Keithley 3700 series Reference Manual page 99

Series 3700 System Switch/Multimeter Reference Manual
All routines that return measurements can return the measurements in a reading buffer.
Synchronous measurements return a single value or both a single value and a reading buffer.
The more advanced user can access the additional information stored in the reading buffer.
A reading buffer is based on a Lua table. The measurements themselves are accessed by
ordinary array access. If rb is a reading buffer, the first measurement is accessed as rb[1]
and the 9th measurement as rb[9], and so on. The additional information in the table is
accessed as additional members of the table.
Reading buffer designations
To access the buffer, include the buffer attribute in the respective command. For example, the
following commands would store five readings from the DMM into a buffer named
"readingbuffer:"
Command
dmm.measurecount = 5
dmm.measure('readingbuffer')
Buffer storage control attributes
Buffer storage attributes are summarized in the following table. To control which elements are
stored in the buffer, assign the desired attribute to the buffer. The following values are all
available per reading buffer. For example, to access the appendmode attribute for a buffer
named rb, send rb.appendmode:
Attribute
appendmode
collectchannels
collecttimestamps
Buffer read-only attributes
Use buffer read-only attributes to access the information contained in an existing buffer. The
following values are available per reading, for example, rb.basetimeseconds[3], would
access the third reading (if enabled). Each is actually a nested table. Related entries are stored
at the same index as the relevant measurement.
Document Number: 3700S-901-01 Rev. A / August 2007
Description
Off or on. If off, a new measurement to this buffer will clear the previous
contents before storing the new measurement. If on, the first new
measurement will be stored at what was formerly rb[n+1]. This attribute is
initialized to off when the buffer is created.
When on, channel or channel pattern information will be stored with
readings in the buffer. This requires eight extra bytes of storage per reading.
This value, off or on, can only be changed when the buffer is empty
(cleared). When the buffer is created, this attribute is initialized to on.
When on, timestamps will be stored with readings in the buffer. This
requires eight extra bytes of storage per reading. This value, off or on, can
only be changed when the buffer is empty (cleared). When the buffer is
created, this attribute is initialized to on.
Section 6: Buffer: Data Storage and Retrieval
Description
Sets how many readings to take with the
dmm.measure command.
Takes the measurement and stores it in the
reading buffer parameter, as specified.
6-5