential of the 50KΩ potentiometer. This is a non-critical setup and the frequency-to-voltage converter (Burr-Brown VF32) shown in the bottom right corner of the drawing
It is only necessary to ensure that there is a proper signal amplitude to trigger the . This integrated circuit provides a stress directly proportional to frequency. The reference voltage for input 1 provides the reference voltage for the log zero point.

This constant voltage is then applied to a constant amplifier (Burr-Brown Log100 module) shown in the bottom center of FIG. This is 3- for every 10V
Connected to maintain a decimal span. The reference current to pin 14 is provided by a simple current regulation circuit shown below the logarithmic amplifier. The output of this unit is a positive value above the 1V input (log1=0) and is inverted by the 0-to-1 gain amplifier A4. The gain setting is switched by a suitable feedback resistor to the multivibrator circuit shown by the dashed line. This amplifier performs two functions.
Its first function is to establish the proportionality constant K using appropriate gain settings as explained in the above section, and its second function is to establish the zero point voltage K in order to correct logε ₀ ′. The goal is to establish

The output of A4 is applied to A3 which acts as a buffer for a digital panel meter DM3100L set for an output of 0 to 5V.
This unit can be adjusted to read 1V for a 10% water concentration, for example. The four amplifiers (A1 through A4) shown in FIG. 3 may be coupled to a "quad op-amp" integrated circuit such as the National Semiconductor LF457.

With slight modifications, this circuit can be tuned to operate at any frequency that responds linearly to the dielectric constant of the ink. The frequencies used in various inks range from below 4KHz to above 300KHz. However, when configuring the meter, care should be taken to minimize stray capacitance and use an amplifier with sufficient gain-bandwidth product and negligible phase shift below 3MHz. It is.

FIG. 4 is a design drawing of a capacitor cell 8 used in the meter of the present invention. This cell is designed, for example, to be placed in series with a 3/4 inch diameter pipe 19 carrying the water-ink mixture of a large scale printing press. The internal member 20 is
It is supported within and electrically isolated from outer member 22 by, for example, nylon screws 24 and nylon spacers 26 . The inner member 20 is a tube with its end closed;
It also functions as one of the plates of the capacitor 8. Oscillator 10 is connected to internal member 20 by metal screw 28 and connector 30.
It is insulated from external member 22 by spacer 26 and insulating bushing 32.

External member 22 functions as the other plate of capacitor cell 8 . It is electrically connected to the oscillator 10 via a connector 34. In this design, approximately 0.2 inch spacing is provided for the flowing water-ink mixture that will guide the capacitor cells.

Opposing surfaces of members 22 and 20 are coated with a thin (0.005-0.010 inch) non-conductive polymer layer (e.g., Teflon or polyvinyl chloride) to remove electrical conductivity and prevent corrosion. is prevented.

Many variations and modifications are possible without departing from the invention. For example, capacitor cell 8
may be designed as a pair of flat parallel plates rather than a concentric tubular design as depicted in FIG. The mixture being measured may contain inks other than lithographic inks, provided that the relationship between dielectric constant and water concentration of the mixture is similar to that for mixtures containing lithographic inks. This measurement is formed by a flowing fluid or simply a group of mixtures. It is therefore to be understood that the particular forms of the invention described above are illustrative and not intended to limit the scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a graph depicting the relationship between water concentration (on a linear scale) and dielectric constant (on a logarithmic scale) for water-ink mixtures consisting of three different types of inks. FIG. 2 is a block diagram of an ink meter circuit according to the present invention. FIG. 3 is a schematic diagram of an ink meter circuit according to the present invention. FIG. 4 is a diagram showing a preferred embodiment of a capacitor cell used in the present invention. In the figure, 8 is a capacitor cell, 10 is an audio frequency oscillator, 12 is a frequency-voltage converter, 14 is a logarithmic amplifier, 16 is a signal conditioner, and 18 is a display device.

Claims (1)

[Scope of Claims] 1. A meter for measuring the concentration of water in a fluid mixture consisting of ink and water, comprising: a capacitor cell containing the fluid mixture; and an audio frequency oscillator circuit, the audio frequency oscillator circuit comprising: , utilizes the capacitor cell to provide capacitance to the oscillator circuit, such that the oscillator circuit provides an output frequency that is inversely proportional to the dielectric constant of the fluid, receives the output frequency of the oscillator circuit and controls the output a frequency-to-voltage converter that converts a frequency to a first voltage output that is directly proportional to the output frequency; a second proportional to the logarithm of the voltage output and directly proportional to the concentration of the water in the fluid mixture of the capacitor cell;
and a display means for receiving and displaying the second voltage output of the logarithmic amplifier, thereby determining the concentration of the water in the fluid mixture in the capacitor cell. A meter for measuring the concentration of water in a fluid mixture consisting of ink and water obtained. 2. The meter of claim 1, wherein the fluid mixture is a flowing fluid mixture and the condenser cell has an inlet and an outlet for receiving and discharging the flowing fluid mixture. 3. The meter of claim 1, including a first amplifier located between the oscillator circuit and the frequency-to-voltage converter to provide a signal of proper amplitude to the frequency-to-voltage converter. 4 a second amplifier receiving the output from said logarithmic amplifier and establishing the proper zero point voltage for the mixture being measured; and a third amplifier receiving the output of said second amplifier and serving as a buffer for said display means. A meter according to claim 1, comprising an amplifier. 5. The meter of claim 1, wherein said oscillator circuit includes selectable resistance and capacitance means for selecting the appropriate feedback to set the frequency for a particular mixture. 6. The capacitor cell comprises an inner cylinder with a closed end coaxially spaced apart within an outer cylinder with an open end, and separate electrical connections for the inner and outer cylinders. and a space between said coaxially spaced cylinders is provided to contain said flowing fluid mixture.
Meter listed in section. 7. A meter for measuring the concentration of water in a flowing fluid mixture consisting of ink and water, comprising: a capacitor cell having an inlet and an outlet for receiving and discharging the fluid mixture; and an audio frequency oscillator circuit; An audio frequency oscillator circuit utilizes the capacitor cell to provide capacitance to the oscillator circuit, whereby the oscillator circuit provides an output frequency that is inversely proportional to the dielectric constant of the fluid, and the oscillator circuit has a specific a first amplifier for amplifying the output of said oscillator circuit, having selectable resistance and capacitance means for selecting an appropriate feedback to set a frequency for the mixture; and a first amplifier for amplifying the output of said oscillator circuit; a frequency-to-voltage converter receiving and converting the output frequency to a first voltage output that is directly proportional to the output frequency; a second proportional to the logarithm of the first voltage output and directly proportional to the concentration of the water in the fluid mixture of the capacitor cell;
a second amplifier that receives the output from the logarithmic amplifier and establishes the proper zero point voltage for the mixture being measured; and a buffer amplifier that receives the output of the second amplifier. and display means for receiving and displaying the output of the buffer amplifier, whereby the concentration of the water in the fluid mixture in the capacitor cell can be measured.