Walchem W900 Series Instruction Manual

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Walchem W900 Series Instruction Manual Manual pdf 66 page image

615.2.21 Virtual Input - DisturbanceA Disturbance type Virtual Input is not a physical input. The value of the virtual input is calculated from a realsensor input plus an equation that defines the real sensor’s impact on a control output that is using a different realsensor. A common example is controlling pH based upon a pH input signal, but modifying control based upon theflow rate, with a Disturbance Type Virtual Input defining the impact of the flow rate on the control output.Based on the disturbance input channel selection, minimum and maximum disturbance input readings, and de-fined multiplier values at the min and max disturbance readings, this Virtual Input generates a value that is used tomultiply to a primary control value. Disturbance input channel values that result in a multiplier output of 1.0 haveno impact on the final control output. The output value is restricted between low and high limits to allow morecomplete control over the impact of disturbance inputs. The value of the multiplier at min disturbance can be eitherhigher or lower than its value at max disturbance, depending upon what effect is desired on the control setpoint.Virtual Input DetailsThe details for a virtual input include the current multiplier value calculated, the current values of the inputs usedin the calculation, alarms, the status, and the input type.SettingsTouch the Settings icon to view or change the settings related to the virtual input.Min Disturbance Enter the value of the disturbance input where the value of the calculated multiplierwill be the Value at Min Disturbance value (set below).Max Disturbance Enter the value of the disturbance input where the value of the calculated multiplierwill be the Value at Max Disturbance (set below).Value at MinDisturbanceEnter the value of the multiplier that will occur when the disturbance input is at theMin Disturbance value.Value at MaxDisturbanceEnter the value of the multiplier that will occur when the disturbance input is at theMax Disturbance value.Min DisturbanceMax DisturbanceDisturbance Input ValueMultiplier Value sent toDisturbance AlgorithmValue atMin DisturbanceValue atMax Disturbance