BEKA BA374NC, Manual, Page: 18 / 27

Fig 7 Trim Menu
The 'ZEro' sub-menu allows the transmitter display
and output current to be independently trimmed at
the bottom of the input range. To make the adjust-
ment connect a calibrator to the transmitter input
terminals to simulate minimum input, or place the
primary element in a vessel at the minimum
temperature. With 'ZEro' displayed, pressing the
P
push-button will cause the temperature display to
return. If the display does not correspond with the
input calibrator or the temperature of the primary
element, operate the
Up or Down button until the
transmitter display is correct. Immediately the Up
or Down button is operated the annunciator in the
top left hand corner of the display will be activated
to warn that any changes in the input signal will be
ignored while this display correction is being made.
When the transmitter display is correct, press P
which will lock the transmitter display and, after
briefly displaying 'Ent', allow the 4/20mA output
current to be trimmed using the
Up or Down push-
button. The output current should be measured
with an accurate DVM or another instrument within
the loop. Operate the
Up or Down buttons until the
required output current is shown on the DVM or
other instrument. When correct, press the
E button
to store the trim correction in permanent memory
and return the BA374NC transmitter to the 'ZEro'
prompt. This completes re-calibration of the
BA374NC transmitter at minimum input.
The transmitter should now be re-calibrated at
maximum input by selecting the 'SPAn' sub-menu
and adjusting the calibrator to simulate maximum
input, or raising the primary element to maximum
temperature. With 'SPAn' displayed, pressing the
P push-button will cause the temperature display to
return. If the display does not correspond with the
input calibrator or the temperature of the primary
element, operate the
Up or Down buttons until the
transmitter display is correct. Immediately the Up
or Down button is operated the annunciator in the
top left hand corner of the display will be activated
to warn that any changes in the input signal will be
ignored while this display correction is being made.
When the transmitter display is correct, press P
which will lock the transmitter display and, after
briefly displaying 'Ent', allow the 4/20mA output
current to be trimmed using the
Up or Down push-
button. Again the output current should be
measured with an accurate DVM or another instru-
ment within the loop. Operate the
Up or Down
buttons until the required output current is shown
on the DVM or other instrument. When correct,
press the
E button to store the trim correction in
permanent memory and return the BA374NC
transmitter to the 'SPAn' prompt. This completes
re-calibration of the BA374NC transmitter at
maximum input.
When calibrating the BA374NC using the Trim
Menu both the zero and span must be adjusted.
The Trim Menu contains a clear function 'CLr'
which enables the small calibration correction
made with the 'ZEro' and 'SPAn' sub-menus to be
removed. To clear the corrections select 'CLr'
from the Trim Menu and press
P. The display will
show 'Ent' for a short while and then return to the
'CLr' prompt.
7.2 Periodic re-calibration using trim menu
The Trim Menu is the best way of making small
calibration adjustments to compensate for any long
term drift which may occur. Initially an annual
check is recommended to achieve maximum
accuracy, although less frequent checks will
usually produce acceptable results.
If the BA374NC internal references are used to
make frequent calibration changes, we
recommend that these references should be
initially checked once per year as described in
sections 6.8.1 to 6.8.5 If the BA374NC is always
calibrated with an external reference, such as a
voltage source using the Trim Menu, it will not be
necessary to check the internal reference.
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