Beckhoff EP3356-0022 Documentation page 82

Commissioning/Configuration
Local storage
The values modified during the theoretical and practical calibration are stored in a local EEPROM.
This can be written to up to 1 million time. In order to prolong the life of the EEPROM, therefore, the
commands should not be executed cyclically.
Self-calibration of the measuring amplifiers
The measuring amplifiers are periodically subjected to examination and self-calibration. Several analog
switches are provided for this purpose, so that the various calibration signals can be connected. It is
important for this process that the entire signal path, including all passive components, is examined at every
phase of the calibration. Only the interference suppression elements (L/C combination) and the analog
switches themselves cannot be examined. In addition, a self-test is carried out at longer intervals.
The self-calibration is carried out every 3 minutes in the default setting.
Self-calibration
• The time interval is set in 100 ms steps with object 0x8000:31 [} 104]; default: 3 min. Duration approx.
150 ms
Self-test
• is additional carried out together with every nth self-calibration. The multiple (n) is set with object
0x8000:32 [} 104]; default: 10 additional duration approx. 70 ms.
By means of the self-calibration of the input stages at the two operating points (zero point and final value),
the two measuring channels are calibrated to each other.
Interface for controller
The self-calibration takes place automatically at the defined intervals. In order to prevent calibration during a
time-critical measurement, the automatic calibration can be disabled via the "Disable calibration" bit in
ControlWord, also permanently. If it should be additional necessary to carry out a manual test, this is started
by a rising edge of the "Start manual calibration" bit in the process image.
While the terminal is performing a self-calibration or a self-test, the "Calibration in progress" bit is set in the
process image. Once started, a self-calibration/self-test cannot be aborted.
If the self-calibration has been disabled by "Disable calibration", it can nevertheless be started by the "Start
calibration" process data bit.
Self-calibration
The self-calibration takes place for the first time directly after starting up the terminal/box. At this
point the external reference voltage must already be applied. If the reference voltage is only applied
later, the self-calibration must be manually initiated (process data bit: „Start calibration"). The self-
calibration must be executed at least once after each start-up. The supply voltage must be applied
during the self-calibration, since otherwise the necessary reference voltages cannot be generated.
A lower measuring accuracy is to be expected if the self-calibration is disabled for a longer period or
permanently.
After a change of the settings in the CoE (range x80nn), a self-calibration will be executed in each case (also
for DisabledCalibration = TRUE), because the settings have an influence to the measuring procedure. CoE
settings should be done as far as possible out of running measuring procedures.
Taring
When taring, the scales are "zeroed" using an arbitrary applied load; i.e. an offset correction is performed.
This is necessary for the gross/net compensation of goods that cannot be weighed without a container that
has a mass of its own.
The EL/EP3356 supports 2 tarings; it is recommended to set a strong filter when taring.
Temporary tare
82 Version: 1.1.0 EP3356-0022