Hanna Instruments HI 504 - Manual (Page 47)

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If the error is due to impossible communication with the
EEPROM or the RTC, all the pH/ORP controller tasks are
stopped, the alarm relay is de-energized, the red LED blinks
and the “Serial bus error” slides forever (repair can not be
postponed).
A software watchdog is provided in order to detect dead loop
conditions or other causes that make the software stuck. If it
happens, a software reset is generated after a time-out of 1
second.
SELFTEST PROCEDURES
The selftest procedure can be made only entering the setup
menu and selecting one of the items of the “tESt” group (t.00
- t.08).
Note All the tests are made while in setup mode, where a time-out
is present. If no action is performed for about 5 minutes, the
mode is automatically exited and the instruments returns to
previous mode.
DISPLAY TEST
The display selftest procedure consists of lighting up all the
display segments together.
• To start the procedure select setup
item t.00 and an “OFF” blink-
ing message will appear on the
primary LCD.
• Press the æ (or ) key once and
the message will switch to a blink-
ing “GO”.
• Press CFM key to confirm or the
æ (or ) key again to return to
the previous status.
• If confirmation is given when the
“OFF” message is blinking, no ac-
tion is performed and it will move
to the next setup item (t.01).
FAULT CONDITIONS
The below fault conditions may be detected by the software:
• EEPROM data error
• serial communication internal bus failure
• software dead loop.
EEPROM data error can be detected through EEPROM test
procedure at start-up or when explicitly requested using setup
menu, or during normal operational mode if a checksum
control fails.
When an EEPROM error is detected during normal mode, a
fault alarm is generated according to the user configuration
for the EEPROM corruption error (see “Alarm” section).
To close an error an EEPROM test (see “Selftest procedures”
section) or reset is required.
As soon as an EEPROM error is detected, the scrolling mes-
sage “EEPROM reset needed - Press up button to reset stored
data or right button to ignore” will appear on the primary
LCD.
If the key is pressed, the process controller restarts opera-
tion, but alarm actions are performed as configured by the
user (see “Alarm - Error configuration” section). Note that
the device will be in Hold mode in any case.
If the æ key is pressed, all the data stored in the EEPROM are
erased and the default values loaded. After that, the device
must be completely recalibrated.
An internal bus error is detected when internal transmission
is not acknowledged or a bus fault occurs for more than a
certain number of unsuccessful transmission attempts (due
for example to a damage occurred to one of the ICs con-
nected to the internal bus). After that the controller displays a
sliding message “Serial bus error”.