Chapter 4 Features and Functions

Scanning With External Instruments

In this configuration, you must set up a scan list to include all desired multiplexer or digital channels. Channels which are not in the list are skipped during the scan. The instrument automatically scans the list of channels in ascending order from slot 100 through slot 300.

For an externally-controlled scan, you must either remove the internal DMM from the HP 34970A or disable it (see “Internal DMM Disable” on page 145). Since the internal DMM is not used, readings from multiplexer channels are not stored in internal reading memory.

External connections are required to synchronize the scan sequence between the HP 34970A and the external instrument. The HP 34970A must notify the external instrument when a relay is closed and settled (including channel delay). The HP 34970A outputs a Channel Closed pulse from pin 5 on the rear-panel connector (see previous page).

In response, the external instrument must notify the HP 34970A when it has finished its measurement and is ready to advance to the next channel in the scan list. The HP 34970A accepts a Channel Advance signal on the External Trigger input line (pin 6).

∙You can configure the event or action that controls the onset of each sweep through the scan list (a sweep is one pass through the scan list). When the internal DMM is removed (or disabled), the default scan interval source is “timer”. For more information, refer to “Scan Interval” on page 80.

∙You can configure the event or action that notifies the HP 34970A to advance to the next channel in the scan list. Note that the Channel Advance source shares the same sources as the scan interval. However, an error is generated if you attempt to set the channel advance source to the same source used for the scan interval.

∙You can specify the number of times the instrument will sweep through the scan list. When the specified number of sweeps have occurred, the scan stops. For more information, refer to “Scan Count” on page 86.

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