XT2640 Operating Manual
13 July 2016
Page 183 of 187
31
CALIBRATION
ADJUSTMENT
Typically calibration adjustment should be rarely needed; however you may wish to perform it at periodic intervals to ensure
optimal performance.
The XT2640 employs internal software calibration adjustments, there are no physical adjustments required. These adjustments
are needed to correct for manufacturing tolerances in the components used in the XT2640.
It is important to note that there is no calibration of electro‐mechanical performance (e.g. high frequency response) or design
defects, giving you a high degree of certainty that the XT2640 maintains its’ specifications.
Calibration adjustment can only be performed via an interface using an application provided on the CD with the XT2640. This
application does not control the source of the voltage or current being used for adjustment, it only controls the XT2640. You
should ensure ‐
o
The computer being used has a suitable interface installed.
o
The computer being used has the supplied XT2640 calibration adjustment application installed.
o
The XT2640 has been properly configured for the interface chosen.
Calibration adjustment should only be performed after the XT2640 has been continuously powered in a stable environment for
at least 1 hour. If the XT2640 has been moved between differing environments, then at least 3 hours should be allowed.
In the procedure below, each installed channel is calibrated separately and the procedure varies automatically depending on the
channel type (the 1
st
letter of the channel code) and the channel current option (the 2
nd
letter of the channel code).
The supplied application automatically saves the measurement configuration of the XT2640 prior to reconfiguring it for
calibration adjustments and restores the saved configuration after calibration adjustment has been completed.
The XT2640 may be adjusted at any frequency between 45 and 450Hz. It normally produces the optimum results to calibrate
the XT2640 at 50, 55 or 60Hz. At these frequencies the specifications of the source are typically the most accurate. When
calibrating at very low signal levels you may experience interference from the local mains supply, in these cases it is
recommended to adjust the XT2640 at a frequency of other than the local mains supply. The accuracy difference in the XT2640
between 50, 55 or 60Hz is extremely small and may be ignored, and the difference between performing the adjustments at near
mains frequency vs. 400Hz for aerospace applications may also be disregarded as the difference in the XT2640 accuracy is
negligible at the adjustment levels.
31.1
EQUIPMENT
REQUIRED
The following equipment will be required during calibration adjustment‐
1.
A short circuit capable of being attached between the V or A terminals of the XT2640 channels (standard 4mm banana terminals
using ¾ inch spacing) and a method of grounding the short circuit. This short circuit should be constructed to minimize
thermally induced EMFs.
2.
(Only required for W, S and A channel types) A source of AC voltages into a 1.2Mohm load (S or A channel types) or 400Kohm
load (W channel types) of 10V, 20V, and 200Vrms at a frequency of between 45 and 450Hz (the use of 50Hz or 60Hz is
recommended) with sufficient amplitude accuracy to ensure the desired ratio between the specified XT2640 accuracy and that
of the applied voltage. For a 4:1 TUR (typically used) the voltage source should have an accuracy of <0.025%+0.75mV (S or W
channel types) or <0.0075%+0.5mV (A channel types) at these levels.
3.
(Only required for L channel types) A source of AC voltages into a 120kohm load of 1V, 2V, and 20Vrms at a frequency of
between 45 and 450Hz (the use of 50Hz or 60Hz is recommended) with sufficient amplitude accuracy to ensure the desired
ratio between the specified XT2640 accuracy and that of the applied voltage. For a 4:1 TUR (typically used) the voltage source
should have an accuracy of <0.0075%+50uV at these levels.
4.
(Only required for channels having the H current option) A source of AC current into a 0.01ohm load (plus the impedance of the
wiring between the XT2640 and the source) at 1A, 2A and 10Arms at a frequency of between 45 and 450Hz (the use of 50Hz or
60Hz is recommended) with sufficient amplitude accuracy to ensure the desired ratio between the specified XT2640 accuracy
and that of the applied current. For a 4:1 TUR (typically used) the current source should have an accuracy of <0.025%+200uA
(S or W channel types) or <0.0075%+125uA (A channel types) at these levels.
5.
(Only required for channels having the D current option) A source of AC current into a 0.02ohm load (plus the impedance of the
wiring between the XT2640 and the source) at 1A, 2A and 10Arms at a frequency of between 45 and 450Hz (the use of 50Hz or
60Hz is recommended) with sufficient amplitude accuracy to ensure the desired ratio between the specified XT2640 accuracy
and that of the applied current. For a 4:1 TUR (typically used) the current source should have an accuracy of <0.025%+125uA
(S or W channel types) or <0.0075%+75uA (A channel types) at these levels.
6.
(Only required for channels having the D current option) A source of AC current into a 0.57ohm load (plus the impedance of the
wiring between the XT2640 and the source) at 100mArms at a frequency of between 45 and 450Hz (the use of 50Hz or 60Hz is
recommended) with sufficient amplitude accuracy to ensure the desired ratio between the specified XT2640 accuracy and that
of the applied current. For a 4:1 TUR (typically used) the current source should have an accuracy of <0.02575% (S or W channel
types) or <0.007875% (A channel types) at these levels.
7.
(Only required for channels having the X current option) A source of AC voltage into a 20.5Kohm load at 0.1V, 0.5V, 2V and
10Vrms at a frequency of between 45 and 450Hz (the use of 50Hz or 60Hz is recommended) with sufficient amplitude accuracy
to ensure the desired ratio between the specified XT2640 accuracy and that of the applied voltage. For a 4:1 TUR (typically
used) the voltage source should have an accuracy of <0.025%+12.5uV (S or W channel types) or <0.0075%+7.5uV (A channel
types) at these levels. Note that some sources may require that you adjust the voltage setting to achieve the correct voltage into
a 20.5Kohm load.