Hach SIGMA 900 User Manual download pdf (Page 29)

Section 4

Page 29

8544operations.fm Flow Proportional Operation

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 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:

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

meter.

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.

----

85,000 gallons

24 samples

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

3,542 gallons/sample

1 pulse

50 gallons

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

× 70.84 pulse/sample=

----

1,750,000 gallons

48 samples

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

36,458 gallons/sample

1 pulse

1,000 gallons

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

× 36.458 pulses/sample=

1 2 ... 24 25 26 27 28 29 30 31 32 33 34 ... 51 52

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Hach SIGMA 900 User Manual Page 29

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