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Operation LXT-220 DO
Teledyne Analytical Instruments 40
Trim
O
C .0
Unit 25.0
O
C
Temperature Calibration
If the 4-20 selected for the HART analog output is assigned to
“missing” or “unused” then the digital representation of the output
current will be “not a number”, but with up to four digital variables still
being transmitted.
3.3.5 Relay Assignments
The next 8 displays are for the relay assignments. The first of the
relay displays is:
Relay 1: ...
Where ... represents an item from the same list that is used for the
4-20 assignments. The procedure for selecting a relay assignment is the
same as for the 4-20 outputs. See Section 3.3.2 4-20mA Output
Assignments.
Up to two relays can be assigned to the same source, so one relay
can be used to control the process, and another relay can be used as an
alarm if the process value is out of limits.
The relay configuration menu provides for 8 relays, but most units
do not have that many relays installed. Some units do not have any
relays installed, but the relay menu will nevertheless be present as the
relays can be retrofitted. The software cannot determine how many
relays are actually present, so the “missing” selection might not reflect
the actual configuration.
A display showing the relay setpoints for each relay is present in the
main menu. If the relay is assigned to a channel 2 function then the display
will be in the channel 2 group. The display is not shown if the “missing” or
“unused” selection is made. A new relay assignment is not necessarily
functional until the setpoints in the span display are set. If a PID controller
is selected as a source then its support displays will also be present.
3.3.6 Temperature Calibration
The next display is for calibrating the process temperature
displayed by the instrument.