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198 Measurement Speed and Accuracy Trade-offs Appendix C
Setting the Resolution The aperture time or NPLC is set as a result of specifying the <resolution>
parameter in the
MEASure or CONFigure command, or by directly setting it
with the
[SENSe:]FREQuency:APERture or [SENSe:]PERiod:APERture
command or
[SENSe:]function:NPLC commands.
Store the Readings in
Multimeter RAM
Instead of Sending
them Directly to the
Computer
There is a major difference between INIT;:FETCh? and READ? after a
CONFigure command.
INIT;:FETCH? When the INITiate command is sent to the HP E1312A or HP E1412A, the
multimeter will store up to 512 readings in Multimeter RAM. For example:
CONF:VOLT:DC
SAMP:COUN 200
INIT ! Stores 200 readings in RAM
FETC? ! Transfers readings to output buffer
The HP E1312A or HP E1412A then takes the readings as soon as its trigger
conditions have been satisfied and stores them in internal memory (RAM).
For example, if the trigger source is
IMMediate, the readings are started once
INITiate is executed. If the trigger source is EXT, then the readings are
started when an external trigger is received.
The
FETCh? command causes the readings that have been stored in the
multimeter RAM to be placed in the multimeter’s output buffer so they can be
retrieved and sent over the HP-IB bus (or other I/O interface such as VXLink).
No readings are output until all readings have been taken and stored in internal
memory (RAM). This results in a burst-then-transfer mode of operation. The
multimeter can store a maximum of 512 readings in its internal memory.
READ? The READ? command does not store readings in internal memory (RAM)
like the
INITiate command does. For example:
CONF:VOLT:DC
SAMP:COUN 200
READ? ! Takes 200 readings and puts them in the output buffer
The READ? command causes the HP E1312A and HP E1412A Multimeter to
start taking readings as soon as the trigger requirements have been met. For
example, if the trigger source is
IMMediate, the readings are started
immediately. If the trigger source is
EXT, then the readings are started when
an external trigger is received. The multimeter immediately places those
readings in the multimeter’s output buffer so they can be retrieved via the
HP-IB bus (or other I/O interface such as VXLink) by the controller. If the
controller cannot take the readings from the output buffer fast enough, the
multimeter will suspend taking measurements until there is room to place the
readings in the output buffer. You can have a variable reading rate if your
controller is busy doing other tasks instead of emptying the output buffer to
make room for more readings.