Rosemount 248, Справочное руководство

Страница: 35 / 80

Reference Manual
00809-0100-4825, Rev BB
August 2005
3-11
Rosemount 248
Alarm and Saturation
The Alarm/Saturation command allows the alarm settings (Hi or Low) and
saturation values to be viewed and changed. To change the alarm values and
saturation values, select the value to be changed, either
2 Low Alarm , 3 High
Alarm , 4 Low Sat. , or 5 High Sat . Enter the desired new value, which must fall
within the guidelines given below.
• The low alarm value must be between 3.50 and 3.75 mA
• The high alarm value must be between 21.0 and 23.0 mA
• The low saturation level must be between the low alarm value plus 0.1
mA and 3.9 mA.
Example: The low alarm value has been set to 3.7 mA. Therefore, the low
saturation level, S, must be 3.8
≤
S
≤
3.9 mA.
• The high saturation level must be between 20.5 mA and the high alarm
value minus 0.1 mA.
Example: The high alarm value has been set to 20.8 mA. Therefore, the low
saturation level, S, must be 20.5
≤
S
≤
20.7 mA.
See “Failure Mode” on page 2-8 for Failure Mode considerations.
Rerange
Reranging the transmitter sets the measurement range to the limits of
expected readings. Setting the measurement range to the limits of expected
readings maximizes transmitter performance; the transmitter is most accurate
when operated within the expected temperature range for your application.
PV Range Values
The PV URV and PV LRV commands, found in the PV Range Values menu
screen, allow the user to set the transmitter’s lower and upper range values
using limits of expected readings. The range of expected readings is defined
by the Lower Range Value (LRV) and Upper Range Value (URV). The
transmitter range values can be reset as often as necessary to reflect
changing process conditions. From the
PV Range Values screen select 1 PV
LRV to change the lower range value and 2 PV URV to change the upper
range value.
NOTE:
The rerange functions should not be confused with the trim functions.
Although the rerange command matches a sensor input to a
4–20 mA output, as in conventional calibration, it does not affect the
transmitter’s interpretation of the input.
Fast Key Sequence 1, 3, 3, 2
Fast Key Sequence
PV URV = 6
PV LRV = 7