Advance Verification Features - Racal Instruments 1256 Manual

Publication No. 980855 Rev. A
Advance
Verification
Features
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K) After the next trigger, channel 1(0) is opened, and the state of
all channels controlled by the 1256 is recalled from
nonvolatile memory. The state of the relays is recalled from
state location 14.
L) After the next trigger, channel 1(224) is closed. Note that the
channels recalled from nonvolatile memory are NOT opened.
M) After the next trigger, channel 1(224) is opened, and channel
1(323) is closed. The scan list has "wrapped around" to the
beginning of the list.
Each time the SCAN command is executed, the previously defined
scan list is deleted.
The present scan list may be deleted using the command
SCAN:DELETE command.
The presently defined scan list may be read using the SCAN?
command. For example, if the scan list shown for the example
above is presently defined, the query:
SCAN?
will generate the reply:
(@1(323),9(0:2),10(8:5),example,1(0),
state14,1(224))
The reply will NOT include module names, even if the SCAN
command used to define the list included module names. Module
numbers are always used when replying to the SCAN? query.
In some applications, it may be desirable for the reason of
reliability to confirm that switches are actually closed or open
based on the commanded state of the system. The 1256 provides
the user with capabilities to detect certain types of switching
failures.
From the standpoint of the 1256, switching failures fall into one of
two classes – detectable and undetectable. An example of an
undetectable failure is where a relay contact has welded closed
through misuse. In this example, the relay coil voltages will verify
properly even though the contact has suffered permanent damage.
There is no easy way to detect this condition without invasively
monitoring the switched-side of the relay. This obviously would
defeat the isolation characteristics of a relay.
The other class of failures – those that are detectable – include coil
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