GB2146130A - Measuring device for detecting and monitoring the filling level of centrifuges - Google Patents

Abstract

In a measuring device for detecting and monitoring the filling level of centrifuges in electrochemical deburring plants, which centrifuges are used for separating the metal hydroxides, produced during the deburring process, from the electrolyte and the filling volume of which is proportional to an electrically detectable measurement quantity, a voltage (U) which is proportional to the workpiece-machining current serves as the measurement quantity. This voltage is converted by means of an electronically controlled voltage/frequency converter (3) into a signal sequence (f1 and f1', respectively) having a voltage-proportional frequency and the signals are counted in a counting device (5). The constant of proportionality between the measurement voltage (U) and the signal frequency (f1 or f1', respectively) is variable so that the counting device (5) can indicate the operating current of the plant in the desired unit, for example in A/h. <IMAGE>

Description

SPECIFICATION Measuring device for detecting and monitoring the filling level of centrifuges The invention is based on a measuring device according to the generic type of the main claim. In plants for the electrochemical machining of workpieces, metal hydroxide is produced during the machining process and is precipitated as sludge. These hydroxides occurring during the erosion process contaminate the electrolyte and impair the efficiency of the plant. For this reason, the electrolyte must be continuously cleaned. The facilities used most frequently for this purpose are special centrifuges in which the hydroxides are separated from the electrolyte by the centrifugal force. On the circumferentiai surface of the centrifuge drum a layer of sludge forms which must be peeled off fully automatically or semi-automatically when a certain thickness is reached.During this proces, it is important to detect the point in time when such draining is to take place, and to trigger the draining process.

According to Faraday's law, the volume of material removed during the electrochemical machining of a workpiece is proportional to the product of electric current (I) and the time (t) during which it flows.

V Kx I xt If the material constant K is known, the quantity of material deposited in the centrifuge can be determined by measuring and multiplying the machining current with the machining time.

For this purpose, electro-mechanical pulse generators with a connected preselection counter have hitherto been used. An electric motor, on the shaft of which a pulse generator disc is mounted, is driven by the current which is produced by the voltage drop across a resistance of the machining circuit and which is proportional to the respective machining current. With each rotation of the pulse generator disc, the latter operates an electric contact which causes a pulse to reach the preselection counter. If the counter reaches the preset value, the draining of the centrifuge is triggered by a signal emitted by the counter. The counter is subsequently reset.

Due to their inaccurate operation, such electro-merchanical pulse generators do not permit an accurate detection of the criteria which are determining for the filling level of the centrifuge. The measurement voltage and frequency have a fixed relationship to each other which is predetermined by the rotational speed of the electric motor, and the numerical values appearing in the counting facility do not provide the operator with direct information concerning the magnitude of the machining current per urrit time (A/h). In addition, a pulse generator equipped with an electric motor is relatively expensive and takes up considerable space within the circuit.

In German Offenlegungsschrift 2,919,694, a measuring device for electric energy (Watthour counter) has been disclosed which is equipped with two converters for converting current and voltage into signal sequencies of different frequency. These frequencies are then multiplied by counting out the signals of the higher frequency in a counting device for the duration, fixed in time, of the lowerfrequency signal. Such a measuring device is used for recording the power costs of electricity consumers where both the current and the voltage are subject to fluctuations. It is thus not automatically suitable for detecting the filling level of the centrifuge of an electrochemical deburring replant because this works with a constant machining voltage and only the current intensity väries as a function of the resistance.In this connection, the work gap, through which the electrolyte flows, between the workpiece and the tool electrode must be considered to be an ohmic resistance.

It changes its magnitude with the width of the gap and the electrolyte concentration (conductivity) and thus affects the current flowing across the gap.

Advantages of the invention By comparison, the device according to the invention, having the characterising features of the main claim, has the advantage that a very accurate detection of the centrifuge filling level is possible by digital measuring methods with low space requirement and costs Compared with the known electromechanical pulse generators, the cost saving is about 50%. As a result of the fact that the voltage/frequency converter is provided with a circuit which allows the proportionality constant between measuring voltage and signal frequency to be changed, the counter display can be calibrated, for example, directly in A/h.

As a result of the measures listed in the subclaims, advantageous further developments and improvements of the measuring device specified in the main claim are possible.

Drawing An illustrative embodiment of the invention is illustrated in the drawing and and is explained in greater detail in the description which follows.. Fig. 1 shows a block diagram of an illustrative embodiment and Fig. 2 shows a signal diagram for explaining the operation.

Description of the illustrative embodiment A current measuring resistance 1 is disposed in the operating circuit of a plant, not SPECIFICATION Imaging or like apparatus This invention relates to imaging or like apparatus (eg.thermal imaging apparatus) having detector means upon which electromagnetic radiation from an object or scene is directed and which detector means requires to be periodically irradiated at a predetermined low level, preferably related to the radiance of the object or scene, in orderto provide a reference, for example a grey level reference.

Hitherto, this irradiation has been achieved by periodically moving an opaque member,forexample in the form of a blade, into the optical path to interrupt the radiation normally incident upon the detector means. Such an arrangement has various shortcomings. Since it is a a mechanical arrangement, it is difficult to drive the blade at precise time intervals especially during conditions ofvibration and acceleration and wherethere are limitations on spaceforthe drive arrangement. Moreover, the opaque blade gives a radiance which is unrelated to the object or scene radiance.

It is therefore an object of the present invention to overcome these shortcomings in a relatively simple manner.

According to the present invention, imaging apparatus having detector means upon which electromagnetic radiation from a source is directed and which detector means requires to be periodically exposed to a predetermined radiance level, includes liquid crystal means located in between the detector means and the source, the liquid crystal means being changeable from a condition in which there is substantially no effect on the radiation directed onto the detector means, to a condition or conditions in which the radiation is diffused, and means to effect such change in condition.

Thus, any mechanically movable parts are eliminated; it is found that in its diffuse condition the liquid crystal means provides a radiance which is related to the object or scene radiance. The liquid crystal means also destroys the structure of the object or scene within the radiation giving a relatively uniform irradiance on the detector means.

One embodiment ofthe invention is illustrated by way of example with referenceto the accompanying drawing.

In this embodiment, a liquid crystal assembly is incorporated in thermal imaging apparatus, the liquid crystal assembly comprising a liquid crystal layer 1.

sandwiched between two germanium discs 2 and 3 respectively. In the normal quiescent condition, the layer 1 is clear. When a voltage is applied across the discs, the layer 1 becomes diffuse to an extent depending upon the magnitude ofthevoltage.

The imaging apparatus itself comprises focussing means 4 by means ofwhich incoming radiation from an object or scene is focussed onto detector means 5, for example an array of detector elements. The detector mears is mounted within a vacuum encap sulation 6 and cooled to its operating temperature by cooling means 7.

Awindowisformed in the encapsulation 6; this, when of germanium or similar material, thus can provide one layer 2 ofthe liquid crystal sandwich. The liquid crystal layer 1 and its two sandwiching layers 2 and 3 lie external to the encapsulation 6 but between it and the focussing means 4. Leads 8,9 allow a voltage to be applied across the germanium discs 2 and 3 of the liquid crystal sandwich.

A suitable liquid crystal layer 1 is of a thickness of several wavelengths of the radiation to be detected. It has a high transmission to those radiation wavelengthsforwhich the apparatus isto be used when in the quiescent condition.

When, periodically, a voltage is applied, the layer 1 scatters the radiation to an extent depending on the magnitude ofthe voltage. If desired, morethan one voltage level may be used to effect different degrees of scattering so that the gains ofthe channels of any amplifier means receiving the outputs of the detector means may be matched as well as having the D.C.

Output levels restored.

Although the sandwiching layers 2 and 3 have been specified as being formed of germanium and are therefore electrically conductive, other infra red transmissive materials can be used. Naturally, ifthese, like zinc sulphide and sapphire, are not electrically conductive, then some form oftreatment is necessary to renderthem so.

Claims (4)

1. Imaging apparatus, having detector means upon which electromagnetic radiation from a source is directed and which detector means requires to be periodically exposed to a predetermined radiance level, including liquid crystal means located in between the detector means and the source, the liquid crystal means being changeable from a condition in which there is substantially no effect on the radiation directed into the detector means, to a condition or conditions in which the radiation is diffused, and means to effect such change in condition.

2. Imaging apparatus according to claim 1 wherein the detector means includes a radiation transparent window, the liquid crystal means comprises a liquid crystal layer sandwiched between two radiation transparent layers, and one of said layers comprises the radiation transparent window.

3. Imaging apparatus according to claim 2 wherein the transparent layers are formed of germanium.

4. Imaging apparatus substantially as described with reference to the accompanying drawing.