GB2144255A - A meter display - Google Patents

Abstract

A meter display (Figs. 1 & 2) in which the main scale (M,E) is supplemented by a dial-shaped scale formed by the common area of overlap between electrodes (V,EV) mounted each side of an electro-optically responsive medium, one set of electrodes (V) being comprised of several segments (V0???,V9). On one side of the medium, the main scale electrodes (M0???,M9) may likewise be of segment form and the main scale of vernier scale electrodes interconnected. Identical waveform select address may be used - eg the address may be by pseudo-random binary sequence signals. The above may be used in conjunction with a digital display for measurement of signal extrema. A pseudo random binary generator applies a set of isogonal signals to the main scale segments M0-M9 and to the vernier scale segments V0 to V9 and to a multiplexer gated by BCD data. The multiplexer selects one of the signals for application to the vernier electrode EV. The vernier scale display is also indicative of whether the measured signal is increasing, decreasing or approaching a stationary value. <IMAGE>

Description

SPECIFICATION Meter display Technical field This invention concerns improvements in or relating to meter displays, and in particular, to addressable electro-optic meter displays.

Background art A typical electro-optic meter display comprises a pair of electrode-bearing plates arranged each side of an electro-optically sensitive medium. Indication is achieved using either electro-optically controlled emission - as in the cases of a rarefied gas medium, or electro-luminescent solids medium, or an electrooptic passive effect - as in the case of a liquid crystal medium. Such displays do not rely upon the movement of mechanical parts, and therefore do not suffer from wear and need little if any maintenance.

They do not suffer from inertia, or from overshoot, and response is virtually instantaneous. The electrodes upon each plate are configured and arranged so that their common area of overlap defines the display area of the meter. In a typical arrangement, the electrodes upon one of the plates are configured in the form of a row or arc of individual segments.

The electrodes upon the other plate have a folded configuration. In the assembled construction each of these electrodes is arranged opposite, and thus overlaps, each segment once only. Thus for example in a 10 x 10 matrix configuration using ten segments and ten folded electrodes, an index can be displayed at any one of a hundred positions, given appropriate address. In this example, as indeed is typical of analogue meters whether mechanical or electro-optic, the accuracy of measurement is only one per cent of full scale deflection (1% f.s.d.). The accuracy therefore is low. Notwithstanding, such meters can be used to measure values to greater than two-significant figures, but this requires the addition of bridge-balance circuits or the like, which allow signal offset and stepwise change of meter sensitivity.Such measurement must be performed in a series of sequential steps. This technique of measurement is barely suited to aid in optimal adjustment of measured signal - ie adjustment to an extremum (max or min) value if signal changes are either frequent or rapid.

Digital displays, on the other hand, are capable of display to many significant figures accuracy. However, to determine whether measured signal is increasing, decreasing or approaching stationary value, it is necessary to record and compare the successive readings. It is therefore no trivial task using a digital display for setting measured signal to a stationary (max, min or inflection) value.

Disclosure of the invention The invention disclosed hereinbelow is intended as an improvement in analogue meter displays, and to provide a means of solution for the problems discussed above. Use is made of a vernier scale to enhance the accuracy of addressable electro-optic analogue meter display.

In accordance with the invention there is provided a meter display comprising a pair of electrodebearing plates arranged each side of an electrooptically sensitive medium, the electrodes each side of the medium being arranged opposite and defining, by their common area of overlap, the main scale display area of the meter, wherein the improvement comprises the addition of a vernier scale, a dial defined by the overlap of further electrodes each side of the medium, the further electrodes upon one of the plates being in the form of a plurality of segments.

It is convenient to choose an electrode arrangement wherein the vernier segment electrodes and the main scale segment electrodes lie upon the same plate and are connected. This affords compatibility with address circuitry of very simple design. In particular, identical waveform select address circuitry is considered most suitable.

In full assembly, the meter display may be combined with a binary-coded decimal output data source, an address signals source and selection electronics responsive to BCD address. With this assembly the vernier scaie allows display overall to three significant figures accuracy- ie 0.1% f.s.d.

What is more the trends for measured signal as displayed upon the dial are readily perceptible.

Clockwise rotation of index aboutthe dial can be interpreted as indicative of signal increase, and anticlockwise rotation as signal decrease. The slowing of the apparent motion of the index, or its rotation reversal, can be used as useful aid in the setting and adjustment of signal stationary values.

Brief introduction ofthe drawings In the drawings accompanying this specification: Figures 1 and 2 are plan drawings showing the electrode configurations for the backplane and frontplane plates, respectively, of an electro-optic addressable analogue meter, an embodiment of the invention; Figure 3 is a circuit diagram for a pseudo-random binary sequence signal generator, a signals source suitable for operation of this meter display; Figure 4 is a block diagram of multiplex selection electronics, electronics usable in conjunction with the signals source shown in the preceding figure; and, Figures 5 and 6 are plan drawings showing the electrode configurations for a vernier scale, a variant of that shown in Figures 1 and 2 above; and, Figure 7 is a block diagram of multiplex selection electronics chosen for address of the variant shown in Figures 5 and 6.

Description of the preferred embodiments Embodiments of the invention will now be described, by way of example only, with reference to the accompany drawings.

In Figures 1 and 2 the electrodes for the backplane plate and frontplane plate are shown. When assembled these plates are located each side of an electro-optically responsive medium, eg a layer of liquid crystal material. Well suited to this application is the material D82E61 blue dye-nematic liquid crystal to which is added approximately 3.9% by weight of CB15 cholesteric liquid crystal. The blue anthraquinone dichroic dye D82, namely 4, 5diamino-2, 7-di-isobutyl-1, 8-dihydroxy anthraquinone, is described in UK Patent Application No GB 2,081,736A.

The liquid crystal materials, E61, CB15, the dye D82 and the dyed nematic material D82E61 are listed in the trade catalogues of BDH Limited, Poole, Dorset, England.] The backplane electrodes shown in Figure 1, comprise one set of electrodes M arranged in an arc, and another set of electrodes V arranged in the form of a dial, to provide for main scale and vernier scale display, respectively. Each set of electrodes, M, V is comprised of ten equal segments Mo to Mg, V0 to V9.

The main scale segments Mo to Mg and the vernier scale segments VO to Vg are connected in pairs Mo and Vg; M1 and V6; ...; Mg and V4 and only ten terminal connections are thus required for address of all twenty segments.

The frontplane electrodes shown in Figure 2 are also arranged in the form of an arc E and of a disc V' for main scale and vernier scale display. The arc electrodes Eo to Eg, ten in number, are of folded configuration and arranged so that upon assembly each electrode Eo to Eg traverses each of the arc segments Mo to Mg opposite, once only. A single electrode of dial shape Ev is provided for the vernier scale.

A pseudo-random binary sequence signal gener ator, a signal source suitable for addressing the display, is shown in Figure 3. This generator 1 is comprised of a clock 3 and shift register 5. An exclusive OR-gate 7 provides feedback to the register input and is connected to output channels So and S3 of the register 5. Exclusive OR-gate feedback provides pseudo-randomisation in the signal codes generated at the output channels of the register 5. Further logic components, a NOR-gate 9 and an AND-gate 11 are included, as shown, to enable initiation of signal generation. This generator 1 provides a set of isogonal signals, ten of which, signals So to Sg are applied as a fixed address to the main scale segments Mo to M9 and to the vernier scale segments V0 to Vg.These ten signals are also passed to the gate inputs of a 10:1 multiplexer, multiplexer 12, as shown in Figure 3. They are applied in the modified order Sg to Sg, So to S4 to inputs lo to 19. This corresponds to the connection arrangement of M5 to Mg and Mo to M4 to V0 to Vg shown in Figure 1. The output channel of this multiplexer is responsive to BCD data. Data input, provided from an external data source, is applied to the four control inputs J0 to J3 of the multiplexer. As the data changes value in the range 0000 to 0101, the multiplexer 12 selects one of the signals So to Sg as appropriate and applies it to the vernier electrode Ev.At the region of the medium between this electrode and a chosen segment electrode, one of the ten electrodes V0 to Vg carrying the identical signal, there is no field and the medium is held in its OFF state. All other segments VO to Vg carry a different signal to that on the single vernier electrode Ev.Afinite voltage difference is thus applied across all other regions of the medium. A segment shape index is thus displayed against the contrasting background provided by the remainder of the display.

With suitable modification, it is possible to connect the backplane electrodes to similar electrodes at an adjacent site (cf UK Patent Application No GB 2,106,298A). One such modification is illustrated in Figures 5 and 6. As in the previous example, the backplane electrodes form ten segments VO to Vg of a dial V. Only one half of these, segments V5to Vg, however are connected to the main scale segments, segments Mo to M4.A part of this modification, mirror-opposite segments V0 and Vs, V1 and V8 --, V4 and V5 are connected at their inner extremity. (In fact segments V0 and Vg, as also V4 and V5, may be united.) It is then possible to gain access to vernier electrodes V0 to V4 and main scale electrodes M5 to Mg to afford connection to adjacent scale electrodes without there being any necessity for cross-over.

Indeed, if desired, a second dial could be included for greater accuracy measurement. The frontplane vernier electrode, however, is now divided into half-portions EL, ER as shown in Figure 6. The selection electronics shown in Figure 7 includes two multiplexers 13, 15. These are used to select one of the signals So to S4, a dump waveform signal S5, and to apply each to one of the two half-electrodes EL, En.

Claims (3)

1. A meter display comprising a pair of electrode-bearing plates arranged each side of an electro-optically sensitive medium, the electrodes each side of the medium being arranged opposite and defining, by their common area of overlap, the main scale display area of the meter, wherein the improvement comprises the addition of a vernier scale, a dial defined by the overlap of further electrodes each side of the medium, the further electrodes upon one of the plates being in the form of plurality of segments.

2. A display as claimed in claim 1 wherein the vernier segment electrodes and the main scale segment electrodes lie upon the same plate and are connected.

3. A meter display constructed, adapted and arranged to operate substantially as described hereinbefore with reference to and as shown in the accompanying drawings.