American Magnetics 135 & 136 Liquid Helium Level Instruments (CE-Marked) - Manual (Page 58)

46 Rev. 3
Virtual Instrument Operation
Running multiple GPIB devices
string. Any settings changed by the VI virtual panel toggle switches or
control fields are saved in permanent memory in the actual instrument.
The control fields and toggle switches function whether the VI is run
exclusively or non-exclusively on the GPIB bus.
If the VI is executed exclusively, then the VI may be gracefully stopped by
using the STOP toggle switch in the lower left corner of the VI. After
stopping the VI, this switch must be placed back in the up position in order
to restart the VI. If you are executing the VI in a non-exclusive polling loop
on the GPIB bus, then the STOP toggle switch has no function and the
user should control the execution of the VI from the controlling parent
VI(s).
5.2.3 Running multiple GPIB devices
The Model 13X via GPIB.vi in the MODEL13X.LLB library is designed to
have exclusive control of the GPIB bus. AMI recognizes this is generally
not the case for a GPIB bus configuration. Therefore, the Non-exclusive
loop control.vi example is provided in the COMP13X.LLB library to
demonstrate how the Model 13X via GPIB.vi can be cooperatively executed
on a GPIB bus with multiple devices connected.
In order to use multiple devices from the same host computer and GPIB
bus, the Model 135/136 should be set to a unique primary address. In
addition to modifications required to use other devices present on the bus,
the user should modify the Non-exclusive loop control.vi to both initialize
and then execute the Model 13X via GPIB.vi at a regular interval. The
longer the interval between execution, the less responsive the VI will
appear. This is due to the fact that the VI assumes periodic execution in
order to poll the virtual switches and control fields for user-initiated
changes. The suggested period between execution is 1 second in order to
exhibit a reasonable level of responsiveness from the VI. The requirement
to constantly poll a virtual panel for changes is an unfortunate
requirement for running these types of continuously executing interfaces
using LabVIEW.