Section 3: Electrical Installation; Cable Length Ttl Mode; Cable Length Open Collector Mode; Table 3-1 Configurations For Open Collector Frequency Outputs - Emerson Daniel 3812 Installation Manual

Daniel 3812 Liquid Ultrasonic Flow Meter Installation Manual
3-9000-765 Rev H

Section 3: Electrical installation

3.1

Cable length TTL mode

The maximum cable length is 2000 feet when the "TTL" mode is selected.
3.2

Cable length Open Collector mode

For the "open collector" mode, the maximum cable length depends on the cable parameters,
pull-up resistance used, the maximum frequency to output, and frequency input parameters
being driven. The following table provides estimated cable lengths for different pull-up resistor
values and different Max Frequency settings in the meter using the following cable parameters.
The table also provides an estimated cable voltage drop which indicates how much voltage will
be across the cabling and effectively indicates to what voltage level the frequency input can be
pulled down to by the frequency output.
If the voltage drop is higher than the voltage required for the frequency input to see a low state,
then the configuration will most likely not work for your system. Performance of frequency
outputs will vary from this table with setup and frequency input being driven.

Table 3-1 Configurations for open collector frequency outputs

Cable
Cable resistance
Length (2 Conductors)
(x1000ft)
Ω
0.5 16.8
1 33.6
2 67.2
4 134.4
0.5 16.8
1 33.6
1.7 57.12
6.5 218.4
The 22 AWG wire characteristics are as follows:
•
•
•
Cable length TTL mode
Pull-up
Cable resistance
Capacitance Resistance
nF
Ω
10.00 1000
20.00 1000
40.00 1000
80.00 1000
10.00 500
20.00 500
34.00 500
130.00 500
Capacitance = 20 pF/ft or 20 nF/1000 ft (between two wires)
Resistance = 0.0168 Ohms/ft or 16.8 Ohms/1000 ft
Pull-up voltage is 24 VDC
Maximum
Total frequency
Resistance Frequency
(Hz)
Ω
1016.8 5000
1033.6 1000
1067.2 1000
1134.4 1000
516.8 5000
533.6 5000
557.12 5000
718.4 1000
Section 3: Electrical installation
Cable voltage
Sink drop
Current (2 Conductors)
(A) VDC
0.024 0.397
0.023 0.780
0.022 1.511
0.021 2.843
0.046 0.780
0.045 1.511
0.043 2.461
0.033 7.296
June 2017
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