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Daniel 3818 LNG Liquid Ultrasonic Meter Installation Manual Section 3: Electrical installation
3-9000-771 Rev A May 2012
Section 3: Electrical installation 35
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.
The 22 AWG wire characteristics are as follows:
• 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
Table 3-1 Configurations for open collector frequency outputs
Cable
Cable
resistance
Cable
Pull-up
resistance
Total
Maximum
frequency
Sink
Cable voltage
drop
Length (2 Conductors) Capacitance Resistance Resistance Frequency Current (2 Conductors)
(x1000ft) nF (Hz) (A) VDC
0.5 16.8 10.00 1000 1016.8 5000 0.024 0.397
1 33.6 20.00 1000 1033.6 1000 0.023 0.780
2 67.2 40.00 1000 1067.2 1000 0.022 1.511
4 134.4 80.00 1000 1134.4 1000 0.021 2.843
0.5 16.8 10.00 500 516.8 5000 0.046 0.780
1 33.6 20.00 500 533.6 5000 0.045 1.511
1.7 57.12 34.00 500 557.12 5000 0.043 2.461
6.5 218.4 130.00 500 718.4 1000 0.033 7.296