Hach 900 manual Therefore, the value for Intv = Cnts is

Section 4

1.Determine the flow increment between samples:

Q 85,000 gallons

f = ---- = --------------------------------------= 3,542 gallons/sample

n 24 samples

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

3,542 gallons/sample ×	-----1-----pulse-----------------	= 70.84 pulse/sample
	50 gallons

Therefore, the value for INTV = _ _ _ _ CNTS is 71.

Example 3

You want to collect 48 samples over a 16-hour period. The total expected flow over this period is 1,750,000 gallons. The flow meter pulse frequency output is one pulse for every 1,000 gallons.

1.Determine the flow increment between samples:

Q 1,750,000 gallons

f = ---- = ----------------------------------------------= 36,458 gallons/sample

n 48 samples

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

36,458 gallons/sample ×	1 pulse	= 36.458 pulses/sample
	1,000-----------------gallons------------------

Therefore, the value for INTV = _ _ _ _ CNTS is 36.

Flow Proportional Sampling, External—Using 4–20 mA Signal Converted to Pulses, Flow Signal Interface The Flow Signal Interface (Cat. No. 2020) is an optional 4–20 mA interface that converts 4–20 mA current signals (from a flow meter) to 12 V dc pulses.

At 20 mA, the interface transmits ten 12-volt pulses per minute. As the current signal decreases, the 12 V pulses decrease proportionally. Typically, users collect a certain number of samples over a given period of time when sampling in proportion to the flow rate.

To calculate the number of 12 V dc output pulses between samples, determine the total number of samples (represented by n in the following examples) that you want to collect, and the period of time over which you want to collect them. Use the three-step method presented below to determine the “Total Count” value that you will enter while programming the Setup section of the sampler.

1.Calculate Q, where Q is the average flow rate (during the sampling program) divided by the maximum flow rate. (The maximum flow rate corresponds to the 20 mA output of the flow meter.)

2.Calculate t, where t is defined as a/n; n is the total number of samples collected over a given period of time; and a represents time in minutes, over which n samples are collected.

3.Multiply Q x t. Enter the result in the programming step:

INTV = _ _ _ _ CNTS.

Note: The product of Q x t is not necessarily a whole number. You must round off the result to the nearest whole number.

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8544operations.fm	Flow Proportional Operation