Campbell Scientific PVS4100/4120/4150 Portable Automatic Samplers - Manual (Page 93)

C-1
Appendix C. Programming 4-20mA for
Flow Proportional Sampling
In order to use the 4-20mA interface with a PVS Sampler, calculations must be
made based on flow. The 4-20mA input is a signal that corresponds to the flow
meter’s output. 20mA is equal to the maximum flow, and 4mA is equal to the
minimum flow. The controller requires a number which reflects the maximum
flow going through the sampler.
The PVS Controller generates 100 pulses per minute internally at the
maximum flow. This number decreases with the amount of flow proportional
to the 4-20mA scale. The Controller requires the number of pulses at maximum
flow. In order to calculate this, use the following formula:
1. Calculate Q. Q = Average flow rate divided by the maximum flow rate.
Rate Flow Maximum
Rate Flow Average
Q =
2. Calculate t.
minute per volume Average
samples between Volume
t =
t is the number of minutes per sample you would like for an average flow rate.
Either choose how long between samples you’d like for average flow, or
calculate based on volume above.
3. Multiply Q x t x 100 (100 pulses at max flow)
This is the number you will input into the Controller at the 4-20mA dialogue.
Example
You want to collect samples every 30 minutes. On average 175gal/min flows
by. Maximum is 300gal/min.
1. Calculate Q.
58333 .
gal/min 300
gal/min 175
Rate Flow Maximum
Rate Flow Average
Q = = =
2. Calculate t.
gal/min 175 Average
samples btwn Gallons 5250
or min/sample 30 t =
3. Multiply Q x t x 100 pulses = 1750 pulses/sample
Enter 1750 into the Controller at the 4-20mA dialogue.