BEKA BA574C, Manual

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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 annunicator 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 BA574C transmitter to the 'ZEro'
prompt. This completes re-calibration of the
BA574C 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 annunicator 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 perma-
nent memory and return the BA574C transmitter to
the 'SPAn' prompt. This completes re-calibration
of the BA574C transmitter at maximum input.
When calibrating the BA574C using the Trim Menu
both the zero and span must be adjusted.
The Trim Menu contains a clear function 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.
6.2 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 BA574C 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 5.8.1 to 5.8.5 If
the BA574C 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.
7. CALIBRATION EXAMPLE
In this example a BA574C is required to display
with maximum resolution the temperature of a type
J thermocouple, and to transmit a 4/20mA signal
representing -10 to 240
o C. If the thermocouple
breaks the 4/20mA output current is to rise to full
scale. The current security code is 1209.
The example is divided into two sections. Steps 1
to 10 explain how to condition the transmitter and to
calibrate the 4/20mA output using the internal
references. This will produce acceptable accuracy
for most applications, but will not compensate for
errors in the thermocouple or load connected to the
4/20mA output. Steps 11 to 13 describe how the
Trim Menu may be used to calibrate the complete
loop and to compensate for thermocouple errors.
Step 1 Initialisation
When power is applied to the loop the
BA574C will automatically perform the
initialisation routine described in section
2, and then display and transmit the
thermocouple temperature using the
existing calibration information.
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