GB2321521A - High visualfeedback metering - Google Patents

High visualfeedback metering Download PDF

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Publication number
GB2321521A
GB2321521A GB9701398A GB9701398A GB2321521A GB 2321521 A GB2321521 A GB 2321521A GB 9701398 A GB9701398 A GB 9701398A GB 9701398 A GB9701398 A GB 9701398A GB 2321521 A GB2321521 A GB 2321521A
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Prior art keywords
meter
over range
intensity
metering
group
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GB9701398A
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GB9701398D0 (en )
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Waring Hayes
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Waring Hayes
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    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B5/00Visible signalling systems, e.g. personal calling systems, remote indication of seats occupied
    • G08B5/22Visible signalling systems, e.g. personal calling systems, remote indication of seats occupied using electric transmission; using electromagnetic transmission
    • G08B5/36Visible signalling systems, e.g. personal calling systems, remote indication of seats occupied using electric transmission; using electromagnetic transmission using visible light sources

Abstract

A system that uses a digital readout in the form of a column or row of indicators may represent a rising level by an increasing number of consecutively illuminated indicators. The additional feedback in the high visual feedback metering shows over-range conditions as a stepped intensity change, in addition to the holding of the over-range indicator, allowing the meter to alert the user to the over-range condition even when viewed well off the central viewing axis.

Description

HIGH VISUAL FEEDBACK METERING This invention relates to a method of improving the information presented by an electronic meter.

Metering is most often used to visually represent a measurement that requires monitoring for safety purposes. This may be a material quantity, such as a fluid level or pressure, or an electrical quantity such as audio level. In a system that uses a digital readout in the form of a column or row of indicators, the measurement is mapped onto the indicators generally by associating an increased number of consecutively illuminated indicators as representative of a higher or greater measurement. A commonly seen example of this form of metering is that used on audio equipment, such as graphic equalisers and power amplifiers to show a measure of audio level at some point within the device.

As with all such metering applications, the function of the meter is to allow the measurement to be monitored effectively, in order to prevent fault or danger conditions from occurring. Approaching over-range conditions in any application using a readout of the type described above is normally represented using different coloured indicators. The lower safe condition range is represented by green or blue indicators, the higher safe condition range by yellow or orange indicators, and above the safe condition range by red indicators.

This type of metering works acceptably as long as the user is able to view the meter directly. This condition is necessary due to the biological makeup of the human eye. The human eye consists of two types of light receptors, known as rods and cones. Cones are primarily responsible for the perception of colour vision, rods for the perception of light intensity.

Rods are about 500 times more sensitive to light than cones, but provide no colour information. The important factor in the makeup of the human eye is related to the distribution of the rods and cones within the eye itself.

Each eye contains approximately 6 million cones, and about 120 million rods. The distribution of receptors on the retina is different for rods and cones - rods are more prevalent in the periphery, cones in the centre. For example, at the very centre of the eye, a region known as the fovea, there are no rods at all, only cones. Moving just off the central visual axis by as little as 10 decreases the density of cones from approximately 150,000 per square millimetre down to less than 20,000 per square millimetre.

However, the density of rods from this point up to approximately 60 offaxis only halves to around 80,000 per square millimetre.

It is a well-founded physiological fact that human peripheral vision is very sensitive to intensity changes, but not to colour perception. Additionally, when metering is used in dimly lit environments, the adaptation of the eye to a low light level depends mainly on rods, and the maximum colour sensitivity shifts to lower wavelength light (greens as opposed to reds).

From this perspective, viewing a meter off-axis will not relay information as effectively as possible. Based on the fact that meters may well appear in groups, and that focusing attention on any one meter may preclude the accurate monitoring of others in the group, a method of alerting the user to an over-range condition will improve the quality of information available from all the meters. Peak hold systems already exist to aid group meter monitoring, but representing an over-range condition is still limited to a change in indicator colour.

According to the present invention there is provided additional feedback from a meter in the form of a large stepped intensity change to all the indicators in the meter during over-range conditions. Also, the over-range indicator will be left illuminated for a fixed time period after the overrange condition has passed permitting the user, having been alerted to the condition by the intensity change, to note which meter (when dealing with a group) displayed the condition.

A specific embodiment of the invention will now be described by way of an example with reference to the accompanying schematic diagram, drawing, and software sections.

Figure 1 shows the schematic diagram for a group of five digital level meters, as may be used in an audio product. The meters are controlled by a serial data stream , presented synchronously using the DATA and CLK inputs to the LED driver integrated circuit. Packets of data are latched into the driver using the LOAD input. This data is able to address each meter individually, presenting new information to display which is latched into an internal register for each meter. The driver takes care of multiplexing the data contained in its internal registers at sufficient speed so that the meters appear continuously illuminated, due to the persistence of human vision.

The frequency of this refresh may be adjusted by writing data to another internal register (known as the scan limit register), allowing up to eight such meters to be controlled. Additionally, and more importantly, the duty cycle of this refresh signal may be controlled, allowing the intensity for the meter group to be adjusted. Another internal register, known as the intensity register, may be written to with a 4-bit number giving sixteen possible intensity levels.

The information presented to the internal data registers responsible for the control of the individual meters is formatted in such a way as to represent an measured level. Figure 2 shows an appropriate front panel layout for the meter group. In this example, each meter represents a specific input on the equipment, monitoring the level appearing at that input. As with all audio equipment, allowing the level to overload will result in audible distortion of the signal, and as such must be avoided. The meters are responsible for relaying information about the available headroom at each input, and so the individual indicators within each meter are coloured green, yellow, and red to indicate low, high, and 'over' ranges respectively.

The software required to control this type of LED driver is given in Figure 3. Discussion of its operation is not applicable to this document.

However, the software detailed in Figure 4 refers to the control of the meters themselves, and so will be explained.

A pair of static (i.e. preserved beyond the lifetime of each call of the function) variables are defined which hold individual timers for the over range hold time (hold~countA, hold~countB), along with a pair of corresponding peak store variables. These are set to a value when a peak (over range) value has been measured, and are held at this value for a fixed time, after which, if no other peak has occurred, they are reset to zero.

Audio metering is normally measured on a logarithmic scale. Just after the declarations code section comes the first reading of a measurement.

This is the line level = read~dsp~W(0); where the function read dsp yU returns a level for the corresponding input - this being passed in as a parameter. This value is a linear measurement of audio level, and is scaled logarithmically by comparing it against a table of pre-defined values placed at intervals on a logarithmic scale. The tables values correspond to physical threshold points for the indicators in each meter.

With reference to the scaling table used for the input metering, the indicators lie on the thresholds as below.

static const signed int in~scaletab[7] = ( 0, 1464, 2919, 5826, 11625, 23195, 29205}; -27 -21 -15 -9 -3 O/R The actual scaling is performed by the section for (i=6; i > = C; i--) /* search table in~scaletab */ if (level > = in~scaletab[i]) break; which will terminate the 'for' loop when the correct threshold has been reached. At this point the variable i will have a value in the range 0 to 6.

This will value is then use to shift a 'bitmap' which is representative of the number of indicators illuminated. The starting 'value' of the bitmap, in the case of the input meters Oxfc, corresponds to the representation of all indicators illuminated. Converting this hexadecimal number to binary demonstrates why this is so. 0xfc in binary is 11111100 - it is clearer now that this represents the 'raw' data to be transmitted to the LED driver, with each bit in this byte corresponding to an indicator in the meter.

valA = Oxfc 6-i; /* shift "all leds on" down according to level If the measured value, after scaling, should only cause the bottom indicator to illuminate (-27dB), then i would have been 1 and (6 - 1) left shifts would have been performed on the byte, leaving the value to be transmitted to the LED driver as 10000000 in binary.

The explanation of the above section, whilst not strictly necessary when considering the over range indication, will clarify the following section which details the operation of the over range indication.

The occurrence of an over range condition is represented by the bitmap (now held in the variable valA or valB) having a value 0xfc - no shifting has been performed on the bitmap, so it still represents the 'all indicators illuminated' state. This is checked in the following section, and appropriate action taken.

if((valA I valB) == Oxfc)/* A or B clipping ?*/ Update~LEDs(INTENSITY, OxOf,IN METERS); /* full intensity for clip if(valA == Oxfc) I pkA = 0x04; /* update peak only on a clip, and light top led hold~countA = 0; /* reset hold time so it's always held for same time */ if(valB == Oxfc) I pkB = 0x04; /* update peak only on a clip, and light top led hold~countB = 0; /* reset hold time so it's always held for same time */ else /* nothing clipping - set intensity back to normal */ Update~LEDs(INTENSTTY, (unsigned ch r)led~brightness,IN~METERS); After the check for over range on either meter, the intensity register for the LED driver is updated with the value OxOf (the four bit nibble being set to maximum) which will cause the indicators for both meters to illuminate at maximum intensity.

It is important to note that both meters will illuminate at maximum intensity in this application - this is where the peak hold action becomes necessary. In the case of a large meter group (each LED drive can control eight such meters) the intensity step of the entire group will alert the user to an over range condition within the group, but ascertaining which meter has actually caused this will not be easily performed, unless the user is in a fortuitous viewing position. Therefore, holding the peak for the over ranged meter is required. The time period for this is such that the user has time to register the over range condition (from a worst case off axis viewing position), move to a more central (on axis) viewing position, and register which meter has its over range indicator illuminated.

The value stored in the variable pkA or pkB is changed to represent a bitmapped value corresponding to the over range indicator being illuminated on its own - 0x04 in binary is 00000100. The 'else' condition in this statement is only responsible for setting the meter group back to its original intensity. This is set elsewhere in the software, and is stored in the variable led~brightness. Additionally, the hold timer associated with the meter is reset to zero, and subsequently checked for hold time timeout.

if(hold~countA > PEAK~HOLD) /* hold peaks for about 1.5 seconds I hold~countA = 0; /* set counter and peak store back to O pkA = 0x00; else hold~countA++; if(hold~countB > PEAK~HOLD) /* hold peaks for about 1.5 seconds I hold~countB = 0; /* set counter and peak store back to 0 */ pkB = 0x00; else hold~countB++; If the hold timer has exceeded the value PEAK~HOLD (stored as constant), then the bitmap is reset to zero (no indicator) and the hold time reset, otherwise the hold timer is incremented.

Finally, the bitmapped information is sent to the LED driver, with appropriate addresses for each meter.

Update~LEDs(DIGITO, (valA I pkA), IN~METERS); /* OR in peak value regardless */ Update LEDs(DIGITO + 1,(valB I pkB), IN~METERS); /* OR in peak value regardless */ The format of this information is meter address, bitmapped data, driver address. The driver address is not strictly necessary in this example, but is applicable in a multi-driver system with many metering groups.

Note that the bitmapped data has the value stored in the pkA or pkB variables logically OR'ed with the shifted bitmap stored in valA or valB.

This allows the over range indicator to remain illuminated as required.

Drawings and Figures accompanying this document are: Figure 1 Example schematic diagram Figure 2 Example front panel meter layout Figure 3 Example LED software driver Figure 4 Example audio metering software

Claims (5)

  1. CLAIMS 1 A metering system in the form of a row or column of discrete indicators may be provided with additional feedback of an over range condition by adjusting the intensity of the indicator group.
  2. 2 The intensity adjustment as claimed in Claim 1 is in the form of a stepped intensity change, in order to alert the user when the meter is viewed off the central viewing axis.
  3. 3 The intensity change above or below the normal intensity as claimed in Claim 2 is held for the duration of the over range condition only.
  4. 4 When the meters are arranged in a group, an over range condition in any one (or more) meter will step the intensity for the entire group.
  5. 5 A metering group as claimed in claim 4, wherein an over range indicator is provided for each metering system and that the indicator remains illuminated for a predetermined period of time after the over range condition has passed.
    5 Indication as to which meter(s) in the group, as in Claim 4, caused the over range condition is given by the 'over range' indicator in that particular meter (or in those particular meters) remaining illuminated for a fixed time period after the over range condition has passed.
    Amendments to the claims have been filed as follows CLAIMS 1 A metering system in the form of a row or column of discrete indicators may be provided with additional feedback of an over range condition by adjusting the normal intensity of the indicators in the row or column.
    2 A metering system as claimed in Claim 1 wherein the adjustment is in the form of a stepped intensity change, in order to alert the user when the meter is viewed off the central viewing axis.
    3 A metering system as claimed in Claim 2 wherein the intensity change is held for the duration of the over range condition only.
    4 A metering group comprising a plurality of metering systems, each system being as claimed in claims 1, 2, or 3, wherein an over range condition in any one or more meter will produce a stepped intensity change in the entire group.
GB9701398A 1997-01-23 1997-01-23 High visual feedback metering Withdrawn GB9701398D0 (en)

Priority Applications (1)

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GB9701398A GB9701398D0 (en) 1997-01-23 1997-01-23 High visual feedback metering

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Application Number Priority Date Filing Date Title
GB9701398A GB9701398D0 (en) 1997-01-23 1997-01-23 High visual feedback metering

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GB9701398D0 GB9701398D0 (en) 1997-03-12
GB2321521A true true GB2321521A (en) 1998-07-29

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB942610A (en) * 1961-08-31 1963-11-27 Royal Vernon O Reilly Apparatus for translating sound into correlated physical effects
US3806919A (en) * 1971-03-15 1974-04-23 Lumatron Corp Light organ
GB2072846A (en) * 1980-03-25 1981-10-07 Sound Attenuators Ltd Noise-level sensing device
EP0298046A2 (en) * 1987-07-03 1989-01-04 Firm DAVOLI ATHOS Device for measuring, indicating and controlling sound pressure (or sound levels) in an environment
US5017837A (en) * 1987-12-11 1991-05-21 Lutron Electronics Co., Inc. Indicator lamp system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB942610A (en) * 1961-08-31 1963-11-27 Royal Vernon O Reilly Apparatus for translating sound into correlated physical effects
US3806919A (en) * 1971-03-15 1974-04-23 Lumatron Corp Light organ
GB2072846A (en) * 1980-03-25 1981-10-07 Sound Attenuators Ltd Noise-level sensing device
EP0298046A2 (en) * 1987-07-03 1989-01-04 Firm DAVOLI ATHOS Device for measuring, indicating and controlling sound pressure (or sound levels) in an environment
US5017837A (en) * 1987-12-11 1991-05-21 Lutron Electronics Co., Inc. Indicator lamp system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
WPI Accession No.87-320090/45 & SU 1301424 A (SHEPELEV) 07.04.87 see abstract *

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