HP 8712C, Руководство пользователя, Страница: 316 / 559

Automating Measurements
Operator Interaction
When limit testing is turned on, the TEST IN/OUT rear-panel BNC
connector indicates the status of the limit test. If the limit test passes, this
TTL output goes high. If the limit test fails, this TTL output goes low. This
signal can be used, for example, as an input to a materials handler.
C A U T I O N
Since the TTL output has limited current drive capability, it should be
buffered when controlling high current devices such as mechanical relays.
Otherwise, damage to the instrument may result.
The limit test TTL can also be used as a general-purpose input, since the
analyzer drive to this line is open collector. When used as an input, limit
testing should be turned the instrument will allow the limit test line
to float high. The line can then be connected to an external switch which
should only pull the signal to ground or let it float (an external circuit should
not drive this line). A push button or foot switch can then be attached to the
line to pull the signal to ground.
The state of the signal can be monitored by the automated system to
determine when the operator is ready for some action. The state of the Limit
TTL line can be read with either the SCPI commands
20 INTEGER X
30 OUTPUT
40 ENTER
or using the
3 0
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