GB2189337A - Indicating and control instruments - Google Patents

Abstract

An indicating instrument, for example a temperature controller, which is responsive to a parameter, such as temperature, of an associated system or apparatus comprises a first display 17, 18 arranged in an annular configuration and providing a visual indication of a set-point value of the parameter, a hand wheel 14 to adjust the set-point value to a different set-point value, and a second display 24 providing a visual indication of an operating condition of the instrument or of the current value of the parameter. This second display 24 is located within the annulus of the analogue set-point display 17, 18. Preferably, the second display 24 provides an indication of the difference between the current value of the parameter and the set-point value as shown by the marker 18. A series of LEDs may be used as the second display 24 in the form of a bar graph. The instrument may be designed to monitor other parameters such as pressure and time. In the case of a time controller, the first display may indicate a set length of time and the second display how much of the time has elapsed. <IMAGE>

Description

SPECIFICATION Indicating and control instruments This invention relates in its broadest sense to indicating instruments, and is more particularly concerned with indicating instruments which also exert a control function. Thus, operating parameters of systems or apparatus, such as temperature, pressure or length of time of operation, may be indicated and/orcontrolied.

Control instruments are known which include a scale or dial having a marker which indicatesthe selected magnitude, i.e. the set point, of an operating condition of an associated system or apparatus. For example, a temperature control for an oven may include a dial marked in degrees Celsius. In orderto select a desired operating temperature, the dial is turned until a pointer on the dial points to the desired temperature. The controller communicates that temperaturetothe oven theremostatandthe oven heats upto that temperature.

However, such controllers give no indication as to whether or not the selected magnitude of the parameter, e.g. the selected temperature, has been reached, or how close the system or apparatus isto reaching it.

It is known, for example in domestic oven controls, to provide a separate indicator light which is extinguished when the desired temperature, or other condition, has been reached. However, such indicators give only a very rough guide as to the exact condition of the system or apparatus.

It would be an advantage, particularly for industrial users, where specific operating conditions must be maintained for satisfactory operation, to provide a clear indication of the deviation of actual conditions from a set point.

It is known to provide a separate meter, for use in conjunction with a control instrument, which gives a reading of an operating condition for comparison with that selected, or which indicates the deviation of the operating condition from that selected. However, the use of such a separate meter, in addition to the control instrument itself, is disadvantageous, inter alia in requiring additional space.

In accordance with the present invention there is provided an indicating instrument responsive to a parameter of an associated system or apparatus, the instrument comprising first display means arranged in an annularconfiguration and providing avisual indication of a set-point value of a differentset-point value, and second display means providing avisual indication of an operating condition of the instrumentorofthecurrentvalueofsaidparameter, wherein said second display means is located within the annulus of said first display means.

Preferably, said second display means provides an indication of the difference between the current value of said parameterandtheset-pointvalue.

Preferably, the second display means comprises one or more lig ht-emtting diodes. With a plurality of light-emitting diodes one can arrange them in a bar-graph configuration to provide a visual indication upscale and downscale of the set-point Alternatively the second display means can be a digital display ofthe current value ofthe parameter.

The first display means may comprise a handwheel rotatably mounted on a casing ofthe instrument and carrying a markerwhich traverses an analogue scale. The scale may be provided around the edge of a circular dial plate which is provided with one or more aperturesthroughwhich the second display means is visible.

In a preferred embodimentofthe invention, the instrument includes an annular potentiometer mounting plate positioned rearwardly of the handwheel,with the annular mounting plate defining a chamber rearwardly of the first display means within which the second display means is located.

The indicating instrument of the present invention is particularly applicable to the indication ofthe temperature, and by extension, to providing temperature control.

However, although the instrument ofthe present invention is particularly applicable to temperature indication and/or control, it can be used also for monitoring other parameters, such as pressure, time, etc. In the case of a time controller, the instrument might include a first scale indicating the set length oftimeforwhich an associated system or apparatus is set to operate, and a second display indicatng how much ofthattime period has elapsed, thus providing an indication as to how much longer the associated system or apparatus will function.

In a preferred embodimentofthe present invention, designed as a temperntu re controller, it is possible to combine the important operational features of constant visual set-point and temperature indication with selectable control and output capabilities.

A preferred embodiment of the invention will now be described by way of example and with reference totheaccompanying drawings, in which: Figure 1 is a front view of the face of a temperature controller constructed in accordance with the present invention; Figure2 is a sectional side view taken along the line ll-ll in Figure 1, details ofthe electronic circuitry being omitted for clarity; and, Figures 3A, 3B and 3Care front face view ofthree different forms oftemperature controller in accordancewiththe presentinvention,each providing a different form of display.

Referring to Fgures 1 and 2 ofthe drawings, a control instrument is illustrated, for use in controlling temperature. The instrument, indicated generally at 10, has a casing 11 which is substantially square in cross-section. One end of the casing is fitted with a standard base 12 havng the usual pin connections for connecting the instrumentto the apparatus which it is to control. The space 13 within the casing houses the necessary electronic circuitry for the instrument, for example in the form of a number of circuit boards.

An annular handwheel 14 is rotatably mounted on the front of the casing 1 1 .As can be seen from Figure 1, the handwheel is generally annular and fits snugly within the casing 11. The wheel has an outer rim 30 which prevents it from sliding right into the casing, and is held in place on the front ofthe casing by a frnt bezel 31. The handwheel has a small recess 32 at the front, in which is fitted a plate 15 of rigid clear plastics material or some other transparent material.

The plate 15 serves as a window through which to view a dial 17 which is carried bya dial mounting plate 16. The dial mounting plate is fixed with respect to the casing in a mannerwhichwill bedescribed hereinafter. The dial is marked off with a temperature scale in degrees Celsius. The transparent plate 15 has a marker arrow 18 marked on it. Thus, as the handwheel is rotated with respect to the casing, the arrow moves overthe scale.

An annular potentiometer mounting plate 20 is provided which is mounted at the front end of casing 11 behind the handwheel 14. The mounting plate 20 is mounted between stops 33 provided within the casing, and the handwheel 14. The mounting plate 20 is generallyannularand has a portion 34 extending forwardly within the handwheel 14. The dial mounting plate has a rearwardly extending portion which fits within the potentiometer mounting plate 20. The potentiometer itself comprises a strip of metal, not visible in the drawings, which extends partially around a seating surface 36 ofthe mounting plate. One end ofthe metal strip is connected to the circuitry. The handwheel carries a contact 37 which presses againstthe metal strip and is also connected to the circuitry.Thus, as the handwheel is rotated,the length of metal, and hence the resistance, between the two connections is varjed.

To complete the construction, a contact plate 40 is provided between the handwheel and the potentiometer mounting plate, which serve to keep the handwheel in place and to close the end ofthe casing 11.

As can be seen from Figure 2, this construction leaves a chamberorspace 22 behindthe dial mounting plate 16 which is not present in the conventional construction. The chamber 22 here houses an array of light-emitting diodes (LEDs) 24.

The LEDs are mounted as a multi-segment bar-graph display in an aperture 23 formed in the dial mounting plate 16 whereby they may be viewed through the transparent plate 15. The LEDs are connected to the potentiometerandto associated sensing means such as thermocouples in such awaythatthey provide an indication of the deviation ofthe actual temperature ofthe assocated system or apparatus from the selected set-pointtemperature. The centre line X-X of the array indicates the selected set-point temperature.If any of the LEDs to the left ofthe centre line are illuminated, this indicates that the actual temperature is lower than that selected, and if any ofthe LEDs to the rightofthe centre line are illuminated, this indicates thatthe actual temperature is higherthan that selected. Preferably, the arrangement is such thatthe number of LEDs which are iit up is proportional to the deviation of temperaturefrom the set-point, and a suitable scale 25 is provided on the row of LEDs. Preferably, the LEDs on the left are green and the LEDs on the right are red. Thus, for example, as the temperature drops below the selected value, successive LEDs, beginning with the LED immediatelyto the left ofthe line X-X, light up.

The necessary connections for the LEDs pass out ofthe chamber 22 and are connected to the circuitry housed in the space 13.

The instrument 10 is preferably the same size as currently available standard temperature controllers. Thus, an existing temperature controller may easily be replaced by a controller such as that described above without the need for any extra space.

The depth A of the casing 11 is 85 mm, and the total length B of the instrument, excluding the pins atthe base, is 215 mm. In an instrumentmanufacturedto the above sizes, the chamber 22 would, alternatively, be sufficiently large to house a small ammeter. Thus, such an ammeter could be used instead ofthe LEDs as the second display, for example two indicate temperature deviation. A second circu larscale indicating the temperature deviation could be provided on the dial mounting plate 16 and a pointer, projecting through a suitable hole in the dial mounting plate, could traverse the second scale.

The electronic circuitry housed in the casing space 13 would perform the usual function of providing appropriate signals to control a thermostat in responsetoanaloguesignalsfromthe potentiometer. Extra circuitrywould be required for comparing the actual temperature of an associated system or apparatus, as sensed for example by thermocouples, with the set-point temperature and causing the LEDs or ammeter to give the appropriate reading.

The controller shown in Figure 1 includes a lock L which is operated to lock the handwheel in place once the desired set-point temperature has been selected. An adjuster A is provided to centre the temperature variations on a desired point.

Figures 3A, 3B and 3C show alternative types of displayfortemperature controllers of the present invention. In Figure3Athere is an analogue set-point display provided by the marker 18 and the circular scale 17. Within the visual area defined by the scale 17 there are two slots in the dial plate 16. The lower slot 50 provides red LED illumination to indicate that the output ofthe temperature controller is "on". The upperslot 52 provides yellow LED illumination indicating that power is "on". Thus, in this embodiment, the visual indication at 52 is indicative of an operating condition of the instrument, not of the current value of the temperature being monitored. Such a low cost instrument is ideally suited to applications where an indication of process temperature is not essential.

Figure3B shows an arrangementwhich is very similartothatshown in Figure 1.Theadditional feature here is the provision of the lowerindicator50 which again is a red LED illumination to indicate output "on".

In Figure 3C,the second display, within the annular analogue set-point display, is a digital display 54 of the current process temperature. In yet a further alternative embodiment, not illustrated, the centre of the instrument could be provided both with an LED display and with a digital display.

As illustrated in the drawings, especially in Figure 2, the instrument of the present invention is a stand-alone instrument for panel, base orwall mounting. Alternatively, the "front end" ofthe instrument, i.e. the part of front ofthe stops 33, can be formed as a panel-mounted module two be used with a separate, indepdently sited control module which provides the control and output functions. The panel-mounted module can be connected to the control module by suitable cable connections. This reduces back-of-panel projection to a minimum. It can also provide additional control functions which would otherwise result in an unacceptable increase in normal instrument body length.

Claims (12)

1. An indicating instrument responsive to a parameter of an associated system or apparatus, the instrument comprising first display means arranged in an annularconfiguration and providing avisual indication of a set-pointvalue of said parameter, means to adjust said set-point value to a different set-point value, and second display means providing avisual indication of an operating condition ofthe instrument or of the current value of said parameter, wherein said second display means is located within the annulus of said first display means.

2. An instrument according to claim 1, in which said second display means provides an indication of the difference between the currentvalue of said parameter and the set-point value.

3. An instrument according to claim 1 or 2, in which said second display means comprises one or more light-emitting diodes.

4. An instrument according to claim 3, in which the second display means comprises a pluraliity of light-emitting diodes arranged in a bar-graph configuration to provide a visual indication upscale and downscale of the set-point value.

5. An instrument according to claim 1, in which said second display means is a digital display ofthe currentvalue of said parameter.

6. An instrument according to any preceding claim, in which the first display means comprises a handwheel rotatably mounted on a casing ofthe instrument and carrying a marker which traverses an analogue scale.

7. An instrument according to claim 6, in which the scale is provided around the edge of a circular dial plate which is provided with one or more apertures through which the second display means is visible.

8. An instrument according to claim 6 or7, which iincludesan annularmounting platefora potentiometer positioned rearwardly of the handwheel, the annular mounting plate defining a chamber rearwardly of said first display means within which said second display means is located.

9. An instrument according to claim 1,which comprises a casing, an annular potentiometer mounting plate positioned within the casing, a potentiometer carried by said mounting plate, a rotatable handwheel positioned forwardly of a circumferentially around the mounting plate, a bezel holding the handwheel on the casing, and a dial plate forwardlyofandwithinthehandwheel and having a scale thereon for association with a marker carried by the handwheel, said second display means being located within a chamber defined by the annular mounting plate and being located substantially centrally ofthe dial plate.

10. An instrument according to any preceding claim, in which the parameter is temperature.

11. An instrument according to any preceding claim, which includes sensing means responsiveto the parameter being monitored, and control means arranged to exert a control function in response to the sensed parameter.

12. An indicating instrument substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3A or Figure 3B or Figure 3C ofthe accompanying drawings.