Hach 900 MAX manual Appendix D How to Calculate Pulses/Counts, Example

Appendix D How to Calculate Pulses/Counts

The sampler is equipped to receive either a momentary dry contact closure or a +5 to +12 V dc pulse from a flow meter, where each pulse represents a known flow increment.

For example, if the flow meter is set to send a flow pulse for every

1000 gallons of measured flow and the sampler can count 1 to 9,999 flow pulses between sample intervals, you can program the sampler to receive 10 pulses between samples to take one sample for every 10,000 gallons of liquid flow.

To determine the number of flow pulses between sample intervals, you must determine the total number of samples (represented by n in the following examples) to be collected, and the period of time over which they are to be collected. You must also know the total flow, Q, during the sampling program. The following two-step method should be useful for determining the value for INTV = _ _ _ _ CNTS during setup.

1.Determine f, where f represents the flow increment between samples and n represents the total number of samples to be collected.

Q f = ----

n

2.Multiply the flow increment between samples, f, by the pulse frequency output of the flow meter (i.e. 1 pulse per 100 gallons, 1 pulse per

1000 gallons, etc.). If the pulse frequency output of the flow meter is not known, consult the flow meter manufacturer.

Note: The final result is not necessarily a whole number. You must round off the result to the nearest whole number.

Flow-Proportional Sampling Intervals - Using External Pulses Hach samplers are equipped to receive either a momentary dry contact closure or +5 to +12 V dc pulse from a flow meter, where each pulse represents a known flow increment.

Example 1

You want to collect 35 samples over a 24-hour period. The total expected flow over this period is 235,000 gallons. The flow meter pulse frequency is

one pulse for every 100 gallons.

1.Determine the flow increment between samples:

Q 235,000 gallons

f = ---- = -----------------------------------------= 6,714 gallons/sample

n 35 samples

2. Multiply the flow increment, f, by the pulse frequency output of the flow meter.

6,714 gallons/sample ⋅	1 pulse	= 67.14 pulse/sample
	100------------gallons------------------

Therefore, the value for INTV = _ _ _ _ CNTS is 67. (67.14 is rounded off to 67.)

Example 2

You want to collect 24 samples over an 8-hour period. The total expected flow over this 8-hour period is 85,000 gallons. The flow meter pulse frequency output is one pulse for every 50 gallons.

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