Compensating For System Offsets - HP E1313A Manual

Compensating for System Offsets

System Wiring Offsets
Important Note for
Thermocouples
Residual Sensor
Offsets
Operation
138 Understanding the HP E1313/E1413
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The HP E1313/E1413 can compensate for offsets in your system's field
wiring. Apply shorts to channels at the Unit-Under-Test (UUT) end of your
field wiring, and then execute the
command. The instrument will measure the voltage at each channel in
ch_list and save those values in RAM as channel Tare constants.
< >
•
You must not use CALibration:TARE
of thermocouple wire. The voltage that a thermocouple wire pair
generates cannot be removed by introducing a short anywhere
between its junction and its connection to an isothermal panel (either
the HP E1313/E1413's terminal module or a remote isothermal
reference block). Thermal voltage is generated along the entire
length of a thermocouple pair where there is any temperature
gradient along that length. To
this way would introduce an unwanted offset in the
voltage/temperature relationship for that thermocouple. If you
inadvertently CALibration:TARE
" Resetting CALibration:TARE" on page 139.
•
You should use CALibration:TARE
(copper wire, not thermocouple wire) between the HP E1313/E1413
and a remote thermocouple reference block. Disconnect the
thermocouples and introduce copper shorting wires between each
channel's HI and LO, then execute
channels.
To remove offsets like those in an unstrained strain gage bridge, execute the
CALibration:TARE command on those channels. The module will then
measure the offsets and as in the wiring case above, remove these offsets
from future measurements. In the strain gage case, this " balances the
bridge" so all measurements have the initial unstrained offset removed to
allow the most accurate high speed measurements possible.
After
CALibration:TARE @<
voltages, it then performs the equivalent of a
operation uses the Tare constants to set a DAC which will remove each
channel offset as " seen" by the module's A/D converter.
The absolute voltage level that
on the A/D range. CALibration:TARE
handle the existing offset voltage. The range that
chooses will become the lowest usable range (range floor) for that channel.
For any channel that has been "
CALibration:TARE (@<
on field wiring that is made up
CALibration:TARE
a thermocouple wire pair, see
to compensate wiring offsets
CALibration:TARE
ch_list measures and stores the offset
>
operation. This
*CAL?
CALibration:TARE can remove is dependent
will choose the lowest range that can
CALibration:TARE
CALibration:TAREd " autorange will not go
ch_list
>)
thermocouple wire
for these
Chapter 4