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Hach SD900 User Manual
Also see for SD900: Basic user manual
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1. Push MENU.2. Go to PROGRAM SETUP>RESTORE.3. Select YES.Constant Time Variable Volume (CTVV) samplingCTVV samples are taken at user-specified constant (fixed) time intervals. However, the actualvolume of each sample is based on the:• Known average flow rate of the site• Actual metered flow rate at the time of sampling• Total sample volume desired• User-specified collection period• Specified sampling intervalThe volume of individual sampling can vary and depends on the flow volumes of the stream atvarious intervals within the collection period. The total sample collected during the entire period canbe slightly above or below the necessary total volume. For these reasons, the manufacturerrecommends that a sampling container is used that has a larger volume than the necessary totalvolume. When CTVV is used for sampling:• Sample distribution menus are not available when CTVV is selected, only composite sampling issupported.• The liquid sensor is always enabled.• The sample distribution is composite.• The run mode is non-continuous.• The first sample is taken after the interval.• Flow source is always 4–20 mA input.The instrument finds the sample volume, based on user inputs and actual metered flow volume. Forexample, the entered values are:• Average flow rate (historical, site specific): 150 gph• Sampling interval: 2 minutes• Total sample volume desired: 1500 mL• Collection period: 30 minutesCalculation 1: Total number of samplesCollection period ÷ Sampling interval = 30 minutes ÷ 2 minutes = 15 samplesCalculation 2: Average sample volumeTotal sample volume desired ÷ Total number of samples = 1500 mL ÷ 15 Samples = 100 mL/sampleCalculation 3: Sample volume per unit of flow rateAverage sample volume ÷ Average flow rate = (100 mL/sample) ÷ 150 gph = 0.66 mL/gphCalculation 4: Collect actual sample volume• If the 4–20 mA flow source is used and the flow rate measured is 140 gph, use sample volumesper unit of flow rate x actual metered flow rate.0.66 mL/gph x 140 gph = 92.4 mL. The sampler will pull a 90 mL sample (rounded off from92.4 mL).• If the flow pulses are used and every pulse count is 2 gallons and 2 counts are received in2 minutes, the flow rate is 120 gph.Sample volumes per unit of flow rate x actual metered flow rate0.66 mL/gph x 120 gph = 79.2 mL. The sampler will pull a 80 mL sample (rounded off from79.2 mL).English 23 |
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