CUB5 - Red Lion Controls - #9

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9 INPUT FREQUENCY CALCULATION The meter determines the input frequency by summing the number of falling edges received during a sample period of time. The sample period begins on the first falling edge. At this falling edge, the meter starts accumulating time towards Low Update and High Update values. Also, the meter starts accumulating the number of falling edges. When the time reaches the Low Update Time value, the meter looks for one more falling edge to end the sample period. If a falling edge occurs (before the High Update Time value is reached), the Rate display will update to the new value and the next sample period will start on the same edge. If the High Update Time value is reached (without receiving a falling edge after reaching Low Update Time), then the sample period will end but the Rate display will be forced to zero. The High Update Time value must be greater than the Low Update Time value. Both values must be greater than 0.0. The input frequency calculated during the sample period, is then shown as a Rate value determined by the scaling calculation. The Low Update Time is the minimum amount of time between display updates for the rate display. Values of 0.1 and 0.2 seconds will update the display correctly but may cause the display to appear unsteady. RATE LOW UPDATE TIME 0.1 to 99.9 seconds The High Update Time is the maximum amount of time before the rate display is forced to zero. (For more explanation, refer to Rate Value Calculation.) The High Update Time must be higher than the Low Update Time and higher than the desired slowest readable speed (one divided by pulses per second). The factory setting of 2.0, will force the display to zero for speeds below 0.5 Hz or a pulse every 2 seconds. RATE HIGH UPDATE TIME 0.2 to 99.9 seconds „u „v 01.0 LO-Udt „u „v 02.0 HI-Udt SCALING FOR RATE INDICATION To scale the rate, enter a Scaling Display value with a corresponding Scaling Input value. These values are internally plotted to a display value of 0 and input value of 0.0 Hz. A linear relationship is formed between these points to yield a rate display value that corresponds to the incoming input signal rate. The meter is capable of showing a rate display value for any linear process. SCALING CALCULATION If a display value versus input signal (in pulses per second) is known, then those values can be entered into Scaling Display (RAtE dSP) and Scaling Input (RAtE INP). No further calculations are needed. If only the number of pulses per ‘single’ unit (i.e. # of pulses per foot) is known, then it can be entered as the Scaling Input value and the Scaling Display value will be entered as the following: NOTES: 1. If # of pulse per unit is less than 10, then multiply both Input and Display values by 10. 2. If # of pulse per unit is less than 1, then multiply both Input and Display values by 100. 3. If the Display value is raised or lowered, then Input value must be raised or lowered by the same proportion (i.e. Display value for per hour is entered by a third less (1200) then Input value is a third less of # of pulses per unit). The same is true if the Input value is raised or lowered, then Display value must be raised or lowered by the same proportion. 4. Both values must be greater than 0.0. EXAMPLE: 1. With 15.1 pulses per foot, show feet per minute in tenths. Scaling Display = 60.0 Scaling Input = 15.1. 2. With 0.25 pulses per gallon, show whole gallons per hour. (To have greater accuracy, multiply both Input and Display values by 10.) Scaling Display = 36000 Scaling Input = 2.5. RATE PER DISPLAY (RAtE dSP) INPUT (RAtE INP) Second 1 # of pulses per unit Minute 60 # of pulses per unit Hour 3600 # of pulses per unit