4.10
1 The automatic calibration procedure is started by either user keyboard input,
triggered by the instrument internal clock or via external contact closure. At this
point the "Calibration in Progress" output signal is turned on.
The first calibration gas is applied and the instrument then waits for the user
specified DV lag. This is the time for the transducer response to settle to its
stable value.
2 At the end of the DV lag period the response of the transducer is measured and
a zero correction calculated. A new value for the correction is stored and applied
to the output immediately which may result in a change. The instrument waits
for one minute in this state to provide a visible chart-recorder trace of the new
output. In addition, the magnitude of the change is stored in the low calibration
history log.
3 The second calibration gas is applied to the transducer and the instrument waits
for the user specified DV lag.
4 At the end of the DV lag period the response of the transducer is measured and
a span correction calculated. A new value for the correction is stored and
applied to the output immediately which may result in a change. The instrument
waits for one minute in this state to provide a visible chart-recorder trace of the
new output. In addition, the magnitude of the change is stored in the high
calibration history log.
5 The first calibration gas is re-applied to the transducer and the instrument waits
for the DV lag.
6 No action is taken at this point for the type of transducer in this example since
both its zero and span calculations have completed.
7 The sample gas is re-admitted to the transducer and the instrument waits for the
user specified DV lag.
8 Upon completion of this final DV lag period the "Calibration in Progress" output
signal is turned off. The instrument is now returned to normal operation.
If auto check had been selected, values of correction parameters would not have been
calculated at points 2 and 4 in the cycle. Instead, differences between the transducer
reading at these points and the specified test gas would be recorded in the
corresponding calibration history log.
For a transducer where calibration gas 1 is the span gas and calibration gas 2 is the
zero gas then the zero calculation occurs at point 4 and the span calculation at point
6 in the cycle.
NOTE
If an out of calibration tolerance fault is generated during the autocalibration
procedure then this may only be removed by performing a subsequent
successful ( ie in limits ) auto calibration.
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