Rosemount 8712, Reference Manual

Page: 37 / 212

Reference Manual
00809-0100-4664, Rev BA
January 2010
3-11
Rosemount 8712
PV URV
(Upper Range Value)
The upper range value (URV), or analog output range, is preset to 30 ft/s at
the factory. The units that appear will be the same as those selected under the
units parameter.
The URV (20 mA point) can be set for both forward or reverse flow rate. Flow
in the forward direction is represented by positive values and flow in the
reverse direction is represented by negative values. The URV can be any
value from –39.3 ft/s to +39.3 ft/s (-12 m/s to +12 m/s), as long as it is at least
1 ft/s (0.3 m/s) from the lower range value (4 mA point). The URV can be set
to a value less than the lower range value. This will cause the transmitter
analog output to operate in reverse, with the current increasing for lower (or
more negative) flow rates.
NOTE
Line size, special units, and density must be selected prior to configuration of
URV and LRV.
PV LRV
(Lower Range Value)
Set the lower range value (LRV), or analog output zero, to change the size of
the range (or span) between the URV and LRV. Under normal circumstances,
the LRV should be set to a value near the minimum expected flow rate to
maximize resolution. The LRV must be between
–39.3 ft/s to +39.3 ft/s (-12 m/s to +12 m/s).
NOTE
Line size, special units, and density must be selected prior to configuration of
URV and LRV.
Example
If the URV is greater than the LRV, the analog output will saturate at 3.9 mA
when the flow rate falls below the selected 4 mA point.
The minimum allowable span between the URV and LRV is 1 ft/s (0.3 m/s).
Do not set the LRV within 1 ft/s (0.3 m/s) of the 20 mA point. For example, if
the URV is set to 15.67 ft/s (4.8 m/s) and if the desired URV is greater than
the LRV, then the highest allowable analog zero setting would be 14.67 ft/s
(4.5 m/s). If the desired URV is less than the LRV, then the lowest allowable
LRV would be 16.67 ft/s (5.1 m/s).
Fast Keys 1, 3, 4
LOI Key ANALOG
OUTPUT RANGE
Fast Keys 1, 3, 5
LOI Key AUX. FUNCTION