Dynasonics DDFXD Doppler Ultrasonic Flow Meter - Manual (Page 35)

06-DPP-UM-00147 02/12 35
b NO
b CM
b NC
a NO
a CM
a NC
I/O: RELAY
P.N. D020-1045-102
ISO-MOD
POWER
RELAY
POWER
SOURCE
FIGURE 3.11B - EXTERNAL RELAY CONNECTIONS
RATE PULSE OUTPUT MODULE
The Rate Pulse Output Module is utilized to transmit information to external counters and PID systems
via a frequency output that is proportional to system flow rate. The frequency output range of the Rate
Pulse Module is 0-2,500 Hz. This module has two types of outputs: one simulates the output of the coil of
a turbine flow meter and the other is an open-collector type that does not source voltage at its output.
Both outputs may be connected simultaneously.
The turbine meter output creates a 500 mV peak-to-peak saw-tooth waveform that is not referenced
to ground. This output can be run to electronic monitors that are compatible with variable reluctance
outputs from coils, such as those found in turbine and paddle-wheel flow meters. The input impedance
of the receiving device should not be smaller than 2,000 Ohms.
The standard pulse output does not output a voltage, but acts as an “open-collector” output requiring an
external power source and pull-up resistor. See Figure 3.12. The MOSFET in the Rate Pulse Module can
support loads of 100 V @ 1 A. Resistor selection is based on the input impedance of the receiving device.
Select a resistor that is a maximum of 10% of the input impedance of the receiving device, but does not
exceed 10k Ohms.