3-26 Measurements and Sourcing Voltage Model 6487 Reference Manual
Triggering considerations
When A-V ohms is selected, the ARM-IN trigger source is forced to TIMER and the time
interval selected will be slightly higher than that required for the A/D integration. For
example, at 1 PLC the integration time is 16.67 msec, so sending the OHM:AVOL:ARM
command will set the ARM-IN timer interval to 18 msec. (The detailed table is below.)
Likewise, the ARM-IN count will be set to INFinite. When exiting A-V ohms with an
AVOL:OHMS:ABOR command or when the desired number of cycles has completed, the
previous trigger model settings will be restored. See Section 7 for additional triggering
information.
Trigger state after A/V ohms
Once an A-V ohms reading sequence has been completed, the instrument will be left in the
trigger IDLE state. If you are operating remotely (GPIB or RS-232), over the front panel,
normal readings will resume after completing A-V ohms (although the “I/¾ TO REARM”
message will obscure these readings untill you press EXIT). Send an INIT:IMM command
to resume taking readings. See Section 7 for more triggering information.
Normal ohms with A-V ohms
Normal ohms (SENS:OHMS:STAT) is not compatible with A-V ohms since the latter
relies on differences between current measurements in time. Therefore, the I | ¾ key is
ignored and the SENS:OHMS:STAT command is rejected with an error +850 “Not
Allowed with A-V Ohms” while A-V ohms is armed.
Buffer operation
The same memory space is used for the regular 3,000 point buffer as for the three A-V
ohms buffers. If there are already readings in the buffer, attempting to arm A-V ohms read-
ings results in a -225 “Out of Memory” error. To avoid inadvertently writing over any
desired readings, either send a TRAC:CLEar command over the bus or attempt to store 0
readings to manually clear the buffer from the front panel. From the front panel, attempt-
ing to select A-V ohms from the CONFIG -> OHMS menu will generate the message
“CLEAR BUFFER” if there are already readings in the buffer.
The converse also applies if you have collected some A-V ohms readings and then press
the STORE key. If the buffer has stored A-V ohms readings, you will be given the
“CLEAR BUFFER” prompt so that you do not inadvertently write over the A-V ohms
PLC
50Hz measurement interval
(milliseconds)
60Hz measurement interval
(milliseconds)
0.02 0002 0002
0.1 0004 0004
1 0022 0018
5 (50Hz)
6 (60Hz)
0102 0102
50 (50Hz)
60 (60Hz)
1002 1002
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