Baker Hughes Panametrics Sentinel LCT8, Руководство пользователя

Страница: 67 / 138

3.6.2.1 Frequency output termination
When driving the Sentinel LCT8 frequency/totalizer output
over distances greater than 100 feet, a 24 AWG twisted-
pair I/O cable is typically used. With a data acquisition
system that requires a high enough voltage to read
the signal (typically a 3 - 4V threshold), the connection
shown in Figure 62 below should be used. This open-drain
configuration provides a clean, ideal signal with a high
enough voltage to trigger the DAC to properly count the
pulses.
Twisted-pair cable >100 ft
External
power supply
(5 to 24 VDC)
Counter
Pull-up
resistor
Sentinel
LCT8
F/T1+
F/T1-
Figure 62: Open-drain frequency output wiring
Carefully select the pull-up resistor to be sure it has a high
enough resistance and wattage rating for the size of the
power supply. Use Table 7 below as a guide to select the
appropriate value.
Table 7: Selecting the Pull-Up resistor
Power supply
voltage (VDC)
Resistor value
(ohms)
Minimum power
rating (W)
5 1200 1/40
5 2400 1/90
9 1200 1/10
9 2400 1/25
12 5100 1/30
12 10,000 1/70
24 5100 1/8
24 10,000 1/15
24 20,000 1/30
Figure 63 below shows a typical output waveform at the end
of a terminated I/O cable when driven by the Sentinel LCT8
in push-pull configuration. This waveform is an example of
what a “good” pulse output should look like.
1000’, 24 AWG, termination 120 ohm, push-pull mode
Amplitude
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
Figure 63: Ideal frequency output signal shape
57