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86 L4400 User’s Guide
3 Operating and Programming
• Two TTL alarm outputs are available on the rear- panel Alarms connector
(Figure 3- 4). You can use these hardware outputs to trigger external alarm
lights, sirens, or send a TTL pulse to your control system. You can also
initiate a scan sweep (no external wiring required) when an alarm event is
logged on a channel. For complete details, refer to “Using the Alarm
Output Lines" on page 88.
• A Factory Reset (*RST command) clears all alarm limits and turns off all
alarms. An Instrument Preset (
SYSTem:PRESet command) or Card Reset
(SYSTem:CPON command) does not clear the alarm limits and does not
turn off alarms.
• The channel numbering scheme for the digital input and totalizer
channels is shown below.
• Pattern comparisons always start on the lowest- numbered channel in the
bank and extend to all channels involved in the channel width.
• Alarms are evaluated continuously on the digital modules, but alarm data
is stored in reading memory only during a scan.
• Each time you start a new scan, the instrument clears all readings
(including alarm data) stored in reading memory from the previous scan.
However, alarm data stored in the alarm queue from the digital modules is
not cleared. Therefore, although the contents of reading memory are
always from the most recent scan, the alarm queue may contain data that
occurred during previous scans or while the instrument was not scanning.
To assign the alarm number to report any alarm conditions on the specified
digital input channels, use the following command.
OUTPut:ALARm[1|2]:SOURce (@<ch_list>)
To configure alarms on the specified digital input channel, use the following
commands (also see the example below).
CALCulate
:COMPare:TYPE {EQUal|NEQual},(@<ch_list>)
:COMPare:DATA <data>,(@<ch_list>)
:COMPare:MASK <mask>,(@<ch_list>)
Select EQUal to generate an alarm when the data read from the port
is equal to CALC:COMP:DATA after being masked by CALC:COMP:MASK.
Select NEQual (not equal) to generate an alarm when the data read from the
port is not equal to CALC:COMP:DATA after being masked by CALC:COMP:MASK.
Digital Input Channel Numbering Totalizer Channel Numbering
L4450A 1101 through 1104
1201 through 1204
1301, 1302
L4452A 1001 through 1004 1005