Reference Manual
00809-0100-4841, Rev. AA
May 2007
Rosemount 3490 Series
4-38
Current Output NOTE:
The current output of the 3490 Series Control Unit is FROZEN when the unit
is in the "off-line" mode.
The Current Output Channel
The Current Output channel is for transmitting the MCU PV value (D800) as a
4-20mA signal.
For example, consider a PV value of 5 metres and the PV range is 0 to 10
metres. This would mean 0 metres is represented by a 4mA signal (0%), 10
metres is represented by 20mA signal (100%) and 5 metres is represented by
a 12mA signal (50%). Therefore, the Current Output channel would output the
PV value as a 4-12mA signal.
Programming involves specifying the PV range with low range (minimum) and
upper range (maximum) values.
Menu:
MAIN MENU / SETUP / [CONTROL UNIT /] OUTPUT / CURRENT OUTPUT
P400 Low Range Val (Factory default is 0.0)
This is the PV value represented by 4mA.
P401 Up Range Val (Factory default is 100.0)
This is the PV value represented by 20mA.
P402 Alarm Actions (Factory default is 3.6mA)
Optional parameter for determining how an alarm, if selected in the ALARM
menu, is indicated on the Current Output channel. Options for P402 are:
• "3.6mA" - fix current output to 3.6 mA to force a low current limit alarm.
• "3.75mA" - fix current output to 3.75 mA to force a low current limit alarm.
• "Hold"- freeze the current output at the present value.
• "21mA"- fix current output to 21 mA to force high current limit alarm.
• "21.75mA"- fix current output to 21.75 mA to force high current limit alarm.
• "22.5mA"- fix current output to 22.5 mA to force high current limit alarm.
NOTE:
The “3.75mA” and “21.75mA” options are the Rosemount standard.
The “3.6 mA” and “22.5 mA” options are the NAMUR NE43 standard.
Alarms and indications are as explained in “About Alarms“ on page 4-60. See
also Table 4-15 on page 4-62 for summary of reporting methods for Alarms.
NOTE:
There is another alarm condition when the current output has reached the
linear limit i.e. saturated. For the Rosemount Standard, this is
≤ 3.9mA or
≥ 20.8mA. For the NAMUR NE43 standard, this is ≤ 3.8mA or ≥ 20.5mA.
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