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API Commands Appendix A
A-38 ChartScan User’s Manual
J
- Calibrate Cold Junction Offset
TYPE
Calibration
EXECUTION
Immediate
SYNTAX
Jchan,
type,
temp
Calibrate the cold-junction offsets for cold-junction compensation of the
thermocouple signals where
chan
is the channel number such that
1
<
chan
<
max
, where max = 128 for ChartScan/1400.
type
is the thermocouple channel type.
temp
is the reference temperature currently being applied to the selected
channel, with the form
nnn.n
in degrees º C.
DESCRIPTION
Note: This command is only for advanced users who perform their own calibration. It is not necessary for
normal, everyday operation.
Active only in calibration mode, the Calibrate Cold Junction Offset (
J
) command is used to calibrate the cold
junction offsets for cold-junction compensation of the thermocouple signals. Each thermocouple input channel
has associated with it one of these temperature sensors. Although calibrated at the factory, these temperature
sensors are subject to component aging which may affect their accuracy over time. The function of the Calibrate
Cold Junction Offset (
J
) command is to allow the adjusting of the internal firmware to compensate for the affects
of component aging.
Since there are 4 cold junction temperature sensors associated with 32 temperature input channels, it is
necessary to select 4 channels. Each channel is associated with one of the 4 cold junction temperature sensors
in order to calibrate all cold junction temperature sensors on a given card.
Note: Four separate channels on each card must be supplied with an accurate thermocouple signal of known
warm junction temperature.
The parameter
type
is the same channel type that is used with the Configure Channels (C) command.
After the command has been issued, the applied thermocouple signal must remain at its value until the trigger
LED stops flashing in order to achieve accurate results. For further details on channel calibration, see Chapter 6.
EXAMPLE
PRINT#1, “OUTPUT07;K12345X”
‘ Enter Calibration Mode
‘ Apply precision temperature
PRINT#1, “OUTPUT07;J1,2,101.7X”
‘ Compute cold junction offset for the temperature
sensor associated with the type K thermocouple
on channel 1 of card #1, at 101.7°C
‘ Wait for command to complete
‘ Remove precision temperature
PRINT#1, “OUTPUT07;EX”
‘ End calibration mode