Hach 900 MAX - Manual (Page 135)

Page 133
8990apdx_pulsecounts.fm How to Calculate Pulses/Counts
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.
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:
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.
f
Q
n
---- =
f
Q
n
----
235,000 gallons
35 samples
------------------------------------------ 6,714 gallons/sample = = =
6,714 gallons/sample
1 pulse
100 gallons
------------------------------ ×
67.14 pulse/sample =