BEKA BA374NC, Руководство пользователя, Страница: 16 / 27

by selecting 'COdE' from the menu and pressing
P .
Fig 6 Location of security code override link
6.8 Calibrating the internal references
WARNING!
Changing the internal references will
alter the instrument performance. Do
not attempt to recalibrate these
references unless you have adequate
test equipment and have read the
following instructions. For routine
calibration of the instrument use the
Trim Menu described in section 7.
If the internal references are used for calibrating
the BA374NC transmitter they may require periodic
checking against external standards. Annual
checks will produce acceptable performance,
although less frequent checks are usually
adequate.
If the BA374NC transmitter is calibrated against an
external voltage, resistance or temperature
calibrator using the Trim Menu, the internal
references should never need re-calibrating.
Details of the Trim Menu are contained in
section 7.
There are four internal references:
Voltage input
3-wire RTD
4-wire RTD
Current output
The input voltage reference must be adjusted first
irrespective of the transmitter application, but it is
only necessary to adjust the other three references
if the function to which they relate is being used.
For example, a BA374NC with a thermocouple
input from which the 4/20mA output current is
being used would require the voltage input and the
current output reference adjusting.
6.8.1 Conditioning internal references: 'Cond'
WARNING!
Changing the internal references will
alter the instrument performance. Do
not attempt to recalibrate these
references unless you have adequate
test equipment and have read the
following instructions. For routine
calibration of the instrument use the
Trim Menu described in section 7.
These functions are contained in a protected
sub-menu to minimise the possibility of accidental
adjustment. Select 'Cond' from the menu and
press
P . The transmitter will display '0000'. Using
the Up and Down buttons and the P button to
move to the next digit enter the password 'SurE.
(Note that 'S' is entered as '5') There is a ten
second time-out on password entry. Pressing
E
will then give access to the sub-menu containing
the four references.
6.8.2 Voltage input reference 'U.IP'
With the BA374NC input terminals connected to an
accurate voltage calibrator, select 'U.IP' from the
'Cond' sub-menu and press
P. The transmitter will
respond by displaying 'Lo' which is a request for an
accurate -75.000mV input. When the input is
correct press
P to store this figure in permanent
memory. The transmitter will display scrolling
decimal points while the reference is being
updated and will then return to the 'Lo' prompt.
Select 'Hi' from the sub-menu which is a request
for an ac75.000mV input. When the input
is correct press
P to store this figure in permanent
memory. The transmitter will display scrolling
decimal points while the reference is being
updated and will then return to the 'Hi' prompt.
This completes adjustment of the voltage input
reference.
6.8.3 3-wire RTD reference '3rtd'
This adjustment, which is only necessary if the
transmitter is used with a three wire resistance
thermometer, should be performed after the
voltage reference has been calibrated. To adjust
the 3-wire RTD reference the resistance
thermometer should be replaced by a 100 ohm
standard resistor or calibrator, with the
compensation loop remaining connected between
terminals 3 and 4. It is preferable to make this
substitution as close to the RTD as possible, but
transmitters may be calibrated in a workshop.
Select '3rtd' from the 'Cond' sub-menu and press
P. The transmitter will display scrolling decimal
points while the reference is being updated
followed by 'Ent' prior to returning to the '3rtd'
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