Light-Emitting Semiconductor Display Apparatus for Displaying a Band Representation of a Voltage Analog of a Measured Parameter

The invention relates to light emitting semiconductor display apparatus for displaying a band representation of a voltage analog of a measured parameter.

According to the invention, there is provided metrology apparatus, for use in conjunction with a transducer and an electrical circuit which together form a voltage analogue of a parameter to be measured, for providing a visual display of the value of the analogue and hence of the parameter, the apparatus comprising a series of semiconductor light emission devices, a terminal for receiving said voltage analogue, and electrical circuitry connected to said terminal and to said devices for causing the devices to emit light in such manner that they provide a band representation of the value of said analogue with a zero value of the analogue being represented by a band terminating intermediate the ends of the said series, and for causing the nature, other than merely the length of the band, of said representation to become visually different if the value of said analogue is not within a predetermined tolerance range.

The electrical circuit which, with the transducer, forms a voltage analogue of the parameter to be measured may be supplied as part of, and included in, the apparatus while the transducer may be supplied separately being disconnectible from the apparatus.

Preferably, a zero value of the analogue is represented by a band of light terminating at the centre of the series of devices thus giving a "centre zero" display.

Preferably said electrical circuitry comprises means for forming a series of different reference voltages, and a series of comparators each having one input connected to receive a respective one of the reference voltages, another input connected to said terminal, and an output connected to control the devices. The reference voltage forming means may comprise a series resistor chain.

When the value of said analogue is not within the predetermined tolerance range, the representation might, for example, flash on and off repeatedly. For this, said electrical circuitry may comprise means for detecting that the value of the analogue is not within the tolerance range and two switches connected in parallel and so as to control the flow of electrical current through said devices, one of the switches being continuously opened and closed in succession during use of the apparatus and the other being connected to be controlled by the detecting means and being closed when the analogue is within said tolerance range. The said detecting means may comprise a pair of comparators each having one input connectible to receive a respective tolerance range limit voltage, another input connected to said terminal, and an output connected to control said other switch.

Advantageously, said circuitry comprises multiplexing means. For example, said devices may be arranged in two groups, the output of each comparator in said series thereof being connected to control one device in each group, and there can be switching means for causing said reference voltage forming means to alternately and repeatedly form first one and then another series of reference voltages and for causing it to be alternately and repeatedly possible for the devices of first one and then the other group of devices to emit light.

The voltage analogue forming circuit, when present, will comprise an input for connection to said transducer and an output connected to said terminal. Preferably, this voltage analogue forming circuit comprises an oscillator having an output available for connection to said transducer, and sampling means for sampling the oscillator output signal which is received at the analogue forming circuit input via the transducer during use of the apparatus, and for supplying at said terminal a direct-current signal representative of the oscillator output signal as received via the transducer. There may be further sampling means which is connected to receive the oscillator output signal directly, to sample it and to supply a direct current signal which is fed so as to determine said series of reference voltages. Preferably, there is inverting and buffering circuitry for forming from the output of the further sampling means a positive reference voltage and a negative reference voltage which are fed along two respective conductors to said switching means which selects these voltages alternately and repeatedly and supplies the selected voltage to said resistor chain. Two potentiometers may each be connected between said two conductors for forming said tolerance range limit voltages.

Preferably, said semiconductor light emission devices comprise light emitting diodes.

In order to set the tolerance limits, it is desirable to have some method of displaying both upper and lower limits simultaneously. It is optionally possible to do this by using the three different modes of display (dark, flashing lights or steady lights) to define the zones of above tolerance, in tolerance and below tolerance. The actual tolerance limits will then be clearly indicated at the two junctions of these zones. Alternatively, the in-tolerance zone could be defined by a solid band of light, both the out-of-tolerance zones being dark.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, the single FIGURE of which comprises a simplified circuit diagram of one embodiment of the invention.

The apparatus may conveniently be used in conjunction with a differential inductance transducer 1 which comprises an inductor having a displaceable core. The transducer is arranged so that the position of its core is affected by a parameter to be measured, e.g. a physical dimension of some manufactured article, and the inductance value of the transducer is thereby affected by that parameter. The transducer is connected in a bridge circuit which produces a voltage analogue of the parameter. An oscillator 2 excites the transducer 1 at about 10 KHZ and also drives a pulse generator 3 which produces a short pulse at each peak of the oscillator waveform. This controls a first sampling circuit 5 which samples the oscillator voltage at intervals determined by the pulse generator and produces a DC reference output proportional to the oscillator amplitude. A second sampling circuit 6 produces a DC output proportional to the core displacement of the transducer 1. The reference output from 5 is buffered and inverted at 8 to produce positive and negative reference signals. These signals are fed through switch S1 to become driving voltages for a resistor chain 13 which produces a series of reference voltages differing by equally spaced steps as the inputs to a series of comparators 14. The comparator outputs drive two chains of light emitting diodes 15, each comparator driving one diode in each chain. The diodes are arranged to form a column light display with one chain of diodes forming the upper half of the column and the other chain forming the lower half. The two diode chains are grounded in turn through switch 16, which is switched in synchronism with S1 at 50Hz, and through the normally closed contact on a relay 12. Because of this multiplexing arrangement in which each comparator drives two of the diodes on a time division basis the number of comparators 14 needed only has to be half the number of diodes 15.

The analogue signal from discriminator 6 is fed through an amplifier and magnification control 7 to the second inputs of all the comparators 14. Thus, those comparators 14 whose reference voltage is below the signal voltage will have a high output, and will illuminate the relevant diode. All others will have a low output, and the associated diodes will be extinguished. The two diodes which are associated with the comparator receiving the lowest reference voltage magnitude are at the centre of the column -- thus the display has a "centre zero".

The upper and lower tolerance limits are set at the potentiometers 10. The voltages appearing at the moving contacts of these potentiometers are buffered and are compared with the analogue by limit comparators 11. While the analogue remains between the tolerance limits, a relay 12 is not energised and the light emitting diode chains are grounded as aforesaid through its normally closed contact. If the analogue goes out of tolerance, this contact opens, and the lights are caused to flash through the action of one contact set--, and after "S2B" insert--of a switch S2 which also comprises a ganged contact set S2A and S2B which is opened and closed at a rate of a few Hertz (typically 4Hz).

The tolerancing setting facility is activated by switching switch S3 comprising ganged contact sets S3A and S3B to "set" position. S3B then shorts out S2B and the contact of the relay 12. This disables the normal out of tolerance indication and S3A connects the comparator chain input to S2A. S2A is switched at a few Hertz (typically 4Hz) between the high and low limit values. The effect of this is that all diodes below the low limit are illuminated for one half of the 4Hz switch cycle, and all diodes below the upper limit (including those below the lower limit) are illuminated for the other half cycle. Thus the diodes below the low limit appear to be continuously illuminated, those between the two limit values flash at the switching rate, and those above the upper limit are not illuminated. The limit points are thus clearly indicated.

it will be appreciated that switch contacts S1 and S2 to the comparator inputs can conveniently be formed by field effect transistors suitably buffered, while the contacts of the switches which are used to ground the light emitting diode chains can be formed from transistors.

It will be seen that in the embodiment described, the output level of the oscillator 2 does not effect the displayed measurement because the oscillator output is used not only to excite the transducer 1 but also to form the reference voltages fed to the comparator chains.

The apparatus may be housed in a housing unit with the series of LED.s forming a column display visible from say the front of the housing unit. The housing unit may then be arranged in conjunction with other similar units to supply displays of several parameters to be measured.