Rosemount 8712, Reference Manual

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Reference Manual
00809-0100-4664, Rev BA
January 2010
Rosemount 8712
4-18
NOTE
Line size, special units, and density must be selected prior to configuration of
URV and LRV.
PV Lower Range Value (LRV)
The lower range value (LRV) is preset to 0 ft/s at the factory. The units that
appear will be the same as those selected under the units parameter.
Reset 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
The LRV can be set to a value greater than the URV, which will cause the
analog output to operate in reverse. In this mode, the analog output will
increase with lower (more negative) flow rates.
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. 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).
NOTE
Line size, special units, and density must be selected prior to configuration of
URV and LRV.
PV Analog Output
The PV analog output displays the current analog output value (mA) of the
transmitter corresponding to the current measured flow rate.
Analog Output Alarm Type
The analog output alarm type displays the alarm mode the 8712 is currently
set for. This value is set by a switch on the electronics board. There are two
available options for this setting:
• High
• Low
Field Comm. 1, 4, 2, 1, 2
LOI Key AUX. FUNCTION
Field Comm. 1, 4, 2, 1, 3
Field Comm. 1, 4, 2, 1, 4