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Page 28

Flow Proportional Operation

8544operations.fm

Section 4

4.11 Flow Proportional Operation

4.11.1 How to Calculate Pulses/Counts

4.11.1.1 Flow Proportional Sampling Intervals—Using External Pulses

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 9999 flow pulses

between sample intervals, the sampler can be programmed 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, 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. 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.

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 1,000

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.

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:

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

meter.

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.

----=

----

235,000 gallons

35 samples

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

6,714 gallons/sample

1 pulse

100 gallons

------------------------------

× 67.14 pulse/sample=

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 51 52

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Hach SIGMA 900 User Manual Page 28

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