Specifications

CALibration:TARE
CALibration:TARE (@<ch_list>) measures offset (or tare) voltage present on the
channels specified and stores the value in on-board RAM as a calibration constant
for those channels. Future measurements made with these channels will be
compensated by the amount of the tare value. Use CAL:TARE to compensate for
voltage offsets in system wiring and residual sensor offsets. Where tare values need
to be retained for long periods, they can be stored in the module’s flash memory
(Electrically Erasable Programmable Read Only Memory) by executing the
CAL:STORe TARE command.
For more information see Compensating for System Offsets on page 97.
Note for
Thermocouples
·
Do not use CAL:TARE on field wiring that is made up of thermocouple wire. The
voltage a thermocouple wire pair generates can not
be removed by introducing a
short anywhere between its junction and its connection to an isothermal panel
(either the VT1419A’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 CAL:TARE thermocouple
wire this way would introduce an unwanted offset in the voltage/temperature
relationship for that channel. If a thermocouple wire pair is inadvertently
"CAL:TARE'd," use CAL:TARE:RESET to reset all tare constants to zero.
·
Do use CAL:TARE to compensate wiring offsets (copper wire, not thermocouple
wire) between the VT1419A and a remote thermocouple reference block.
Disconnect the thermocouples and introduce copper shorting wires between each
channel’s HI and LO, then execute CAL:TARE for these channels.
Parameters
Parameter
Name
Parameter
Type
Range of
Values
Default
Units
ch_list channel list (string) 100 - 163 none
Comments
·
CAL:TARE also performs the equivalent of a *CAL? operation. This operation
uses the Tare constants to set a DAC which will remove each channel offset as
“seen” by the module’s A/D converter. As an example assume that the system
wiring to channel 0 generates a +0.1 volt offset with 0 volts (a short) applied at
the Unit Under Test (UUT). Before CAL:TARE the module would return a
reading of 0.1 volts for channel 0. After CAL:TARE (@100), the module will
return a reading of 0 volts with a short applied at the UUT and the system wiring
offset will be removed from all measurements of the signal to channel 0.
·
Set Amplifier/Filter SCP gain before CAL:TARE. For best accuracy, choose the
gain that will be used during measurements. If the range or gain setup is changed
later, be sure to perform another *CAL? operation.
·
Output SCP channels referenced in <ch_list> will not be affected by CAL:TARE.
Some output have input channels associated with them in order to approximately
VT1419A Command Reference
CALibration
212 Chapter 6
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