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Isco 4700 Refrigerated Sampler
Section 3 Programming
3-14
If the flow measurement device sends flow rate data via a
4-20 mA current loop instead of flow pulses, the sampler converts
this analog current to flow pulses representative of a volume.
The sampler assumes that the current is linear from 4 mA at
zero flow to 20 mA at the full-scale flow rate. This factory-cali-
brated conversion produces one pulse every 12 seconds (5 flow
pulses per minute) at 20 mA and scales the pulse intervals until
there are no pulses at 4 mA. See Table 3-2 for flow pulse
intervals at various currents.
Table 3-2 Flow Pulse Intervals at Various
Input
Current (mA)
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
To calculate the number of flow pulses to enter in this sampler
programming screen, follow the steps below.
1. Determine the full scale flow rate (Q
sented by the flow measurement device at 20 mA.
2. Divide Q
by a time factor (F
max
resented by a single flow pulse. The time factor you choose
is determined time unit on which the flow rate is based:
Input Currents
Seconds Between
Pulses
∞ (no pulses)
192
96
64
48
38.4
32
27.4
24
21.3
19.2
17.4
16
14.8
13.7
12.7
12
) that is repre-
max
) to find the volume rep-
time
% of Full Scale
Flow Rate
0
6.25
12.5
18.75
25
31.25
37.5
43.75
50
56.25
62.5
68.75
75
81.25
87.5
93.75
100
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