Agilent Technologies 3458A User Manual page 118

Result = Reading - OFFSET
10 OPTION BASE 1
20 DIM Rdgs(20)
30 OUTPUT 722;"PRESET NORM"
40 OUTPUT 722;"MATH NULL"
50 OUTPUT 722;"TRIG SGL"
60 OUTPUT 722;"SMATH OFFSET,3.05"
70 OUTPUT 722;"NRDGS 20"
80 OUTPUT 722;"TRIG SYN"
90 ENTER 722;Rdgs(*)
100 PRINT Rdgs(*)
110 END
10 OPTION BASE 1
20 DIM Rdgs(20)
30 OUTPUT 722;"PRESET NORM"
40 OUTPUT 722;"MEM FIFO"
118 Chapter 4 Making Measurements
Where:
OFFSET is the value stored in the OFFSET register (typically the first
reading).
Reading is any reading following the first reading.
After you select the NULL operation, the first reading made (real-time) or
the first reading taken from memory (post-process) is stored in the OFFSET
register. The value of this reading is then subtracted from all subsequent
readings. If you do not want the first reading to be the null value, you can
write another value to the OFFSET register using the SMATH command.
You must wait, however, until after the first reading is made (real-time) or
recalled (post-process) before changing the value.
A typical application of the NULL operation is in making more accurate
2-wire ohms measurements. To do this, select 2-wire ohms (OHM command)
and short the ends of the test leads together. Now enable the NULL operation.
The first reading taken (the lead resistance) is stored in the OFFSET register.
Connect the test leads to the unknown resistance to be measured. The
multimeter then subtracts the value in the OFFSET register from all
subsequent readings until the math NULL operation is disabled. This method
is not as accurate as 4-wire ohms because the resistance of the test leads
connected together probably will not be the same as when they are connected
to the unknown resistance. Also, the resistance of the test leads is checked
only once for a series of measurements and the test lead resistance may
change.
The following program performs the real-time NULL math operation on 20
readings. After executing the NULL command, the first reading is triggered
by line 50. The value in the OFFSET register is then changed to 3.05. The
20 readings are triggered by line 90 and 3.05 is subtracted from each reading.
The following program performs the post-process NULL operation on 20
readings. After executing the MMATH NULL command, 21 readings are
taken and stored in reading memory in FIFO mode. Line 80 recalls the first
reading taken which is stored in the OFFSET register. The value in the
OFFSET register is then changed to 3.05. The remaining 20 readings in
memory are recalled and the NULL operation is performed on each.
!COMPUTER ARRAY NUMBERING STARTS AT 1
!DIMENSION ARRAY FOR 20 READINGS
!PRESET, NRDGS 1,AUTO, DCV 10
!ENABLE REAL-TIME NULL MATH OPERATION
!TRIGGER 1 READING, STORED IN OFFSET
!WRITE 3.05 TO OFFSET REGISTER
!20 READINGS PER TRIGGER
!SYN TRIGGER EVENT
!SYN EVENT, ENTER NULL CORRECTED READINGS
!PRINT NULL CORRECTED READINGS
!COMPUTER ARRAY NUMBERING STARTS AT 1
!DIMENSION ARRAY FOR 20 READINGS\
!PRESET,NRDGS 1,AUTO, DCV 10
!ENABLE READING MEMORY, FIFO MODE