FMG490 INSTRUCTIONS
Page 18
CONFIGURATION
Cable Shield.
In general, the cable shield and its bare drain
wire should be left unconnected at the user equipment end of
the cable to minimize “ground loop” problems.
Pulse Output Configuration.
A pulse output is standard
on all models. Since this is an isolated output, the external
equipment must include a DC power source to regenerate the
pulse from the open-collector output (transistor equivalent
of a contact closure). A pull-up or pull-down resistor may
be needed if not included in the user equipment as shown
in the diagrams. Both the power source and resistor may be
supplied internally in some types of control and monitoring
devices. If not, as for most PLC discrete input modules, they
must be added externally at the module input terminals. The
pulse output rate in volume units/pulse can be set by the user
via the SETP tab on the meter’s setup menus.
Because the pulse output of an FMG490 meter is set by the
user, care must be taken to assure the output pulses do
not exceed the maximum frequency of the meter while also
ensuring a reasonable resolution.
K-factor: Remember that SETP is expressed in units totaled
per output pulse (G/P if using gallons) while K-factors are
expressed in pulses per gallon (P/G.) To determine K-factor
from SETP, divide 1 by SETP (if SETP is expressed in gallons.)
Conversely, 1 divided by the K-factor equals SETP
FMG490 meters that were initially configured as battery
powered units have a maximum output frequency of 150 Hz.
Those that were initially configured as powered units have a
maximum output frequency of 200 Hz.
Because all pulse outputs (SETP) are configured in (rate) units
totaled per pulse, all sizes of meters can be configured with
the same SETP values
For example, if your rate is chosen as gallons per minute
(GPM) the table below applies. If your rate is different, simply
use your rate label in place of (GPM.) The numerical values will
remain the same.
Pulse Units.
The units of measure of SETP are independently
selectable and are not tied to rate or total. Upon change of the
SETP unit, the pulse output may take up to 10 seconds, or the
duration of one pulse (whichever is longer) to take effect.
If Pulse Output is Inconsistent.
The PDAMP filter may need
to be increased.
Pulse Width Timing.
The unit and value of SETP must be
chosen to keep the duration between meter pulse outputs to
less than 500 seconds.
SETP
Flow Rate at 1
Hz (GPM)
Flow Rate at
200 Hz (GPM)
Powered Meters
Flow Rate at
150 Hz (GPM)
Battery Powered
Meters
0.1
6
1200
900
0.2
12
2400
1800
0.3
18
3600
2700
0.4
24
4800
3600
0.5
30
6000
4500
0.6
36
7200
5400
0.7
42
8400
6300
0.8
48
9600
7200
0.9
54
10800
8100
1.0
60
12000
9000
Lower frequency output pulses (1 pulse for some particular
number of gallons) can also be set.
Any output frequency can be determined by:
Rate (units/minute) ÷ SETP (units/pulse) = pulse/minute
Hz = pulse/minute ÷ 60 seconds / minutes
Analog Output (4-20mA) Configuration.
(Not available
on battery only units.)
Since the meter’s analog output
is isolated and passive, loop power must be supplied
externally as shown previously. (In addition, an external
resistor R
L
will be needed to convert the loop current to
voltage for voltage-only input devices.) The meter’s loop
transmitter minimum voltage drop is 6Vdc (8Vdc with
HART) which, with wiring resistance and loop power supply
voltage, will determine the maximum resistance for R
L
. The
flow rates corresponding to 4 and 20mA can be set by the
user via the SET 4 and SET20 tabs on the meter’s setup
menus.
