User Guide - Eurotherm Ltda

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nanodac RECORDER/CONTROLLER: USER GUIDEFigure 4.5.2 shows a typical totaliser configuration page.Virtual Channel.1.MainDescriptorTypeOperationPVStatusResolutionUnitsUnits ScalerLow Cut OffHigh Cut OffInput1PeriodPresetPreset ValueRolloverRollover ValueDisableVirtualChan1TotaliserOn180.3625 unitsGood4units10100000327.11 secNo0No1000000Input 1Totaliser1 to 10 6Input 1RolloverCounter 110 6 to 10 12Input 1RolloverCounter 210 12 to 10 18RolloverUsing cascaded counters to expandthe totalisation range.Figure 4.5.2 Typical totaliser configuration menuDescriptorTypeOperationPVStatusResolutionUnitsUnits ScalerAllows the user to enter a descriptor (20 characters max.) for the totaliser.Select: Math, Counter or Totaliser.Allows the user to enable (‘On’) or disable (‘Off’) the totaliser.Read only. This is the dynamic output value of the totaliser.Read only. Shows the status of the totaliser.The Resolution parameter allows the number of decimal places (up to 6) to be set forthe totalised value as displayed on the instrument panel. It does not affect the resolutionof the totalisation process. Up to 6 decimal places may be set for the totalised value.Allows a units string of up to five characters to be entered for the totalised value.Allows a units scaler to be selected. Typically this will be used to scale between unittypes rather than to influence time period.One example of this would be when an input is measured in Litres/Minute, and Periodhas been set to 1Minute. If UnitsScaler is set to 1 then the total volume will be measuredin Litres. If the volume is required in Cubic Metres then conversion of the total will beneeded. There are 1000 Litres in a Cubic Metre so the UnitsScaler should be set to1000. This produces an additional division of 1000 and results in a total output in CubicMetres.Another example would be a requirement for the output in Gallons rather than litres,still with an input being measured in Litres/Minute. There are 4.54609 litres in an imperialgallon so the UnitsScaler would be set to 4.54609. (For a US Gallon the figure wouldbe 3.78541.)Low Cut Off Used to restrict the input operating range of the totaliser. Minimum value = -100 000High Cut Off Used to restrict the input operating range of the totaliser. Maximum value = 100 000Page 92HA030554Issue 7 Nov 12
nanodac RECORDER/CONTROLLER: USER GUIDEInput1PeriodPresetPreset ValueRolloverRollover ValueLow Cut Off and High Cut Off are particularly important as they directly affect the totalisationprocess. Together these two parameters define the range of valid inputs to thetotalisation process. If Input1 value lies between them, then the input is considered validand it contributes to the total for any period during which it remains valid. Negativeinput values are allowed and will cause the totaliser to decrease in value for negativevalues. The total increases with positive values.If the input lies outside the region defined by these CutOff parameters then it will beignored and not contribute to the total.Many applications do not wish to use negative values and so LowCutOff would thennormally be set to 0. Occasionally though, calibration errors at the low scale end couldcause unacceptable errors in the total. In these circumstances, it may be necessary toconsider setting LowCutOff to a small positive value.An example where this may be needed is when a process has a very low input value forlong periods of time interspersed with short periods of high input values. The cumulativeeffect of slightly inaccurate low input values for long periods could then reduce theaccuracy of the overall total recorded.Thoughtful use may produce an increase in the overall accuracy of the total; inappropriateuse could introduce significant inaccuracy.The value of the source. May be entered manually, or this parameter can be wired froman external channel PV. Input1 is the input signal representing an external measurementwhich is in the form of Units/Time-Unit, i.e. a rate. The sampling rate internal tothe block is fixed at the instrument tick rate of 8 times/second, taking one sample every125mSec.The Period parameter divides the signal being applied to Input1 by the number whichis needed to generate a Total PV which is scaled in appropriate time units. There is aselection of preset values available for the Period parameter. These are listed in Table1 below. The totaliser equation works in seconds. If the totalised channel units are otherthan ‘per second’, a period scaler different from the default (1 sec) must be used. The‘Period’ field presents a number of fixed periods from 0.125 seconds to 24 hours for selection.Setting this to ‘Yes’ causes the totaliser to adopt the Preset Value. The field returns immediatelyto ‘No’. The totaliser can also be preset by an external source ‘wired’ to thisparameter.Allows the entry of a value, from which the totaliser is to start incrementing or decrementing.The direction of the count is set by the sign of the units scaler: positive = increment;negative = decrement.This is the rollover output which will be set for one execution cycle when the totaliserrolls over. This output can be used to expand the range of the totaliser by wiring it tothe Trigger input of a counter.This is the value at which the totaliser will rollover to 0. It is configurable (default1,000,000). When the totaliser rolls over the difference between the rollover value andthe calculated output will be added to 0.Example 1: with a rollover value of 1000, a current output of 999 and an input of 5, thenthe output will become 4.Example 2: with a rollover value of -1000, a current output of -999 and an input of-5, then the output will become -4.Note: in both examples, the Rollover output will be set for 1 execution cycle.Many applications do not require very large values to be totalised and can be scaled sothat the Rollover Value will never be reached. The instrument default value of 10^6 isgenerally satisfactory for these. If, however, higher values are expected, a larger Rollovervalue than this will have to be used. When configuring very large values the numberstored on the instrument display may be slightly larger or slightly smaller. This happensbecause the numbers are stored in the instrument in IEEE representation as used by allcomputing systems to save space. The trade-off is that very large values are stored witha small inaccuracy, which increases as the value being stored increases. As an example,HA030554Issue 7 Nov 12Page 93
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User Guide - Eurotherm Ltda

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