Reference Manual
00809-0100-4004, Rev BA
August 2010
Rosemount 8800D
2-18
Pulse Output
NOTE
Remember when using the pulse output, all power to the electronics
is still supplied over the 4–20 mA signal wiring.
The flowmeter provides an isolated transistor switch-closure frequency output
signal proportional to flow, as shown in Figure 2-12. The
frequency limits are as follows:
• Maximum Frequency = 10000 Hz
• Minimum Frequency = 0.0000035 Hz (1 pulse/79 hours)
• Duty Cycle = 50%
• External Supply Voltage (V
s
): 5 to 30 V dc
• Load Resistance (R
L
): 100 to 100 k
• Max Switching Current = 75 mA >= V
S
/R
L
• Switch Closure: Transistor, open collector
Open contact < 50
A leakage
Close contact < 20
The output may drive an externally powered electromechanical or electronic
totalizer, or may serve as a direct input to a control element.
To connect the wires, remove the FIELD TERMINALS side cover
of the electronics housing. Connect the wires as shown in Figure 2-15.
NOTE
When using pulse output, be sure to follow these precautions:
• Shielded twisted pair is required when the pulse output and 4–20 mA
output are run in the same conduit or cable trays. Shielded wire will
also reduce false triggering caused by noise pickup. Wiring should be
24 AWG or larger and not exceed 5,000 ft. (1500 m).
• Do not connect the powered signal wiring to the test terminals. Power
could damage the test diode in the test connection.
• Do not run signal wiring in conduit or open trays with power wiring, or
near heavy electrical equipment. If needed, ground signal wiring at any
one point on the signal loop, such as the negative terminal of the power
supply. The electronics housing is grounded to the meter body.
Figure 2-12. Example: The pulse output will maintain a 50 percent duty cycle
for all frequencies
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