Rosemount 8712, Reference Manual

Page: 60 / 212

Reference Manual
00809-0100-4664, Rev BA
January 2010
Rosemount 8712
4-22
Example
The maximum flow rate is 10,000 gpm. Set the pulse output scaling such that
the transmitter outputs 10,000 Hz at 10,000 gpm.
NOTE
Changes to pulse width are only required when there is a minimum pulse
width required for external counters, relays, etc. If frequency generated by the
transmitter requires a smaller pulse width than the pulse width selected, the
transmitter will automatically go to 50% duty cycle.
Example
The external counter is ranged for 350 gpm and pulse is set for one gallon.
Assuming the pulse width is 0.5 ms, the maximum frequency output is 5.833
Hz.
Example
The upper range value (20 mA) is 3000 gpm. To obtain the highest resolution
of the pulse output, 10,000 Hz is scaled to the full scale analog reading.
Pulse Scaling
Flow Rate (gpm)
(60 s/min)(Frequency)
----------------------------------------------------------- =
Pulse Scaling
10,000 gpm
(60 s/min)(10,000 Hz)
---------------------------------------------------------- =
Pulse Scaling 0.0167 gal/pulse =
1 Pulse 0.0167 gallon =
Frequency
Flow Rate (gpm)
(60 s/min)(Pulse Scaling gal/pulse)
---------------------------------------------------------------------------------------------- =
Frequency
350 gpm
(60 s/min)(1 gal/pulse)
----------------------------------------------------------- =
Frequency 5.833 Hz =
Pulse Scaling
Flow Rate (gpm)
(60 s/min)(Frequency)
----------------------------------------------------------- =
3000 gpm
(60 s/min)(10,000Hz)
-------------------------------------------------------- =
0.005 gal/pulse =
1 Pulse 0.005 gallon =